Produced by Alan Millar and the Online Distributed Proofreading Team.



[Transcriber's Note: The illustrations have been included with
the eBook version of this work. The image files have been named
in a straightforward manner that corresponds to the numbering in
the text; thus, Illustration 7 is included as file "fig007.png",
while Illustration (A) 22 is included as file "fig022a.png".]






THE RADIO AMATEUR'S HAND BOOK

[Illustration: A. Frederick Collins, Inventor of the Wireless
Telephone, 1899. Awarded Gold Medal for same, Alaska Yukon Pacific
Exposition, 1909.]




THE RADIO AMATEUR'S HAND BOOK

A Complete, Authentic and Informative Work on Wireless Telegraphy and
Telephony

BY

A. FREDERICK COLLINS

Inventor of the Wireless Telephone 1899; Historian of Wireless
1901-1910; Author of "Wireless Telegraphy" 1905

1922




TO

WILLIAM MARCONI

INVENTOR OF THE WIRELESS TELEGRAPH




INTRODUCTION


Before delving into the mysteries of receiving and sending messages
without wires, a word as to the history of the art and its present day
applications may be of service. While popular interest in the subject
has gone forward by leaps and bounds within the last two or three
years, it has been a matter of scientific experiment for more than a
quarter of a century.

The wireless telegraph was invented by William Marconi, at Bologna,
Italy, in 1896, and in his first experiments he sent dot and dash
signals to a distance of 200 or 300 feet. The wireless telephone was
invented by the author of this book at Narberth, Penn., in 1899, and
in his first experiments the human voice was transmitted to a distance
of three blocks.

The first vital experiments that led up to the invention of the
wireless telegraph were made by Heinrich Hertz, of Germany, in 1888
when he showed that the spark of an induction coil set up electric
oscillations in an open circuit, and that the energy of these waves
was, in turn, sent out in the form of electric waves. He also showed
how they could be received at a distance by means of a ring detector,
which he called a _resonator_

In 1890, Edward Branly, of France, showed that metal filings in a tube
cohered when electric waves acted on them, and this device he termed a
_radio conductor_; this was improved upon by Sir Oliver Lodge, who
called it a coherer. In 1895, Alexander Popoff, of Russia, constructed
a receiving set for the study of atmospheric electricity, and this
arrangement was the earliest on record of the use of a detector
connected with an aerial and the earth.

Marconi was the first to connect an aerial to one side of a spark gap
and a ground to the other side of it. He used an induction coil to
energize the spark gap, and a telegraph key in the primary circuit to
break up the current into signals. Adding a Morse register, which
printed the dot and dash messages on a tape, to the Popoff receptor he
produced the first system for sending and receiving wireless telegraph
messages.

[Illustration: Collins' Wireless Telephone Exhibited at the Madison
Square Garden, October 1908.]

After Marconi had shown the world how to telegraph without connecting
wires it would seem, on first thought, to be an easy matter to
telephone without wires, but not so, for the electric spark sets up
damped and periodic oscillations and these cannot be used for
transmitting speech. Instead, the oscillations must be of constant
amplitude and continuous. That a direct current arc light transforms a
part of its energy into electric oscillations was shown by Firth and
Rogers, of England, in 1893.

The author was the first to connect an arc lamp with an aerial and a
ground, and to use a microphone transmitter to modulate the sustained
oscillations so set up. The receiving apparatus consisted of a
variable contact, known as a _pill-box_ detector, which Sir Oliver
Lodge had devised, and to this was connected an Ericsson telephone
receiver, then the most sensitive made. A later improvement for
setting up sustained oscillations was the author's _rotating
oscillation arc_.

Since those memorable days of more than two decades ago, wonderful
advances have been made in both of these methods of transmitting
intelligence, and the end is as yet nowhere in sight. Twelve or
fifteen years ago the boys began to get fun out of listening-in to
what the ship and shore stations were sending and, further, they began
to do a little sending on their own account. These youngsters, who
caused the professional operators many a pang, were the first wireless
amateurs, and among them experts were developed who are foremost in
the practice of the art today.

Away back there, the spark coil and the arc lamp were the only known
means for setting up oscillations at the sending end, while the
electrolytic and crystal detectors were the only available means for
the amateur to receive them. As it was next to impossible for a boy to
get a current having a high enough voltage for operating an
oscillation arc lamp, wireless telephony was out of the question for
him, so he had to stick to the spark coil transmitter which needed
only a battery current to energize it, and this, of course, limited
him to sending Morse signals. As the electrolytic detector was
cumbersome and required a liquid, the crystal detector which came into
being shortly after was just as sensitive and soon displaced the
former, even as this had displaced the coherer.

A few years ahead of these amateurs, that is to say in 1905, J. A.
Fleming, of England, invented the vacuum tube detector, but ten more
years elapsed before it was perfected to a point where it could
compete with the crystal detector. Then its use became general and
workers everywhere sought to, and did improve it. Further, they found
that the vacuum tube would not only act as a detector, but that if
energized by a direct current of high voltage it would set up
sustained oscillations like the arc lamp, and the value of sustained
oscillations for wireless telegraphy as well as wireless telephony had
already been discovered.

The fact that the vacuum tube oscillator requires no adjustment of its
elements, that its initial cost is much less than the oscillation arc,
besides other considerations, is the reason that it popularized
wireless telephony; and because continuous waves have many advantages
over periodic oscillations is the reason the vacuum tube oscillator is
replacing the spark coil as a wireless telegraph transmitter.
Moreover, by using a number of large tubes in parallel, powerful
oscillations can be set up and, hence, the waves sent out are radiated
to enormous distances.

While oscillator tubes were being experimented with in the research
laboratories of the General Electric, the Westinghouse, the Radio
Corporation of America, and other big companies, all the youthful
amateurs in the country had learned that by using a vacuum tube as a
detector they could easily get messages 500 miles away. The use of
these tubes as amplifiers also made it possible to employ a loud
speaker, so that a room, a hall, or an out-of-door audience could hear
clearly and distinctly everything that was being sent out.

The boy amateur had only to let father or mother listen-in, and they
were duly impressed when he told them they were getting it from KDKA
(the Pittsburgh station of the Westinghouse Co.), for was not
Pittsburgh 500 miles away! And so they, too, became enthusiastic
wireless amateurs. This new interest of the grown-ups was at once met
not only by the manufacturers of apparatus with complete receiving and
sending sets, but also by the big companies which began broadcasting
regular programs consisting of music and talks on all sorts of
interesting subjects.

This is the wireless, or radio, as the average amateur knows it today.
But it is by no means the limit of its possibilities. On the contrary,
we are just beginning to realize what it may mean to the human race.
The Government is now utilizing it to send out weather, crop and
market reports. Foreign trade conditions are being reported. The Naval
Observatory at Arlington is wirelessing time signals.

Department stores are beginning to issue programs and advertise by
radio! Cities are also taking up such programs, and they will
doubtless be included soon among the regular privileges of the
tax-payers. Politicians address their constituents. Preachers reach
the stay-at-homes. Great singers thrill thousands instead of hundreds.
Soon it will be possible to hear the finest musical programs,
entertainers, and orators, without budging from one's easy chair.

In the World War wireless proved of inestimable value. Airplanes,
instead of flying aimlessly, kept in constant touch with headquarters.
Bodies of troops moved alertly and intelligently. Ships at sea talked
freely, over hundreds of miles. Scouts reported. Everywhere its
invisible aid was invoked.

In time of peace, however, it has proved and will prove the greatest
servant of mankind. Wireless messages now go daily from continent to
continent, and soon will go around the world with the same facility.
Ships in distress at sea can summon aid. Vessels everywhere get the
day's news, even to baseball scores. Daily new tasks are being
assigned this tireless, wireless messenger.

Messages have been sent and received by moving trains, the Lackawanna
and the Rock Island railroads being pioneers in this field. Messages
have also been received by automobiles, and one inventor has
successfully demonstrated a motor car controlled entirely by wireless.
This method of communication is being employed more and more by
newspapers. It is also of great service in reporting forest fires.

Colleges are beginning to take up the subject, some of the first being
Tufts College, Hunter College, Princeton, Yale, Harvard, and Columbia,
which have regularly organized departments for students in wireless.

Instead of the unwieldy and formidable looking apparatus of a short
time ago, experimenters are now vying with each other in making small
or novel equipment. Portable sets of all sorts are being fashioned,
from one which will go into an ordinary suitcase, to one so small it
will easily slip into a Brownie camera. One receiver depicted in a
newspaper was one inch square! Another was a ring for the finger, with
a setting one inch by five-eighths of an inch, and an umbrella as a
"ground." Walking sets with receivers fastened to one's belt are also
common. Daily new novelties and marvels are announced.

Meanwhile, the radio amateur to whom this book is addressed may have
his share in the joys of wireless. To get all of these good things out
of the ether one does not need a rod or a gun--only a copper wire made
fast at either end and a receiving set of some kind. If you are a
sheer beginner, then you must be very careful in buying your
apparatus, for since the great wave of popularity has washed wireless
into the hearts of the people, numerous companies have sprung up and
some of these are selling the veriest kinds of junk.

And how, you may ask, are you going to be able to know the good from
the indifferent and bad sets? By buying a make of a firm with an
established reputation. I have given a few offhand at the end of this
book. Obviously there are many others of merit--so many, indeed, that
it would be quite impossible to get them all in such a list, but these
will serve as a guide until you can choose intelligently for yourself.

A. F. C.




CONTENTS


CHAPTER

I. HOW TO BEGIN WIRELESS

Kinds of Wireless Systems--Parts of a Wireless System--The Easiest Way
to Start--About Aerial Wire Systems--About the Receiving
Apparatus--About Transmitting Stations--Kinds of Transmitters--The
Spark Gap Wireless Telegraph Transmitter--The Vacuum Table Telegraph
Transmitter--The Wireless Telephone Transmitter.

II. PUTTING UP YOUR AERIAL

Kinds of Aerial Wire Systems--How to Put Up a Cheap Receiving
Aerial--A Two-wire Aerial--Connecting in the Ground--How to Put up a
Good Aerial--An Inexpensive Good Aerial--The Best Aerial That Can be
Made--Assembling the Aerial--Making a Good Ground.

III. SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS

Assembled Wireless Receiving Sets--Assembling Your Own Receiving
Set--The Crystal Detector--The Tuning Coil--The Loose Coupled Tuning
Coil--Fixed and Variable Condensers--About Telephone Receivers--
Connecting Up the Parts--Receiving Set No. 2--Adjusting the No. 1
Set--The Tuning Coil--Adjusting the No. 2 Set.

IV. SIMPLE TELEGRAPH SENDING SETS

A Cheap Transmitting Set (No. 1)--The Spark Coil--The Battery--The
Telegraph Key--The Spark Gap--The Tuning Coil--The High-tension
Condenser--A Better Transmitting Set (No. 2)--The Alternating Current
Transformer--The Wireless Key--The Spark Gap--The High-tension
Condenser--The Oscillation Transformer--Connecting Up the
Apparatus--For Direct Current--How to Adjust Your Transmitter. Turning
With a Hot Wire Ammeter--To Send Out a 200-meter Wave Length--The Use
of the Aerial Switch--Aerial Switch for a Complete Sending and
Receiving Set--Connecting in the Lightning Switch.

V. ELECTRICITY SIMPLY EXPLAINED

Electricity at Rest and in Motion--The Electric Current and its
Circuit--Current and the Ampere--Resistance and the Ohm--What Ohm's
Law Is--What the Watt and Kilowatt Are--Electromagnetic
Induction--Mutual Induction--High-frequency Currents--Constants of an
Oscillation Circuit--What Capacitance Is--What Inductance Is--What
Resistance Is--The Effect of Capacitance.

VI. HOW THE TRANSMITTING AND RECEIVING SETS WORK

How Transmitting Set No. 1 Works--The Battery and Spark Coil
Circuit--Changing the Primary Spark Coil Current Into Secondary
Currents--What Ratio of Transformation Means--The Secondary Spark Coil
Circuit--The Closed Oscillation Circuit--How Transmitting Set No. 2
Works-With Alternating Current--With Direct Current--The Rotary Spark
Gap--The Quenched Spark Gap--The Oscillation Transformer--How
Receiving Set No. 1 Works--How Receiving Set No. 2 Works.

VII. MECHANICAL AND ELECTRICAL TUNING

Damped and Sustained Mechanical Vibrations--Damped and Sustained
Oscillations--About Mechanical Tuning--About Electric Tuning.

VIII. A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET

Assembled Vacuum Tube Receiving Set--A Simple Vacuum Tube Receiving
Set--The Vacuum Tube Detector--Three Electrode Vacuum Tube
Detector--The Dry Cell and Storage Batteries--The Filament
Rheostat--Assembling the Parts--Connecting Up the Parts--Adjusting the
Vacuum Tube Detector Receiving Set.

IX. VACUUM TUBE AMPLIFIER RECEIVING SETS

A Grid Leak Amplifier Receiving Set. With Crystal Detector--The Fixed
Resistance Unit, or Grid Leak--Assembling the Parts for a Crystal
Detector Set--Connecting up the Parts for a Crystal Detector--A Grid
Leak Amplifying Receiving Set With Vacuum Tube Detector--A Radio
Frequency Transformer Amplifying Receiving Set--An Audio Frequency
Transformer Amplifying Receiving Set--A Six Step Amplifier Receiving
Set with a Loop Aerial--How to Prevent Howling.

X. REGENERATIVE AMPLIFICATION RECEIVING SETS

The Simplest Type of Regenerative Receiving Set--With Loose Coupled
Tuning Coil--Connecting Up the Parts--An Efficient Regenerative
Receiving Set. With Three Coil Loose Coupler--The A Battery
Potentiometer--The Parts and How to Connect Them Up--A Regenerative
Audio Frequency Amplifier--The Parts and How to Connect Them Up.

XI. SHORT WAVE REGENERATIVE RECEIVING SETS

A Short Wave Regenerative Receiver, with One Variometer and Three
Variable Condensers--The Variocoupler--The Variometer--Connecting Up
the Parts--Short Wave Regenerative Receiver with Two Variometers and
Two Variable Condensers--The Parts and How to Connect Them Up.

XII. INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING SETS

Intermediate Wave Receiving Sets--Intermediate Wave Set With Loading
Coils--The Parts and How to Connect Them Up--An Intermediate Wave Set
with Variocoupler Inductance Coils--The Parts and How to Connect Them
Up--A Long Wave Receiving Set--The Parts and How to Connect Them Up.

XIII. HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING SET

What the Heterodyne or Beat Method Is--The Autodyne or Self-heterodyne
Long Wave Receiving Set--The Parts and Connections of an Autodyne or
Self-heterodyne, Receiving Set--The Separate Heterodyne Long Wave
Receiving Set--The Parts and Connections of a Separate Heterodyne Long
Wave Receiving Set.

XIV. HEADPHONES AND LOUD SPEAKERS

Wireless Headphones--How a Bell Telephone Receiver is Made--How a
Wireless Headphone is Made--About Resistance, Turns of Wire and
Sensitivity of Headphones--The Impedance of Headphones--How the
Headphones Work--About Loud Speakers--The Simplest Type of Loud
Speaker--Another Simple Kind of Loud Speaker--A Third Kind of Simple
Loud Speaker--A Super Loud Speaker.

XV. OPERATION OF VACUUM TUBE RECEPTORS

What is Meant by Ionization--How Electrons are Separated from
Atoms--Action of the Two Electrode Vacuum Tube--How the Two Electrode
Tube Acts as a Detector--How the Three Electrode Tube Acts as a
Detector--How the Vacuum Tube Acts as an Amplifier--The Operation of a
Simple Vacuum Tube Receiving Set--Operation of a Regenerative Vacuum
Tube Receiving Set--Operation of Autodyne and Heterodyne Receiving
Sets--The Autodyne, or Self-Heterodyne Receiving Set--The Separate
Heterodyne Receiving Set.

XVI. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH DIRECT CURRENT

Sources of Current for Telegraph Transmitting Sets--An Experimental
Continuous Wave Telegraph Transmitter--The Apparatus You Need--The
Tuning Coil--The Condensers--The Aerial Ammeter--The Buzzer and Dry
Cell--The Telegraph Key--The Vacuum Tube Oscillator--The Storage
Battery--The Battery Rheostat--The Oscillation Choke Coil--Transmitter
Connectors--The Panel Cutout--Connecting Up the Transmitting
Apparatus--A 100-mile C. W. Telegraph Transmitter--The Apparatus You
Need--The Tuning Coil--The Aerial Condenser--The Aerial Ammeter--The
Grid and Blocking Condensers--The Key Circuit Apparatus--The 5 Watt
Oscillator Vacuum Tube--The Storage Battery and Rheostat--The Filament
Voltmeter--The Oscillation Choke Coil--The Motor-generator Set--The
Panel Cut-out--The Protective Condenser--Connecting Up the
Transmitting Apparatus--A 200-mile C. W. Telegraph Transmitter--A
500-mile C. W. Telegraph Transmitter--The Apparatus and Connections--
The 50-watt Vacuum Tube Oscillator--The Aerial Ammeter--The Grid Leak
Resistance--The Oscillation Choke Coil--The Filament Rheostat--The
Filament Storage Battery--The Protective Condenser--The
Motor-generator--A 1000-mile C. W. Telegraph Transmitter.

XVII. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING
CURRENT

A 100-mile C. W. Telegraph Transmitting Set--The Apparatus
Required--The Choke Coils--The Milli-ammeter--The A. C. Power
Transformer--Connecting Up the Apparatus--A 200- to 500-mile C. W.
Telegraph Transmitting Set-A 500- to 1000-mile C. W. Telegraph
Transmitting Set--The Apparatus Required--The Alternating Current
Power Transformer-Connecting Up the Apparatus.

XVIII. WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND
ALTERNATING CURRENTS

A Short Distance Wireless Telephone Transmitting Set--With 110-volt
Direct Lighting Current--The Apparatus You Need--The Microphone
Transmitter--Connecting Up the Apparatus--A 25- to 50-mile Wireless
Telephone Transmitter--With Direct Current Motor Generator--The
Apparatus You Need--The Telephone Induction Coil--The Microphone
Transformer--The Magnetic Modulator--How the Apparatus is Connected
Up--A 50- to 100-mile Wireless Telephone Transmitter--With Direct
Current Motor Generator--The Oscillation Choke Coil--The Plate and
Grid Circuit Reactance Coils--Connecting up the Apparatus--A 100- to
200-mile Wireless Telephone Transmitter--With Direct Current Motor
Generator--A 50- to 100-mile Wireless Telephone Transmitting Set--With
100-volt Alternating Current--The Apparatus You Need--The Vacuum Tube
Rectifier--The Filter Condensers--The Filter Reactance Coil--
Connecting Up the Apparatus--A 100- to 200-mile Wireless Telephone
Transmitting Set--With 110-volt Alternating Current--Apparatus
Required.

XIX. THE OPERATION OF VACUUM TUBE TRANSMITTERS

The Operation of the Vacuum Tube Oscillator--The Operation of C. W.
Telegraph Transmitters with Direct Current--Short Distance C. W.
Transmitter--The Operation of the Key Circuit--The Operation of C. W.
Telegraph Transmitting with Direct Current--The Operation of C. W.
Telegraph Transmitters with Alternating Current--With a Single
Oscillator Tube--Heating the Filament with Alternating Current--The
Operation of C. W. Telegraph Transmitters with Alternating Current--
With Two Oscillator Tubes--The Operation of Wireless Telephone
Transmitters with Direct Current--Short Distance Transmitter--The
Microphone Transmitter--The Operation of Wireless Telephone
Transmitters with Direct Current--Long Distance Transmitters--The
Operation of Microphone Modulators--The Induction Coil--The Microphone
Transformer--The Magnetic Modulator--Operation of the Vacuum Tube as a
Modulator--The Operation of Wireless Telephone Transmitters with
Alternating Current--The Operation of Rectifier Vacuum Tubes--The
Operation of Reactors and Condensers.

XX. HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS.

The Crystal Detector--The Tuning Coil--The Headphone--How to Mount the
Parts--The Condenser--How to Connect Up the Receptor.

APPENDIX

Useful Information--Glossary--Wireless Don'ts.




LIST OF FIGURES


Fig. 1.--Simple Receiving Set

Fig. 2.--Simple Transmitting Set

(A) Fig. 3.--Flat Top, or Horizontal Aerial

(B) Fig. 3.--Inclined Aerial

(A) Fig. 4.--Inverted L Aerial

(B) Fig. 4--T Aerial

Fig. 5.--Material for a Simple Aerial Wire System

(A) Fig. 6.--Single Wire Aerial for Receiving

(B) Fig. 6.--Receiving Aerial with Spark Gap Lightning Arrester

(C) Fig. 6.--Aerial with Lightning Switch

Fig. 7.--Two-wire Aerial

(A) Fig. 8.--Part of a Good Aerial

(B) Fig. 8.--The Spreaders

(A) Fig. 9.--The Middle Spreader

(B) Fig. 9.--One End of Aerial Complete

(C) Fig. 9.--The Leading in Spreader

(A) Fig. 10.--Cross Section of Crystal Detector

(B) Fig. 10.--The Crystal Detector Complete

(A) Fig. 11.--Schematic Diagram of a Double Slide Tuning Coil

(B) Fig. 11.--Double Slide Tuning Coil Complete

(A) Fig. 12.--Schematic Diagram of a Loose Coupler

(B) Fig. 12.--Loose Coupler Complete

(A) Fig. 13.--How a Fixed Receiving Condenser is Built up

(B) Fig. 13.--The Fixed Condenser Complete

(C) and (D) Fig. 13.--Variable Rotary Condenser

Fig. 14.--Pair of Wireless Headphones

(A) Fig. 15.--Top View of Apparatus Layout for Receiving Set No. 1

(B) Fig. 15.--Wiring Diagram for Receiving Set No. 1

(A) Fig. 16.--Top View of Apparatus Layout for Receiving Set No. 2

(B) Fig. 16.--Wiring Diagram for Receiving Set No. 2

Fig. 17.--Adjusting the Receiving Set

(A) and (B) Fig. 18.--Types of Spark Coils for Set No. 1

(C) Fig. 18.--Wiring Diagram of Spark Coil

Fig. 19.--Other Parts for Transmitting Set No. 1

(A) Fig. 20.--Top View of Apparatus Layout for Sending Set No. 1

(B) Fig. 20.--Wiring of Diagram for Sending Set No. 1

Fig. 21.--Parts for Transmitting Set No. 2

(A) Fig. 22.--Top View of Apparatus Layout for Sending Set No. 2

(B) Fig. 22.--Wiring Diagram for Sending Set No. 2

Fig. 23.--Using a 110-volt Direct Current with an Alternating current
Transformer

Fig. 24.--Principle of the Hot Wire Ammeter

Fig. 25.--Kinds of Aerial Switches

Fig. 26.--Wiring Diagram for a Complete Sending and Receiving Set No. 1

Fig. 27.--Wiring Diagram for Complete Sending and Receiving Set No. 2

Fig. 28.--Water Analogue for Electric Pressure

Fig. 29.--Water Analogues for Direct and Alternating Currents

Fig. 30.--How the Ammeter and Voltmeter are Used

Fig. 31.--Water Valve Analogue of Electric Resistance

(A) and (B) Fig. 32.--How an Electric Current is Changed into Magnetic
Lines of Force and These into an Electric Current

(C) and (D) Fig. 32.--How an Electric Current Sets up a Magnetic Field

Fig. 33.--The Effect of Resistance on the Discharge of an Electric
Current

Fig. 34.--Damped and Sustained Mechanical Vibrations

Fig. 35.--Damped and Sustained Electric Oscillations

Fig. 36.--Sound Wave and Electric Wave Tuned Senders and Receptors

Fig. 37.--Two Electrode Vacuum Tube Detectors

Fig. 38.--Three Electrode Vacuum Tube Detector and Battery Connections

Fig. 39.--A and B Batteries for Vacuum Tube Detectors

Fig. 40.--Rheostat for the A or Storage-battery Current

(A) Fig. 41.--Top View of Apparatus Layout for Vacuum Tube Detector
Receiving Set

(B) Fig. 41.--Wiring Diagram of a Simple Vacuum Tube Receiving Set

Fig. 42.--Grid Leaks and How to Connect them Up

Fig. 43.--Crystal Detector Receiving Set with Vacuum Tube Amplifier
(Resistance Coupled)

(A) Fig. 44.--Vacuum Tube Detector Receiving Set with One Step
Amplifier (Resistance Coupled)

(B) Fig. 44.--Wiring Diagram for Using One A or Storage Battery with
an Amplifier and a Detector Tube

(A) Fig. 45.--Wiring Diagram for Radio Frequency Transformer
Amplifying Receiving Set

(B) Fig. 45.--Radio Frequency Transformer

(A) Fig. 46.--Audio Frequency Transformer

(B) Fig. 46.--Wiring Diagram for Audio Frequency Transformer
Amplifying Receiving Set. (With Vacuum Tube Detector and Two Step
Amplifier Tubes)

(A) Fig. 47.--Six Step Amplifier with Loop Aerial

(B) Fig. 47.--Efficient Regenerative Receiving Set (With Three Coil
Loose Coupler Tuner)

Fig. 48.--Simple Regenerative Receiving Set (With Loose Coupler Tuner)

(A) Fig. 49.--Diagram of Three Coil Loose Coupler

(B) Fig. 49.--Three Coil Loose Coupler Tuner

Fig. 50.--Honeycomb Inductance Coil

Fig. 51.--The Use of the Potentiometer

Fig. 52.--Regenerative Audio Frequency Amplifier Receiving Set

Fig. 53.--How the Vario Coupler is Made and Works

Fig. 54.--How the Variometer is Made and Works

Fig. 55.--Short Wave Regenerative Receiving Set (One Variometer
and Three Variable Condensers)

Fig. 56.--Short Wave Regenerative Receiving Set (Two Variometer
and Two Variable Condensers)

Fig. 57.--Wiring Diagram Showing Fixed Loading Coils for Intermediate
Wave Set

Fig. 58.--Wiring Digram of Intermediate Wave Receptor with One Vario
Coupler and 12 Section Bank-wound Inductance Coil

Fig. 59.--Wiring Diagram Showing Long Wave Receptor with Vario
Couplers and 8 Bank-wound Inductance Coils

Fig. 60.--Wiring Diagram of Long Wave Autodyne, or Self-heterodyne
Receptor (Compare with Fig. 77)

Fig. 61.--Wiring Diagram of Long Wave Separate Heterodyne Receiving
Set

Fig. 62.--Cross Section of Bell Telephone Receiver

Fig. 63.--Cross Section of Wireless Headphone

Fig. 64.--The Wireless Headphone

Fig. 65.--Arkay Loud Speaker

Fig. 66.--Amplitone Loud Speaker

Fig. 67.--Amplitron Loud Speaker

Fig. 68.--Magnavox Loud Speaker

Fig. 69.--Schematic Diagram of an Atom

Fig. 70.--Action of Two-electrode Vacuum Tube

(A) and (B) Fig. 71.--How a Two-electrode Tube Acts as Relay or a
Detector

(C) Fig. 71--Only the Positive Part of Oscillations Goes through the
Tube

(A) and (B) Fig. 72.--How the Positive and Negative Voltages of the
Oscillations Act on the Electrons

(C) Fig. 72.--How the Three-electrode Tube Acts as Detector and
Amplifier

(D) Fig. 72.--How the Oscillations Control the Flow of the Battery
Current through the Tube

Fig. 73.--How the Heterodyne Receptor Works

Fig. 74.--Separate Heterodyne Oscillator

(A) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter.

(B) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter.

Fig. 76.--Experimental C. W. Telegraph Transmitter

Fig. 77--Apparatus of 100-mile C. W. Telegraph Transmitter

Fig. 78.--5- to 50-watt C. W. Telegraph Transmitter (with a Single
Oscillation Tube)

Fig. 79.--200-mile C. W. Telegraph Transmitter (with Two Tubes in
Parallel)

Fig. 80.--50-watt Oscillator Vacuum Tube

Fig. 81.--Alternating Current Power Transformer (for C. W. Telegraphy
and Wireless Telephony)

Fig. 82.--Wiring Diagram for 200- to 500-mile C. W. Telegraph
Transmitting Set. (With Alternating Current.)

Fig. 83--Wiring Diagram for 500- to 1000-mile C. W. Telegraph
Transmitter

Fig. 84.--Standard Microphone Transmitter

Fig. 85.--Wiring Diagram of Short Distance Wireless Telephone Set.
(Microphone in Aerial Wire.)

Fig. 86.--Telephone Induction Coil (used with Microphone Transmitter).

Fig. 87.--Microphone Transformer Used with Microphone Transmitter

Fig. 88.--Magnetic Modulator Used with Microphone Transmitter

(A) Fig. 89.--Wiring Diagram of 25--to 50-mile Wireless Telephone.
(Microphone Modulator Shunted Around Grid-leak Condenser)

(B) Fig. 89.--Microphone Modulator Connected in Aerial Wire

Fig. 90.--Wiring Diagram of 50- to 100-mile Wireless Telephone
Transmitting Set

Fig. 91.--Plate and Grid Circuit Reactor

Fig. 92.--Filter Reactor for Smoothing Out Rectified Currents

Fig. 93.--100- to 200-mile Wireless Telephone Transmitter

(A) and (B) Fig. 94.--Operation of Vacuum Tube Oscillators

(C) Fig. 94.--How a Direct Current Sets up Oscillations

Fig. 95.--Positive Voltage Only Sets up Oscillations

Fig. 96.--Rasco Baby Crystal Detector

Fig. 97.--How the Tuning Coil is Made

Fig. 98.--Mesco loop-ohm Head Set

Fig. 99.--Schematic Layout of the $5.00 Receiving Set

Fig. 100.--Wiring Diagram for the $5.00 Receiving Set




LIST OF ILLUSTRATIONS


A. Frederick Collins, Inventor of the Wireless Telephone, 1899.
  Awarded Gold Medal for same, Alaska Yukon Pacific Exposition, 1909

Collins' Wireless Telephone Exhibited at the Madison Square Garden,
  October, 1908

General Pershing "Listening-in"

The World's Largest Radio Receiving Station. Owned by the Radio
  Corporation of America at Rocky Point near Port Jefferson, L. I.

First Wireless College in the World, at Tufts College, Mass

Alexander Graham Bell, Inventor of the Telephone, now an ardent
  Radio Enthusiast

World's Largest Loud Speaker ever made. Installed in Lytle
  Park, Cincinnati, Ohio, to permit President Harding's
  Address at Point Pleasant, Ohio, during the Grant Centenary
  Celebration to be heard within a radius of one square

United States Naval High Power Station, Arlington, Va. General
  view of Power Room. At the left can be seen the Control
  Switchboards, and overhead, the great 30 K.W. Arc Transmitter
  with Accessories

The Transformer and Tuner of the World's Largest Radio Station.
  Owned by the Radio Corporation of America at Rocky Point
  near Port Jefferson, L. I.

Broadcasting Government Reports by Wireless from Washington.
  This shows Mr. Gale at work with his set in the Post Office
  Department

Wireless Receptor, the size of a Safety Match Box. A Youthful
  Genius in the person of Kenneth R. Hinman, who is only
  twelve years old, has made a Wireless Receiving Set that fits
  neatly into a Safety Match Box. With this Instrument and
  a Pair of Ordinary Receivers, he is able to catch not only
  Code Messages but the regular Broadcasting Programs from
  Stations Twenty and Thirty Miles Distant

Wireless Set made into a Ring, designed by Alfred G. Rinehart, of
  Elizabeth, New Jersey. This little Receptor is a Practical Set;
  it will receive Messages, Concerts, etc., measures 1" by 5/8" by
  7/8". An ordinary Umbrella is used as an Aerial




CHAPTER I

HOW TO BEGIN WIRELESS


In writing this book it is taken for granted that you are: _first_,
one of the several hundred thousand persons in the United States who
are interested in wireless telegraphy and telephony; _second_, that
you would like to install an apparatus in your home, and _third_, that
it is all new to you.

Now if you live in a city or town large enough to support an
electrical supply store, there you will find the necessary apparatus
on sale, and someone who can tell you what you want to know about it
and how it works. If you live away from the marts and hives of
industry you can send to various makers of wireless apparatus
[Footnote: A list of makers of wireless apparatus will be found in the
_Appendix_.] for their catalogues and price-lists and these will give
you much useful information. But in either case it is the better plan
for you to know before you start in to buy an outfit exactly what
apparatus you need to produce the result you have in mind, and this
you can gain in easy steps by reading this book.

Kinds of Wireless Systems.--There are two distinct kinds of wireless
systems and these are: the _wireless telegraph_ system, and the
_wireless telephone_ system. The difference between the wireless
telegraph and the wireless telephone is that the former transmits
messages by means of a _telegraph key_, and the latter transmits
conversation and music by means of a _microphone transmitter_. In
other words, the same difference exists between them in this respect
as between the Morse telegraph and the Bell telephone.

Parts of a Wireless System.--Every complete wireless station, whether
telegraph or telephone, consists of three chief separate and distinct
parts and these are: (a) the _aerial wire system_, or _antenna_ as it
is often called, (b) the _transmitter_, or _sender_, and (c) the
_receiver_, or, more properly, the _receptor_. The aerial wire is
precisely the same for either wireless telegraphy or wireless
telephony. The transmitter of a wireless telegraph set generally uses
a _spark gap_ for setting up the electric oscillations, while usually
for wireless telephony a _vacuum tube_ is employed for this purpose.
The receptor for wireless telegraphy and telephony is the same and may
include either a _crystal detector_ or a _vacuum tube detector_, as
will be explained presently.

The Easiest Way to Start.--First of all you must obtain a government
license to operate a sending set, but you do not need a license to put
up and use a receiving set, though you are required by law to keep
secret any messages which you may overhear. Since no license is needed
for a receiving set the easiest way to break into the wireless game is
to put up an aerial and hook up a receiving set to it; you can then
listen-in and hear what is going on in the all-pervading ether around
you, and you will soon find enough to make things highly entertaining.

Nearly all the big wireless companies have great stations fitted with
powerful telephone transmitters and at given hours of the day and
night they send out songs by popular singers, dance music by jazz
orchestras, fashion talks by and for the ladies, agricultural reports,
government weather forecasts and other interesting features. Then by
simply shifting the slide on your tuning coil you can often tune-in
someone who is sending _Morse_, that is, messages in the dot and dash
code, or, perhaps a friend who has a wireless telephone transmitter
and is talking. Of course, if you want to _talk back_ you must have a
wireless transmitter, either telegraphic or telephonic, and this is a
much more expensive part of the apparatus than the receptor, both in
its initial cost and in its operation. A wireless telegraph
transmitter is less costly than a wireless telephone transmitter and
it is a very good scheme for you to learn to send and receive
telegraphic messages.

At the present time, however, there are fifteen amateur receiving
stations in the United States to every sending station, so you can see
that the majority of wireless folks care more for listening in to the
broadcasting of news and music than to sending out messages on their
own account. The easiest way to begin wireless, then, is to put up an
aerial and hook up a receiving set to it.

About Aerial Wire Systems.--To the beginner who wants to install a
wireless station the aerial wire system usually looms up as the
biggest obstacle of all, and especially is this true if his house is
without a flag pole, or other elevation from which the aerial wire can
be conveniently suspended.

If you live in the congested part of a big city where there are no
yards and, particularly, if you live in a flat building or an
apartment house, you will have to string your aerial wire on the roof,
and to do this you should get the owner's, or agent's, permission.
This is usually an easy thing to do where you only intend to receive
messages, for one or two thin wires supported at either end of the
building are all that are needed. If for any reason you cannot put
your aerial on the roof then run a wire along the building outside of
your apartment, and, finally, if this is not feasible, connect your
receiver to a wire strung up in your room, or even to an iron or a
brass bed, and you can still get the near-by stations.

An important part of the aerial wire system is the _ground_, that is,
your receiving set must not only be connected with the aerial wire,
but with a wire that leads to and makes good contact with the moist
earth of the ground. Where a house or a building is piped for gas,
water or steam, it is easy to make a ground connection, for all you
have to do is to fasten the wire to one of the pipes with a clamp.
[Footnote: Pipes are often insulated from the ground, which makes them
useless for this purpose.] Where the house is isolated then a lot of
wires or a sheet of copper or of zinc must be buried in the ground at
a sufficient depth to insure their being kept moist.

About the Receiving Apparatus.--You can either buy the parts of the
receiving apparatus separate and hook them up yourself, or you can buy
the apparatus already assembled in a set which is, in the beginning,
perhaps, the better way.

The simplest receiving set consists of (1) a _detector_, (2) a _tuning
coil_, and (3) a _telephone receiver_ and these three pieces of
apparatus are, of course, connected together and are also connected to
the aerial and ground as the diagram in Fig. 1 clearly shows. There
are two chief kinds of detectors used at the present time and these
are: (a) the _crystal detector_, and (b) the _vacuum tube detector_.
The crystal detector is the cheapest and simplest, but it is not as
sensitive as the vacuum tube detector and it requires frequent
adjustment. A crystal detector can be used with or without a battery
while the vacuum tube detector requires two small batteries.

[Illustration: Fig. 1.--Simple Receiving Set.]

A tuning coil of the simplest kind consists of a single layer of
copper wire wound on a cylinder with an adjustable, or sliding,
contact, but for sharp tuning you need a _loose coupled tuning coil_.
Where a single coil tuner is used a _fixed_ condenser should be
connected around the telephone receivers. Where a loose coupled tuner
is employed you should have a variable condenser connected across the
_closed oscillation circuit_ and a _fixed condenser_ across the
telephone receivers.

When listening-in to distant stations the energy of the received
wireless waves is often so very feeble that in order to hear
distinctly an _amplifier_ must be used. To amplify the incoming sounds
a vacuum tube made like a detector is used and sometimes as many as
half-a-dozen of these tubes are connected in the receiving circuit, or
in _cascade_, as it is called, when the sounds are _amplified_, that
is magnified, many hundreds of times.

The telephone receiver of a receiving set is equally as important as
the detector. A single receiver can be used but a pair of receivers
connected with a head-band gives far better results. Then again the
higher the resistance of the receivers the more sensitive they often
are and those wound to as high a resistance as 3,200 ohms are made for
use with the best sets. To make the incoming signals, conversation or
music, audible to a room full of people instead of to just yourself
you must use what is called a _loud speaker_. In its simplest form
this consists of a metal cone like a megaphone to which is fitted a
telephone receiver.

About Transmitting Stations--Getting Your License.--If you are going
to install a wireless sending apparatus, either telegraphic or
telephonic, you will have to secure a government license for which no
fee or charge of any kind is made. There are three classes of licenses
issued to amateurs who want to operate transmitting stations and these
are: (1) the _restricted amateur license_, (2) the _general amateur
license_, and (3) the _special amateur license_.

If you are going to set up a transmitter within five nautical miles of
any naval wireless station then you will have to get a _restricted
amateur license_ which limits the current you use to half a _kilowatt_
[Footnote: A _Kilowatt_ is 1,000 _watts_. There are 746 watts in a
horsepower.] and the wave length you send out to 200 _meters_. Should
you live outside of the five-mile range of a navy station then you can
get a general amateur license and this permits you to use a current of
1 kilowatt, but you are likewise limited to a wave length of 200
meters. But if you can show that you are doing some special kind of
wireless work and not using your sending station for the mere pleasure
you are getting out of it you may be able to get a _special amateur
license_ which gives you the right to send out wave lengths up to 375
meters.

When you are ready to apply for your license write to the _Radio
Inspector_ of whichever one of the following districts you live in:

  First District..............Boston, Mass.
  Second   "    ..............New York City
  Third    "    ..............Baltimore, Md.
  Fourth   "    ..............Norfolk, Va.
  Fifth    "    ..............New Orleans, La.
  Sixth    "    ............. San Francisco, Cal.
  Seventh  "    ............. Seattle, Wash.
  Eighth   "    ............. Detroit, Mich.
  Ninth    "    ..............Chicago, Ill.

Kinds of Transmitters.--There are two general types of transmitters
used for sending out wireless messages and these are: (1) _wireless
telegraph_ transmitters, and (2) _wireless telephone_ transmitters.
Telegraph transmitters may use either: (a) a _jump-spark_, (b) an
_electric arc_, or (c) a _vacuum tube_ apparatus for sending out dot
and dash messages, while telephone transmitters may use either, (a) an
_electric arc_, or (b) a _vacuum tube_ for sending out vocal and
musical sounds. Amateurs generally use a _jump-spark_ for sending
wireless telegraph messages and the _vacuum tube_ for sending wireless
telephone messages.

The Spark Gap Wireless Telegraph Transmitter.--The simplest kind of a
wireless telegraph transmitter consists of: (1) a _source of direct or
alternating current_, (2) a _telegraph key_, (3) a _spark-coil_ or a
_transformer_, (4) a _spark gap_, (5) an _adjustable condenser_ and
(6) an _oscillation transformer_. Where _dry cells_ or a _storage
battery_ must be used to supply the current for energizing the
transmitter a spark-coil can be employed and these may be had in
various sizes from a little fellow which gives 1/4-inch spark up to a
larger one which gives a 6-inch spark. Where more energy is needed it
is better practice to use a transformer and this can be worked on an
alternating current of 110 volts, or if only a 110 volt direct current
is available then an _electrolytic interrupter_ must be used to make
and break the current. A simple transmitting set with an induction
coil is shown in Fig. 2.

[Illustration: Fig 2.--Simple Transmitting Set.]

A wireless key is made like an ordinary telegraph key except that
where large currents are to be used it is somewhat heavier and is
provided with large silver contact points. Spark gaps for amateur work
are usually of: (1) the _plain_ or _stationary type_, (2) the
_rotating type_, and (3) the _quenched gap_ type. The plain spark-gap
is more suitable for small spark-coil sets, and it is not so apt to
break down the transformer and condenser of the larger sets as the
rotary gap. The rotary gap on the other hand tends to prevent _arcing_
and so the break is quicker and there is less dragging of the spark.
The quenched gap is more efficient than either the plain or rotary gap
and moreover it is noiseless.

Condensers for spark telegraph transmitters can be ordinary Leyden
jars or glass plates coated with tin or copper foil and set into a
frame, or they can be built up of mica and sheet metal embedded in an
insulating composition. The glass plate condensers are the cheapest
and will serve your purpose well, especially if they are immersed in
oil. Tuning coils, sometimes called _transmitting inductances_ and
_oscillation transformers_, are of various types. The simplest kind is
a transmitting inductance which consists of 25 or 30 turns of copper
wire wound on an insulating tube or frame. An oscillation transformer
is a loose coupled tuning coil and it consists of a primary coil
formed of a number of turns of copper wire wound on a fixed insulating
support, and a secondary coil of about twice the number of turns of
copper wire which is likewise fixed in an insulating support, but the
coils are relatively movable. An _oscillation transformer_ (instead of
a _tuning coil_), is required by government regulations unless
_inductively coupled_.

The Vacuum Tube Telegraph Transmitter.--This consists of: (1) a
_source of direct or alternating current_, (2) a _telegraph key_, (3) a
_vacuum tube oscillator_, (4) a _tuning coil_, and (5) a _condenser_.
This kind of a transmitter sets up _sustained_ oscillations instead of
_periodic_ oscillations which are produced by a spark gap set. The
advantages of this kind of a system will be found explained in Chapter
XVI.

The Wireless Telephone Transmitter.--Because a jump-spark sets up
_periodic oscillations_, that is, the oscillations are discontinuous,
it cannot be used for wireless telephony. An electric arc or a vacuum
tube sets up _sustained_ oscillations, that is, oscillations which are
continuous. As it is far easier to keep the oscillations going with a
vacuum tube than it is with an arc the former means has all but
supplanted the latter for wireless telephone transmitters. The
apparatus required and the connections used for wireless telephone
sets will be described in later chapters.

Useful Information.--It would be wise for the reader to turn to the
Appendix, beginning with page 301 of this book, and familiarize
himself with the information there set down in tabular and graphic
form. For example, the first table gives abbreviations of electrical
terms which are in general use in all works dealing with the subject.
You will also find there brief definitions of electric and magnetic
units, which it would be well to commit to memory; or, at least, to
make so thoroughly your own that when any of these terms is mentioned,
you will know instantly what is being talked about.




CHAPTER II

PUTTING UP YOUR AERIAL


As inferred in the first chapter, an aerial for receiving does not
have to be nearly as well made or put up as one for sending. But this
does not mean that you can slipshod the construction and installation
of it, for however simple it is, the job must be done right and in
this case it is as easy to do it right as wrong.

To send wireless telegraph and telephone messages to the greatest
distances and to receive them as distinctly as possible from the
greatest distances you must use for your aerial (1) copper or aluminum
wire, (2) two or more wires, (3) have them the proper length, (4) have
them as high in the air as you can, (5) have them well apart from each
other, and (6) have them well insulated from their supports. If you
live in a flat building or an apartment house you can string your
aerial wires from one edge of the roof to the other and support them
by wooden stays as high above it as may be convenient.

Should you live in a detached house in the city you can usually get
your next-door neighbor to let you fasten one end of the aerial to his
house and this will give you a good stretch and a fairly high aerial.
In the country you can stretch your wires between the house and barn
or the windmill. From this you will see that no matter where you live
you can nearly always find ways and means of putting up an aerial that
will serve your needs without going to the expense of erecting a mast.

Kinds of Aerial Wire Systems.--An amateur wireless aerial can be
anywhere from 25 feet to 100 feet long and if you can get a stretch of
the latter length and a height of from 30 to 75 feet you will have one
with which you can receive a thousand miles or more and send out as
much energy as the government will allow you to send.

The kind of an aerial that gives the best results is one whose wire,
or wires, are _horizontal_, that is, parallel with the earth under it
as shown at A in Fig. 3. If only one end can be fixed to some elevated
support then you can secure the other end to a post in the ground, but
the slope of the aerial should not be more than 30 or 35 degrees from
the horizontal at most as shown at B.

[Illustration: (A) Fig. 3.--Flat top, or Horizontal Aerial.]

[Illustration: (B) Fig. 3.--Inclined Aerial.]

The _leading-in wire_, that is, the wire that leads from and joins the
aerial wire with your sending and receiving set, can be connected to
the aerial anywhere it is most convenient to do so, but the best
results are had when it is connected to one end as shown at A in Fig.
4, in which case it is called an _inverted L aerial_, or when it is
connected to it at the middle as shown at B, when it is called a _T
aerial_. The leading-in wire must be carefully insulated from the
outside of the building and also where it passes through it to the
inside. This is done by means of an insulating tube known as a
_leading-in insulator_, or _bulkhead insulator_ as it is sometimes
called.

[Illustration: (A) Fig. 4.--Inverted L Aerial.]

[Illustration: (B) Fig. 4.--T Aerial.]

As a protection against lightning burning out your instruments you can
use either: (1) an _air-gap lightning arrester,_ (2) a _vacuum tube
protector_, or (3) a _lightning switch_, which is better. Whichever
of these devices is used it is connected in between the aerial and an
outside ground wire so that a direct circuit to the earth will be
provided at all times except when you are sending or receiving. So
your aerial instead of being a menace really acts during an electrical
storm like a lightning rod and it is therefore a real protection. The
air-gap and vacuum tube lightning arresters are little devices that
can be used only where you are going to receive, while the lightning
switch must be used where you are going to send; indeed, in some
localities the _Fire Underwriters_ require a large lightning switch to
be used for receiving sets as well as sending sets.

How to Put Up a Cheap Receiving Aerial.--The kind of an aerial wire
system you put up will depend, chiefly, on two things, and these are:
(1) your pocketbook, and (2) the place where you live.

A Single Wire Aerial.--This is the simplest and cheapest kind of a
receiving aerial that can be put up. The first thing to do is to find
out the length of wire you need by measuring the span between the two
points of support; then add a sufficient length for the leading-in
wire and enough more to connect your receiving set with the radiator
or water pipe.

You can use any size of copper or aluminum wire that is not smaller
than _No. 16 Brown and Sharpe gauge._ When you buy the wire get also
the following material: (1) two _porcelain insulators_ as shown at A
in Fig. 5; (2) three or four _porcelain knob insulators_, see B; (3)
either (a) an _air gap lightning arrester,_ see C, or (b) a _lightning
switch_ see D; (4) a _leading-in porcelain tube insulator,_ see E, and
(5) a _ground clamp_, see F.

[Illustration: Fig. 5.--Material for a Simple Aerial Wire System.]

To make the aerial slip each end of the wire through a hole in each
insulator and twist it fast; next cut off and slip two more pieces of
wire through the other holes in the insulators and twist them fast and
then secure these to the supports at the ends of the building. Take
the piece you are going to use for the leading-in wire, twist it
around the aerial wire and solder it there when it will look like A in
Fig. 6. Now if you intend to use the _air gap lightning arrester_
fasten it to the wall of the building outside of your window, and
bring the leading-in wire from the aerial to the top binding post of
your arrester and keep it clear of everything as shown at B. If your
aerial is on the roof and you have to bring the leading-in wire over
the cornice or around a corner fix a porcelain knob insulator to the
one or the other and fasten the wire to it.

[Illustration: (A) Fig. 6.--Single Wire Aerial for Receiving.]

[Illustration: (B) Fig. 6.--Receiving Aerial with Air Gap Lightning
Arrester.]

[Illustration: (C) Fig. 6.--Aerial with Lightning Switch.]

Next bore a hole through the frame of the window at a point nearest
your receiving set and push a porcelain tube 5/8 inch in diameter and
5 or 6 inches long, through it. Connect a length of wire to the top
post of the arrester or just above it to the wire, run this through
the leading-in insulator and connect it to the slider of your tuning
coil. Screw the end of a piece of heavy copper wire to the lower post
of the arrester and run it to the ground, on porcelain knobs if
necessary, and solder it to an iron rod or pipe which you have driven
into the earth. Finally connect the fixed terminal of your tuning coil
with the water pipe or radiator inside of the house by means of the
ground clamp as shown in the diagrammatic sketch at B in Fig. 6 and
you are ready to tune in.

If you want to use a lightning switch instead of the air-gap arrester
then fasten it to the outside wall instead of the latter and screw the
free end of the leading-in wire from the aerial to the middle post of
it as shown at C in Fig. 6. Run a wire from the top post through the
leading-in insulator and connect it with the slider of your tuning
coil. Next screw one end of a length of heavy copper wire to the lower
post of the aerial switch and run it to an iron pipe in the ground as
described above in connection with the spark-gap lightning arrester;
then connect the fixed terminal of your tuning coil with the radiator
or water pipe and your aerial wire system will be complete as shown at
C in Fig. 6.

A Two-wire Aerial.--An aerial with two wires will give better results
than a single wire and three wires are better than two, but you must
keep them well apart. To put up a two-wire aerial get (1) enough _No.
16_, or preferably _No. 14_, solid or stranded copper or aluminum
wire, (2) four porcelain insulators, see B in Fig. 5, and (3) two
sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the
_spreaders_, and bore 1/8-inch hole through each end of each one. Now
twist the ends of the wires to the insulators and then cut off four
pieces of wire about 6 feet long and run them through the holes in the
wood spreaders. Finally twist the ends of each pair of short wires to
the free ends of the insulators and then twist the free ends of the
wires together.

For the leading-in wire that goes to the lightning switch take two
lengths of wire and twist one end of each one around the aerial wires
and solder them there. Twist the short wire around the long wire and
solder this joint also when the aerial will look like Fig. 7. Bring
the free end of the leading-in wire down to the middle post of the
lightning switch and fasten it there and connect up the receiver to it
and the ground as described under the caption of _A Single Wire
Aerial_.

[Illustration: Fig. 7.--Two Wire Aerial.]

Connecting in the Ground.--If there is a gas or water system or a
steam-heating plant in your house you can make your ground connection
by clamping a ground clamp to the nearest pipe as has been previously
described. Connect a length of bare or insulated copper wire with it
and bring this up to the table on which you have your receiving set.
If there are no grounded pipes available then you will have to make a
good ground which we shall describe presently and lead the ground wire
from your receiving set out of the window and down to it.

How to Put Up a Good Aerial.--While you can use the cheap aerial
already described for a small spark-coil sending set you should have a
better insulated one for a 1/2 or a 1 kilowatt transformer set. The
cost for the materials for a good aerial is small and when properly
made and well insulated it will give results that are all out of
proportion to the cost of it.

An Inexpensive Good Aerial.--A far better aerial, because it is more
highly insulated, can be made by using _midget insulators_ instead of
the porcelain insulators described under the caption of _A Single Wire
Aerial_ and using a small _electrose leading-in insulator_ instead of
the porcelain bushing. This makes a good sending aerial for small sets
as well as a good receiving aerial.

The Best Aerial that Can Be Made.--To make this aerial get the
following material together: (1) enough _stranded or braided wire_ for
three or four lengths of parallel wires, according to the number you
want to use (2) six or eight _electrose ball insulators_, see B, Fig.
8; (3) two 5-inch or 10-inch _electrose strain insulators_, see C; (4)
six or eight _S-hooks_, see D; one large _withe_ with one eye for
middle of end spreader, see E; (6) two smaller _withes_ with one eye
each for end spreader, see E; (7) two still smaller _withes_, with two
eyes each for the ends of the end spreaders, see E (8) two _thimbles_,
see F, for 1/4-inch wire cable; (9) six or eight _hard rubber tubes_
or _bushings_ as shown at G; and (10) two _end spreaders_, see H; one
_middle spreader_, see I; and one _leading-in spreader_, see J.

[Illustration: (A) Fig. 8--Part of a Good Aerial.]

[Illustration: (B) Fig. 8.--The Spreaders.]

For this aerial any one of a number of kinds of wire can be used and
among these are (a) _stranded copper wire;_ (b) _braided copper wire;_
(c) _stranded silicon bronze wire,_ and (d) _stranded phosphor bronze
wire_. Stranded and braided copper wire is very flexible as it is
formed of seven strands of fine wire twisted or braided together and
it is very good for short and light aerials. Silicon bronze wire is
stronger than copper wire and should be used where aerials are more
than 100 feet long, while phosphor bronze wire is the strongest aerial
wire made and is used for high grade aerials by the commercial
companies and the Government for their high-power stations.

The spreaders should be made of spruce, and should be 4 feet 10 inches
long for a three-wire aerial and 7 feet 1 inch long for a four-wire
aerial as the distance between the wires should be about 27 inches.
The end spreaders can be turned cylindrically but it makes a better
looking job if they taper from the middle to the ends. They should be
2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends.
The middle spreader can be cylindrical and 2 inches in diameter. It
must have holes bored through it at equidistant points for the hard
rubber tubes; each of these should be 5/8 inch in diameter and have a
hole 5/32 inch in diameter through it for the aerial wire. The
leading-in spreader is also made of spruce and is 1-1/2 inches square
and 26 inches long. Bore three or four 5/8-inch holes at equidistant
points through this spreader and insert hard rubber tubes in them as
with the middle spreader.

Assembling the Aerial.--Begin by measuring off the length of each wire
to be used and see to it that all of them are of exactly the same
length. Now push the hard rubber insulators through the holes in the
middle spreader and thread the wires through the holes in the
insulators as shown at A in Fig 9.

Next twist the ends of each wire to the rings of the ball insulators
and then put the large withes on the middle of each of the end
spreaders; fix the other withes on the spreaders so that they will be
27 inches apart and fasten the ball insulators to the eyes in the
withes with the S-hooks. Now slip a thimble through the eye of one of
the long strain insulators, thread a length of stranded steel wire 1/4
inch in diameter through it and fasten the ends of it to the eyes in
the withes on the ends of the spreaders.

[Illustration: (A) Fig. 9.--Middle Spreader.]

[Illustration: (B) Fig. 9.--One End of Aerial Complete.]

[Illustration: (C) Fig. 9.--Leading in Spreader.]

Finally fasten a 40-inch length of steel stranded wire to each of the
eyes of the withes on the middle of each of the spreaders, loop the
other end over the thimble and then wrap the end around the wires that
are fixed to the ends of the spreaders. One end of the aerial is shown
complete at B in Fig. 9, and from this you can see exactly how it is
assembled. Now cut off three or four pieces of wire 15 or 20 feet long
and twist and solder each one to one of the aerial wires; then slip
them through the hard rubber tubes in the leading-in spreader, bring
their free ends together as at C and twist and solder them to a length
of wire long enough to reach to your lightning switch or instruments.

Making a Good Ground.--Where you have to make a _ground_ you can do so
either by (1) burying sheets of zinc or copper in the moist earth; (2)
burying a number of wires in the moist earth, or (3) using a
_counterpoise_. To make a ground of the first kind take half a dozen
large sheets of copper or zinc, cut them into strips a foot wide,
solder them all together with other strips and bury them deeply in the
ground.

It is easier to make a wire ground, say of as many or more wires as
you have in your aerial and connect them together with cross wires. To
put such a ground in the earth you will have to use a plow to make the
furrows deep enough to insure them always being moist. In the
counterpoise ground you make up a system of wires exactly like your
aerial, that is, you insulate them just as carefully; then you support
them so that they will be as close to the ground as possible and yet
not touch it or anything else. This and the other two grounds just
described should be placed directly under the aerial wire if the best
results are to be had. In using a counterpoise you must bring the wire
from it up to and through another leading-in insulator to your
instruments.




CHAPTER III

SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS


With a crystal detector receiving set you can receive either
telegraphic dots and dashes or telephonic speech and music. You can
buy a receiving set already assembled or you can buy the different
parts and assemble them yourself. An assembled set is less bother in
the beginning but if you like to experiment you can _hook up_, that
is, connect the separate parts together yourself and it is perhaps a
little cheaper to do it this way. Then again, by so doing you get a
lot of valuable experience in wireless work and an understanding of
the workings of wireless that you cannot get in any other way.

Assembled Wireless Receiving Sets.--The cheapest assembled receiving
set [Footnote: The Marvel, made by the Radio Mfg. Co., New York City.]
advertised is one in which the detector and tuning coil is mounted in
a box. It costs $15.00, and can be bought of dealers in electric
supplies generally.

This price also includes a crystal detector, an adjustable tuning
coil, a single telephone receiver with head-band and the wire,
porcelain insulators, lightning switch and ground clamp for the aerial
wire system. It will receive wireless telegraph and telephone messages
over a range of from 10 to 25 miles.

Another cheap unit receptor, that is, a complete wireless receiving
set already mounted which can be used with a single aerial is sold for
$25.00. [Footnote: The Aeriola Jr., made by the Westinghouse Company,
Pittsburgh, Pa.] This set includes a crystal detector, a variable
tuning coil, a fixed condenser and a pair of head telephone receivers.
It can also be used to receive either telegraph or telephone messages
from distances up to 25 miles. The aerial equipment is not included in
this price, but it can be bought for about $2.50 extra.

Assembling Your Own Receiving Set.--In this chapter we shall go only
into the apparatus used for two simple receiving sets, both of which
have a _crystal detector_. The first set includes a _double-slide
tuning coil_ and the second set employs a _loose-coupled tuning coil_,
or _loose coupler_, as it is called for short. For either set you can
use a pair of 2,000- or 3,000-ohm head phones.

[Illustration: original © Underwood and Underwood. General Pershing
Listening In.]

The Crystal Detector.--A crystal detector consists of: (1) _the
frame_, (2) _the crystal_, and (3) _the wire point_. There are any
number of different designs for frames, the idea being to provide a
device that will (a) hold the sensitive crystal firmly in place, and
yet permit of its removal, (b) to permit the _wire point_, or
_electrode_, to be moved in any direction so that the free point of it
can make contact with the most sensitive spot on the crystal and (c)
to vary the pressure of the wire on the crystal.

A simple detector frame is shown in the cross-section at A in Fig. 10;
the crystal, which may be _galena_, _silicon_ or _iron pyrites_, is
held securely in a holder while the _phosphor-bronze wire point_ which
makes contact with it, is fixed to one end of a threaded rod on the
other end of which is a knob. This rod screws into and through a
sleeve fixed to a ball that sets between two brass standards and this
permits an up and down or a side to side adjustment of the metal point
while the pressure of it on the crystal is regulated by the screw.

[Illustration: (A) Fig. 10.--Cross Section of Crystal Detector.]

[Illustration: (B) Fig. 10.--The Crystal Detector Complete.]

A crystal of this kind is often enclosed in a glass cylinder and this
makes it retain its sensitiveness for a much longer time than if it
were exposed to dust and moisture. An upright type of this detector
can be bought for $2.25, while a horizontal type, as shown at B, can
be bought for $2.75. Galena is the crystal that is generally used,
for, while it is not quite as sensitive as silicon and iron pyrites,
it is easier to obtain a sensitive piece.

The Tuning Coil.--It is with the tuning coil that you _tune in_ and
_tune out_ different stations and this you do by sliding the contacts
to and fro over the turns of wire; in this way you vary the
_inductance_ and _capacitance_, that is, the _constants_ of the
receiving circuits and so make them receive _electric waves_, that is,
wireless waves, of different lengths.

The Double Slide Tuning Coil.--With this tuning coil you can receive
waves from any station up to 1,000 meters in length. One of the ends
of the coil of wire connects with the binding post marked _a_ in Fig.
11, and the other end connects with the other binding post marked _b_,
while one of the sliding contacts is connected to the binding post
_c_, and the _other sliding contact_ is connected with the binding
post _d_.

[Illustration: (A) Fig. 11.--Schematic Diagram of Double Slide Tuning
Coil.]

[Illustration: (B) Fig. 11.--Double Slide Tuning Coil Complete.]

When connecting in the tuning coil, only the post _a_ or the post _b_
is used as may be most convenient, but the other end of the wire which
is connected to a post is left free; just bear this point in mind when
you come to connect the tuning coil up with the other parts of your
receiving set. The tuning coil is shown complete at B and it costs
$3.00 or $4.00. A _triple slide_ tuning coil constructed like the
double slide tuner just described, only with more turns of wire on it,
makes it possible to receive wave lengths up to 1,500 meters. It costs
about $6.00.

The Loose Coupled Tuning Coil.--With a _loose coupler_, as this kind
of a tuning coil is called for short, very _selective tuning_ is
possible, which means that you can tune in a station very sharply, and
it will receive any wave lengths according to size of coils. The
primary coil is wound on a fixed cylinder and its inductance is varied
by means of a sliding contact like the double slide tuning coil
described above. The secondary coil is wound on a cylinder that slides
in and out of the primary coil. The inductance of this coil is varied
by means of a switch that makes contact with the fixed points, each of
which is connected with every twentieth turn of wire as shown in the
diagram A in Fig. 12. The loose coupler, which is shown complete at B,
costs in the neighborhood of $8.00 or $10.00.

[Illustration: (A) Fig. 12.--Schematic Diagram of Loose Coupler.]

[Illustration: (B) Fig. 12.--Loose Coupler Complete.]

Fixed and Variable Condensers.--You do not require a condenser for a
simple receiving set, but if you will connect a _fixed condenser_
across your headphones you will get better results, while a _variable
condenser_ connected in the _closed circuit of a direct coupled
receiving set_, that is, one where a double slide tuning coil is used,
makes it easy to tune very much more sharply; a variable condenser is
absolutely necessary where the circuits are _inductively coupled_,
that is, where a loose coupled tuner is used.

A fixed condenser consists of a number of sheets of paper with leaves
of tin-foil in between them and so built up that one end of every
other leaf of tin-foil projects from the opposite end of the paper as
shown at A in Fig. 13. The paper and tin-foil are then pressed
together and impregnated with an insulating compound. A fixed
condenser of the exact capacitance required for connecting across the
head phones is mounted in a base fitted with binding posts, as shown
at B, and costs 75 cents. (Paper ones 25 cents.)

[Illustration: (A) Fig. 13.--How a Fixed Receiving Condenser is Built
up.]

[Illustration: (B) Fig. 13.--The Fixed Condenser Complete.]

[Illustration: (C) and (D) Fig. 13.--The Variable Rotary Condenser.]

A variable condenser, see C, of the rotating type is formed of a set
of fixed semi-circular metal plates which are slightly separated from
each other and between these a similar set of movable semi-circular
metal plates is made to interleave; the latter are secured to a shaft
on the top end of which is a knob and by turning it the capacitance of
the condenser, and, hence, of the circuit in which it is connected, is
varied. This condenser, which is shown at D, is made in two sizes, the
smaller one being large enough for all ordinary wave lengths while the
larger one is for proportionately longer wave lengths. These
condensers cost $4.00 and $5.00 respectively.

About Telephone Receivers.--There are a number of makes of head
telephone receivers on the market that are designed especially for
wireless work. These phones are wound to _resistances_ of from 75
_ohms_ to 8,000 _ohms_, and cost from $1.25 for a receiver
without a cord or headband to $15.00 for a pair of phones with a cord
and head band. You can get a receiver wound to any resistance in
between the above values but for either of the simple receiving sets
such as described in this chapter you ought to have a pair wound to at
least 2,000 ohms and these will cost you about $5.00. A pair of head
phones of this type is shown in Fig. 14.

[Illustration: Fig. 14.--Pair of Wireless Head Phones.]

Connecting Up the Parts--Receiving Set No. 1.--For this set get (1) a
_crystal detector_, (2) a _two-slide tuning coil_, (3) a _fixed
condenser_, and (4) a pair of 2,000 ohm head phones. Mount the
detector on the right-hand side of a board and the tuning coil on the
left-hand side. Screw in two binding posts for the cord ends of the
telephone receivers at _a_ and _b_ as shown at A in Fig. 15. This done
connect one of the end binding posts of the tuning coil with the
ground wire and a post of one of the contact slides with the lightning
arrester or switch which leads to the aerial wire.

[Illustration: Fig. 15.--Top View of Apparatus Layout for Receiving
Set No. 1.]

[Illustration: (B) Fig. 15.--Wiring Diagram for Receiving Set No. 1.]

Now connect the post of the other contact slide to one of the posts of
the detector and the other post of the latter with the binding post
_a_, then connect the binding post _b_ to the ground wire and solder
the joint. Next connect the ends of the telephone receiver cord to the
posts _a_ and _b_ and connect a fixed condenser also with these posts,
all of which are shown in the wiring diagram at B, and you are ready
to adjust the set for receiving.

Receiving Set No. 2.--Use the same kind of a detector and pair of head
phones as for _Set No. 1_, but get (1) a _loose coupled tuning coil_,
and (2) a _variable condenser_. Mount the loose coupler at the back of
a board on the left-hand side and the variable condenser on the
right-hand side. Then mount the detector in front of the variable
condenser and screw two binding posts, _a_ and _b_, in front of the
tuning coil as shown at A in Fig. 16.

[Illustration: Fig. 16.--Top view of Apparatus Layout for Receiving
Set No. 2.]

[Illustration: (B) Fig. 16.--Wiring Diagram for Receiving Set No. 2.]

Now connect the post of the sliding contact of the loose coupler with
the wire that runs to the lightning switch and thence to the aerial;
connect the post of the primary coil, which is the outside coil, with
the ground wire; then connect the binding post leading to the switch
of the secondary coil, which is the inside coil, with one of the posts
of the variable condenser, and finally, connect the post that is
joined to one end of the secondary coil with the other post of the
variable condenser.

This done, connect one of the posts of the condenser with one of the
posts of the detector, the other post of the detector with the binding
post _a_, and the post _b_ to the other post of the variable
condenser. Next connect a fixed condenser to the binding posts _a_ and
_b_ and then connect the telephone receivers to these same posts, all
of which is shown in the wiring diagram at B. You are now ready to
adjust the instruments. In making the connections use No. 16 or 18
insulated copper wire and scrape the ends clean where they go into the
binding posts. See, also, that all of the connections are tight and
where you have to cross the wires keep them apart by an inch or so and
always cross them at right angles.

Adjusting the No. 1 Set--The Detector.--The first thing to do is to
test the detector in order to find out if the point of the contact
wire is on a sensitive spot of the crystal. To do this you need a
_buzzer_, a _switch_ and a _dry cell_. An electric bell from which the
gong has been removed will do for the buzzer, but you can get one that
is made specially for the purpose, for 75 cents, which gives out a
clear, high-pitched note that sounds like a high-power station.

Connect one of the binding posts of the buzzer with one post of the
switch, the other post of the latter with the zinc post of the dry
cell and the carbon post of this to the other post of the buzzer. Then
connect the post of the buzzer that is joined to the vibrator, to the
ground wire as shown in the wiring diagram, Fig. 17. Now close the
switch of the buzzer circuit, put on your head phones, and move the
wire point of the detector to various spots on the crystal until you
hear the sparks made by the buzzer in your phones.

[Illustration: Fig. 17.--Adjusting the Receiving Set.]

Then vary the pressure of the point on the crystal until you hear the
sparks as loud as possible. After you have made the adjustment open
the switch and disconnect the buzzer wire from the ground wire of your
set. This done, be very careful not to jar the detector or you will
throw it out of adjustment and then you will have to do it all over
again. You are now ready to tune the set with the tuning coil and
listen in.

The Tuning Coil.--To tune this set move the slide A of the
double-slide tuner, see B in Fig. 15, over to the end of the coil that
is connected with the ground wire and the slide B near the opposite
end of the coil, that is, the one that has the free end. Now move the
slide A toward the B slide and when you hear the dots and dashes, or
speech or music, that is coming in as loud as you can move the B slide
toward the A slide until you hear still more loudly. A very few trials
on your part and you will be able to tune in or tune out any station
you can hear, if not too close or powerful.

[Illustration: original © Underwood and Underwood. The World's
Largest Radio Receiving Station. Owned by the Radio Corporation of
America at Rocky Point near Point Jefferson, L.I.]

Adjusting the No. 2 Set.--First adjust the crystal detector with the
buzzer set as described above with _Set No. 1,_ then turn the knob of
your variable condenser so that the movable plates are just half-way
in, pull the secondary coil of your loose-coupled tuner half way out;
turn the switch lever on it until it makes a contact with the middle
contact point and set the slider of the primary coil half way between
the ends.

Now listen in for telegraphic signals or telephonic speech or music;
when you hear one or the other slide the secondary coil in and out of
the primary coil until the sounds are loudest; now move the contact
switch over the points forth and back until the sounds are still
louder, then move the slider to and fro until the sounds are yet
louder and, finally, turn the knob of the condenser until the sounds
are clear and crisp. When you have done all of these things you have,
in the parlance of the wireless operator, _tuned in_ and you are ready
to receive whatever is being sent.




CHAPTER IV

SIMPLE TELEGRAPH SENDING SETS


A wireless telegraph transmitting set can be installed for a very
small amount of money provided you are content with one that has a
limited range. Larger and better instruments can, of course, be had
for more money, but however much you are willing to spend still you
are limited in your sending radius by the Government's rules and
regulations. The best way, and the cheapest in the end, to install a
telegraph set is to buy the separate parts and hook them up yourself.

The usual type of wireless telegraph transmitter employs a _disruptive
discharge,_ or _spark,_ as it is called, for setting up the
oscillating currents in the aerial wire system and this is the type of
apparatus described in this chapter. There are two ways to set up the
sparks and these are: (1) with an _induction coil,_ or _spark-coil,_
as it is commonly called, and (2) with an _alternating current
transformer_, or _power transformer_, as it is sometimes called. Where
you have to generate the current with a battery you must use a spark
coil, but if you have a 110-volt direct or alternating lighting
current in your home you can use a transformer which will give you
more power.

A Cheap Transmitting Set (No. 1).--For this set you will need: (1) a
_spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4)
a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation
transformer_. There are many different makes and styles of these parts
but in the last analysis all of them are built on the same underlying
bases and work on the same fundamental principles.

The Spark-Coil.--Spark coils for wireless work are made to give sparks
from 1/4 inch in length up to 6 inches in length, but as a spark coil
that gives less than a 1-inch spark has a very limited output it is
best to get a coil that gives at least a 1-inch spark, as this only
costs about $8.00, and if you can get a 2- or a 4-inch spark coil so
much the better. There are two general styles of spark coils used for
wireless and these are shown at A and B in Fig. 18.

[Illustration: (A) and (B) Fig. 18.--Types of Spark Coils for Set. No.
1.]

[Illustration: (C) Fig. 18.--Wiring Diagram of Spark Coil]

A spark coil of either style consists of (_a_) a soft _iron core_ on
which is wound (_b_) a couple of layers of heavy insulated wire and
this is called the _primary coil_, (_c_) while over this, but
insulated from it, is wound a large number of turns of very fine
insulated copper wire called the _secondary coil_; (d) an
_interrupter_, or _vibrator_, as it is commonly called, and, finally,
(e) a _condenser_. The core, primary and secondary coils form a unit
and these are set in a box or mounted on top of a hollow wooden base.
The condenser is placed in the bottom of the box, or on the base,
while the vibrator is mounted on one end of the box or on top of the
base, and it is the only part of the coil that needs adjusting.

The vibrator consists of a stiff, flat spring fixed at one end to the
box or base while it carries a piece of soft iron called an _armature_
on its free end and this sets close to one end of the soft iron core.
Insulated from this spring is a standard that carries an adjusting
screw on the small end of which is a platinum point and this makes
contact with a small platinum disk fixed to the spring. The condenser
is formed of alternate sheets of paper and tinfoil built up in the
same fashion as the receiving condenser described under the caption of
_Fixed and Variable Condensers_, in Chapter III.

The wiring diagram C shows how the spark coil is wired up. One of the
battery binding posts is connected with one end of the primary coil
while the other end of the latter which is wound on the soft iron core
connects with the spring of the vibrator. The other battery binding
post connects with the standard that supports the adjusting screw. The
condenser is shunted across the vibrator, that is, one end of the
condenser is connected with the spring and the other end of the
condenser is connected with the adjusting screw standard. The ends of
the secondary coil lead to two binding posts, which are usually placed
on top of the spark coil and it is to these that the spark gap is
connected.

The Battery.--This can be formed of dry cells or you can use a storage
battery to energize your coil. For all coils that give less than a
1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils
use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry
cells. The way the dry cells are connected together to form a battery
will be shown presently. A dry cell is shown at A in Fig, 19.

[Illustration: Fig. 19.--Other parts for Transmitting Set No. 1]

The Telegraph Key.--You can use an ordinary Morse telegraph key for
the sending set and you can get one with a japanned iron base for
$1.50 (or better, one made of brass and which has 1/8-inch silver
contact points for $3.00. A key of the latter kind is shown at B).

The Spark gap.--It is in the _spark gap_ that the high tension spark
takes place. The apparatus in which the spark takes place is also
called the _spark gap_. It consists of a pair of zinc plugs, called
_electrodes_, fixed to the ends of a pair of threaded rods, with knobs
on the other ends, and these screw into and through a pair of
standards as shown at _c_. This is called a _fixed_, or _stationary
spark gap_ and costs about $1.00.

The Tuning Coil.--The _transmitting inductance_, or _sending tuning
coil_, consists of 20 to 30 turns of _No. 8 or 9_ hard drawn copper
wire wound on a slotted insulated form and mounted on a wooden base.
It is provided with _clips_ so that you can cut in and cut out as many
turns of wire as you wish and so tune the sending circuits to send out
whatever wave length you desire. It is shown at _d_, and costs about
$5.00. See also _Oscillation Transformer_, page 63 [Chapter IV].

The High Tension Condenser.--High tension condensers, that is,
condensers which will stand up under _high potentials_, or electric
pressures, can be bought in units or sections. These condensers are
made up of thin brass plates insulated with a special compound and
pressed into a compact form. The _capacitance_ [Footnote: This is the
capacity of the condenser.] of one section is enough for a
transmitting set using a spark coil that gives a 2 inch spark or less
and two sections connected together should be used for coils giving
from 2 to 4 inch sparks. It is shown at _e_.

Connecting Up the Apparatus.--Your sending set should be mounted on a
table, or a bench, where it need not be moved. Place the key in about
the middle of the table and down in front, and the spark coil to the
left and well to the back but so that the vibrator end will be to the
right, as this will enable you to adjust it easily. Place the battery
back of the spark coil and the tuning coil (oscillation transformer)
to the right of the spark coil and back of the key, all of which is
shown in the layout at A in Fig. 20.

[Illustration: (A) Fig. 20.--Top View of Apparatus Layout for Sending
Set No. 1.]

[Illustration: (B) Fig. 20.--Wiring of Diagram for Sending Set No. 1.]

For the _low voltage circuit_, that is the battery circuit, use _No.
12_ or _14_ insulated copper wire. Connect all of the dry cells
together in _series_, that is, connect the zinc of one cell with the
carbon of the next and so on until all of them are connected up. Then
connect the carbon of the end cell with one of the posts of the key,
the zinc of the other end cell with one of the primary posts of the
spark coil and the other primary post of the spark coil with the other
post of the key, when the primary circuit will be complete.

For the _high tension circuits_, that is, the _oscillation circuits_,
you may use either bare or insulated copper wire but you must be
careful that they do not touch the table, each other, or any part of
the apparatus, except, of course, the posts they are connected with.
Connect one of the posts of the secondary coil of the spark coil with
one of the posts of the spark gap, and the other post with one of the
posts of the condenser; then connect the other post of the condenser
with the lower spring clip of the tuning coil and also connect this
clip with the ground. This done, connect the middle spring clip with
one of the posts of the spark gap, and, finally, connect the top clip
with the aerial wire and your transmitting set is ready to be tuned. A
wiring diagram of the connections is shown at B. As this set is tuned
in the same way as _Set No. 2_ which follows, you are referred to the
end of this chapter.

A Better Transmitting Set (No. 2).--The apparatus for this set
includes: (1) an _alternating current transformer_, (2) a _wireless
telegraph key_, (3) a _fixed_, a _rotary_, or a _quenched spark gap_,
(4) a _condenser_, and (5) an _oscillation transformer_. If you have a
110 volt direct lighting current in your home instead of 110 volt
alternating current, then you will also need (6) an _electrolytic
interrupter_, for in this case the primary circuit of the transformer
must be made and broken rapidly in order to set up alternating
currents in the secondary coil.

The Alternating Current Transformer.--An alternating current, or
power, transformer is made on the same principle as a spark coil, that
is, it has a soft iron core, a primary coil formed of a couple of
layers of heavy wire, and a secondary coil wound up of a large number
of turns of very fine wire. Unlike the spark coil, however, which has
an _open magnetic core_ and whose secondary coil is wound on the
primary coil, the transformer has a _closed magnetic core_, with the
primary coil wound on one of the legs of the core and the secondary
wound on the other leg. It has neither a vibrator nor a condenser. A
plain transformer is shown at A in Fig. 21.

[Illustration: Fig. 21.--Parts for Transmitting Set No. 2.]

A transformer of this kind can be bought either (a) _unmounted_, that
is, just the bare transformer, or (b) _fully mounted_, that is, fitted
with an iron stand, mounted on an insulating base on which are a pair
of primary binding posts, while the secondary is provided with a
_safety spark gap_. There are three sizes of transformers of this kind
made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they
deliver a secondary current of 9,000, 11,000 and 25,000 volts,
according to size, and cost $16.00, $22.00 and $33.00 when fully
mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are
unmounted. All of these transformers operate on 110 volt, 60 cycle
current and can be connected directly to the source of alternating
current.

The Wireless Key.--For this transmitting set a standard wireless key
should be used as shown at B. It is made about the same as a regular
telegraph key but it is much heavier, the contact points are larger
and instead of the current being led through the bearings as in an
ordinary key, it is carried by heavy conductors directly to the
contact points. This key is made in three sizes and the first will
carry a current of 5 _amperes_[Footnote: See _Appendix_ for
definition.] and costs $4.00, the second will carry a current of 10
amperes and costs $6.50, while the third will carry a current of 20
amperes and costs $7.50.

The Spark Gap.--Either a fixed, a rotary, or a quenched spark gap can
be used with this set, but the former is seldom used except with
spark-coil sets, as it is very hard to keep the sparks from arcing
when large currents are used. A rotary spark gap comprises a wheel,
driven by a small electric motor, with projecting plugs, or
electrodes, on it and a pair of stationary plugs on each side of the
wheel as shown at C. The number of sparks per second can be varied by
changing the speed of the wheel and when it is rotated rapidly it
sends out signals of a high pitch which are easy to read at the
receiving end. A rotary gap with a 110-volt motor costs about $25.00.

A quenched spark gap not only eliminates the noise of the ordinary gap
but, when properly designed, it increases the range of an induction
coil set some 200 per cent. A 1/4 kilowatt quenched gap costs $10.00.
[Footnote: See Appendix for definition.]

The High Tension Condenser.--Since, if you are an amateur, you can
only send out waves that are 200 meters in length, you can only use a
condenser that has a capacitance of .007 _microfarad_. [Footnote: See
Appendix for definition.] A sectional high tension condenser like the
one described in connection with _Set No. 1_ can be used with this
set but it must have a capacitance of not more than .007 microfarad. A
condenser of this value for a 1/4-kilowatt transformer costs $7.00;
for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt
transformer $21.00. See E, Fig. 19.

The Oscillation Transformer.--With an oscillation transformer you can
tune much more sharply than with a single inductance coil tuner. The
primary coil is formed of 6 turns of copper strip, or No. 9 copper
wire, and the secondary is formed of 9 turns of strip, or wire. The
primary coil, which is the outside coil, is hinged to the base and can
be raised or lowered like the lid of a box. When it is lowered the
primary and secondary coils are in the same plane and when it is
raised the coils set at an angle to each other. It is shown at D and
costs $5.00.

Connecting Up the Apparatus. For Alternating Current.--Screw the key
to the table about the middle of it and near the front edge; place the
high tension condenser back of it and the oscillation transformer back
of the latter; set the alternating current transformer to the left of
the oscillation transformer and place the rotary or quenched spark gap
in front of it.

Now bring a pair of _No. 12_ or _14_ insulated wires from the 110 volt
lighting leads and connect them with a single-throw, double-pole
switch; connect one pole of the switch with one of the posts of the
primary coil of the alternating power transformer and connect the
other post of the latter with one of the posts of your key, and the
other post of this with the other pole of the switch. Now connect the
motor of the rotary spark gap to the power circuit and put a
single-pole, single-throw switch in the motor circuit, all of which is
shown at A in Fig. 22.

[Illustration: (A) Fig. 22.--Top View of Apparatus Layout for Sending
Set No. 2.]

[Illustration: (B) Fig. 22.--Wiring Diagram for Sending Set No. 2.]

Next connect the posts of the secondary coil to the posts of the
rotary or quenched spark gap and connect one post of the latter to one
post of the condenser, the other post of this to the post of the
primary coil of the oscillation transformer, which is the inside coil,
and the clip of the primary coil to the other spark gap post. This
completes the closed oscillation circuit. Finally connect the post of
the secondary coil of the oscillation transformer to the ground and
the clip of it to the wire leading to the aerial when you are ready to
tune the set. A wiring diagram of the connections is shown at B.

For Direct Current.--Where you have 110 volt direct current you must
connect in an electrolytic interrupter. This interrupter, which is
shown at A and B in Fig. 23, consists of (1) a jar filled with a
solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead
electrode having a large surface fastened to the cover of surface that
sets in a porcelain sleeve and whose end rests on the bottom of the
jar.

[Illustration: Fig. 23.--Using 110 Volt Direct Current with an
Alternating Current Transformer.]

When these electrodes are connected in series with the primary of a
large spark coil or an alternating current transformer, see C, and a
direct current of from 40 to 110 volts is made to pass through it, the
current is made and broken from 1,000 to 10,000 times a minute. By
raising or lowering the sleeve, thus exposing more or less of the
platinum, or alloy point, the number of interruptions per minute can
be varied at will. As the electrolytic interrupter will only operate
in one direction, you must connect it with its platinum, or alloy
anode, to the + or _positive_ power lead and the lead cathode to the -
or _negative_ power lead. You can find out which is which by
connecting in the interrupter and trying it, or you can use a polarity
indicator. An electrolytic interrupter can be bought for as little as
$3.00.

How to Adjust Your Transmitter. Tuning With a Hot Wire Ammeter.--A
transmitter can be tuned in two different ways and these are: (1) by
adjusting the length of the spark gap and the tuning coil so that the
greatest amount of energy is set up in the oscillating circuits, and
(2) by adjusting the apparatus so that it will send out waves of a
given length.

To adjust the transmitter so that the circuits will be in tune you
should have a _hot wire ammeter_, or radiation ammeter, as it is
called, which is shown in Fig. 24. It consists of a thin platinum wire
through which the high-frequency currents surge and these heat it; the
expansion and contraction of the wire moves a needle over a scale
marked off into fractions of an ampere. When the spark gap and tuning
coil of your set are properly adjusted, the needle will swing farthest
to the right over the scale and you will then know that the aerial
wire system, or open oscillation circuit, and the closed oscillation
circuit are in tune and radiating the greatest amount of energy.

[Illustration: Fig. 24.--Principle of the Hot Wire Ammeter.]

To Send Out a 200 Meter Wave Length.--If you are using a condenser
having a capacitance of .007 microfarad, which is the largest capacity
value that the Government will allow an amateur to use, then if you
have a hot wire ammeter in your aerial and tune the inductance coil or
coils until the ammeter shows the largest amount of energy flowing
through it you will know that your transmitter is tuned and that the
aerial is sending out waves whose length is 200 meters. To tune to
different wave lengths you must have a _wave-meter_.

The Use of the Aerial Switch.--Where you intend to install both a
transmitter and a receptor you will need a throwover switch, or
_aerial switch_, as it is called. An ordinary double-pole,
double-throw switch, as shown at A in Fig. 25, can be used, or a
switch made especially for the purpose as at B is handier because the
arc of the throw is much less.

[Illustration: Fig. 25.--Kinds of Aerial Switches.]

Aerial Switch for a Complete Sending and Receiving Set.--You can buy a
double-pole, double-throw switch mounted on a porcelain base for about
75 cents and this will serve for _Set No. 1_. Screw this switch on
your table between the sending and receiving sets and then connect one
of the middle posts of it with the ground wire and the other middle
post with the lightning switch which connects with the aerial. Connect
the post of the tuning coil with one of the end posts of the switch
and the clip of the tuning coil with the other and complementary post
of the switch. This done, connect one of the opposite end posts of the
switch to the post of the receiving tuning coil and connect the
sliding contact of the latter with the other and complementary post of
the switch as shown in Fig. 26.

[Illustration: Fig. 26.--Wiring Diagram for Complete Sending and
Receiving Set No. 1.]

Connecting in the Lightning Switch.--The aerial wire connects with the
middle post of the lightning switch, while one of the end posts lead
to one of the middle posts of the aerial switch. The other end post of
the lightning switch leads to a separate ground outside the building,
as the wiring diagrams Figs. 26 and 27 show.

[Illustration: Fig. 27.--Wiring Diagram for Complete Sending and
Receiving Set No. 2.]




CHAPTER V

ELECTRICITY SIMPLY EXPLAINED


It is easy to understand how electricity behaves and what it does if
you get the right idea of it at the start. In the first place, if you
will think of electricity as being a fluid like water its fundamental
actions will be greatly simplified. Both water and electricity may be
at rest or in motion. When at rest, under certain conditions, either
one will develop pressure, and this pressure when released will cause
them to flow through their respective conductors and thus produce a
current.

Electricity at Rest and in Motion.--Any wire or a conductor of any
kind can be charged with electricity, but a Leyden jar, or other
condenser, is generally used to hold an electric charge because it has
a much larger _capacitance_, as its capacity is called, than a wire.
As a simple analogue of a condenser, suppose you have a tank of water
raised above a second tank and that these are connected together by
means of a pipe with a valve in it, as shown at A in Fig. 28.

[Illustration: Fig. 28.--Water Analogue for Electric Pressure.]

[Illustration: original © Underwood and Underwood. First Wireless
College in the World, at Tufts College, Mass.]

Now if you fill the upper tank with water and the valve is turned off,
no water can flow into the lower tank but there is a difference of
pressure between them, and the moment you turn the valve on a current
of water will flow through the pipe. In very much the same way when
you have a condenser charged with electricity the latter will be under
_pressure,_ that is, a _difference of potential_ will be set up, for
one of the sheets of metal will be charged positively and the other
one, which is insulated from it, will be charged negatively, as shown
at B. On closing the switch the opposite charges rush together and
form a current which flows to and fro between the metal plates.
[Footnote: Strictly speaking it is the difference of potential that
sets up the electromotive force.]

The Electric Current and Its Circuit.--Just as water flowing through a
pipe has _quantity_ and _pressure_ back of it and the pipe offers
friction to it which tends to hold back the water, so, likewise, does
electricity flowing in a circuit have: (1) _quantity_, or _current
strength_, or just _current_, as it is called for short, or
_amperage_, and (2) _pressure_, or _potential difference_, or
_electromotive force_, or _voltage_, as it is variously called, and
the wire, or circuit, in which the current is flowing has (3)
_resistance_ which tends to hold back the current.

A definite relation exists between the current and its electromotive
force and also between the current, electromotive force and the
resistance of the circuit; and if you will get this relationship
clearly in your mind you will have a very good insight into how direct
and alternating currents act. To keep a quantity of water flowing in a
loop of pipe, which we will call the circuit, pressure must be applied
to it and this may be done by a rotary pump as shown at A in Fig. 29;
in the same way, to keep a quantity of electricity flowing in a loop
of wire, or circuit, a battery, or other means for generating electric
pressure must be used, as shown at B.

[Illustration: Fig. 29.--Water Analogues for Direct and Alternating
Currents.]

If you have a closed pipe connected with a piston pump, as at C, as
the piston moves to and fro the water in the pipe will move first one
way and then the other. So also when an alternating current generator
is connected to a wire circuit, as at D, the current will flow first
in one direction and then in the other, and this is what is called an
_alternating current_.

Current and the Ampere.--The amount of water flowing in a closed pipe
is the same at all parts of it and this is also true of an electric
current, in that there is exactly the same quantity of electricity at
one point of the circuit as there is at any other.

The amount of electricity, or current, flowing in a circuit in a
second is measured by a unit called the _ampere_, [Footnote: For
definition of _ampere_ see _Appendix._] and it is expressed by the
symbol I. [Footnote: This is because the letter C is used for the
symbol of _capacitance_] Just to give you an idea of the quantity of
current an _ampere_ is we will say that a dry cell when fresh gives a
current of about 20 amperes. To measure the current in amperes an
instrument called an _ammeter_ is used, as shown at A in Fig. 30, and
this is always connected in _series_ with the line, as shown at B.

[Illustration: Fig. 30.--How the Ammeter and Voltmeter are Used.]

Electromotive Force and the Volt.--When you have a pipe filled with
water or a circuit charged with electricity and you want to make them
flow you must use a pump in the first case and a battery or a dynamo
in the second case. It is the battery or dynamo that sets up the
electric pressure as the circuit itself is always charged with
electricity.

The more cells you connect together in _series_ the greater will be
the electric pressure developed and the more current it will move
along just as the amount of water flowing in a pipe can be increased
by increasing the pressure of the pump. The unit of electromotive
force is the _volt_, and this is the electric pressure which will
force a current of _1 ampere_ through a resistance of _1 ohm_; it is
expressed by the symbol _E_. A fresh dry cell will deliver a current
of about 1.5 volts. To measure the pressure of a current in volts an
instrument called a _voltmeter_ is used, as shown at C in Fig. 30, and
this is always connected across the circuit, as shown at D.

Resistance and the Ohm.--Just as a water pipe offers a certain amount
of resistance to the flow of water through it, so a circuit opposes
the flow of electricity in it and this is called _resistance_.
Further, in the same way that a small pipe will not allow a large
amount of water to flow through it, so, too, a thin wire limits the
flow of the current in it.

If you connect a _resistance coil_ in a circuit it acts in the same
way as partly closing the valve in a pipe, as shown at A and B in Fig.
31. The resistance of a circuit is measured by a unit called the
_ohm_, and it is expressed by the symbol _R_. A No. 10, Brown and
Sharpe gauge soft copper wire, 1,000 feet long, has a resistance of
about 1 ohm. To measure the resistance of a circuit an apparatus
called a _resistance bridge is used_. The resistance of a circuit can,
however, be easily calculated, as the following shows.

[Illustration: Fig. 31.--Water Valve Analogue of Electric Resistance.
A- a valve limits the flow of water. B- a resistance limits the flow
of current.]

What Ohm's Law Is.--If, now, (1) you know what the current flowing in
a circuit is in _amperes_, and the electromotive force, or pressure,
is in _volts_, you can then easily find what the resistance is in
_ohms_ of the circuit in which the current is flowing by this formula:

     Volts                   E
    --------- = Ohms,  or   --- = R
     Amperes                 I

That is, if you divide the current in amperes by the electromotive
force in volts the quotient will give you the resistance in ohms.

Or (2) if you know what the electromotive force of the current is in
_volts_ and the resistance of the circuit is in _ohms_ then you can
find what the current flowing in the circuit is in _amperes_, thus:

    Volts                   E
    ----- = Amperes,  or   --- = I
    Ohms                    R

That is, by dividing the resistance of the circuit in ohms, by the
electromotive force of the current you will get the amperes flowing in
the circuit.

Finally (3) if you know what the resistance of the circuit is in
_ohms_ and the current is in _amperes_ then you can find what the
electromotive force is in _volts_ since:

    Ohms x Amperes = Volts,  or   R x I = E

That is, if you multiply the resistance of the circuit in ohms by the
current in amperes the result will give you the electromotive force in
volts.

From this you will see that if you know the value of any two of the
constants you can find the value of the unknown constant by a simple
arithmetical process. This relation between these three constants is
known as _Ohm's Law_ and as they are very important you should
memorize them.

What the Watt and Kilowatt Are.--Just as _horsepower_ or _H.P._, is
the unit of work that steam has done or can do, so the _watt_ is the
unit of work that an electric current has done or can do. To find the
_watts_ a current develops you need only to multiply the _amperes_ by
the _volts_. There are _746 watts_ to _1 horsepower, and 1,000 watts
are equal to 1 kilowatt_.

Electromagnetic Induction.--To show that a current of electricity sets
up a magnetic field around it you have only to hold a compass over a
wire whose ends are connected with a battery when the needle will
swing at right angles to the length of the wire. By winding an
insulated wire into a coil and connecting the ends of the latter with
a battery you will find, if you test it with a compass, that the coil
is magnetic.

This is due to the fact that the energy of an electric current flowing
in the wire is partly changed into magnetic lines of force which
rotate at right angles about it as shown at A in Fig. 32. The
magnetic field produced by the current flowing in the coil is
precisely the same as that set up by a permanent steel magnet.
Conversely, when a magnetic line of force is set up a part of its
energy goes to make up electric currents which whirl about in a like
manner, as shown at B.

[Illustration: (A) and (B) Fig. 32.--How an Electric Current is
Changed into Magnetic Lines of Force and These into an Electric
Current.]

[Illustration: (C) and (D) Fig. 32.--How an Electric Current Sets up a
Magnetic Field.]

Self-induction or Inductance.--When a current is made to flow in a
coil of wire the magnetic lines of force produced are concentrated, as
at C, just as a lens concentrates rays of light, and this forms an
intense _magnetic field_, as it is called. Now if a bar of soft iron
is brought close to one end of the coil of wire, or, better still, if
it is pushed into the coil, it will be magnetized by _electromagnetic
induction,_ see D, and it will remain a magnet until the current is
cut off.

Mutual Induction.--When two loops of wire, or better, two coils of
wire, are placed close together the electromagnetic induction between
them is reactive, that is, when a current is made to flow through one
of the coils closed magnetic lines of force are set up and when these
cut the other loop or turns of wire of the other coil, they in turn
produce electric currents in it.

It is the mutual induction that takes place between two coils of wire
which makes it possible to transform _low voltage currents_ from a
battery or a 110 volt source of current into high pressure currents,
or _high potential currents_, as they are called, by means of a spark
coil or a transformer, as well as to _step up_ and _step down_ the
potential of the high frequency currents that are set up in sending
and receiving oscillation transformers. Soft iron cores are not used
in oscillation inductance coils and oscillation transformers for the
reason that the frequency of the current is so high the iron would not
have time to magnetize and demagnetize and so would not help along the
mutual induction to any appreciable extent.

High-Frequency Currents.--High frequency currents, or electric
oscillations as they are called, are currents of electricity that
surge to and fro in a circuit a million times, more or less, per
second. Currents of such high frequencies will _oscillate_, that is,
surge to and fro, in an _open circuit_, such as an aerial wire system,
as well as in a _closed circuit_.

Now there is only one method by which currents of high frequency, or
_radio-frequency_, as they are termed, can be set up by spark
transmitters, and this is by discharging a charged condenser through a
circuit having a small resistance. To charge a condenser a spark coil
or a transformer is used and the ends of the secondary coil, which
delivers the high potential alternating current, are connected with
the condenser. To discharge the condenser automatically a _spark,_ or
an _arc,_ or the _flow of electrons_ in a vacuum tube, is employed.

Constants of an Oscillation Circuit.--An oscillation circuit, as
pointed out before, is one in which high frequency currents surge or
oscillate. Now the number of times a high frequency current will surge
forth and back in a circuit depends upon three factors of the latter
and these are called the constants of the circuit, namely: (1) its
_capacitance,_ (2) its _inductance_ and (3) its _resistance._

What Capacitance Is.--The word _capacitance_ means the _electrostatic
capacity_ of a condenser or a circuit. The capacitance of a condenser
or a circuit is the quantity of electricity which will raise its
pressure, or potential, to a given amount. The capacitance of a
condenser or a circuit depends on its size and form and the voltage of
the current that is charging it.

The capacitance of a condenser or a circuit is directly proportional
to the quantity of electricity that will keep the charge at a given
potential. The _farad,_ whose symbol is _M,_ is the unit of
capacitance and a condenser or a circuit to have a capacitance of one
farad must be of such size that one _coulomb,_ which is the unit of
electrical quantity, will raise its charge to a potential of one volt.
Since the farad is far too large for practical purposes a millionth of
a farad, or _microfarad_, whose symbol is _mfd._, is used.

What Inductance Is.--Under the sub-caption of _Self-induction_ and
_Inductance_ in the beginning of this chapter it was shown that it was
the inductance of a coil that makes a current flowing through it
produce a strong magnetic field, and here, as one of the constants of
an oscillation circuit, it makes a high-frequency current act as
though it possessed _inertia_.

Inertia is that property of a material body that requires time and
energy to set in motion, or stop. Inductance is that property of an
oscillation circuit that makes an electric current take time to start
and time to stop. Because of the inductance, when a current flows
through a circuit it causes the electric energy to be absorbed and
changes a large part of it into magnetic lines of force. Where high
frequency currents surge in a circuit the inductance of it becomes a
powerful factor. The practical unit of inductance is the _henry_ and
it is represented by the symbol _L_.

What Resistance Is.--The resistance of a circuit to high-frequency
currents is different from that for low voltage direct or alternating
currents, as the former do not sink into the conductor to nearly so
great an extent; in fact, they stick practically to the surface of it,
and hence their flow is opposed to a very much greater extent. The
resistance of a circuit to high frequency currents is generally found
in the spark gap, arc gap, or the space between the electrodes of a
vacuum tube. The unit of resistance is, as stated, the _ohm_, and its
symbol is _R_.

The Effect of Capacitance, Inductance and Resistance on Electric
Oscillations.--If an oscillation circuit in which high frequency
currents surge has a large resistance, it will so oppose the flow of
the currents that they will be damped out and reach zero gradually, as
shown at A in Fig. 33. But if the resistance of the circuit is small,
and in wireless circuits it is usually so small as to be negligible,
the currents will oscillate, until their energy is damped out by
radiation and other losses, as shown at B.

[Illustration: Fig. 33.--The Effect of Resistance on the Discharge of
an Electric Current.]

As the capacitance and the inductance of the circuit, which may be
made of any value, that is amount, you wish, determines the _time
period_, that is, the length of time for a current to make one
complete oscillation, it must be clear that by varying the values of
the condenser and the inductance coil you can make the high frequency
current oscillate as fast or as slow as you wish within certain
limits. Where the electric oscillations that are set up are very fast,
the waves sent out by the aerial will be short, and, conversely, where
the oscillations are slow the waves emitted will be long.




CHAPTER VI

HOW THE TRANSMITTING AND RECEIVING SETS WORK


The easiest way to get a clear conception of how a wireless
transmitter sends out electric waves and how a wireless receptor
receives them is to take each one separately and follow: (1) in the
case of the transmitter, the transformation of the low voltage direct,
or alternating current into high potential alternating currents; then
find out how these charge the condenser, how this is discharged by the
spark gap and sets up high-frequency currents in the oscillation
circuits; then (2) in the case of the receptor, to follow the high
frequency currents that are set up in the aerial wire and learn how
they are transformed into oscillations of lower potential when they
have a larger current strength, how these are converted into
intermittent direct currents by the detector and which then flow into
and operate the telephone receiver.

How Transmitting Set No. 1 Works. The Battery and Spark Coil
Circuit.--When you press down on the knob of the key the silver points
of it make contact and this closes the circuit; the low voltage direct
current from the battery now flows through the primary coil of the
spark coil and this magnetizes the soft iron core. The instant it
becomes magnetic it pulls the spring of the vibrator over to it and
this breaks the circuit; when this takes place the current stops
flowing through the primary coil; this causes the core to lose its
magnetism when the vibrator spring flies back and again makes contact
with the adjusting screw; then the cycle of operations is repeated.

A condenser is connected across the contact points of the vibrator
since this gives a much higher voltage at the ends of the secondary
coil than where the coil is used without it; this is because: (1) the
self-induction of the primary coil makes the pressure of the current
rise and when the contact points close the circuit again it discharges
through the primary coil, and (2) when the break takes place the
current flows into the condenser instead of arcing across the contact
points.

Changing the Primary Spark Coil Current Into Secondary Currents.--Now
every time the vibrator contact points close the primary circuit the
electric current in the primary coil is changed into closed magnetic
lines of force and as these cut through the secondary coil they set up
in it a _momentary current_ in one direction. Then the instant the
vibrator points break apart the primary circuit is opened and the
closed magnetic lines of force contract and as they do so they cut the
turns of wire in the secondary coil in the opposite direction and this
sets up another momentary current in the secondary coil in the other
direction. The result is that the low voltage direct current of the
battery is changed into alternating currents whose frequency is
precisely that of the spring vibrator, but while the frequency of the
currents is low their potential, or voltage, is enormously increased.

What Ratio of Transformation Means.--To make a spark coil step up the
low voltage direct current into high potential alternating current the
primary coil is wound with a couple of layers of thick insulated
copper wire and the secondary is wound with a thousand, more or less,
number of turns with very fine insulated copper wire. If the primary
and secondary coils were wound with the same number of turns of wire
then the pressure, or voltage, of the secondary coil at its terminals
would be the same as that of the current which flowed through the
primary coil. Under these conditions the _ratio of transformation_, as
it is called, would be unity.

The ratio of transformation is directly proportional to the number of
turns of wire on the primary and secondary coils and, since this is
the case, if you wind 10 turns of wire on the primary coil and 1,000
turns of wire on the secondary coil then you will get 100 times as
high a pressure, or voltage, at the terminals of the secondary as that
which you caused to flow through the primary coil, but, naturally, the
current strength, or amperage, will be proportionately decreased.

The Secondary Spark Coil Circuit.--This includes the secondary coil
and the spark gap which are connected together. When the alternating,
but high potential, currents which are developed by the secondary
coil, reach the balls, or _electrodes_, of the spark gap the latter
are alternately charged positively and negatively.

Now take a given instant when one electrode is charged positively and
the other one is charged negatively, then when they are charged to a
high enough potential the electric strain breaks down the air gap
between them and the two charges rush together as described in the
chapter before this one in connection with the discharge of a
condenser. When the charges rush together they form a current which
burns out the air in the gap and this gives rise to the spark, and as
the heated gap between the two electrodes is a very good conductor the
electric current surges forth and back with high frequency, perhaps a
dozen times, before the air replaces that which has burned out. It is
the inrushing air to fill the vacuum of the gap that makes the
crackling noise which accompanies the discharge of the electric spark.

In this way then electric oscillations of the order of a million, more
or less, are produced and if an aerial and a ground wire are connected
to the spark balls, or electrodes, the oscillations will surge up and
down it and the energy of these in turn, are changed into electric
waves which travel out into space. An open circuit transmitter of this
kind will send out waves that are four times as long as the aerial
itself, but as the waves it sends out are strongly damped the
Government will not permit it to be used.

The Closed Oscillation Circuit.--By using a closed oscillation circuit
the transmitter can be tuned to send out waves of a given length and
while the waves are not so strongly damped more current can be sent
into the aerial wire system. The closed oscillation circuit consists
of: (1) a _spark gap_, (2) a _condenser_ and (3) an _oscillation
transformer_. The high potential alternating current delivered by the
secondary coil not only charges the spark gap electrodes which
necessarily have a very small capacitance, but it charges the
condenser which has a large capacitance and the value of which can be
changed at will.

Now when the condenser is fully charged it discharges through the
spark gap and then the electric oscillations set up surge to and fro
through the closed circuit. As a closed circuit is a very poor
radiator of energy, that is, the electric oscillations are not freely
converted into electric waves by it, they surge up to, and through the
aerial wire; now as the aerial wire is a good radiator nearly all of
the energy of the electric oscillations which surge through it are
converted into electric waves.

How Transmitting Set No. 2 Works. With Alternating Current. The
operation of a transmitting set that uses an alternating current
transformer, or _power transformer,_ as it is sometimes called, is
even more simple than one using a spark coil. The transformer needs no
vibrator when used with alternating current. The current from a
generator flows through the primary coil of the transformer and the
alternations of the usual lighting current is 60 cycles per second.
This current sets up an alternating magnetic field in the core of the
transformer and as these magnetic lines of force expand and contract
they set up alternating currents of the same frequency but of much
higher voltage at the terminals of the secondary coil according to the
ratio of the primary and secondary turns of wire as explained under
the sub-caption of _Ratio of Transformation_.

With Direct Current.--When a 110 volt direct current is used to
energize the power transformer an _electrolytic_ interruptor is needed
to make and break the primary circuit, just as a vibrator is needed
for the same purpose with a spark coil. When the electrodes are
connected in series with the primary coil of a transformer and a
source of direct current having a potential of 40 to 110 volts,
bubbles of gas are formed on the end of the platinum, or alloy anode,
which prevent the current from flowing until the bubbles break and
then the current flows again, in this way the current is rapidly made
and broken and the break is very sharp.

Where this type of interrupter is employed the condenser that is
usually shunted around the break is not necessary as the interrupter
itself has a certain inherent capacitance, due to electrolytic action,
and which is called its _electrolytic capacitance_, and this is large
enough to balance the self-induction of the circuit since the greater
the number of breaks per minute the smaller the capacitance required.

The Rotary Spark Gap.--In this type of spark gap the two fixed
electrodes are connected with the terminals of the secondary coil of
the power transformer and also with the condenser and primary of the
oscillation transformer. Now whenever any pair of electrodes on the
rotating disk are in a line with the pair of fixed electrodes a spark
will take place, hence the pitch of the note depends on the speed of
the motor driving the disk. This kind of a rotary spark-gap is called
_non-synchronous_ and it is generally used where a 60 cycle
alternating current is available but it will work with other higher
frequencies.

The Quenched Spark Gap.--If you strike a piano string a single quick
blow it will continue to vibrate according to its natural period. This
is very much the way in which a quenched spark gap sets up
oscillations in a coupled closed and open circuit. The oscillations
set up in the primary circuit by a quenched spark make only three or
four sharp swings and in so doing transfer all of their energy over to
the secondary circuit, where it will oscillate some fifty times or
more before it is damped out, because the high frequency currents are
not forced, but simply oscillate to the natural frequency of the
circuit. For this reason the radiated waves approach somewhat the
condition of continuous waves, and so sharper tuning is possible.

The Oscillation Transformer.--In this set the condenser in the closed
circuit is charged and discharged and sets up oscillations that surge
through the closed circuit as in _Set No. 1_. In this set, however, an
oscillation transformer is used and as the primary coil of it is
included in the closed circuit the oscillations set up in it produce
strong oscillating magnetic lines of force. The magnetic field thus
produced sets up in turn electric oscillations in the secondary coil
of the oscillation transformer and these surge through the aerial wire
system where their energy is radiated in the form of electric waves.

The great advantage of using an oscillation transformer instead of a
simple inductance coil is that the capacitance of the closed circuit
can be very much larger than that of the aerial wire system. This
permits more energy to be stored up by the condenser and this is
impressed on the aerial when it is radiated as electric waves.

How Receiving Set No. I Works.--When the electric waves from a distant
sending station impinge on the wire of a receiving aerial their energy
is changed into electric oscillations that are of exactly the same
frequency (assuming the receptor is tuned to the transmitter) but
whose current strength (amperage) and potential (voltage) are very
small. These electric waves surge through the closed circuit but when
they reach the crystal detector the contact of the metal point on the
crystal permits more current to flow through it in one direction than
it will allow to pass in the other direction. For this reason a
crystal detector is sometimes called a _rectifier_, which it really
is.

Thus the high frequency currents which the steel magnet cores of the
telephone receiver would choke off are changed by the detector into
intermittent direct currents which can flow through the magnet coils
of the telephone receiver. Since the telephone receiver chokes off the
oscillations, a small condenser can be shunted around it so that a
complete closed oscillation circuit is formed and this gives better
results.

When the intermittent rectified current flows through the coils of the
telephone receiver it energizes the magnet as long as it lasts, when
it is de-energized; this causes the soft iron disk, or _diaphragm_ as
it is called, which sets close to the ends of the poles of the magnet,
to vibrate; and this in turn gives forth sounds such as dots and
dashes, speech or music, according to the nature of the electric waves
that sent them out at the distant station.

How Receiving Set No. 2 Works.--When the electric oscillations that
are set up by the incoming electric waves on the aerial wire surge
through the primary coil of the oscillation transformer they produce a
magnetic field and as the lines of force of the latter cut the
secondary coil, oscillations of the same frequency are set up in it.
The potential (voltage) of these oscillations are, however, _stepped
down_ in the secondary coil and, hence, their current strength
(amperes) is increased.

The oscillations then flow through the closed circuit where they are
rectified by the crystal detector and transformed into sound waves by
the telephone receiver as described in connection with _Set No. 1_.
The variable condenser shunted across the closed circuit permits finer
secondary tuning to be done than is possible without it. Where you
are receiving continuous waves from a wireless telephone transmitter
(speech or music) you have to tune sharper than is possible with the
tuning coil alone and to do this a variable condenser connected in
parallel with the secondary coil is necessary.




CHAPTER VII

MECHANICAL AND ELECTRICAL TUNING


There is a strikingly close resemblance between _sound waves_ and the
way they are set up in _the air_ by a mechanically vibrating body,
such as a steel spring or a tuning fork, and _electric waves_ and the
way they are set up in _the ether_ by a current oscillating in a
circuit. As it is easy to grasp the way that sound waves are produced
and behave something will be told about them in this chapter and also
an explanation of how electric waves are produced and behave and thus
you will be able to get a clear understanding of them and of tuning in
general.

Damped and Sustained Mechanical Vibrations.--If you will place one end
of a flat steel spring in a vice and screw it up tight as shown at A
in Fig. 34, and then pull the free end over and let it go it will
vibrate to and fro with decreasing amplitude until it comes to rest as
shown at B. When you pull the spring over you store up energy in it
and when you let it go the stored up energy is changed into energy of
motion and the spring moves forth and back, or _vibrates_ as we call
it, until all of its stored up energy is spent.

[Illustration: Fig. 34.--Damped and Sustained Mechanical Vibrations.]

If it were not for the air surrounding it and other frictional losses,
the spring would vibrate for a very long time as the stored up energy
and the energy of motion would practically offset each other and so
the energy would not be used up. But as the spring beats the air the
latter is sent out in impulses and the conversion of the vibrations of
the spring into waves in the air soon uses up the energy you have
imparted to it and it comes to rest.

In order to send out _continuous waves_ in the air instead of _damped
waves_ as with a flat steel spring you can use an _electric driven
tuning fork_, see C, in which an electromagnet is fixed on the inside
of the prongs and when this is energized by a battery current the
vibrations of the prongs of the fork are kept going, or are
_sustained_, as shown in the diagram at D.

Damped and Sustained Electric Oscillations.--The vibrating steel
spring described above is a very good analogue of the way that damped
electric oscillations which surge in a circuit set up and send out
periodic electric waves in the ether while the electric driven tuning
fork just described is likewise a good analogue of how sustained
oscillations surge in a circuit and set up and send out continuous
electric waves in the ether as the following shows.

Now the inductance and resistance of a circuit such as is shown at A
in Fig. 35, slows down, and finally damps out entirely, the electric
oscillations of the high frequency currents, see B, where these are
set up by the periodic discharge of a condenser, precisely as the
vibrations of the spring are damped out by the friction of the air and
other resistances that act upon it. As the electric oscillations surge
to and fro in the circuit it is opposed by the action of the ether
which surrounds it and electric waves are set up in and sent out
through it and this transformation soon uses up the energy of the
current that flows in the circuit.

[Illustration: Fig. 35.--Damped and Sustained Electric Oscillations.]

To send out _continuous waves_ in the ether such as are needed for
wireless telephony instead of _damped waves_ which are, at the present
writing, generally used for wireless telegraphy, an _electric
oscillation arc_ or a _vacuum tube oscillator_ must be used, see C,
instead of a spark gap. Where a spark gap is used the condenser in the
circuit is charged periodically and with considerable lapses of time
between each of the charging processes, when, of course, the condenser
discharges periodically and with the same time element between them.
Where an oscillation arc or a vacuum tube is used the condenser is
charged as rapidly as it is discharged and the result is the
oscillations are sustained as shown at D.

About Mechanical Tuning.--A tuning fork is better than a spring or a
straight steel bar for setting up mechanical vibrations. As a matter
of fact a tuning fork is simply a steel bar bent in the middle so that
the two ends are parallel. A handle is attached to middle point of the
fork so that it can be held easily and which also allows it to vibrate
freely, when the ends of the prongs alternately approach and recede
from one another. When the prongs vibrate the handle vibrates up and
down in unison with it, and imparts its motion to the _sounding box_,
or _resonance case_ as it is sometimes called, where one is used.

If, now, you will mount the fork on a sounding box which is tuned so
that it will be in resonance with the vibrations of the fork there
will be a direct reinforcement of the vibrations when the note emitted
by it will be augmented in strength and quality. This is called
_simple resonance_. Further, if you mount a pair of forks, each on a
separate sounding box, and have the forks of the same size, tone and
pitch, and the boxes synchronized, that is, tuned to the same
frequency of vibration, then set the two boxes a foot or so apart, as
shown at A in Fig. 36, when you strike one of the forks with a rubber
hammer it will vibrate with a definite frequency and, hence, send out
sound waves of a given length. When the latter strike the second fork
the impact of the molecules of air of which the sound waves are formed
will set its prongs to vibrating and it will, in turn, emit sound
waves of the same length and this is called _sympathetic resonance_,
or as we would say in wireless the forks are _in tune_.

[Illustration: Fig. 36.--Sound Wave and Electric Wave Tuned Senders
and Receptors. A - variable tuning forks for showing sound wave
tuning. B - variable oscillation circuits for showing electric wave
tuning.]

Tuning forks are made with adjustable weights on their prongs and by
fixing these to different parts of them the frequency with which the
forks vibrate can be changed since the frequency varies inversely with
the square of the length and directly with the thickness [Footnote:
This law is for forks having a rectangular cross-section. Those having
a round cross-section vary as the radius.] of the prongs. Now by
adjusting one of the forks so that it vibrates at a frequency of, say,
16 per second and adjusting the other fork so that it vibrates at a
frequency of, say, 18 or 20 per second, then the forks will not be in
tune with each other and, hence, if you strike one of them the other
will not respond. But if you make the forks vibrate at the same
frequency, say 16, 20 or 24 per second, when you strike one of them
the other will vibrate in unison with it.

About Electric Tuning.--Electric resonance and electric tuning are
very like those of acoustic resonance and acoustic tuning which I have
just described. Just as acoustic resonance may be simple or
sympathetic so electric resonance may be simple or sympathetic. Simple
acoustic resonance is the direct reinforcement of a simple vibration
and this condition is had when a tuning fork is mounted on a sounding
box. In simple electric resonance an oscillating current of a given
frequency flowing in a circuit having the proper inductance and
capacitance may increase the voltage until it is several times greater
than its normal value. Tuning the receptor circuits to the transmitter
circuits are examples of sympathetic electric resonance. As a
demonstration if you have two Leyden jars (capacitance) connected in
circuit with two loops of wire (inductance) whose inductance can be
varied as shown at B in Fig. 36, when you make a spark pass between
the knobs of one of them by means of a spark coil then a spark will
pass in the gap of the other one provided the inductance of the two
loops of wire is the same. But if you vary the inductance of the one
loop so that it is larger or smaller than that of the other loop no
spark will take place in the second circuit.

When a tuning fork is made to vibrate it sends out waves in the air,
or sound waves, in all directions and just so when high frequency
currents surge in an oscillation circuit they send out waves in the
ether, or electric waves, that travel in all directions. For this
reason electric waves from a transmitting station cannot be sent to
one particular station, though they do go further in one direction
than in another, according to the way your aerial wire points.

Since the electric waves travel out in all directions any receiving
set properly tuned to the wave length of the sending station will
receive the waves and the only limit on your ability to receive from
high-power stations throughout the world depends entirely on the wave
length and sensitivity of your receiving set. As for tuning, just as
changing the length and the thickness of the prongs of a tuning fork
varies the frequency with which it vibrates and, hence, the length of
the waves it sends out, so, too, by varying the capacitance of the
condenser and the inductance of the tuning coil of the transmitter the
frequency of the electric oscillations set up in the circuit may be
changed and, consequently, the length of the electric waves they send
out. Likewise, by varying the capacitance and the inductance of the
receptor the circuits can be tuned to receive incoming electric waves
of whatever length within the limitation of the apparatus.




CHAPTER VIII

A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET


While you can receive dots and dashes from spark wireless telegraph
stations and hear spoken words and music from wireless telephone
stations with a crystal detector receiving set such as described in
Chapter III, you can get stations that are much farther away and hear
them better with a _vacuum tube detector_ receiving set.

Though the vacuum tube detector requires two batteries to operate it
and the receiving circuits are somewhat more complicated than where a
crystal detector is used still the former does not have to be
constantly adjusted as does the latter and this is another very great
advantage. Taken all in all the vacuum tube detector is the most
sensitive and the most satisfactory of the detectors that are in use
at the present time.

Not only is the vacuum tube a detector of electric wave signals and
speech and music but it can also be used to _amplify_ them, that is,
to make them stronger and, hence, louder in the telephone receiver and
further its powers of amplification are so great that it will
reproduce them by means of a _loud speaker_, just as a horn amplifies
the sounds of a phonograph reproducer, until they can be heard by a
room or an auditorium full of people. There are two general types of
loud speakers, though both use the principle of the telephone
receiver. The construction of these loud speakers will be fully
described in a later chapter.

Assembled Vacuum Tube Receiving Sets.--You can buy a receiving set
with a vacuum tube detector from the very simplest type, which is
described in this chapter, to those that are provided with
_regenerative circuits_ and _amplifying_ tubes or both, which we shall
describe in later chapters, from dealers in electrical apparatus
generally. While one of these sets costs more than you can assemble a
set for yourself, still, especially in the beginning, it is a good
plan to buy an assembled one for it is fitted with a _panel_ on which
the adjusting knobs of the rheostat, tuning coil and condenser are
mounted and this makes it possible to operate it as soon as you get it
home and without the slightest trouble on your part.

You can, however, buy all the various parts separately and mount them
yourself. If you want the receptor simply for receiving then it is a
good scheme to have all of the parts mounted in a box or enclosed
case, but if you want it for experimental purposes then the parts
should be mounted on a base or a panel so that all of the connections
are in sight and accessible.

A Simple Vacuum Tube Receiving Set.--For this set you should use: (1)
a _loose coupled tuning coil,_ (2) a _variable condenser,_ (3) a
_vacuum tube detector,_ (4) an A or _storage battery_ giving 6 volts,
(5) a B or _dry cell battery_ giving 22-1/2 volts, (6) a _rheostat_
for varying the storage battery current, and (7) a pair of 2,000-ohm
_head telephone receivers_. The loose coupled tuning coil, the
variable condenser and the telephone receivers are the same as those
described in Chapter III.

The Vacuum Tube Detector. With Two Electrodes.--A vacuum tube in its
simplest form consists of a glass bulb like an incandescent lamp in
which a _wire filament_ and a _metal plate_ are sealed as shown in
Fig. 37, The air is then pumped out of the tube and a vacuum left or
after it is exhausted it is filled with nitrogen, which cannot burn.

[Illustration: Fig. 37.--Two Electrode Vacuum Tube Detectors.]

When the vacuum tube is used as a detector, the wire filament is
heated red-hot and the metal plate is charged with positive
electricity though it remains cold. The wire filament is formed into a
loop like that of an incandescent lamp and its outside ends are
connected with a 6-volt storage battery, which is called the A
battery; then the + or _positive_ terminal of a 22-1/2 volt dry cell
battery, called the B battery, is connected to the metal plate while
the - or _negative_ terminal of the battery is connected to one of the
terminals of the wire filament. The diagram, Fig. 37, simply shows how
the two electrode vacuum tube, the A or dry battery, and the B or
storage battery are connected up.

Three Electrode Vacuum Tube Detector.--The three electrode vacuum tube
detector shown at A in Fig. 38, is much more sensitive than the two
electrode tube and has, in consequence, all but supplanted it. In this
more recent type of vacuum tube the third electrode, or _grid_, as it
is called, is placed between the wire filament and the metal plate and
this allows the current to be increased or decreased at will to a very
considerable extent.

[Illustration: Fig. 38.--Three Electrode Vacuum Tube Detector and
Battery Connections.]

The way the three electrode vacuum tube detector is connected with the
batteries is shown at B. The plate, the A or dry cell battery and one
terminal of the filament are connected in _series_--that is, one after
the other, and the ends of the filament are connected to the B or
storage battery. In assembling a receiving set you must, of course,
have a socket for the vacuum tube. A vacuum tube detector costs from
$5.00 to $6.00.

The Dry Cell and Storage Batteries.--The reason that a storage battery
is used for heating the filament of the vacuum tube detector is
because the current delivered is constant, whereas when a dry cell
battery is used the current soon falls off and, hence, the heat of the
filament gradually grows less. The smallest A or 6 volt storage
battery on the market has a capacity of 20 to 40 ampere hours, weighs
13 pounds and costs about $10.00. It is shown at A in Fig. 39. The B
or dry cell battery for the vacuum tube plate circuit that gives
22-1/2 volts can be bought already assembled in sealed boxes. The
small size is fitted with a pair of terminals while the larger size is
provided with _taps_ so that the voltage required by the plate can be
adjusted as the proper operation of the tube requires careful
regulation of the plate voltage. A dry cell battery for a plate
circuit is shown at B.

[Illustration: Fig. 39.--A and B Batteries for Vacuum
Tube Detectors.]

The Filament Rheostat.--An adjustable resistance, called a _rheostat_,
must be used in the filament and storage battery circuit so that the
current flowing through the filament can be controlled to a nicety.
The rheostat consists of an insulating and a heat resisting form on
which is wound a number of turns of resistance wire. A movable contact
arm that slides over and presses on the turns of wire is fixed to the
knob on top of the rheostat. A rheostat that has a resistance of 6
ohms and a current carrying capacity of 1.5 amperes which can be
mounted on a panel board is the right kind to use. It is shown at A
and B in Fig. 40 and costs $1.25.

[Illustration: Fig. 40.--Rheostat for the A or Storage Battery
Current.]

Assembling the Parts.--Begin by placing all of the separate parts of
the receiving set on a board or a base of other material and set the
tuning coil on the left hand side with the adjustable switch end
toward the right hand side so that you can reach it easily. Then set
the variable condenser in front of it, set the vacuum tube detector at
the right hand end of the tuning coil and the rheostat in front of the
detector. Place the two sets of batteries back of the instruments and
screw a couple of binding posts _a_ and _b_ to the right hand lower
edge of the base for connecting in the head phones all of which is
shown at A in Fig. 41.

[Illustration: (A) Fig. 41.--Top View of Apparatus Layout for a Vacuum
Tube Detector Receiving Set.]

[Illustration: (B) Fig. 41.--Wiring Diagram of a Simple Vacuum Tube
Receiving Set.]

Connecting Up the Parts.--To wire up the different parts begin by
connecting the sliding contact of the primary coil of the loose
coupled tuning coil (this you will remember is the outside one that is
wound with fine wire) to the upper post of the lightning switch and
connect one terminal of this coil with the water pipe. Now connect the
free end of the secondary coil of the tuning coil (this is the inside
coil that is wound with heavy wire) to one of the binding posts of the
variable condenser and connect the movable contact arm of the
adjustable switch of the primary of the tuning coil with the other
post of the variable condenser.

Next connect the grid of the vacuum tube to one of the posts of the
condenser and then connect the plate of the tube to the _carbon
terminal_ of the B or dry cell battery which is the + or _positive
pole_ and connect the _zinc terminal_ of the - or _negative_ pole to
the binding post _a_, connect the post _b_ to the other side of the
variable condenser and then connect the terminals of the head phones
to the binding posts _a_ and _b_. Whatever you do be careful not to
get the plate connections of the battery reversed.

Now connect one of the posts of the rheostat to one terminal of the
filament and the other terminal of the filament to the - or _negative_
terminal of the A or storage battery and the + or _positive_ terminal
of the A or storage battery to the other post of the rheostat. Finally
connect the + or positive terminal of the A or storage battery with
the wire that runs from the head phones to the variable condenser, all
of which is shown in the wiring diagram at B in Fig. 41.

Adjusting the Vacuum Tube Detector Receiving Set.--A vacuum tube
detector is tuned exactly in the same way as the _Crystal Detector Set
No. 2_ described in Chapter III, in-so-far as the tuning coil and
variable condenser are concerned. The sensitivity of the vacuum tube
detector receiving set and, hence, the distance over which signals and
other sounds can be heard depends very largely on the sensitivity of
the vacuum tube itself and this in turn depends on: (1) the right
amount of heat developed by the filament, or _filament brilliancy_ as
it is called, (2) the right amount of voltage applied to the plate,
and (3) the extent to which the tube is exhausted where this kind of a
tube is used.

To vary the current flowing from the A or storage battery
through the filament so that it will be heated to the right degree you
adjust the rheostat while you are listening in to the signals or other
sounds. By carefully adjusting the rheostat you can easily find the
point at which it makes the tube the most sensitive. A rheostat is
also useful in that it keeps the filament from burning out when the
current from the battery first flows through it. You can very often
increase the sensitiveness of a vacuum tube after you have used it for
a while by recharging the A or storage battery.

The degree to which a vacuum tube has been exhausted has a very
pronounced effect on its sensitivity. The longer the tube is used the
lower its vacuum gets and generally the less sensitive it becomes.
When this takes place (and you can only guess at it) you can very
often make it more sensitive by warming it over the flame of a candle.
Vacuum tubes having a gas content (in which case they are, of course,
no longer vacuum tubes in the strict sense) make better detectors than
tubes from which the air has been exhausted and which are sealed off
in this evacuated condition because their sensitiveness is not
dependent on the degree of vacuum as in the latter tubes. Moreover, a
tube that is completely exhausted costs more than one that is filled
with gas.




CHAPTER IX

VACUUM TUBE AMPLIFIER RECEIVING SETS


The reason a vacuum tube detector is more sensitive than a crystal
detector is because while the latter merely _rectifies_ the
oscillating current that surges in the receiving circuits, the former
acts as an _amplifier_ at the same time. The vacuum tube can be used
as a separate amplifier in connection with either: (1) a _crystal
detector_ or (2) a _vacuum tube detector_, and (_a_) it will amplify
either the _radio frequency currents_, that is the high frequency
oscillating currents which are set up in the oscillation circuits or
(_b_) it will amplify the _audio frequency currents_, that is, the
_low frequency alternating_ currents that flow through the head phone
circuit.

To use the amplified radio frequency oscillating currents or amplified
audio frequency alternating currents that are set up by an amplifier
tube either a high resistance, called a _grid leak_, or an _amplifying
transformer_, with or without an iron core, must be connected with the
plate circuit of the first amplifier tube and the grid circuit of the
next amplifier tube or detector tube, or with the wire point of a
crystal detector. Where two or more amplifier tubes are coupled
together in this way the scheme is known as _cascade amplification._

Where either a _radio frequency transformer_, that is one without the
iron core, or an _audio frequency transformer_, that is one with the
iron core, is used to couple the amplifier tube circuits together
better results are obtained than where a high resistance grid leak is
used, but the amplifying tubes have to be more carefully shielded from
each other or they will react and set up a _howling_ noise in the head
phones. On the other hand grid leaks cost less but they are more
troublesome to use as you have to find out for yourself the exact
resistance value they must have and this you can do only by testing
them out.

A Grid Leak Amplifier Receiving Set. With Crystal Detector.--The
apparatus you need for this set includes: (1) a _loose coupled tuning
coil_, (2) a _variable condenser_, (3) _two fixed condensers_, (4) a
_crystal detector_, or better a _vacuum tube detector_, (5) an A or _6
volt storage battery_, (6) a _rheostat_, (7) a B or 22-1/2 _volt dry
cell battery_, (8) a fixed resistance unit, or _leak grid_ as it is
called, and (9) a pair of _head-phones_. The tuning coil, variable
condenser, fixed condensers, crystal detectors and head-phones are
exactly the same as those described in _Set No. 2_ in Chapter III.
The A and B batteries are exactly the same as those described in
Chapter VIII. The _vacuum tube amplifier_ and the _grid leak_ are the
only new pieces of apparatus you need and not described before.

The Vacuum Tube Amplifier.--This consists of a three electrode vacuum
tube exactly like the vacuum tube detector described in Chapter VIII
and pictured in Fig. 38, except that instead of being filled with a
non-combustible gas it is evacuated, that is, the air has been
completely pumped out of it. The gas filled tube, however, can be used
as an amplifier and either kind of tube can be used for either radio
frequency or audio frequency amplification, though with the exhausted
tube it is easier to obtain the right plate and filament voltages for
good working.

The Fixed Resistance Unit, or Grid Leak.--Grid leaks are made in
different ways but all of them have an enormously high resistance.
One way of making them consists of depositing a thin film of gold on a
sheet of mica and placing another sheet of mica on top to protect it
the whole being enclosed in a glass tube as shown at A in Fig. 42.
These grid leaks are made in units of from 50,000 ohms (.05 megohm) to
5,000,000 ohms (5 megohms) and cost from $1 to $2.

[Illustration: Fig. 42.--Grid Leaks and How to Connect Them up.]

As the _value_ of the grid leak you will need depends very largely
upon the construction of the different parts of your receiving set and
on the kind of aerial wire system you use with it you will have to try
out various resistances until you hit the right one. The resistance
that will give the best results, however, lies somewhere between
500,000 ohms (1/2 a megohm) and 3,000,000 ohms (3 megohms) and the
only way for you to find this out is to buy 1/2, 1 and 2 megohm grid
leak resistances and connect them up in different ways, as shown at B,
until you find the right value.

Assembling the Parts for a Crystal Detector Set.--Begin by laying the
various parts out on a base or a panel with the loose coupled tuning
coil on the left hand side, but with the adjustable switch of the
secondary coil on the right hand end or in front according to the way
it is made. Then place the variable condenser, the rheostat, the
crystal detector and the binding posts for the head phones in front of
and in a line with each other. Set the vacuum tube amplifier back of
the rheostat and the A and B batteries back of the parts or in any
other place that may be convenient. The fixed condensers and the grid
leak can be placed anywhere so that it will be easy to connect them in
and you are ready to wire up the set.

Connecting Up the Parts for a Crystal Detector.--First connect the
sliding contact of the primary of the tuning coil to the leading-in
wire and one of the end wires of the primary to the water pipe, as
shown in Fig. 43. Now connect the adjustable arm that makes contact
with one end of the secondary of the tuning coil to one of the posts
of the variable condenser; then connect the other post of the latter
with a post of the fixed condenser and the other post of this with the
grid of the amplifying tube.

[Illustration: Fig. 43.--Crystal Detector Receiving Set with Vacuum
Tube Amplifier (Resistance Coupled).]

Connect the first post of the variable condenser to the + or _positive
electrode_ of the A battery and its - or _negative electrode_ with the
rotating contact arm of the rheostat. Next connect one end of the
resistance coil of the rheostat to one of the posts of the amplifier
tube that leads to the filament and the other filament post to the +
or _positive electrode_ of the A battery. This done connect the
_negative_, that is, the _zinc pole_ of the B battery to the positive
electrode of the A battery and connect the _positive_, or _carbon
pole_ of the former with one end of the grid leak and connect the
other end of this to the plate of the amplifier tube.

To the end of the grid leak connected with the plate of the amplifier
tube connect the metal point of your crystal detector, the crystal of
the latter with one post of the head phones and the other post of them
with the other end of the grid leak and, finally, connect a fixed
condenser in _parallel_ with--that is across the ends of the grid
leak, all of which is shown in the wiring diagram in Fig. 43.

A Grid Leak Amplifying Receiving Set With Vacuum Tube Detector.--A
better amplifying receiving set can be made than the one just
described by using a vacuum tube detector instead of the crystal
detector. This set is built up exactly like the crystal detector
described above and shown in Fig. 43 up to and including the grid leak
resistance, but shunted across the latter is a vacuum tube detector,
which is made and wired up precisely like the one shown at A in Fig.
41 in the chapter ahead of this one. The way a grid leak and vacuum
tube detector with a one-step amplifier are connected up is shown at A
in Fig. 44. Where you have a vacuum tube detector and one or more
amplifying tubes connected up, or in _cascade_ as it is called, you
can use an A, or storage battery of 6 volts for all of them as shown
at B in Fig. 44, but for every vacuum tube you use you must have a B
or 22-1/2 volt dry battery to charge the plate with.

[Illustration: (A) Fig. 44--Vacuum Tube Detector Set with One Step
Amplifier (Resistance Coupled).]

[Illustration: (B) Fig. 44.--Wiring Diagram for Using One A or Storage
Battery with an Amplifier and a Detector Tube.]

A Radio Frequency Transformer Amplifying Receiving Set.--Instead of
using a grid leak resistance to couple up the amplifier and detector
tube circuits you can use a _radio frequency transformer_, that is, a
transformer made like a loose coupled tuning coil, and without an iron
core, as shown in the wiring diagram at A in Fig. 45. In this set,
which gives better results than where a grid leak is used, the
amplifier tube is placed in the first oscillation circuit and the
detector tube in the second circuit.

[Illustration: (A) Fig. 45.--Wiring Diagram for a Radio Frequency
Transformer Amplifying Receiving Set.]

[Illustration: (B) Fig. 45.--Radio Frequency Transformer.]

Since the radio frequency transformer has no iron core the high
frequency, or _radio frequency_ oscillating currents, as they are
called, surge through it and are not changed into low frequency, or
_audio frequency_ pulsating currents, until they flow through the
detector. Since the diagram shows only one amplifier and one radio
frequency transformer, it is consequently a _one step amplifier_;
however, two, three or more, amplifying tubes can be connected up by
means of an equal number of radio frequency transformers when you will
get wonderful results. Where a six step amplifier, that is, where six
amplifying tubes are connected together, or in _cascade_, the first
three are usually coupled up with radio frequency transformers and the
last three with audio frequency transformers. A radio frequency
transformer is shown at B and costs $6 to $7.

An Audio Frequency Transformer Amplifying Receiving Set.--Where audio
frequency transformers are used for stepping up the voltage of the
current of the detector and amplifier tubes, the radio frequency
current does not get into the plate circuit of the detector at all for
the reason that the iron core of the transformer chokes them off,
hence, the succeeding amplifiers operate at audio frequencies. An
audio frequency transformer is shown at A in Fig. 46 and a wiring
diagram showing how the tubes are connected in _cascade_ with the
transformers is shown at B; it is therefore a two-step audio frequency
receiving set.

[Illustration: (A) Fig. 46.--Audio Frequency Transformer.]

[Illustration: (B) Fig. 46--Wiring Diagram for an Audio Frequency
Transformer Amplifying Receiving Set. (With Vacuum Tube Detector and
Two Step Amplifier Tubes.)]

A Six Step Amplifier Receiving Set With a Loop Aerial.--By using a
receiving set having a three step radio frequency and a three step
audio frequency, that is, a set in which there are coupled three
amplifying tubes with radio frequency transformers and three
amplifying tubes with audio frequency transformers as described under
the caption _A Radio Frequency Transformer Receiving Set_, you can use
a _loop aerial_ in your room thus getting around the difficulties--if
such there be--in erecting an out-door aerial. You can easily make a
loop aerial by winding 10 turns of _No. 14_ or _16_ copper wire about
1/16 inch apart on a wooden frame two feet on the side as shown in
Fig. 47. With this six step amplifier set and loop aerial you can
receive wave lengths of 150 to 600 meters from various high power
stations which are at considerable distances away.

[Illustration: (A) Fig. 47.--Six Step Amplifier with Loop Aerial.]

[Illustration: (B) Fig. 47.--Efficient Regenerative Receiving Set.
(With Three Coil Loose Coupler Tuner.)]

How to Prevent Howling.--Where radio frequency or audio frequency
amplifiers are used to couple your amplifier tubes in cascade you must
take particular pains to shield them from one another in order to
prevent the _feed back_ of the currents through them, which makes the
head phones or loud speaker _howl_. To shield them from each other the
tubes should be enclosed in metal boxes and placed at least 6 inches
apart while the transformers should be set so that their cores are at
right angles to each other and these also should be not less than six
inches apart.




CHAPTER X

REGENERATIVE AMPLIFICATION RECEIVING SETS


While a vacuum tube detector has an amplifying action of its own, and
this accounts for its great sensitiveness, its amplifying action can
be further increased to an enormous extent by making the radio
frequency currents that are set up in the oscillation circuits react
on the detector.

Such currents are called _feed-back_ or _regenerative_ currents and
when circuits are so arranged as to cause the currents to flow back
through the detector tube the amplification keeps on increasing until
the capacity of the tube itself is reached. It is like using steam
over and over again in a steam turbine until there is no more energy
left in it. A system of circuits which will cause this regenerative
action to take place is known as the _Armstrong circuits_ and is so
called after the young man who discovered it.

Since the regenerative action of the radio frequency currents is
produced by the detector tube itself and which sets up an amplifying
effect without the addition of an amplifying tube, this type of
receiving set has found great favor with amateurs, while in
combination with amplifying tubes it multiplies their power
proportionately and it is in consequence used in one form or another
in all the better sets.

There are many different kinds of circuits which can be used to
produce the regenerative amplification effect while the various kinds
of tuning coils will serve for coupling them; for instance a two or
three slide single tuning coil will answer the purpose but as it does
not give good results it is not advisable to spend either time or
money on it. A better scheme is to use a loose coupler formed of two
or three honeycomb or other compact coils, while a _variocoupler_ or a
_variometer_ or two will produce the maximum regenerative action.

The Simplest Type of Regenerative Receiving Set. With Loose Coupled
Tuning Coil.--While this regenerative set is the simplest that will
give anything like fair results it is here described not on account of
its desirability, but because it will serve to give you the
fundamental idea of how the _feed-back_ circuit is formed.

For this set you need: (1) a _loose-coupled tuning coil_ such as
described in Chapter III, (2) a _variable condenser_ of _.001 mfd._
(microfarad) capacitance; (3) one _fixed condenser_ of _.001 mfd._;
(4) one _fixed condenser_ for the grid leak circuit of _.00025 mfd._;
(5) a _grid leak_ of 1/2 to 2 megohms resistance; (6) a _vacuum tube
detector_; (7) an _A 6 volt battery_; (8) a _rheostat_; (9) a _B 22
1/2 volt battery_; and (10) a pair of _2000 ohm head phones_.

Connecting Up the Parts.--Begin by connecting the leading-in wire of
the aerial with the binding post end of the primary coil of the loose
coupler as shown in the wiring diagram Fig. 48 and then connect the
sliding contact with the water pipe or other ground. Connect the
binding post end of the primary coil with one post of the variable
condenser, connect the other post of this with one of the posts of the
_.00025 mfd._ condenser and the other end of this with the grid of the
detector tube; then around this condenser shunt the grid leak
resistance.

[Illustration: Fig. 48.--Simple Regenerative Receiving Set. (With
Loose Coupler Tuner.)]

Next connect the sliding contact of the primary coil with the other
post of the variable condenser and from this lead a wire on over to
one of the terminals of the filament of the vacuum tube; to the other
terminal of the filament connect one of the posts of the rheostat and
connect the other post to the - or negative electrode of the A
battery and then connect the + or positive electrode of it to the
other terminal of the filament.

Connect the + or positive electrode of the A battery with one post of
the .001 mfd. fixed condenser and connect the other post of this to
one of the ends of the secondary coil of the tuning coil and which is
now known as the _tickler coil_; then connect the other end of the
secondary, or tickler coil to the plate of the vacuum tube. In the
wiring diagram the secondary, or tickler coil is shown above and in a
line with the primary coil but this is only for the sake of making the
connections clear; in reality the secondary, or tickler coil slides to
and fro in the primary coil as shown and described in Chapter III.
Finally connect the _negative_, or zinc pole of the _B battery_ to one
side of the fixed condenser, the _positive_, or carbon, pole to one of
the terminals of the head phones and the other terminal of this to the
other post of the fixed condenser when your regenerative set is
complete.

An Efficient Regenerative Receiving Set. With Three Coil Loose
Coupler.--To construct a really good regenerative set you must use a
loose coupled tuner that has three coils, namely a _primary_, a
_secondary_ and a _tickler coil_. A tuner of this kind is made like an
ordinary loose coupled tuning coil but it has a _third_ coil as shown
at A and B in Fig. 49. The middle coil, which is the _secondary_, is
fixed to the base, and the large outside coil, which is the _primary_,
is movable, that is it slides to and fro over the middle coil, while
the small inside coil, which is the _tickler_, is also movable and can
slide in or out of the middle _coil_. None of these coils is variable;
all are wound to receive waves up to 360 meters in length when used
with a variable condenser of _.001 mfd_. capacitance. In other words
you slide the coils in and out to get the right amount of coupling and
you tune by adjusting the variable condenser to get the exact wave
length you want.

[Illustration: (A) Fig. 49.--Diagram of a Three Coil Coupler.]

[Illustration: (B) Fig. 49.--Three Coil Loose Coupler Tuner.]

With Compact Coils.--Compact coil tuners are formed of three fixed
inductances wound in flat coils, and these are pivoted in a mounting
so that the distance between them and, therefore, the coupling, can be
varied, as shown at A in Fig. 50. These coils are wound up by the
makers for various wave lengths ranging from a small one that will
receive waves of any length up to 360 meters to a large one that has a
maximum of 24,000 meters. For an amateur set get three of the smallest
coils when you can not only hear amateur stations that send on a 200
meter wave but broadcasting stations that send on a 360 meter wave.

[Illustration: Fig. 50.--Honeycomb Inductance Coil.]

These three coils are mounted with panel plugs which latter fit into a
stand, or mounting, so that the middle coil is fixed, that is,
stationary, while the two outside coils can be swung to and fro like a
door; this scheme permits small variations of coupling to be had
between the coils and this can be done either by handles or by means
of knobs on a panel board. While I have suggested the use of the
smallest size coils, you can get and use those wound for any wave
length you want to receive and when those are connected with
variometers and variable condensers, and with a proper aerial, you
will have a highly efficient receptor that will work over all ranges
of wave lengths. The smallest size coils cost about $1.50 apiece and
the mounting costs about $6 or $7 each.

The A Battery Potentiometer.--This device is simply a resistance like
the rheostat described in connection with the preceding vacuum tube
receiving sets but it is wound to 200 or 300 ohms resistance as
against 1-1/2 to 6 ohms of the rheostat. It is, however, used as well
as the rheostat. With a vacuum tube detector, and especially with one
having a gas-content, a potentiometer is very necessary as it is only
by means of it that the potential of the plate of the detector can be
accurately regulated. The result of proper regulation is that when the
critical potential value is reached there is a marked increase in the
loudness of the sounds that are emitted by the head phones.

As you will see from A in Fig. 51 it has three taps. The two taps
which are connected with the ends of the resistance coil are shunted
around the A battery and the third tap, which is attached to the
movable contact arm, is connected with the B battery tap, see B, at
which this battery gives 18 volts. Since the A battery gives 6 volts
you can vary the potential of the plate from 18 to 24 volts. The
potentiometer must never be shunted around the B battery or the latter
will soon run down. A potentiometer costs a couple of dollars.

[Illustration: (A) Fig. 51.--The Use of the Potentiometer.]

The Parts and How to Connect Them Up.--For this regenerative set you
will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2)
two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025
mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube
detector_; (6) a _6 volt A battery_; (7) _a rheostat_; (8) a
_potentiometer_; (9) an _18_ or _20 volt B battery_; (10) a _fixed
condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000
ohm head phones_.

To wire up the parts connect the leading-in wire of the aerial with
the primary coil, which is the middle one of the tuner, and connect
the other terminal with the ground. Connect the ends of the secondary
coil, which is the middle one, with the posts of the variable
condenser and connect one of the posts of the latter with one post of
the fixed .00025 mfd. condenser and the other post of this with the
grid; then shunt the grid leak around it. Next connect the other post
of the variable condenser to the - or _negative_ electrode of the _A
battery_; the + or _positive_ electrode of this to one terminal of the
detector filament and the other end of the latter to the electrode of
the A battery.

Now connect one end of the tickler coil with the detector plate and
the other post to the fixed .001 mfd. condenser, then the other end of
this to the positive or carbon pole of the B battery.

This done shunt the potentiometer around the A battery and run a wire
from the movable contact of it (the potentiometer) over to the 18 volt
tap, (see B, Fig. 51), of the B battery.

Finally, shunt the head phones and the .001 mfd. fixed condenser and
you are ready to try out conclusions.

A Regenerative Audio Frequency Amplifier Receiving Set.--The use of
amateur regenerative cascade audio frequency receiving sets is getting
to be quite common. To get the greatest amplification possible with
amplifying tubes you have to keep a negative potential on the grids.
You can, however, get very good results without any special charging
arrangement by simply connecting one post of the rheostat with the
negative terminal of the filament and connecting the _low potential_
end of the secondary of the tuning coil with the - or negative
electrode of the A battery. This scheme will give the grids a negative
bias of about 1 volt. You do not need to bother about these added
factors that make for high efficiency until after you have got your
receiving set in working order and understand all about it.

The Parts and How to Connect Them Up.--Exactly the same parts are
needed for this set as the one described above, but in addition you
will want: (1) two more _rheostats_; (2) _two_ more sets of B 22-1/2
_volt batteries_; (3) _two amplifier tubes_, and (4) _two audio
frequency transformers_ as described in Chapter IX and pictured at A
in Fig. 46.

To wire up the parts begin by connecting the leading-in wire to one
end of the primary of the tuning coil and then connect the other end
of the coil with the ground. A variable condenser of .001 mfd.
capacitance can be connected in the ground wire, as shown in Fig. 52,
to good advantage although it is not absolutely needed. Now connect
one end of the secondary coil to one post of a _.001 mfd._ variable
condenser and the other end of the secondary to the other post of the
condenser.

[Illustration: Fig. 52.--Regenerative Audio Frequency Amplifier
Receiving Set.]

Next bring a lead (wire) from the first post of the variable condenser
over to the post of the first fixed condenser and connect the other
post of the latter with the grid of the detector tube. Shunt 1/2 to 2
megohm grid leak resistance around the fixed condenser and then
connect the second post of the variable condenser to one terminal of
the detector tube filament. Run this wire on over and connect it with
the first post of the second rheostat, the second post of which is
connected with one terminal of the filament of the first amplifying
tube; then connect the first post of the rheostat with one end of the
secondary coil of the first audio frequency transformer, and the other
end of this coil with the grid of the first amplifier tube.

Connect the lead that runs from the second post of variable condenser
to the first post of the third rheostat, the second post of which is
connected with one terminal of the second amplifying tube; then
connect the first post of the rheostat with one end of the secondary
coil of the second audio frequency transformer and the other end of
this coil with the grid of the second amplifier tube.

This done connect the - or negative electrode of the A battery
with the second post of the variable condenser and connect the + or
positive electrode with the free post of the first rheostat, the other
post of which connects with the free terminal of the filament of the
detector. From this lead tap off a wire and connect it to the free
terminal of the filament of the first amplifier tube, and finally
connect the end of the lead with the free terminal of the filament of
the second amplifier tube.

Next shunt a potentiometer around the A battery and connect the
third post, which connects with the sliding contact, to the negative
or zinc pole of a B battery, then connect the positive or
carbon pole of it to the negative or zinc pole of a second B
battery and the positive or carbon pole of the latter with one end of
the primary coil of the second audio frequency transformer and the
other end of it to the plate of the first amplifying tube. Run the
lead on over and connect it to one of the terminals of the second
fixed condenser and the other terminal of this with the plate of the
second amplifying tube. Then shunt the headphones around the
condenser.

Finally connect one end of the tickler coil of the tuner with the
plate of the detector tube and connect the other end of the tickler to
one end of the primary coil of the first audio frequency transformer
and the other end of it to the wire that connects the two B
batteries together.




CHAPTER XI

SHORT WAVE REGENERATIVE RECEIVING SETS


A _short wave receiving set_ is one that will receive a range of
wave lengths of from 150 to 600 meters while the distance over which
the waves can be received as well as the intensity of the sounds
reproduced by the headphones depends on: (1) whether it is a
regenerative set and (2) whether it is provided with amplifying tubes.

High-grade regenerative sets designed especially for receiving amateur
sending stations that must use a short wave length are built on the
regenerative principle just like those described in the last chapter
and further amplification can be had by the use of amplifier tubes as
explained in Chapter IX, but the new feature of these sets is the use
of the _variocoupler_ and one or more _variometers_. These tuning
devices can be connected up in different ways and are very popular
with amateurs at the present time.

Differing from the ordinary loose coupler the variometer has no
movable contacts while the variometer is provided with taps so that
you can connect it up for the wave length you want to receive. All you
have to do is to tune the oscillation circuits to each other is to
turn the _rotor_, which is the secondary coil, around in the _stator_,
as the primary coil is called in order to get a very fine variation of
the wave length. It is this construction that makes _sharp tuning_
with these sets possible, by which is meant that all wave lengths are
tuned out except the one which the receiving set is tuned for.

A Short Wave Regenerative Receiver--With One Variometer and Three
Variable Condensers.--This set also includes a variocoupler and a
_grid coil_. The way that the parts are connected together makes it a
simple and at the same time a very efficient regenerative receiver for
short waves. While this set can be used without shielding the parts
from each other the best results are had when shields are used.

The parts you need for this set include: (1) one _variocoupler_; (2)
one _.001 microfarad variable condenser_; (3) one _.0005 microfarad
variable condenser_; (4) one _.0007 microfarad variable condenser_;
(5) _one 2 megohm grid leak_; (6) one _vacuum tube detector_; (7) one
_6 volt A battery_; (8) one _6 ohm_, 1-1/2 _ampere rheostat_; (9) one
_200 ohm potentiometer_; (10) one 22-1/2 _volt B battery_; (11) one
_.001 microfarad fixed condenser_, (12) one pair of _2,000 ohm
headphones_, and (13) a _variometer_.

The Variocoupler.--A variocoupler consists of a primary coil wound on
the outside of a tube of insulating material and to certain turns of
this taps are connected so that you can fix the wave length which your
aerial system is to receive from the shortest wave; i.e., 150 meters
on up by steps to the longest wave, i.e., 600 meters, which is the
range of most amateur variocouplers that are sold in the open market.
This is the part of the variocoupler that is called the _stator_.

The secondary coil is wound on the section of a ball mounted on a
shaft and this is swung in bearings on the stator so that it can turn
in it. This part of the variocoupler is called the _rotor_ and is
arranged so that it can be mounted on a panel and adjusted by means of
a knob or a dial. A diagram of a variocoupler is shown at A in Fig.
53, and the coupler itself at B. There are various makes and
modifications of variocouplers on the market but all of them are about
the same price which is $6.00 or $8.00.

[Illustration: Fig. 53.--How the Variocoupler is Made and Works.]

The Variometer.--This device is quite like the variocoupler, but with
these differences: (1) the rotor turns in the stator, which is also
the section of a ball, and (2) one end of the primary is connected
with one end of the secondary coil. To be really efficient a
variometer must have a small resistance and a large inductance as well
as a small dielectric loss. To secure the first two of these factors
the wire should be formed of a number of fine, pure copper wires each
of which is insulated and the whole strand then covered with silk.
This kind of wire is the best that has yet been devised for the
purpose and is sold under the trade name of _litzendraht_.

A new type of variometer has what is known as a _basket weave_, or
_wavy wound_ stator and rotor. There is no wood, insulating compound
or other dielectric materials in large enough quantities to absorb the
weak currents that flow between them, hence weaker sounds can be heard
when this kind of a variometer is used. With it you can tune sharply
to waves under 200 meters in length and up to and including wave
lengths of 360 meters. When amateur stations of small power are
sending on these short waves this style of variometer keeps the
electric oscillations at their greatest strength and, hence, the
reproduced sounds will be of maximum intensity. A wiring diagram of a
variometer is shown at A in Fig. 54 and a _basketball_ variometer is
shown complete at B.

[Illustration: Fig. 54.--How the Variometer is Made and Works.]

Connecting Up the Parts.--To hook-up the set connect the leading-in
wire to one end of the primary coil, or stator, of the variocoupler
and solder a wire to one of the taps that gives the longest wave
length you want to receive. Connect the other end of this wire with
one post of a .001 microfarad variable condenser and connect the other
post with the ground as shown in Fig. 55. Now connect one end of the
secondary coil, or rotor, to one post of a .0007 mfd. variable
condenser, the other post of this to one end of the grid coil and the
other end of this with the remaining end of the rotor of the
variocoupler.

[Illustration: Fig. 55.--Short Wave Regenerative Receiving Set (one
Variometer and three Variable Condensers.)]

Next connect one post of the .0007 mfd. condenser with one of the
terminals of the detector filament; then connect the other post of
this condenser with one post of the .0005 mfd. variable condenser and
the other post of this with the grid of the detector, then shunt the
megohm grid leak around the latter condenser. This done connect the
other terminal of the filament to one post of the rheostat, the other
post of this to the - or negative electrode of the 6 volt A
battery and the + or positive electrode of the latter to the other
terminal of the filament.

Shunt the potentiometer around the A battery and connect the sliding
contact with the - or zinc pole of the B battery and the + or carbon
pole with one terminal of the headphone; connect the other terminal to
one of the posts of the variometer and the other post of the
variometer to the plate of the detector. Finally shunt a .001 mfd.
fixed condenser around the headphones. If you want to amplify the
current with a vacuum tube amplifier connect in the terminals of the
amplifier circuit shown at A in Figs. 44 or 45 at the point where
they are connected with the secondary coil of the loose coupled tuning
coil, in those diagrams with the binding posts of Fig. 55 where the
phones are usually connected in.

Short Wave Regenerative Receiver. With Two Variometers and Two
Variable Condensers.--This type of regenerative receptor is very
popular with amateurs who are using high-grade short-wave sets. When
you connect up this receptor you must keep the various parts well
separated. Screw the variocoupler to the middle of the base board or
panel, and secure the variometers on either side of it so that the
distance between them will be 9 or 10 inches. By so placing them the
coupling will be the same on both sides and besides you can shield
them from each other easier.

For the shield use a sheet of copper on the back of the panel and
place a sheet of copper between the parts, or better, enclose the
variometers and detector and amplifying tubes if you use the latter in
sheet copper boxes. When you set up the variometers place them so that
their stators are at right angles to each other for otherwise the
magnetic lines of force set up by the coils of each one will be
mutually inductive and this will make the headphones or loud speaker
_howl_. Whatever tendency the receptor has to howl with this
arrangement can be overcome by putting in a grid leak of the right
resistance and adjusting the condenser.

The Parts and How to Connect Them Up.--For this set you require: (1)
one _variocoupler_; (2) two _variometers_; (3) one _.001 microfarad
variable condenser_; (4) one _.0005 microfarad variable condenser_;
(5) one _2 megohm grid leak resistance_; (6) one _vacuum tube
detector_; (7) one _6 volt A battery_; (8) one _200 ohm
potentiometer_; (9) one _22-1/2 volt B battery_; (10) one _.001
microfarad fixed condenser_, and (11) one pair of _2,000 ohm
headphones_.

To wire up the set begin by connecting the leading-in wire to the
fixed end of the primary coil, or _stator_, of the variocoupler, as
shown in Fig. 56, and connect one post of the .001 mfd. variable
condenser to the stator by soldering a short length of wire to the tap
of the latter that gives the longest wave you want to receive. Now
connect one end of the secondary coil, or _rotor_, of the variocoupler
with one post of the .0005 mfd. variable condenser and the other part
to the grid of the detector tube. Connect the other end of the rotor
of the variocoupler to one of the posts of the first variometer and
the other post of this to one of the terminals of the detector
filament.

[Illustration: Fig. 56.--Short Wave Regenerative Receiving Set (two
Variometers and two Variable Condensers.)]

Connect this filament terminal with the - or negative electrode of the
A battery and the + or positive electrode of this with one post
of the rheostat and lead a wire from the other post to the free
terminal of the filament. This done shunt the potential around the
A battery and connect the sliding contact to the - or zinc pole
of the B battery and the + or carbon pole of this to one
terminal of the headphones, while the other terminal of this leads to
one of the posts of the second variometer, the other post of which is
connected to the plate of the detector tube. If you want to add an
amplifier tube then connect it to the posts instead of the headphones
as described in the foregoing set.




CHAPTER XII

INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING SETS


All receiving sets that receive over a range of wave lengths of from
150 meters to 3,000 meters are called _intermediate wave sets_ and all
sets that receive wave lengths over a range of anything more than
3,000 meters are called _long wave sets_. The range of intermediate
wave receptors is such that they will receive amateur, broadcasting,
ship and shore Navy, commercial, Arlington's time and all other
stations using _spark telegraph damped waves_ or _arc_ or _vacuum tube
telephone continuous waves_ but not _continuous wave telegraph
signals_, unless these have been broken up into groups at the
transmitting station. To receive continuous wave telegraph signals
requires receiving sets of special kind and these will be described in
the next chapter.

Intermediate Wave Receiving Sets.--There are two chief schemes
employed to increase the range of wave lengths that a set can receive
and these are by using: (1) _loading coils_ and _shunt condensers_,
and (2) _bank-wound coils_ and _variable condensers_. If you have a
short-wave set and plan to receive intermediate waves with it then
loading coils and fixed condensers shunted around them affords you the
way to do it, but if you prefer to buy a new receptor then the better
way is to get one with bank-wound coils and variable condensers; this
latter way preserves the electrical balance of the oscillation
circuits better, the electrical losses are less and the tuning easier
and sharper.

Intermediate Wave Set With Loading Coils.--For this intermediate wave
set you can use either of the short-wave sets described in the
foregoing chapter. For the loading coils use _honeycomb coils_, or
other good compact inductance coils, as shown in Chapter X and having
a range of whatever wave length you wish to receive. The following
table shows the range of wave length of the various sized coils when
used with a variable condenser having a .001 microfarad _capacitance_,
the approximate _inductance_ of each coil in _millihenries_ and prices
at the present writing:

TABLE OF CHARACTERISTICS OF HONEYCOMB COILS

                     Approximate Wave
                   Length in Meters in

  Millihenries
  Inductance         .001 mfd. Variable           Mounted
    Appx.              Air Condenser.            on Plug

     .040                130--  375               $1.40

     .075                180--  515                1.40

     .15                 240--  730                1.50

     .3                  330-- 1030                1.50

     .6                  450-- 1460                1.55

    1.3                  660-- 2200                1.60

    2.3                  930-- 2850                1.65

    4.5                 1300-- 4000                1.70

    6.5                 1550-- 4800                1.75

   11.                  2050-- 6300                1.80

   20.                  3000-- 8500                2.00

   40.                  4000--12000                2.15

   65.                  5000--15000                2.35

  100.                  6200--19000                2.60

  125.                  7000--21000                3.00

  175.                  8200--24000                3.50

These and other kinds of compact coils can be bought at electrical
supply houses that sell wireless goods. If your aerial is not very
high or long you can use loading coils, but to get anything like
efficient results with them you must have an aerial of large
capacitance and the only way to get this is to put up a high and long
one with two or more parallel wires spaced a goodly distance apart.

The Parts and How to Connect Them Up.--Get (1) _two honeycomb or other
coils_ of the greatest wave length you want to receive, for in order
to properly balance the aerial, or primary oscillation circuit, and
the closed, or secondary oscillation circuit, you have to tune them to
the same wave length; (2) two _.001 mfd. variable condensers_, though
fixed condensers will do, and (3) two small _single-throw double-pole
knife switches_ mounted on porcelain bases.

To use the loading coils all you have to do is to connect one of them
in the aerial above the primary coil of the loose coupler, or
variocoupler as shown in the wiring diagram in Fig. 57, then shunt one
of the condensers around it and connect one of the switches around
this; this switch enables you to cut in or out the loading coil at
will. Likewise connect the other loading coil in one side of the
closed, or secondary circuit between the variable .0007 mfd. condenser
and the secondary coil of the loose coupler or variocoupler as shown
in Fig. 53. The other connections are exactly the same as shown in
Figs. 44 and 45.

[Illustration: Fig. 57.--Wiring Diagram Showing Fixed Loading Coils
for Intermediate Wave Set.]

An Intermediate Wave Set With Variocoupler Inductance Coils.--By using
the coil wound on the rotor of the variocoupler as the tickler the
coupling between the detector tube circuits and the aerial wire system
increases as the set is tuned for greater wave lengths. This scheme
makes the control of the regenerative circuit far more stable than it
is where an ordinary loose coupled tuning coil is used.

When the variocoupler is adjusted for receiving very long waves the
rotor sets at right angles to the stator and, since when it is in this
position there is no mutual induction between them, the tickler coil
serves as a loading coil for the detector plate oscillation circuit.
Inductance coils for short wave lengths are usually wound in single
layers but _bank-wound coils_, as they are called are necessary to get
compactness where long wave lengths are to be received. By winding
inductance coils with two or more layers the highest inductance values
can be obtained with the least resistance. A wiring diagram of a
multipoint inductance coil is shown in Fig. 58. You can buy this
intermediate wave set assembled and ready to use or get the parts and
connect them up yourself.

[Illustration: Fig. 58.--Wiring Diagram for Intermediate Wave Receptor
with one Variocoupler and 12 section Bank-wound Inductance Coil.]

The Parts and How to Connect Them Up.--For this regenerative
intermediate wave set get: (1) one _12 section triple bank-wound
inductance coil_, (2) one _variometer_, and (3) all the other parts
shown in the diagram Fig. 58 except the variocoupler. First connect
the free end of the condenser in the aerial to one of the terminals of
the stator of the variocoupler; then connect the other terminal of the
stator with one of the ends of the bank-wound inductance coil and
connect the movable contact of this with the ground.

Next connect a wire to the aerial between the variable condenser and
the stator and connect this to one post of a .0005 microfarad fixed
condenser, then connect the other post of this with the grid of the
detector and shunt a 2 megohm grid leak around it. Connect a wire to
the ground wire between the bank-wound inductance coil and the ground
proper, i.e., the radiator or water pipe, connect the other end of
this to the + electrode of the A battery and connect this end also to
one of the terminals of the filament. This done connect the other
terminal of the filament to one post of the rheostat and the other
post of this to the - or negative side of the A battery.

To the + electrode of the A battery connect the - or zinc pole of the
B battery and connect the + or carbon pole of the latter with one post
of the fixed .001 microfarad condenser. This done connect one terminal
of the tickler coil which is on the rotor of the variometer to the
plate of the detector and the other terminal of the tickler to the
other post of the .001 condenser and around this shunt your
headphones. Or if you want to use one or more amplifying tubes connect
the circuit of the first one, see Fig. 45, to the posts on either side
of the fixed condenser instead of the headphones.

A Long Wave Receiving Set.--The vivid imagination of Jules Verne never
conceived anything so fascinating as the reception of messages without
wires sent out by stations half way round the world; and in these days
of high power cableless stations on the five continents you can
listen-in to the messages and hear what is being sent out by the
Lyons, Paris and other French stations, by Great Britain, Italy,
Germany and even far off Russia and Japan.

A long wave set for receiving these stations must be able to tune to
wave lengths up to 20,000 meters. Differing from the way in which the
regenerative action of the short wave sets described in the preceding
chapter is secured and which depends on a tickler coil and the
coupling action of the detector in this long wave set, [Footnote: All
of the short wave and intermediate wave receivers described, are
connected up according to the wiring diagram used by the A. H. Grebe
Company, Richmond Hill, Long Island, N. Y.] this action is obtained by
the use of a tickler coil in the plate circuit which is inductively
coupled to the grid circuit and this feeds back the necessary amount
of current. This is a very good way to connect up the circuits for the
reason that: (1) the wiring is simplified, and (2) it gives a single
variable adjustment for the entire range of wave lengths the receptor
is intended to cover.

The Parts and How to Connect Them Up.--The two chief features as far
as the parts are concerned of this long wave length receiving set are
(1) the _variable condensers_, and (2) the _tuning inductance coils_.
The variable condenser used in series with the aerial wire system has
26 plates and is equal to a capacitance of _.0008 mfd._ which is the
normal aerial capacitance. The condenser used in the secondary coil
circuit has 14 plates and this is equal to a capacitance of _.0004
mfd_.

There are a number of inductance coils and these are arranged so that
they can be connected in or cut out and combinations are thus formed
which give a high efficiency and yet allow them to be compactly
mounted. The inductance coils of the aerial wire system and those of
the secondary coil circuit are practically alike. For wave lengths up
to 2,200 meters _bank litz-wound coils_ are used and these are
wound up in 2, 4 and 6 banks in order to give the proper degree of
coupling and inductance values.

Where wave lengths of more than 2,200 meters are to be received
_coto-coils_ are used as these are the "last word" in inductance coil
design, and are especially adapted for medium as well as long wave
lengths. [Footnote: Can be had of the Coto Coil Co., Providence, R. I.]
These various coils are cut in and out by means of two five-point
switches which are provided with auxiliary levers and contactors for
_dead-ending_ the right amount of the coils. In cutting in coils for
increased wave lengths, that is from 10,000 to 20,000 meters, all of
the coils of the aerial are connected in series as well as all of the
coils of the secondary circuit. The connections for a long wave
receptor are shown in the wiring diagram in Fig. 59.

[Illustration: Fig. 59.--Wiring Diagram Showing Long Wave Receptor
with Variocouplers and Bank-wound Inductance Coils]




CHAPTER XIII

HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING SET


Any of the receiving sets described in the foregoing chapters will
respond to either: (1) a wireless telegraph transmitter that uses a
spark gap and which sends out periodic electric waves, or to (2) a
wireless telephone transmitter that uses an arc or a vacuum tube
oscillator and which sends out continuous electric waves. To receive
wireless _telegraph_ signals, however, from a transmitter that uses an
arc or a vacuum tube oscillator and which sends out continuous waves,
either the transmitter or the receptor must be so constructed that the
continuous waves will be broken up into groups of audio frequency and
this is done in several different ways.

There are four different ways employed at the present time to break up
the continuous waves of a wireless telegraph transmitter into groups
and these are: (_a_) the _heterodyne_, or _beat_, method, in which
waves of different lengths are impressed on the received waves and so
produces beats; (_b_) the _tikker_, or _chopper_ method, in which the
high frequency currents are rapidly broken up; (_c_) the variable
condenser method, in which the movable plates are made to rapidly
rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is
often called, and which is really a modified form of and an
improvement on the tikker. The heterodyne method will be described in
this chapter.

What the Heterodyne or Beat Method Is.--The word _heterodyne_ was
coined from the Greek words _heteros_ which means _other_, or
_different_, and _dyne_ which means _power_; in other words it means
when used in connection with a wireless receptor that another and
different high frequency current is used besides the one that is
received from the sending station. In music a _beat_ means a regularly
recurrent swelling caused by the reinforcement of a sound and this is
set up by the interference of sound waves which have slightly
different periods of vibration as, for instance, when two tones take
place that are not quite in tune with each other. This, then, is the
principle of the heterodyne, or beat, receptor.

In the heterodyne, or beat method, separate sustained oscillations,
that are just about as strong as those of the incoming waves, are set
up in the receiving circuits and their frequency is just a little
higher or a little lower than those that are set up by the waves
received from the distant transmitter. The result is that these
oscillations of different frequencies interfere and reinforce each
other when _beats_ are produced, the period of which is slow enough to
be heard in the headphones, hence the incoming signals can be heard
only when waves from the sending station are being received. A fuller
explanation of how this is done will be found in Chapter XV.

The Autodyne or Self-Heterodyne Long-Wave Receiving Set.--This is the
simplest type of heterodyne receptor and it will receive periodic
waves from spark telegraph transmitters or continuous waves from an
arc or vacuum tube telegraph transmitter. In this type of receptor the
detector tube itself is made to set up the _heterodyne oscillations_
which interfere with those that are produced by the incoming waves
that are a little out of tune with it.

With a long wave _autodyne_, or _self-heterodyne_ receptor, as this
type is called, and a two-step audio-frequency amplifier you can
clearly hear many of the cableless stations of Europe and others that
send out long waves. For receiving long wave stations, however, you
must have a long aerial--a single wire 200 or more feet in length will
do--and the higher it is the louder will be the signals. Where it is
not possible to put the aerial up a hundred feet or more above the
ground, you can use a lower one and still get messages in
_International Morse_ fairly strong.

The Parts and Connections of an Autodyne, or Self-Heterodyne,
Receiving Set.--For this long wave receiving set you will need: (1)
one _variocoupler_ with the primary coil wound on the stator and the
secondary coil and tickler coil wound on the rotor, or you can use
three honeycomb or other good compact coils of the longest wave you
want to receive, a table of which is given in Chapter XII; (2) two
_.001 mfd. variable condensers_; (3) one _.0005 mfd. variable
condenser_; (4) one _.5 to 2 megohm grid leak resistance_; (5) one
_vacuum tube detector_; (6) one _A battery_; (7) one _rheostat_; (8)
one _B battery_; (9) one _potentiometer_; (10) one _.001 mfd. fixed
condenser_ and (11) one pair of _headphones_. For the two-step
amplifier you must, of course, have besides the above parts the
amplifier tubes, variable condensers, batteries rheostats,
potentiometers and fixed condensers as explained in Chapter IX. The
connections for the autodyne, or self-heterodyne, receiving set are
shown in Fig. 60.

[Illustration: Fig. 60.--Wiring Diagram of Long Wave Antodyne, or
Self-Heterodyne Receptor.]

The Separate Heterodyne Long Wave Receiving Set.--This is a better
long wave receptor than the self heterodyne set described above for
receiving wireless telegraph signals sent out by a continuous long
wave transmitter. The great advantage of using a separate vacuum tube
to generate the heterodyne oscillations is that you can make the
frequency of the oscillations just what you want it to be and hence
you can make it a little higher or a little lower than the
oscillations set up by the received waves.

The Parts and Connections of a Separate Heterodyne Long Wave Receiving
Set.--The parts required for this long wave receiving set are: (1)
four honeycomb or other good _compact inductance_ coils of the longest
wave length that you want to receive; (2) three _.001 mfd. variable
condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _1
megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one
_A battery_; (7) two rheostats; (8) two _B batteries_, one of which is
supplied with taps; (9) one _potentiometer_; (10) one _vacuum tube
amplifier_, for setting up the heterodyne oscillations; (11) a pair of
_headphones_ and (12) all of the parts for a _two-step amplifier_ as
detailed in Chapter IX, that is if you are going to use amplifiers.
The connections are shown in Fig. 61.

[Illustration: Fig. 61.--Wiring Diagram of Long Wave Separate
Heterodyne Receiving Set.]

In using either of these heterodyne receivers be sure to carefully
adjust the B battery by means of the potentiometer.

[Footnote: The amplifier tube in this case is used as a generator of
oscillations.]




CHAPTER XIV

HEADPHONES AND LOUD SPEAKERS


Wireless Headphones.--A telephone receiver for a wireless receiving
set is made exactly on the same principle as an ordinary Bell
telephone receiver. The only difference between them is that the
former is made flat and compact so that a pair of them can be fastened
together with a band and worn on the head (when it is called a
_headset_), while the latter is long and cylindrical so that it can be
held to the ear. A further difference between them is that the
wireless headphone is made as sensitive as possible so that it will
respond to very feeble currents, while the ordinary telephone receiver
is far from being sensitive and will respond only to comparatively
large currents.

How a Bell Telephone Receiver Is Made.--An ordinary telephone receiver
consists of three chief parts and these are: (1) a hard-rubber, or
composition, shell and cap, (2) a permanent steel bar magnet on one
end of which is wound a coil of fine insulated copper wire, and (3) a
soft iron disk, or _diaphragm_, all of which are shown in the
cross-section in Fig. 62. The bar magnet is securely fixed inside of
the handle so that the outside end comes to within about 1/32 of an
inch of the diaphragm when this is laid on top of the shell and the
cap is screwed on.

[Illustration: Fig. 62.--Cross-section of Bell telephone Receiver.]

[Illustration: original © Underwood and Underwood. Alexander Graham
Bell, Inventor of the Telephone, now an ardent Radio Enthusiast.]

The ends of the coil of wire are connected with two binding posts
which are in the end of the shell, but are shown in the picture at the
sides for the sake of clearness. This coil usually has a resistance of
about 75 ohms and the meaning of the _ohmic resistance_ of a receiver
and its bearing on the sensitiveness of it will be explained a little
farther along. After the disk, or diaphragm, which is generally made
of thin, soft sheet iron that has been tinned or japanned, [Footnote:
A disk of photographic tin-type plate is generally used.] is placed
over the end of the magnet, the cap, which has a small opening in it,
is screwed on and the receiver is ready to use.

How a Wireless Headphone Is Made.--For wireless work a receiver of the
watch-case type is used and nearly always two such receivers are
connected with a headband. It consists of a permanent bar magnet bent
so that it will fit into the shell of the receiver as shown at A in
Fig. 63.

[Illustration: Fig. 63.--Wireless Headphone.]

The ends of this magnet, which are called _poles_, are bent up, and
hence this type is called a _bipolar_ receiver. The magnets are wound
with fine insulated wire as before and the diaphragm is held securely
in place over them by screwing on the cap.

About Resistance, Turns of Wire and Sensitivity of Headphones.--If you
are a beginner in wireless you will hear those who are experienced
speak of a telephone receiver as having a resistance of 75 ohms, 1,000
ohms, 2,000 or 3,000 ohms, as the case may be; from this you will
gather that the higher the resistance of the wire on the magnets the
more sensitive the receiver is. In a sense this is true, but it is not
the resistance of the magnet coils that makes it sensitive, in fact,
it cuts down the current, but it is the _number of turns_ of wire on
them that determines its sensitiveness; it is easy to see that this is
so, for the larger the number of turns the more often will the same
current flow round the cores of the magnet and so magnetize them to a
greater extent.

But to wind a large number of turns of wire close enough to the cores
to be effective the wire must be very small and so, of course, the
higher the resistance will be. Now the wire used for winding good
receivers is usually No. 40, and this has a diameter of .0031 inch;
consequently, when you know the ohmic resistance you get an idea of
the number of turns of wire and from this you gather in a general way
what the sensitivity of the receiver is.

A receiver that is sensitive enough for wireless work should be wound
to not less than 1,000 ohms (this means each ear phone), while those
of a better grade are wound to as high as 3,000 ohms for each one. A
high-grade headset is shown in Fig. 64. Each phone of a headset should
be wound to the same resistance, and these are connected in series as
shown. Where two or more headsets are used with one wireless receiving
set they must all be of the same resistance and connected in series,
that is, the coils of one head set are connected with the coils of the
next head set and so on to form a continuous circuit.

[Illustration: Fig. 64.--Wireless Headphone.]

The Impedance of Headphones.--When a current is flowing through a
circuit the material of which the wire is made not only opposes its
passage--this is called its _ohmic resistance_--but a
_counter-electromotive force_ to the current is set up due to the
inductive effects of the current on itself and this is called
_impedance_. Where a wire is wound in a coil the impedance of the
circuit is increased and where an alternating current is used the
impedance grows greater as the frequency gets higher. The impedance of
the magnet coils of a receiver is so great for high frequency
oscillations that the latter cannot pass through them; in other words,
they are choked off.

How the Headphones Work.--As you will see from the cross-sections in
Figs. 62 and 63 there is no connection, electrical or mechanical,
between the diaphragm and the other parts of the receiver. Now when
either feeble oscillations, which have been rectified by a detector,
or small currents from a B battery, flow through the magnet coils the
permanent steel magnet is energized to a greater extent than when no
current is flowing through it. This added magnetic energy makes the
magnet attract the diaphragm more than it would do by its own force.
If, on the other hand, the current is cut off the pull of the magnet
is lessened and as its attraction for the diaphragm is decreased the
latter springs back to its original position. When varying currents
flow through the coils the diaphragm vibrates accordingly and sends
out sound waves.

About Loud Speakers.--The simplest acoustic instrument ever invented
is the _megaphone_, which latter is a Greek word meaning _great
sound_. It is a very primitive device and our Indians made it out of
birch-bark before Columbus discovered America. In its simplest form it
consists of a cone-shaped horn and as the speaker talks into the small
end the concentrated sound waves pass out of the large end in whatever
direction it is held.

Now a loud speaker of whatever kind consists of two chief parts and
these are: (1) a _telephone receiver_, and (2) a _megaphone_, or
_horn_ as it is called. A loud speaker when connected with a wireless
receiving set makes it possible for a room, or an auditorium, full of
people, or an outdoor crowd, to hear what is being sent out by a
distant station instead of being limited to a few persons listening-in
with headphones. To use a loud speaker you should have a vacuum tube
detector receiving set and this must be provided with a one-step
amplifier at least.

To get really good results you need a two-step amplifier and then
energize the plate of the second vacuum tube amplifier with a 100 volt
B battery; or if you have a three-step amplifier then use the
high voltage on the plate of the third amplifier tube. Amplifying
tubes are made to stand a plate potential of 100 volts and this is the
kind you must use. Now it may seem curious, but when the current flows
through the coils of the telephone receiver in one direction it gives
better results than when it flows through in the other direction; to
find out the way the current gives the best results try it out both
ways and this you can do by simply reversing the connections.

The Simplest Type of Loud Speaker.--This loud speaker, which is
called, the Arkay, [Footnote: Made by the Riley-Klotz Mfg. Co.,
Newark, N. J.] will work on a one- or two-step amplifier. It consists
of a brass horn with a curve in it and in the bottom there is an
adapter, or frame, with a set screw in it so that you can fit in one
of your headphones and this is all there is to it. The construction is
rigid enough to prevent overtones, or distortion of speech or music.
It is shown in Fig. 65.

[Illustration: Fig. 65.--Arkay Loud Speaker.]

Another Simple Kind of Loud Speaker.--Another loud speaker, see Fig.
66, is known as the _Amplitone_ [Footnote: Made by the American
Pattern, Foundry and Machine Co., 82 Church Street, N. Y. C.] and it
likewise makes use of the headphones as the sound producer. This
device has a cast metal horn which improves the quality of the sound,
and all you have to do is to slip the headphones on the inlet tubes of
the horn and it is ready for use. The two headphones not only give a
longer volume of sound than where a single one is used but there is a
certain blended quality which results from one phone smoothing out the
imperfections of the other.

[Illustration: Fig. 66.--Amplitone Loud Speaker.]

A Third Kind of Simple Loud Speaker.--The operation of the
_Amplitron_, [Footnote: Made by the Radio Service Co., 110 W. 40th
Street, N. Y.] as this loud speaker is called, is slightly different
from others used for the same purpose. The sounds set up by the
headphone are conveyed to the apex of an inverted copper cone which is
7 inches long and 10 inches in diameter. Here it is reflected by a
parabolic mirror which greatly amplifies the sounds. The amplification
takes place without distortion, the sounds remaining as clear and
crisp as when projected by the transmitting station. By removing the
cap from the receiver the shell is screwed into a receptacle on the
end of the loud speaker and the instrument is ready for use. It is
pictured in Fig. 67.

[Illustration: Fig. 67.--Amplitron Loud Speaker.]

A Super Loud Speaker.--This loud speaker, which is known as the
_Magnavox Telemegafone_, was the instrument used by Lt. Herbert E.
Metcalf, 3,000 feet in the air, and which startled the City of
Washington on April 2, 1919, by repeating President Wilson's _Victory
Loan Message_ from an airplane in flight so that it was distinctly
heard by 20,000 people below.

This wonderful achievement was accomplished through the installation
of the _Magnavox_ and amplifiers in front of the Treasury Building.
Every word Lt. Metcalf spoke into his wireless telephone transmitter
was caught and swelled in volume by the _Telemegafones_ below and
persons blocks away could hear the message plainly. Two kinds of these
loud speakers are made and these are: (1) a small loud speaker for the
use of operators so that headphones need not be worn, and (2) a large
loud speaker for auditorium and out-door audiences.

[Illustration: original © Underwood and Underwood. World's Largest
Loud Speaker ever made. Installed in Lytle Park, Cincinnati, Ohio, to
permit President Harding's Address at Point Pleasant, Ohio, during the
Grant Centenary Celebration to be heard within a radius of one
square.]

Either kind may be used with a one- or two-step amplifier or with a
cascade of half a dozen amplifiers, according to the degree of
loudness desired. The _Telemegafone_ itself is not an amplifier in the
true sense inasmuch as it contains no elements which will locally
increase the incoming current. It does, however, transform the
variable electric currents of the wireless receiving set into sound
vibrations in a most wonderful manner.

A _telemegafone_ of either kind is formed of: (1) a telephone receiver
of large proportions, (2) a step-down induction coil, and (3) a 6 volt
storage battery that energizes a powerful electromagnet which works
the diaphragm. An electromagnet is used instead of a permanent magnet
and this is energized by a 6-volt storage battery as shown in the
wiring diagram at A in Fig. 68. One end of the core of this magnet is
fixed to the iron case of the speaker and together these form the
equivalent of a horseshoe magnet. A movable coil of wire is supported
from the center of the diaphragm the edge of which is rigidly held
between the case and the small end of the horn. This coil is placed
over the upper end of the magnet and its terminals are connected to
the secondary of the induction coil. Now when the coil is energized by
the current from the amplifiers it and the core act like a solenoid in
that the coil tends to suck the core into it; but since the core is
fixed and the coil is movable the core draws the coil down instead.
The result is that with every variation of the current that flows
through the coil it moves up and down and pulls and pushes the
diaphragm down and up with it. The large amplitude of the vibrations
of the latter set up powerful sound waves which can be heard several
blocks away from the horn. In this way then are the faint incoming
signals, speech and music which are received by the amplifying
receiving set reproduced and magnified enormously. The _Telemegafone_
is shown complete at B.

[Illustration: Fig. 68.--Magnavox Loud Speaker.]




CHAPTER XV

OPERATION OF VACUUM TUBE RECEPTORS


From the foregoing chapters you have seen that the vacuum tube can be
used either as a _detector_ or an _amplifier_ or as a _generator_ of
electric oscillations, as in the case of the heterodyne receiving set.
To understand how a vacuum tube acts as a detector and as an amplifier
you must first know what _electrons_ are. The way in which the vacuum
tube sets up sustained oscillations will be explained in Chapter XVIII
in connection with the _Operation of Vacuum Tube Transmitters_.

What Electrons Are.--Science teaches us that masses of matter are made
up of _molecules_, that each of these is made up of _atoms_, and each
of these, in turn, is made up of a central core of positive particles
of electricity surrounded by negative particles of electricity as
shown in the schematic diagram, Fig. 69. The little black circles
inside the large circle represent _positive particles of electricity_
and the little white circles outside of the large circle represent
_negative particles of electricity_, or _electrons_ as they are
called.

[Illustration: Fig. 69.--Schematic Diagram of an Atom.]

It is the number of positive particles of electricity an atom has that
determines the kind of an element that is formed when enough atoms of
the same kind are joined together to build it up. Thus hydrogen, which
is the lightest known element, has one positive particle for its
nucleus, while uranium, the heaviest element now known, has 92
positive particles. Now before leaving the atom please note that it is
as much smaller than the diagram as the latter is smaller than our
solar system.

What Is Meant by Ionization.--A hydrogen atom is not only lighter but
it is smaller than the atom of any other element while an electron is
more than a thousand times smaller than the atom of which it is a
part. Now as long as all of the electrons remain attached to the
surface of an atom its positive and negative charges are equalized and
it will, therefore, be neither positive nor negative, that is, it will
be perfectly neutral. When, however, one or more of its electrons are
separated from it, and there are several ways by which this can be
done, the atom will show a positive charge and it is then called a
_positive ion_.

In other words a _positive ion_ is an atom that has lost some of its
negative electrons while a _negative ion_ is one that has acquired
some additional negative _electrons_. When a number of electrons are
being constantly given by the atoms of an element, which let us
suppose is a metal, and are being attracted to atoms of another
element, which we will say is also a metal, a flow of electrons takes
place between the two oppositely charged elements and form a current
of negative electricity as represented by the arrows at A in Fig. 70.

[Illustration: Fig. 70.--Action of Two-electrode Vacuum Tube.]

When a stream of electrons is flowing between two metal elements, as a
filament and a plate in a vacuum tube detector, or an amplifier, they
act as _carriers_ for more negative electrons and these are supplied
by a battery as we shall presently explain. It has always been
customary for us to think of a current of electricity as flowing from
the positive pole of a battery to the negative pole of it and hence we
have called this the _direction of the current_. Since the electronic
theory has been evolved it has been shown that the electrons, or
negative charges of electricity, flow from the negative to the
positive pole and that the ionized atoms, which are more positive than
negative, flow in the opposite direction as shown at B.

How Electrons are Separated from Atoms.--The next question that arises
is how to make a metal throw off some of the electrons of the atoms of
which it is formed. There are several ways that this can be done but
in any event each atom must be given a good, hard blow. A simple way
to do this is to heat a metal to incandescence when the atoms will
bombard each other with terrific force and many of the electrons will
be knocked off and thrown out into the surrounding space.

But all, or nearly all, of them will return to the atoms from whence
they came unless a means of some kind is employed to attract them to
the atoms of some other element. This can be done by giving the latter
piece of metal a positive charge. If now these two pieces of metal are
placed in a bulb from which the air has been exhausted and the first
piece of metal is heated to brilliancy while the second piece of metal
is kept positively electrified then a stream of electrons will flow
between them.

Action of the Two Electrode Vacuum Tube.--Now in a vacuum tube
detector a wire filament, like that of an incandescent lamp, is
connected with a battery and this forms the hot element from which the
electrons are thrown off, and a metal plate with a terminal wire
secured to it is connected to the positive or carbon tap of a dry
battery; now connect the negative or zinc tap of this with one end of
a telephone receiver and the other end of this with the terminals of
the filament as shown at A in Fig. 71. If now you heat the filament
and hold the phone to your ear you can hear the current from the B
battery flowing through the circuit.

[Illustration: (A) and (B) Fig. 71.--How a Two Electrode Tube Acts as
a Relay or a Detector.]

[Illustration: (C) Fig. 71.--Only the Positive Part of Oscillations
Goes through the Tube.]

Since the electrons are negative charges of electricity they are not
only thrown off by the hot wire but they are attracted by the positive
charged metal plate and when enough electrons pass, or flow, from the
hot wire to the plate they form a conducting path and so complete the
circuit which includes the filament, the plate and the B or
plate battery, when the current can then flow through it. As the
number of electrons that are thrown off by the filament is not great
and the voltage of the plate is not high the current that flows
between the filament and the plate is always quite small.

How the Two Electrode Tube Acts as a Detector.--As the action of a two
electrode tube as a detector [Footnote: The three electrode vacuum
tube has entirely taken the place of the two electrode type.] is
simpler than that of the three electrode vacuum tube we shall describe
it first. The two electrode vacuum tube was first made by Mr. Edison
when he was working on the incandescent lamp but that it would serve
as a detector of electric waves was discovered by Prof. Fleming, of
Oxford University, London. As a matter of fact, it is not really a
detector of electric waves, but it acts as: (1) a _rectifier_ of the
oscillations that are set up in the receiving circuits, that is, it
changes them into pulsating direct currents so that they will flow
through and affect a telephone receiver, and (2) it acts as a _relay_
and the feeble received oscillating current controls the larger direct
current from the B battery in very much the same way that a telegraph
relay does. This latter relay action will be explained when we come to
its operation as an amplifier.

We have just learned that when the stream of electrons flow from the
hot wire to the cold positive plate in the tube they form a conducting
path through which the battery current can flow. Now when the electric
oscillations surge through the closed oscillation circuit, which
includes the secondary of the tuning coil, the variable condenser, the
filament and the plate as shown at B in Fig. 71 the positive part of
them passes through the tube easily while the negative part cannot get
through, that is, the top, or positive, part of the wave-form remains
intact while the lower, or negative, part is cut off as shown in the
diagram at C. As the received oscillations are either broken up into
wave trains of audio frequency by the telegraph transmitter or are
modulated by a telephone transmitter they carry the larger impulses of
the direct current from the B battery along with them and these flow
through the headphones. This is the reason the vacuum tube amplifies
as well as detects.

How the Three Electrode Tube Acts as a Detector.--The vacuum tube as a
detector has been made very much more sensitive by the use of a third
electrode shown in Fig. 72. In this type of vacuum tube the third
electrode, or _grid_, is placed between the filament and the plate and
this controls the number of electrons flowing from the filament to the
plate; in passing between these two electrodes they have to go through
the holes formed by the grid wires.

[Illustration: (A) and (B) Fig. 72.--How the Positive and Negative
Voltages of Oscillations Act on the Electrons.]

[Illustration: (C) Fig. 72.--How the Three Electrode Tube Acts as a
Detector and Amplifier.]

[Illustration: (D) Fig. 72.--How the Oscillations Control the Flow of
the Battery Current through the Tube.]

If now the grid is charged to a higher _negative_ voltage than the
filament the electrons will be stopped by the latter, see A, though
some of them will go through to the plate because they travel at a
high rate of speed. The higher the negative charge on the grid the
smaller will be the number of electrons that will reach the plate and,
of course, the smaller will be the amount of current that will flow
through the tube and the headphones from the B battery.

On the other hand if the grid is charged _positively_, see B, then
more electrons will strike the plate than when the grid is not used or
when it is negatively charged. But when the three electrode tube is
used as a detector the oscillations set up in the circuits change the
grid alternately from negative to positive as shown at C and hence the
voltage of the B battery current that is allowed to flow through the
detector from the plate to the filament rises and falls in unison with
the voltage of the oscillating currents. The way the positive and
negative voltages of the oscillations which are set up by the incoming
waves, energize the grid; how the oscillator tube clips off the
negative parts of them, and, finally, how these carry the battery
current through the tube are shown graphically by the curves at D.

How the Vacuum Tube Acts as an Amplifier.--If you connect up the
filament and the plate of a three electrode tube with the batteries
and do not connect in the grid, you will find that the electrons which
are thrown off by the filament will not get farther than the grid
regardless of how high the voltage is that you apply to the plate.
This is due to the fact that a large number of electrons which are
thrown off by the filament strike the grid and give it a negative
charge, and consequently, they cannot get any farther. Since the
electrons do not reach the plate the current from the B battery cannot
flow between it and the filament.

Now with a properly designed amplifier tube a very small negative
voltage on the grid will keep a very large positive voltage on the
plate from sending a current through the tube, and oppositely, a very
small positive voltage on the grid will let a very large plate current
flow through the tube; this being true it follows that any small
variation of the voltage from positive to negative on the grid and the
other way about will vary a large current flowing from the plate to
the filament.

In the Morse telegraph the relay permits the small current that is
received from the distant sending station to energize a pair of
magnets, and these draw an armature toward them and close a second
circuit when a large current from a local battery is available for
working the sounder. The amplifier tube is a variable relay in that
the feeble currents set up by the incoming waves constantly and
proportionately vary a large current that flows through the
headphones. This then is the principle on which the amplifying tube
works.

The Operation of a Simple Vacuum Tube Receiving Set.--The way a simple
vacuum tube detector receiving set works is like this: when the
filament is heated to brilliancy it gives off electrons as previously
described. Now when the electric waves impinge on the aerial wire they
set up oscillations in it and these surge through the primary coil of
the loose coupled tuning coil, a diagram of which is shown at B in
Fig. 41.

The energy of these oscillations sets up oscillations of the same
frequency in the secondary coil and these high frequency currents
whose voltage is first positive and then negative, surge in the closed
circuit which includes the secondary coil and the variable condenser.
At the same time the alternating positive and negative voltage of the
oscillating currents is impressed on the grid; at each change from +
to - and back again it allows the electrons to strike the plate and
then shuts them off; as the electrons form the conducting path between
the filament and the plate the larger direct current from the B
battery is permitted to flow through the detector tube and the
headphones.

Operation of a Regenerative Vacuum Tube Receiving Set.--By feeding
back the pulsating direct current from the B battery through the
tickler coil it sets up other and stronger oscillations in the
secondary of the tuning coil when these act on the detector tube and
increase its sensitiveness to a remarkable extent. The regenerative,
or _feed back_, action of the receiving circuits used will be easily
understood by referring back to B in Fig. 47.

When the waves set up oscillations in the primary of the tuning coil
the energy of them produces like oscillations in the closed circuit
which includes the secondary coil and the condenser; the alternating
positive and negative voltages of these are impressed on the grid and
these, as we have seen before, cause similar variations of the direct
current from the B battery which acts on the plate and which
flows between the latter and the filament.

This varying direct current, however, is made to flow back through the
third, or tickler coil of the tuning coil and sets up in the secondary
coil and circuits other and larger oscillating currents and these
augment the action of the oscillations produced by the incoming waves.
These extra and larger currents which are the result of the feedback
then act on the grid and cause still larger variations of the current
in the plate voltage and hence of the current of the B battery
that flows through the detector and the headphones. At the same time
the tube keeps on responding to the feeble electric oscillations set
up in the circuits by the incoming waves. This regenerative action of
the battery current augments the original oscillations many times and
hence produce sounds in the headphones that are many times greater
than where the vacuum tube detector alone is used.

Operation of Autodyne and Heterodyne Receiving Sets.--On page 109
[Chapter VII] we discussed and at A in Fig. 36 is shown a picture of
two tuning forks mounted on sounding boxes to illustrate the principle
of electrical tuning. When a pair of these forks are made to vibrate
exactly the same number of times per second there will be a
condensation of the air between them and the sound waves that are sent
out will be augmented. But if you adjust one of the forks so that it
will vibrate 256 times a second and the other fork so that it will
vibrate 260 times a second then there will be a phase difference
between the two sets of waves and the latter will augment each other 4
times every second and you will hear these rising and falling sounds
as _beats_.

Now electric oscillations set up in two circuits that are coupled
together act in exactly the same way as sound waves produced by two
tuning forks that are close to each other. Since this is true if you
tune one of the closed circuits so that the oscillations in it will
have a frequency of a 1,000,000 and tune the other circuit so that the
oscillations in it have a frequency of 1,001,000 a second then the
oscillations will augment each other 1,000 times every second.

As these rising and falling currents act on the pulsating currents
from the B battery which flow through the detector tube and the
headphones you will hear them as beats. A graphic representation of
the oscillating currents set up by the incoming waves, those produced
by the heterodyne oscillator and the beats they form is shown in Fig.
73. To produce these beats a receptor can use: (1) a single vacuum
tube for setting up oscillations of both frequencies when it is called
an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum
tube for setting up the oscillations for the second circuit when it is
called a _heterodyne_ receptor.

[Illustration: Fig. 73.--How the Heterodyne Receptor Works.]

The Autodyne, or Self-Heterodyne Receiving Set.--Where only one vacuum
tube is used for producing both frequencies you need only a
regenerative, or feed-back receptor; then you can tune the aerial wire
system to the incoming waves and tune the closed circuit of the
secondary coil so that it will be out of step with the former by 1,000
oscillations per second, more or less, the exact number does not
matter in the least. From this you will see that any regenerative set
can be used for autodyne, or self-heterodyne, reception.

The Separate Heterodyne Receiving Set.--The better way, however, is to
use a separate vacuum tube for setting up the heterodyne oscillations.
The latter then act on the oscillations that are produced by the
incoming waves and which energize the grid of the detector tube. Note
that the vacuum tube used for producing the heterodyne oscillations is
a _generator_ of electric oscillations; the latter are impressed on
the detector circuits through the variable coupling, the secondary of
which is in series with the aerial wire as shown in Fig. 74. The way
in which the tube acts as a generator of oscillations will be told in
Chapter XVIII.

[Illustration: Fig. 74.--Separate Heterodyne Oscillator.]




CHAPTER XVI

CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH DIRECT CURRENT


In the first part of this book we learned about spark-gap telegraph
sets and how the oscillations they set up are _damped_ and the waves
they send out are _periodic_. In this and the next chapter we shall
find out how vacuum tube telegraph transmitters are made and how they
set up oscillations that are _sustained_ and radiate waves that are
_continuous_.

Sending wireless telegraph messages by continuous waves has many
features to recommend it as against sending them by periodic waves and
among the most important of these are that the transmitter can be: (1)
more sharply tuned, (2) it will send signals farther with the same
amount of power, and (3) it is noiseless in operation. The
disadvantageous features are that: (1) a battery current is not
satisfactory, (2) its circuits are somewhat more complicated, and (3)
the oscillator tubes burn out occasionally. There is, however, a
growing tendency among amateurs to use continuous wave transmitters
and they are certainly more up-to-date and interesting than spark gap
sets.

Now there are two practical ways by which continuous waves can be set
up for sending either telegraphic signals or telephonic speech and
music and these are with: (a) an _oscillation arc lamp_, and (b) a
_vacuum tube oscillator_. The oscillation arc was the earliest known
way of setting up sustained oscillations, and it is now largely used
for commercial high power, long distance work. But since the vacuum
tube has been developed to a high degree of efficiency and is the
scheme that is now in vogue for amateur stations we shall confine our
efforts here to explaining the apparatus necessary and how to wire the
various parts together to produce several sizes of vacuum tube
telegraph transmitters.

Sources of Current for Telegraph Transmitting Sets.--Differing from a
spark-gap transmitter you cannot get any appreciable results with a
low voltage battery current to start with. For a purely experimental
vacuum tube telegraph transmitter you can use enough B batteries to
operate it but the current strength of these drops so fact when they
are in use, that they are not at all satisfactory for the work.

You can, however, use 110 volt direct current from a lighting circuit
as your initial source of power to energize the plate of the vacuum
tube oscillator of your experimental transmitter. Where you have a 110
volt _direct current_ lighting service in your home and you want a
higher voltage for your plate, you will then have to use a
motor-generator set and this costs money. If you have 110 volt
_alternating current_ lighting service at hand your troubles are over
so far as cost is concerned for you can step it up to any voltage you
want with a power transformer. In this chapter will be shown how to
use a direct current for your source of initial power and in the next
chapter how to use an alternating current for the initial power.

An Experimental Continuous Wave Telegraph Transmitter.--You will
remember that in Chapter XV we learned how the heterodyne receiver
works and that in the separate heterodyne receiving set the second
vacuum tube is used solely to set up oscillations. Now while this
extra tube is used as a generator of oscillations these are, of
course, very weak and hence a detector tube cannot be used to generate
oscillations that are useful for other purposes than heterodyne
receptors and measurements.

There is a vacuum tube amplifier [Footnote: This is the _radiation_
UV-201, made by the Radio Corporation of America, Woolworth Bldg., New
York City.] made that will stand a plate potential of 100 volts, and
this can be used as a generator of oscillations by energizing it with
a 110 volt direct current from your lighting service. Or in a pinch
you can use five standard B batteries to develop the plate voltage,
but these will soon run down. But whatever you do, never use a
current from a lighting circuit on a tube of any kind that has a rated
plate potential of less than 100 volts.

The Apparatus You Need.--For this experimental continuous wave
telegraph transmitter get the following pieces of apparatus: (1) one
_single coil tuner with three clips_; (2) one _.002 mfd. fixed
condenser_; (3) three _.001 mfd. condensers_; (4) one _adjustable grid
leak_; (5) one _hot-wire ammeter_; (6) one _buzzer_; (7) one _dry
cell_; (8) one _telegraph key_; (9) one _100 volt plate vacuum tube
amplifier_; (10) one _6 volt storage battery_; (11) one _rheostat_;
(12) one _oscillation choke coil_; (13) one _panel cut-out_ with a
_single-throw, double-pole switch_, and a pair of _fuse sockets_ on
it.

The Tuning Coil.--You can either make this tuning coil or buy one. To
make it get two disks of wood 3/4-inch thick and 5 inches in diameter
and four strips of hard wood, or better, hard rubber or composition
strips, such as _bakelite_, 1/2-inch thick, 1 inch wide and 5-3/4
inches long, and screw them to the disks as shown at A in Fig. 75. Now
wrap on this form about 25 turns of No. 8 or 10, Brown and Sharpe
gauge, bare copper wire with a space of 1/8-inch between each turn.
Get three of the smallest size terminal clips, see B, and clip them on
to the different turns, when your tuning coil is ready for use. You
can buy a coil of this kind for $4.00 or $5.00.

The Condensers.--For the aerial series condenser get one that has a
capacitance of .002 mfd. and that will stand a potential of 3,000
volts. [Footnote: The U C-1014 _Faradon_ condenser made by the Radio
Corporation of America will serve the purpose.] It is shown at C. The
other three condensers, see D, are also of the fixed type and may have
a capacitance of .001 mfd.; [Footnote: List No. 266; fixed receiving
condenser, sold by the Manhattan Electrical Supply Co.] the blocking
condenser should preferably have a capacitance of 1/2 a mfd. In these
condensers the leaves of the sheet metal are embedded in composition.
The aerial condenser will cost you $2.00 and the others 75 cents each.

[Illustration: (A) Fig. 75.--Apparatus for Experimental C. W.
Telegraph Transmitter.]

[Illustration: Fig. 75.--Apparatus for Experimental C. W. Telegraph
Transmitter.]

The Aerial Ammeter.--This instrument is also called a _hot-wire_
ammeter because the oscillating currents flowing through a piece of
wire heat it according to their current strength and as the wire
contracts and expands it moves a needle over a scale. The ammeter is
connected in the aerial wire system, either in the aerial side or the
ground side--the latter place is usually the most convenient. When you
tune the transmitter so that the ammeter shows the largest amount of
current surging in the aerial wire system you can consider that the
oscillation circuits are in tune. A hot-wire ammeter reading to 2.5
amperes will serve your needs, it costs $6.00 and is shown at E in
Fig. 75.

[Illustration: United States Naval High Power Station, Arlington Va.
General view of Power Room. At the left can be seen the Control
Switchboards, and overhead, the great 30 K.W. Arc Transmitter with
Accessories.]

The Buzzer and Dry Cell.--While a heterodyne, or beat, receptor can
receive continuous wave telegraph signals an ordinary crystal or
vacuum tube detector receiving set cannot receive them unless they are
broken up into trains either at the sending station or at the
receiving station, and it is considered the better practice to do this
at the former rather than at the latter station. For this small
transmitter you can use an ordinary buzzer as shown at F. A dry cell
or two must be used to energize the buzzer. You can get one for about
75 cents.

The Telegraph Key.--Any kind of a telegraph key will serve to break up
the trains of sustained oscillations into dots and dashes. The key
shown at G is mounted on a composition base and is the cheapest key
made, costing $1.50.

The Vacuum Tube Oscillator.--As explained before you can use any
amplifying tube that is made for a plate potential of 100 volts. The
current required for heating the filament is about 1 ampere at 6
volts. A porcelain socket should be used for this tube as it is the
best insulating material for the purpose. An amplifier tube of this
type is shown at H and costs $6.50.

The Storage Battery.--A storage battery is used to heat the filament
of the tube, just as it is with a detector tube, and it can be of any
make or capacity as long as it will develop 6 volts. The cheapest 6
volt storage battery on the market has a 20 to 40 ampere-hour capacity
and sells for $13.00.

The Battery Rheostat.--As with the receptors a rheostat is needed to
regulate the current that heats the filament. A rheostat of this kind
is shown at I and is listed at $1.25.

The Oscillation Choke Coil.--This coil is connected in between the
oscillation circuits and the source of current which feeds the
oscillator tube to keep the oscillations set up by the latter from
surging back into the service wires where they would break down the
insulation. You can make an oscillation choke coil by winding say 100
turns of No. 28 Brown and Sharpe gauge double cotton covered magnet
wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches
long.

Transmitter Connectors.--For connecting up the different pieces of
apparatus of the transmitter it is a good scheme to use _copper
braid_; this is made of braided copper wire in three sizes and sells
for 7,15 and 20 cents a foot respectively. A piece of it is pictured
at J.

The Panel Cut-Out.--This is used to connect the cord of the 110-volt
lamp socket with the transmitter. It consists of a pair of _plug
cutouts and a single-throw, double-pole_ switch mounted on a porcelain
base as shown at K. In some localities it is necessary to place these
in an iron box to conform to the requirements of the fire
underwriters.

Connecting Up the Transmitting Apparatus.--The way the various pieces
of apparatus are connected together is shown in the wiring diagram.
Fig. 76. Begin by connecting one post of the ammeter with the wire
that leads to the aerial and the other post of it to one end of the
tuning coil; connect clip _1_ to one terminal of the .002 mfd. 3,000
volt aerial condenser and the other post of this with the ground.

[Illustration: Fig. 76--Experimental C.W. Telegraph Transmitter]

Now connect the end of the tuning coil that leads to the ammeter with
one end of the .001 mfd. grid condenser and the other end of this with
the grid of the vacuum tube. Connect the telegraph key, the buzzer and
the dry cell in series and then shunt them around the grid condenser.
Next connect the plate of the tube with one end of the .001 mfd.
blocking condenser and the other end of this with the clip _2_ on the
tuning coil.

Connect one end of the filament with the + or positive electrode of
the storage battery, the - or negative electrode of this with one post
of the rheostat and the other post of the latter with the other end of
the filament; then connect clip _3_ with the + or positive side of the
storage battery. This done connect one end of the choke coil to the
conductor that leads to the plate and connect the other end of the
choke coil to one of the taps of the switch on the panel cut-out.
Connect the + or positive electrode of the storage battery to the
other switch tap and between the switch and the choke coil connect the
protective condenser across the 110 volt feed wires. Finally connect
the lamp cord from the socket to the plug fuse taps when your
experimental continuous wave telegraph transmitter is ready to use.

A 100 Mile C. W. Telegraph Transmitter.--Here is a continuous
wave telegraph transmitter that will cover distances up to 100 miles
that you can rely on. It is built on exactly the same lines as the
experimental transmitter just described, but instead of using a 100
volt plate amplifier as a makeshift generator of oscillations it
employs a vacuum tube made especially for setting up oscillations and
instead of having a low plate voltage it is energized with 350 volts.

The Apparatus You Need.--For this transmitter you require: (1) one
_oscillation transformer_; (2) one _hot-wire ammeter_; (3) one _aerial
series condenser_; (4) one _grid leak resistance_; (5) one _chopper_;
(6) one _key circuit choke coil_; (7) one _5 watt vacuum tube
oscillator_; (8) one _6 volt storage battery_; (9) one _battery
rheostat_; (10) one _battery voltmeter_; (11) one _blocking
condenser_; (12) one _power circuit choke coil_, and (13) one
_motor-generator_.

The Oscillation Transformer.--The tuning coil, or _oscillation
transformer_ as this one is called, is a conductively coupled
tuner--that is, the primary and secondary coils form one continuous
coil instead of two separate coils. This tuner is made up of 25 turns
of thin copper strip, 3/8 inch wide and with its edges rounded, and
this is secured to a wood base as shown at A in Fig. 77. It is fitted
with one fixed tap and three clips to each of which a length of copper
braid is attached. It has a diameter of 6-1/4 inches, a height of
7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00.

[Illustration: Fig. 77.--Apparatus of 100 Mile C. W. Telegraph
Transmitter.]

The Aerial Condenser.--This condenser is made up of three fixed
condensers of different capacitances, namely .0003, .0004 and .0005
mfd., and these are made to stand a potential of 7500 volts. The
condenser is therefore adjustable and, as you will see from the
picture B, it has one terminal wire at one end and three terminal
wires at the other end so that one, two or three condensers can be
used in series with the aerial. A condenser of this kind costs $5.40.

The Aerial Ammeter.--This is the same kind of a hot-wire ammeter
already described in connection with the experimental set, but it
reads to 5 amperes.

The Grid and Blocking Condensers.--Each of these is a fixed condenser
of .002 mfd. capacitance and is rated to stand 3,000 volts. It is
made like the aerial condenser but has only two terminals. It costs
$2.00.

The Key Circuit Apparatus.--This consists of: (1) the _grid leak_; (2)
the _chopper_; (3) the _choke coil_, and (4) the _key_. The grid leak
is connected in the lead from the grid to the aerial to keep the
voltage on the grid at the right potential. It has a resistance of
5000 ohms with a mid-tap at 2500 ohms as shown at C. It costs $2.00.

The chopper is simply a rotary interrupter driven by a small motor. It
comprises a wheel of insulating material in which 30 or more metal
segments are set in an insulating disk as shown at D. A metal contact
called a brush is fixed on either side of the wheel. It costs about
$7.00 and the motor to drive it is extra. The choke coil is wound up
of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered
magnet wire on a spool which has a diameter of 2 inches and a length
of 3-1/4 inches.

The 5 Watt Oscillator Vacuum Tube.--This tube is made like the
amplifier tube described for use with the preceding experimental
transmitter, but it is larger, has a more perfect vacuum, and will
stand a plate potential of 350 volts while the plate current is .045
ampere. The filament takes a current of a little more than 2 amperes
at 7.5 volts. A standard 4-tap base is used with it. The tube costs
$8.00 and the porcelain base is $1.00 extra. It is shown at E.

The Storage Battery and Rheostat.--This must be a 5-cell battery so
that it will develop 10 volts. A storage battery of any capacity can
be used but the lowest priced one costs about $22.00. The rheostat for
regulating the battery current is the same as that used in the
preceding experimental transmitter.

The Filament Voltmeter.--To get the best results it is necessary that
the voltage of the current which heats the filament be kept at the
same value all of the time. For this transmitter a direct current
voltmeter reading from 0 to 15 volts is used. It is shown at F and
costs $7.50. The Oscillation Choke Coil.--This is made exactly like
the one described in connection with the experimental transmitter.

The Motor-Generator Set.--Where you have only a 110 or a 220 volt
direct current available as a source of power you need a
_motor-generator_ to change it to 350 volts, and this is an expensive
piece of apparatus. It consists of a single armature core with a motor
winding and a generator winding on it and each of these has its own
commutator. Where the low voltage current flows into one of the
windings it drives its as a motor and this in turn generates the
higher voltage current in the other winding. Get a 100 watt 350 volt
motor-generator; it is shown at F and costs about $75.00.

The Panel Cut-Out.--This switch and fuse block is the same as that
used in the experimental set.

The Protective Condenser.--This is a fixed condenser having a
capacitance of 1 mfd. and will stand 750 volts. It costs $2.00.

Connecting Up the Transmitting Apparatus.--From all that has gone
before you have seen that each piece of apparatus is fitted with
terminal, wires, taps or binding posts. To connect up the parts of
this transmitter it is only necessary to make the connections as shown
in the wiring diagram Fig. 78.

[Illustration: Fig. 78.--5 to 50 Watt C. W. Telegraph Transmitter.
(With Single Oscillation Tube.)]

A 200 Mile C. W. Telegraph Transmitter.--To make a continuous wave
telegraph transmitter that will cover distances up to 200 miles all
you have to do is to use two 5 watt vacuum tubes in _parallel_, all of
the rest of the apparatus being exactly the same. Connecting the
oscillator tubes up in parallel means that the two filaments are
connected across the leads of the storage battery, the two grids on
the same lead that goes to the aerial and the two plates on the same
lead that goes to the positive pole of the generator. Where two or
more oscillator tubes are used only one storage battery is needed, but
each filament must have its own rheostat. The wiring diagram Fig. 79
shows how the two tubes are connected up in parallel.

[Illustration: Fig. 79.--200 Mile C.W. Telegraph Transmitter (With Two
Tubes in Parallel.)]

A 500 Mile C. W. Telegraph Transmitter.--For sending to distances of
over 200 miles and up to 500 miles you can use either: (1) three or
four 5 watt oscillator tubes in parallel as described above, or (2)
one 50 watt oscillator tube. Much of the apparatus for a 50 watt tube
set is exactly the same as that used for the 5 watt sets. Some of the
parts, however, must be proportionately larger though the design all
the way through remains the same.

The Apparatus and Connections.--The aerial series condenser, the
blocking condenser, the grid condenser, the telegraph key, the
chopper, the choke coil in the key circuit, the filament voltmeter and
the protective condenser in the power circuit are identical with those
described for the 5 watt transmitting set.

The 50 Watt Vacuum Tube Oscillator.--This is the size of tube
generally used by amateurs for long distance continuous wave
telegraphy. A single tube will develop 2 to 3 amperes in your aerial.
The filament takes a 10 volt current and a plate potential of 1,000
volts is needed. One of these tubes is shown in Fig. 80 and the cost
is $30.00. A tube socket to fit it costs $2.50 extra.

[Illustration: Fig. 80.--50 Watt Oscillator Vacuum Tube.]

The Aerial Ammeter.--This should read to 5 amperes and the cost is
$6.25.

The Grid Leak Resistance.--It has the same resistance, namely 5,000
ohms as the one used with the 5 watt tube transmitter, but it is a
little larger. It is listed at $1.65.

The Oscillation Choke Coil.--The choke coil in the power circuit is
made of about 260 turns of No. 30 B. & S. cotton covered magnet wire
wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long.

The Filament Rheostat.--This is made to take care of a 10 volt current
and it costs $10.00.

The Filament Storage Battery.--This must develop 12 volts and one
having an output of 40 ampere-hours costs about $25.00.

The Protective Condenser.--This condenser has a capacitance of 1 mfd.
and costs $2.00.

The Motor-Generator.--Where you use one 50 watt oscillator tube you
will need a motor-generator that develops a plate potential of 1000
volts and has an output of 200 watts. This machine will stand you
about $100.00.

The different pieces of apparatus for this set are connected up
exactly the same as shown in the wiring diagram in Fig. 78.

A 1000 Mile C. W. Telegraph Transmitter.--All of the parts of this
transmitting set are the same as for the 500 mile transmitter just
described except the motor generator and while this develops the same
plate potential, i.e., 1,000 volts, it must have an output of 500
watts; it will cost you in the neighborhood of $175.00. For this long
distance transmitter you use two 50 watt oscillator tubes in parallel
and all of the parts are connected together exactly the same as for
the 200 mile transmitter shown in the wiring diagram in Fig. 79.




CHAPTER XVII

CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING CURRENT


Within the last few years alternating current has largely taken the
place of direct current for light, heat and power purposes in and
around towns and cities and if you have alternating current service in
your home you can install a long distance continuous wave telegraph
transmitter with very little trouble and at a comparatively small
expense.

A 100 Mile C. W. Telegraph Transmitting Set.--The principal pieces of
apparatus for this transmitter are the same as those used for the _100
Mile Continuous Wave Telegraph Transmitting Set_ described and
pictured in the preceding chapter which used direct current, except
that an _alternating current power transformer_ is employed instead of
the more costly _motor-generator_.

The Apparatus Required.--The various pieces of apparatus you will need
for this transmitting set are: (1) one _hot-wire ammeter_ for the
aerial as shown at E in Fig. 75, but which reads to 5 amperes instead
of to 2.5 amperes; (2) one _tuning coil_ as shown at A in Fig. 77; (3)
one aerial condenser as shown at B in Fig. 77; (4) one _grid leak_ as
shown at C in Fig. 77; (5) one _telegraph key_ as shown at G in Fig.
75; (6) one _grid condenser_, made like the aerial condenser but
having only two terminals; (7) one _5 watt oscillator tube_ as shown
at E in Fig. 77; (8) one _.002 mfd. 3,000 volt by-pass condenser_,
made like the aerial and grid condensers; (9) one pair of _choke
coils_ for the high voltage secondary circuit; (10) one
_milli-ammeter_; (11) one A. C. _power transformer_; (12) one
_rheostat_ as shown at I in Fig. 75, and (13) one _panel cut-out_ as
shown at K in Fig. 75.

The Choke Coils.--Each of these is made by winding about 100 turns of
No. 28, Brown and Sharpe gauge, cotton covered magnet wire on a spool
2 inches in diameter and 2-1/2 inches long, when it will have an
inductance of about 0.5 _millihenry_ [Footnote: A millihenry is
1/1000th part of a henry.] at 1,000 cycles.

The Milli-ammeter.--This is an alternating current ammeter and reads
from 0 to 250 _milliamperes_; [Footnote: A _milliampere_ is the
1/1000th part of an ampere.] and is used for measuring the secondary
current that energizes the plate of the oscillator tube. It looks like
the aerial ammeter and costs about $7.50.

The A. C. Power Transformer.--Differing from the motor generator set
the power transformer has no moving parts. For this transmitting set
you need a transformer that has an input of 325 volts. It is made to
work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the
range of voltage of the ordinary alternating lighting current. This
adjustment for voltage is made by means of taps brought out from the
primary coil to a rotary switch.

The high voltage secondary coil which energizes the plate has an
output of 175 watts and develops a potential of from 350 to 1,100
volts. The low voltage secondary coil which heats the filament has an
output of 175 watts and develops 7.5 volts. This transformer, which is
shown in Fig. 81, is large enough to take care of from one to four 5
watt oscillator tubes. It weighs about 15 pounds and sells for $25.00.

[Illustration: Fig. 81.--Alternation Current Power Transformer. (For
C. W. Telegraphy and Wireless Telephony.)]

[Illustration: The Transformer and Tuner of the World's Largest Radio
Station. Owned by the Radio Corporation of America at Rocky Point near
Port Jefferson L.I.]

Connecting Up the Apparatus.--The wiring diagram Fig. 82 shows clearly
how all of the connections are made. It will be observed that a
storage battery is not needed as the secondary coil of the transformer
supplies the current to heat the filament of the oscillator. The
filament voltmeter is connected across the filament secondary coil
terminals, while the plate milli-ammeter is connected to the mid-taps
of the plate secondary coil and the filament secondary coil.

[Illustration: Fig. 82. Wiring Diagram for 200 to 500 Mile C.W.
Telegraph Transmitting Set. (With Alternating Current)]

A 200 to 500 Mile C. W. Telegraph Transmitting Set.--Distances of from
200 to 500 miles can be successfully covered with a telegraph
transmitter using two, three or four 5 watt oscillator tubes in
parallel. The apparatus needed is identical with that used for the 100
mile transmitter just described. The tubes are connected in parallel
as shown in the wiring diagram in Fig. 83.

[Illustration: Fig. 83.--Wiring Diagram for 500 to 1000 Mile C. W.
Telegraph Transmitter.]

A 500 to 1,000 Mile C. W. Telegraph Transmitting Set.--With the
apparatus described for the above set and a single 50 watt oscillator
tube a distance of upwards of 500 miles can be covered, while with two
50 watt oscillator tubes in parallel you can cover a distance of 1,000
miles without difficulty, and nearly 2,000 miles have been covered
with this set.

The Apparatus Required.--All of the apparatus for this C. W.
telegraph transmitting set is the same as that described for the 100
and 200 mile sets but you will need: (1) one or two _50 watt
oscillator tubes with sockets;_ (2) one _key condenser_ that has a
capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one
_0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5
amperes, and (5) an _A. C. power transformer_ for one or two 50 watt
tubes.

[Illustration: Broadcasting Government Reports by Wireless from
Washington. This shows Mr. Gale at work with his set in the Post
Office Department.]

The Alternating Current Power Transformer.--This power transformer is
made exactly like the one described in connection with the preceding
100 mile transmitter and pictured in Fig. 81, but it is considerably
larger. Like the smaller one, however, it is made to work with a 50 to
60 cycle current at 102.5 to 115 volts and, hence, can be used with
any A. C. lighting current.

It has an input of 750 volts and the high voltage secondary coil which
energizes the plate has an output of 450 watts and develops 1,500 to
3,000 volts. The low voltage secondary coil which heats the filament
develops 10.5 volts. This transformer will supply current for one or
two 50-watt oscillator tubes and it costs about $40.00.

Connecting Up the Apparatus.--Where a single oscillator tube is used
the parts are connected as shown in Fig. 82, and where two tubes are
connected in parallel the various pieces of apparatus are wired
together as shown in Fig. 83. The only difference between the 5 watt
tube transmitter and the 50 watt tube transmitter is in the size of
the apparatus with one exception; where one or two 50 watt tubes are
used a second condenser of large capacitance (1 mfd.) is placed in the
grid circuit and the telegraph key is shunted around it as shown in
the diagram Fig. 83.




CHAPTER XVIII

WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND ALTERNATING
CURRENTS


In time past the most difficult of all electrical apparatus for the
amateur to make, install and work was the wireless telephone. This was
because it required a _direct current_ of not less than 500 volts to
set up the sustained oscillations and all ordinary direct current for
lighting purposes is usually generated at a potential of 110 volts.

Now as you know it is easy to _step-up_ a 110 volt alternating current
to any voltage you wish with a power transformer but until within
comparatively recent years an alternating current could not be used
for the production of sustained oscillations for the very good reason
that the state of the art had not advanced that far. In the new order
of things these difficulties have all but vanished and while a
wireless telephone transmitter still requires a high voltage direct
current to operate it this is easily obtained from 110 volt source of
alternating current by means of _vacuum tube rectifiers_.

The pulsating direct currents are then passed through a filtering
reactance coil, called a _reactor_, and one or more condensers, and
these smooth them out until they approximate a continuous direct
current. The latter is then made to flow through a vacuum tube
oscillator when it is converted into high frequency oscillations and
these are _varied_, or _modulated_, as it is called, by a _microphone
transmitter_ such as is used for ordinary wire telephony. The energy
of these sustained modulated oscillations is then radiated into space
from the aerial in the form of electric waves.

The distance that can be covered with a wireless telephone transmitter
is about one-fourth as great as that of a wireless telegraph
transmitter having the same input of initial current, but it is long
enough to satisfy the most enthusiastic amateur. For instance with a
wireless telephone transmitter where an amplifier tube is used to set
up the oscillations and which is made for a plate potential of 100
volts, distances up to 10 or 15 miles can be covered.

With a single 5 watt oscillator tube energized by a direct current of
350 volts from either a motor-generator or from a power transformer
(after it has been rectified and smoothed out) speech and music can be
transmitted to upwards of 25 miles. Where two 5 watt tubes connected
in parallel are used wireless telephone messages can be transmitted to
distances of 40 or 50 miles. Further, a single 50 watt oscillator tube
will send to distances of 50 to 100 miles while two of these tubes in
parallel will send from 100 to 200 miles. Finally, where four or five
oscillator tubes are connected in parallel proportionately greater
distances can be covered.

A Short Distance Wireless Telephone Transmitting Set-With 110 Volt
Direct Lighting Current.--For this very simple, short distance
wireless telephone transmitting set you need the same apparatus as
that described and pictured in the beginning of Chapter XVI for a
_Short Distance C. W. Telegraph Transmitter_, except that you use a
_microphone transmitter_ instead of a _telegraph key_. If you have a
110 volt direct lighting current in your home you can put up this
short distance set for very little money and it will be well worth
your while to do so.

The Apparatus You Need.--For this set you require: (1) one _tuning
coil_ as shown at A and B in Fig. 75; (2) one _aerial ammeter_ as
shown at C in Fig. 75; (3) one _aerial condenser_ as shown at C in
Fig. 75; (4) one _grid, blocking and protective condenser_ as shown at
D in Fig. 75; (5) one _grid leak_ as shown at C in Fig. 77; (6) one
_vacuum tube amplifier_ which is used as an _oscillator_; (7) one _6
volt storage battery_; (8) one _rheostat_ as shown at I in Fig. 75;
(9) one _oscillation choke coil_; (10) one _panel cut-out_ as shown at
K in Fig. 75 and an ordinary _microphone transmitter_.

The Microphone Transmitter.--The best kind of a microphone to use with
this and other telephone transmitting sets is a _Western Electric No.
284-W_. [Footnote: Made by the Western Electric Company, Chicago,
Ill.] This is known as a solid back transmitter and is the standard
commercial type used on all long distance Bell telephone lines. It
articulates sharply and distinctly and there are no current variations
to distort the wave form of the voice and it will not buzz or sizzle.
It is shown in Fig. 84 and costs $2.00. Any other good microphone
transmitter can be used if desired.

[Illustration: Fig. 84.--Standard Microphone Transmitter.]

Connecting Up the Apparatus.--Begin by connecting the leading-in wire
with one of the terminals of the microphone transmitter, as shown in
the wiring diagram Fig. 85, and the other terminal of this to one end
of the tuning coil. Now connect _clip 1_ of the tuning coil to one of
the posts of the hot-wire ammeter, the other post of this to one end
of aerial condenser and, finally, the other end of the latter with the
water pipe or other ground. The microphone can be connected in the
ground wire and the ammeter in the aerial wire and the results will be
practically the same.

[Illustration: Fig. 85.--Wiring Diagram of Short Distance Wireless
Telephone Set. (Microphone in Aerial Wire.)]

Next connect one end of the grid condenser to the post of the tuning
coil that makes connection with the microphone and the other end to
the grid of the tube, and then shunt the grid leak around the
condenser. Connect the + or _positive_ electrode of the storage
battery with one terminal of the filament of the vacuum tube, the
other terminal of the filament with one post of the rheostat and the
other post of this with the - or _negative_ electrode of the battery.
This done, connect _clip 2_ of the tuning coil to the + or _positive_
electrode of the battery and bring a lead from it to one of the switch
taps of the panel cut-out.

Now connect _clip 3_ of the tuning coil with one end of the blocking
condenser, the other end of this with one terminal of the choke coil
and the other terminal of the latter with the other switch tap of the
cut-out. Connect the protective condenser across the direct current
feed wires between the panel cut-out and the choke coil. Finally
connect the ends of a lamp cord to the fuse socket taps of the
cut-out, and connect the other ends to a lamp plug and screw it into
the lamp socket of the feed wires. Screw in a pair of 5 ampere _fuse
plugs_, close the switch and you are ready to tune the transmitter and
talk to your friends.

A 25 to 50 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--Where you have to start with 110 or 220 volt direct
current and you want to transmit to a distance of 25 miles or more you
will have to install a _motor-generator_. To make this transmitter you
will need exactly the same apparatus as that described and pictured
for the _100 Mile C. W. Telegraph Transmitting Set_ in Chapter XVI,
except that you must substitute a _microphone transmitter_ and a
_telephone induction coil_, or a _microphone transformer_, or still
better, a _magnetic modulator_, for the telegraph key and chopper.

The Apparatus You Need.--To reiterate; the pieces of apparatus you
need are: (1) one _aerial ammeter_ as shown at E in Fig. 75; (2) one
_tuning coil_ as shown at A in Fig. 77; (3) one _aerial condenser_ as
shown at B in Fig. 77; (4) one _grid leak_ as shown at C in Fig. 77;
(5) one _grid, blocking_ and _protective condenser_; (6) one _5 watt
oscillator tube_ as shown at E in Fig. 77; (7) one _rheostat_ as shown
at I in Fig. 75; (8) one _10 volt (5 cell) storage battery_; (9) one
_choke coil_; (10) one _panel cut-out_ as shown at K in Fig. 75, and
(11) a _motor-generator_ having an input of 110 or 220 volts and an
output of 350 volts.

In addition to the above apparatus you will need: (12) a _microphone
transmitter_ as shown in Fig. 84; (13) a battery of four dry cells or
a 6 volt storage battery, and either (14) a _telephone induction coil_
as shown in Fig. 86; (15) a _microphone transformer_ as shown in Fig.
87; or a _magnetic modulator_ as shown in Fig. 88. All of these parts
have been described, as said above, in Chapter XVI, except the
microphone modulators.

[Illustration: Fig. 86.--Telephone Induction Coil. (Used with
Microphone Transmitter.)]

[Illustration: Fig. 87.--Microphone Transformer. (Used with Microphone
Transmitter.)]

[Illustration: Fig. 88.--Magnetic Modulator. (Used with Microphone
Transmitter.)]

The Telephone Induction Coil.--This is a little induction coil that
transforms the 6-volt battery current after it has flowed through and
been modulated by the microphone transmitter into alternating currents
that have a potential of 1,000 volts of more. It consists of a primary
coil of _No. 20 B. and S._ gauge cotton covered magnet wire wound on a
core of soft iron wires while around the primary coil is wound a
secondary coil of _No. 30_ magnet wire. Get a _standard telephone
induction coil_ that has a resistance of 500 or 750 ohms and this will
cost you a couple of dollars.

The Microphone Transformer.--This device is built on exactly the same
principle as the telephone induction coil just described but it is
more effective because it is designed especially for modulating the
oscillations set up by vacuum tube transmitters. As with the telephone
induction coil, the microphone transmitter is connected in series with
the primary coil and a 6 volt dry or storage battery.

In the better makes of microphone transformer, there is a third
winding, called a _side tone_ coil, to which a headphone can be
connected so that the operator who is speaking into the microphone can
listen-in and so learn if his transmitter is working up to standard.

The Magnetic Modulator.--This is a small closed iron core transformer
of peculiar design and having a primary and a secondary coil wound on
it. This device is used to control the variations of the oscillating
currents that are set up by the oscillator tube. It is made in three
sizes and for the transmitter here described you want the smallest
size, which has an output of 1/2 to 1-1/2 amperes. It costs about
$10.00.

How the Apparatus Is Connected Up.--The different pieces of apparatus
are connected together in exactly the same way as the _100 Mile C. W.
Telegraph Set_ in Chapter XVI except that the microphone transmitter
and microphone modulator (whichever kind you use) is substituted for
the telegraph key and chopper.

Now there are three different ways that the microphone and its
modulator can be connected in circuit. Two of the best ways are shown
at A and B in Fig. 89. In the first way the secondary terminals of the
modulator are shunted around the grid leak in the grid circuit as at
A, and in the second the secondary terminals are connected in the
aerial as at B. Where an induction coil or a microphone transformer is
used they are shunted around a condenser, but this is not necessary
with the magnetic modulator. Where a second tube is used as in Fig. 90
then the microphone and its modulator are connected with the grid
circuit and _clip 3_ of the tuning coil.

[Illustration: Fig. 89.--Wiring Diagram of 25 to 50 Mile Wireless
Telephone. (Microphone Modulator Shunted Around Grid-Leak Condenser.)]

[Illustration: (B) Fig. 89.--Microphone Modulator Connected in Aerial
Wire.]

[Illustration: Fig. 90.--Wiring Diagram of 50 to 100 Mile Wireless
Telephone Transmitting Set.]

A 50 to 100 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--As the initial source of current available is taken
to be a 110 or 220 volt direct current a motor-generator having an
output of 350 volts must be used as before. The only difference
between this transmitter and the preceding one is that: (1) two 5 watt
tubes are used, the first serving as an _oscillator_ and the second as
a _modulator_; (2) an _oscillation choke coil_ is used in the plate
circuit; (3) a _reactance coil_ or _reactor_, is used in the plate
circuit; and (4) a _reactor_ is used in the grid circuit.

The Oscillation Choke Coil.--You can make this choke coil by winding
about 275 turns of _No. 28 B. and S. gauge_ cotton covered magnet wire
on a spool 2 inches in diameter and 4 inches long. Give it a good
coat of shellac varnish and let it dry thoroughly.

The Plate and Grid Circuit Reactance Coils.--Where a single tube is
used as an oscillator and a second tube is employed as a modulator, a
_reactor_, which is a coil of wire wound on an iron core, is used in
the plate circuit to keep the high voltage direct current of the
motor-generator the same at all times. Likewise the grid circuit
reactor is used to keep the voltage of the grid at a constant value.
These reactors are made alike and a picture of one of them is shown in
Fig. 91 and each one will cost you $5.75.

[Illustration: Fig. 91.--Plate and Grid Circuit Reactor.]

Connecting up the Apparatus.--All of the different pieces of apparatus
are connected up as shown in Fig. 89. One of the ends of the secondary
of the induction coil, or the microphone transformer, or the magnetic
modulator is connected to the grid circuit and the other end to _clip
3_ of the tuning coil.

A 100 to 200 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--By using the same connections shown in the wiring
diagrams in Fig. 89 and a single 50 watt oscillator tube your
transmitter will then have a range of 100 miles or so, while if you
connect up the apparatus as shown in Fig. 90 and use two 50 watt tubes
you can work up to 200 miles. Much of the apparatus for a 50 watt
oscillator set where either one or two tubes are used is of the same
size and design as that just described for the 5 watt oscillator sets,
but, as in the C. W. telegraph sets, some of the parts must be
proportionately larger. The required parts are (1) the _50 watt tube_;
(2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the
_filament storage battery_; and (5) the _magnetic modulator_. All of
these parts, except the latter, are described in detail under the
heading of a _500 Mile C. W. Telegraph Transmitting Set_ in Chapter
XVI, and are also pictured in that chapter.

It is not advisable to use an induction coil for the modulator for
this set, but use, instead, either a telephone transformer, or better,
a magnetic modulator of the second size which has an output of from
1-1/2 to 3-1/2 amperes. The magnetic modulator is described and
pictured in this chapter.

A 50 to 100 Mile Wireless Telephone Transmitting Set--With 110 Volt
Alternating Current.--If you have a 110 volt [Footnote: Alternating
current for lighting purposes ranges from 102.5 volts to 115 volts, so
we take the median and call it 110 volts.] alternating current
available you can use it for the initial source of energy for your
wireless telephone transmitter. The chief difference between a
wireless telephone transmitting set that uses an alternating current
and one that uses a direct current is that: (1) a _power transformer_
is used for stepping up the voltage instead of a motor-generator, and
(2) a _vacuum tube rectifier_ must be used to convert the alternating
current into direct current.

The Apparatus You Need.--For this telephone transmitting set you need:
(1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone
modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry
battery_ or a 6 volt storage battery; (6) one _microphone
transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9)
one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11)
one _blocking condenser_; (12) one _oscillation choke coil_; (13) two
_filter condensers_; (14) one _filter reactance coil_; (15) an
_alternating current power transformer_, and (16) two _20 watt
rectifier vacuum tubes_.

All of the above pieces of apparatus are the same as those described
for the _100 Mile C. W. Telegraph Transmitter_ in Chapter XVII,
except: (a) the _microphone modulator_; (b) the _microphone
transmitter_ and (c) the _dry_ or _storage battery_, all of which are
described in this chapter; and the new parts which are: (d) the
_rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the
_filter reactance coil_; further and finally, the power transformer
has a _third_ secondary coil on it and it is this that feeds the
alternating current to the rectifier tubes, which in turn converts it
into a pulsating direct current.

The Vacuum Tube Rectifier.--This rectifier has two electrodes, that
is, it has a filament and a plate like the original vacuum tube
detector, The smallest size rectifier tube requires a plate potential
of 550 volts which is developed by one of the secondary coils of the
power transformer. The filament terminal takes a current of 7.5 volts
and this is supplied by another secondary coil of the transformer.
This rectifier tube delivers a direct current of 20 watts at 350
volts. It looks exactly like the 5 watt oscillator tube which is
pictured at E in Fig. 77. The price is $7.50.

The Filter Condensers.--These condensers are used in connection with
the reactance coil to smooth out the pulsating direct current after it
has passed through the rectifier tube. They have a capacitance of 1
mfd. and will stand 750 volts. These condensers cost about $2.00 each.

The Filter Reactance Coil.--This reactor which is shown in Fig. 92,
has about the same appearance as the power transformer but it is
somewhat smaller. It consists of a coil of wire wound on a soft iron
core and has a large inductance, hence the capacitance of the filter
condensers are proportionately smaller than where a small inductance
is used which has been the general practice. The size you require for
this set has an output of 160 milliamperes and it will supply current
for one to four 5 watt oscillator tubes. This size of reactor costs
$11.50.

[Illustration: Fig. 92.--Filter Reactor for Smoothing out Rectified
Currents.]

Connecting Up the Apparatus.--The wiring diagram in Fig. 93 shows how
the various pieces of apparatus for this telephone transmitter are
connected up. You will observe: (1) that the terminals of the power
transformer secondary coil which develops 10 volts are connected to
the filaments of the oscillator tubes; (2) that the terminals of the
other secondary coil which develops 10 volts are connected with the
filaments of the rectifier tubes; (3) that the terminals of the third
secondary coil which develops 550 volts are connected with the plates
of the rectifier tubes; (4) that the pair of filter condensers are
connected in parallel and these are connected to the mid-taps of the
two filament secondary coils; (5) that the reactance coil and the
third filter condenser are connected together in series and these are
shunted across the filter condensers, which are in parallel; and,
finally, (6) a lead connects the mid-tap of the 550-volt secondary
coil of the power transformer with the connection between the reactor
and the third filter condenser.

[Illustration: Fig 93.--100 to 200 Mile Wireless Telephone
Transmitter.]

A 100 to 200 Mile Wireless Telephone Transmitting Set--With 110 Volt
Alternating Current.--This telephone transmitter is built up of
exactly the same pieces of apparatus and connected up in precisely the
same way as the one just described and shown in Fig. 93.

Apparatus Required.--The only differences between this and the
preceding transmitter are: (1) the _magnetic modulator_, if you use
one, should have an output of 3-1/2 to 5 amperes; (2) you will need
two _50 watt oscillator tubes with sockets_; (3) two _150 watt
rectifier tubes with sockets_; (4) an _aerial ammeter_ that reads to
_5 amperes_; (5) three _1 mfd. filter condensers_ in parallel; (6)
_two filter condensers of 1 mfd. capacitance_ that will stand _1750
volts_; and (6) a _300 milliampere filter reactor_.

The apparatus is wired up as shown in Fig. 93.




CHAPTER XIX

THE OPERATION OF VACUUM TUBE TRANSMITTERS


The three foregoing chapters explained in detail the design and
construction of (1) two kinds of C. W. telegraph transmitters, and (2)
two kinds of wireless telephone transmitters, the difference between
them being whether they used (A) a direct current, or (B) an
alternating current as the initial source of energy. Of course there
are other differences between those of like types as, for instance,
the apparatus and connections used (_a_) in the key circuits, and
(_b_) in the microphone circuits. But in all of the transmitters
described of whatever type or kind the same fundamental device is used
for setting up sustained oscillations and this is the _vacuum tube_.

The Operation of the Vacuum Tube Oscillator.--The operation of the
vacuum tube in producing sustained oscillations depends on (1) the
action of the tube as a valve in setting up the oscillations in the
first place and (2) the action of the grid in amplifying the
oscillations thus set up, both of which we explained in Chapter XIV.
In that chapter it was also pointed out that a very small change in
the grid potential causes a corresponding and larger change in the
amount of current flowing from the plate to the filament; and that if
a vacuum tube is used for the production of oscillations the initial
source of current must have a high voltage, in fact the higher the
plate voltage the more powerful will be the oscillations.

To understand how oscillations are set up by a vacuum tube when a
direct current is applied to it, take a look at the simple circuits
shown in Fig. 94. Now when you close the switch the voltage from the
battery charges the condenser and keeps it charged until you open it
again; the instant you do this the condenser discharges through the
circuit which includes it and the inductance coil, and the discharge
of a condenser is always oscillatory.

[Illustration: (A) and (B) Fig. 94. Operation of Vacuum Tube
Oscillators.]

Where an oscillator tube is included in the circuits as shown at A and
B in Fig. 94, the grid takes the place of the switch and any slight
change in the voltage of either the grid or the plate is sufficient to
start a train of oscillations going. As these oscillations surge
through the tube the positive parts of them flow from the plate to the
filament and these carry more of the direct current with them.

To make a tube set up powerful oscillations then, it is only necessary
that an oscillation circuit shall be provided which will feed part of
the oscillations set up by the tube back to the grid circuit and when
this is done the oscillations will keep on being amplified until the
tube reaches the limit of its output.

[Illustration: (C) Fig. 94.--How a Direct Current Sets up
Oscillations.]

The Operation of C. W. Telegraph Transmitters With Direct
Current--Short Distance C. W. Transmitter.--In the transmitter shown
in the wiring diagram in Fig. 76 the positive part of the 110 volt
direct current is carried down from the lamp socket through one side
of the panel cut-out, thence through the choke coil and to the plate
of the oscillator tube, when the latter is charged to the positive
sign. The negative part of the 110 volt direct current then flows down
the other wire to the filament so that there is a difference of
potential between the plate and the filament of 110 volts. Now when
the 6-volt battery current is switched on the filament is heated to
brilliancy, and the electrons thrown off by it form a conducting path
between it and the plate; the 110 volt current then flows from the
latter to the former.

Now follow the wiring from the plate over to the blocking condenser,
thence to _clip 3_ of the tuning coil, through the turns of the latter
to _clip 2_ and over to the filament and, when the latter is heated,
you have a _closed oscillation circuit_. The oscillations surging in
the latter set up other and like oscillations in the tuning coil
between the end of which is connected with the grid, the aerial and
the _clip 2_, and these surge through the circuit formed by this
portion of the coil, the grid condenser and the filament; this is the
amplifying circuit and it corresponds to the regenerative circuit of a
receiving set.

When oscillations are set up in it the grid is alternately charged to
the positive and negative signs. These reversals of voltage set up
stronger and ever stronger oscillations in the plate circuit as before
explained. Not only do the oscillations surge in the closed circuits
but they run to and fro on the aerial wire when their energy is
radiated in the form of electric waves. The oscillations are varied by
means of the telegraph key which is placed in the grid circuit as
shown in Fig. 76.

The Operation of the Key Circuit.--The effect in a C. W. transmitter
when a telegraph key is connected in series with a buzzer and a
battery and these are shunted around the condenser in the grid
circuit, is to rapidly change the wave form of the sustained
oscillations, and hence, the length of the waves that are sent out.
While no sound can be heard in the headphones at the receiving station
so long as the points of the key are not in contact, when they are in
contact the oscillations are modulated and sounds are heard in the
headphones that correspond to the frequency of the buzzer in the key
circuit.

The Operation of C. W. Telegraph Transmitters with Direct
Current.--The chief differences between the long distance sets which
use a direct current, i.e., those described in Chapter XVI, and the
short distance transmitting sets are that the former use: (1) a
motor-generator set for changing the low voltage direct current into
high voltage direct current, and (2) a chopper in the key circuit. The
way the motor-generator changes the low- into high-voltage current has
been explained in Chapter XVI.

The chopper interrupts the oscillations surging through the grid
circuit at a frequency that the ear can hear, that is to say, about
800 to 1,000 times per second. When the key is open, of course, the
sustained oscillations set up in the circuits will send out continuous
waves but when the key is closed these oscillations are broken up and
then they send out discontinuous waves. If a heterodyne receiving set,
see Chapter XV, is being used at the other end you can dispense with
the chopper and the key circuit needed is very much simplified. The
operation of key circuits of the latter kind will be described
presently.

The Operation of C. W. Telegraph Transmitters with Alternating
Current--With a Single Oscillator Tube.--Where an oscillator tube
telegraph transmitter is operated by a 110 volt alternating current as
the initial source of energy, a buzzer, chopper or other interruptor
is not needed in the key circuit. This is because oscillations are set
up only when the plate is energized with the positive part of the
alternating current and this produces an intermittent musical tone in
the headphones. Hence this kind of a sending set is called a _tone
transmitter_.

Since oscillations are set up only by the positive part or voltage of
an alternating current it is clear that, as a matter of fact, this
kind of a transmitter does not send out continuous waves and therefore
it is not a C. W. transmitter. This is graphically shown by the curve
of the wave form of the alternating current and the oscillations that
are set up by the positive part of it in Fig. 95. Whenever the
positive half of the alternating current energizes the plate then
oscillations are set up by the tube and, conversely, when the negative
half of the current charges the plate no oscillations are produced.

[Illustration: Fig. 95.--Positive Voltage only sets up Oscillations.]

You will also observe that the oscillations set up by the positive
part of the current are not of constant amplitude but start at zero
the instant the positive part begins to energize the plate and they
keep on increasing in amplitude as the current rises in voltage until
the latter reaches its maximum; then as it gradually drops again to
zero the oscillations decrease proportionately in amplitude with it.

Heating the Filament with Alternating Current.--Where an alternating
current power transformer is used to develop the necessary plate
voltage a second secondary coil is generally provided for heating the
filament of the oscillation tube. This is better than a direct current
for it adds to the life of the filament. When you use an alternating
current to heat the filament keep it at the same voltage rather than
at the same amperage (current strength). To do this you need only to
use a voltmeter across the filament terminals instead of an ammeter in
series with it; then regulate the voltage of the filament with a
rheostat.

The Operation of C. W. Telegraph Transmitters with Alternating
Current--With Two Oscillator Tubes.--By using two oscillator tubes and
connecting them up with the power transformer and oscillating circuits
as shown in the wiring diagram in Fig. 83 the plates are positively
energized alternately with every reversal of the current and,
consequently, there is no time period between the ending of the
oscillations set up by one tube and the beginning of the oscillations
set up by the other tube. In other words these oscillations are
sustained but as in the case of those of a single tube, their
amplitude rises and falls. This kind of a set is called a _full wave
rectification transmitter_.

The waves radiated by this transmitter can be received by either a
crystal detector or a plain vacuum-tube detector but the heterodyne
receptor will give you better results than either of the foregoing
types.

The Operation of Wireless Telephone Transmitters with Direct
Current--Short Distance Transmitter.--The operation of this short
distance wireless telephone transmitter, a wiring diagram of which is
shown in Fig. 85 is exactly the same as that of the _Direct Current
Short Distance C. W. Telegraph Transmitter_ already explained in this
chapter. The only difference in the operation of these sets is the
substitution of the _microphone transmitter_ for the telegraph key.

The Microphone Transmitter.--The microphone transmitter that is used
to vary, or modulate, the sustained oscillations set up by the
oscillator tube and circuits is shown in Fig. 84. By referring to the
diagram at A in this figure you will readily understand how it
operates. When you speak into the mouthpiece the _sound waves_, which
are waves in the air, impinge upon the diaphragm and these set it into
vibration--that is, they make it move to and fro.

When the diaphragm moves toward the back of the transmitter it forces
the carbon granules that are in the cup closer together; this lowers
their resistance and allows more current from the battery to flow
through them; when the pressure of the air waves is removed from the
diaphragm it springs back toward the mouth-piece and the carbon
granules loosen up when the resistance offered by them is increased
and less current can flow through them. Where the oscillation current
in the aerial wire is small the transmitter can be connected directly
in series with the latter when the former will surge through it. As
you speak into the microphone transmitter its resistance is varied and
the current strength of the oscillations is varied accordingly.

The Operation of Wireless Telephone Transmitters with Direct
Current--Long Distance Transmitters.--In the wireless telephone
transmitters for long distance work which were shown and described in
the preceding chapter a battery is used to energize the microphone
transmitter, and these two elements are connected in series with a
_microphone modulator_. This latter device may be either (1) a
_telephone induction coil_, (2) a _microphone transformer_, or (3) a
_magnetic modulator_; the first two of these devices step-up the
voltage of the battery current and the amplified voltage thus
developed is impressed on the oscillations that surge through the
closed oscillation circuit or the aerial wire system according to the
place where you connect it. The third device works on a different
principle and this will be described a little farther along.

The Operation of Microphone Modulators--The Induction Coil.--This
device is really a miniature transformer, see A in Fig. 86, and its
purpose is to change the 6 volt direct current that flows through the
microphone into 100 volts alternating current; in turn, this is
impressed on the oscillations that are surging in either (1) the grid
circuit as shown at A in Fig. 89, and in Fig. 90, (2) the aerial wire
system, as shown at B in Fig. 89 and Fig. 93. When the current from
the battery flows through the primary coil it magnetizes the soft iron
core and as the microphone varies the strength of the current the high
voltage alternating currents set up in the secondary coil of the
induction coil are likewise varied, when they are impressed upon and
modulate the oscillating currents.

The Microphone Transformer.--This is an induction coil that is
designed especially for wireless telephone modulation. The iron core
of this transformer is also of the open magnetic circuit type, see A
in Fig. 87, and the _ratio_ of the turns [Footnote: See Chapter VI] of
the primary and the secondary coil is such that when the secondary
current is impressed upon either the grid circuit or the aerial wire
system it controls the oscillations flowing through it with the
greatest efficiency.

The Magnetic Modulator.--This piece of apparatus is also called a
_magnetic amplifier_. The iron core is formed of very thin plates, or
_laminations_ as they are called, and this permits high-frequency
oscillations to surge in a coil wound on it. In this transformer, see
A in Fig. 88, the current flowing through the microphone varies the
magnetic permeability of the soft iron core by the magnetic saturation
of the latter. Since the microphone current is absolutely distinct
from the oscillating currents surging through the coil of the
transformer a very small direct current flowing through a coil on the
latter will vary or modulate very large oscillating currents surging
through the former. It is shown connected in the aerial wire system
at A in Fig. 88, and in Fig. 93.

Operation of the Vacuum Tube as a Modulator.--Where a microphone
modulator of the induction coil or microphone transformer type is
connected in the grid circuit or aerial wire system the modulation is
not very effective, but by using a second tube as a _modulator_, as
shown in Fig. 90, an efficient degree of modulation can be had. Now
there are two methods by which a vacuum tube can be used as a
modulator and these are: (1) by the _absorption_ of the energy of the
current set up by the oscillator tube, and (2) by _varying_ the direct
current that energizes the plate of the oscillator tube.

The first of these two methods is not used because it absorbs the
energy of the oscillating current produced by the tube and it is
therefore wasteful. The second method is an efficient one, as the
direct current is varied before it passes into the oscillator tube.
This is sufficient reason for describing only the second method. The
voltage of the grid of the modulator tube is varied by the secondary
coil of the induction coil or microphone transformer, above described.
In this way the modulator tube acts like a variable resistance but it
amplifies the variations impressed on the oscillations set up by the
oscillator tube. As the magnetic modulator does the same thing a
vacuum tube used as a modulator is not needed where the former is
employed. For this reason a magnetic modulator is the cheapest in the
long run.

The Operation of Wireless Telephone Transmitters with Alternating
Current.--Where an initial alternating current is used for wireless
telephony, the current must be rectified first and then smoothed out
before passing into the oscillator tube to be converted into
oscillations. Further so that the oscillations will be sustained, two
oscillator tubes must be used, and, finally, in order that the
oscillations may not vary in amplitude the alternating current must be
first changed into direct current by a pair of rectifier vacuum tubes,
as shown in Fig. 93. When this is done the plates will be positively
charged alternately with every reversal of the current in which case
there will be no break in the continuity of the oscillations set up
and therefore in the waves that are sent out.

The Operation of Rectifier Vacuum Tubes.--The vacuum tube rectifier is
simply a two electrode vacuum tube. The way in which it changes a
commercial alternating current into pulsating direct current is the
same as that in which a two electrode vacuum tube detector changes an
oscillating current into pulsating direct currents and this has been
explained in detail under the heading of _The Operation of a Two
Electrode Vacuum Tube Detector_ in Chapter XII. In the _C. W.
Telegraph Transmitting Sets_ described in Chapter XVII, the oscillator
tubes act as rectifiers as well as oscillators but for wireless
telephony the alternating current must be rectified first so that a
continuous direct current will result.

The Operation of Reactors and Condensers.--A reactor is a single coil
of wire wound on an iron core, see Fig. 90 and A in Fig. 91, and it
should preferably have a large inductance. The reactor for the plate
and grid circuit of a wireless telephone transmitter where one or more
tubes are used as modulators as shown in the wiring diagram in Fig.
90, and the filter reactor shown in Fig. 92, operate in the same way.

When an alternating current flows through a coil of wire the reversals
of the current set up a _counter electromotive force_ in it which
opposes, that is _reacts_, on the current, and the _higher_ the
frequency of the current the _greater_ will be the _reactance_. When
the positive half of an alternating current is made to flow through a
large resistance the current is smoothed out but at the same time a
large amount of its energy is used up in producing heat.

But when the positive half of an alternating current is made to flow
through a large inductance it acts like a large resistance as before
and likewise smooths out the current, but none of its energy is wasted
in heat and so a coil having a large inductance, which is called an
_inductive reactance_, or just _reactor_ for short, is used to smooth
out, or filter, the alternating current after it has been changed into
a pulsating direct current by the rectifier tubes.

A condenser also has a reactance effect on an alternating current but
different from an induction coil the _lower_ the frequency the
_greater_ will be the reactance. For this reason both a filter reactor
and _filter condensers_ are used to smooth out the pulsating direct
currents.




CHAPTER XX

HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS


In the chapters on _Receptors_ you have been told how to build up
high-grade sets. But there are thousands of boys, and, probably, not a
few men, who cannot afford to invest $25.00, more or less, in a
receiving set and would like to experiment in a small way.

The following set is inexpensive, and with this cheap, little portable
receptor you can get the Morse code from stations a hundred miles
distant and messages and music from broadcasting stations if you do
not live too far away from them. All you need for this set are: (1) a
_crystal detector_, (2) a _tuning coil_ and (3) an _earphone_. You can
make a crystal detector out of a couple of binding posts, a bit of
galena and a piece of brass wire, or, better, you can buy one all
ready to use for 50 cents.

[Illustration: Wireless Receptor, the size of a Safety Match Box. A
Youthful Genius in the person of Kenneth R. Hinman, Who is only twelve
years old, has made a Wireless Receiving Set that fits neatly into a
Safety Match Box. With this Instrument and a Pair of Ordinary
Receivers, He is able to catch not only Code Messages but the regular
Broadcasting Programs from Stations Twenty and Thirty Miles Distant.]

The Crystal Detector.--This is known as the _Rasco baby_ detector and
it is made and sold by the _Radio Specialty Company_, 96 Park Place,
New York City. It is shown in Fig. 96. The base is made of black
composition and on it is mounted a standard in which a rod slides and
on one end of this there is fixed a hard rubber adjusting knob while
the other end carries a thin piece of _phosphor-bronze wire_, called a
_cat-whisker_. To secure the galena crystal in the cup you simply
unscrew the knurled cap, place it in the cavity of the post and screw
the cap back on again. The free end of the cat-whisker wire is then
adjusted so that it will rest lightly on the exposed part of the
galena.

[Illustration: Fig. 96.--Rasco Baby Crystal Detector.]

The Tuning Coil.--You will have to make this tuning coil, which you
can do at a cost of less than $1.00, as the cheapest tuning coil you
can buy costs at least $3.00, and we need the rest of our $5.00 to
invest in the earphone. Get a cardboard tube, such as is used for
mailing purposes, 2 inches in diameter and 3 inches long, see A in
Fig. 97. Now wind on 250 turns of _No. 40 Brown and Sharpe gauge plain
enameled magnet wire_. You can use _No. 40 double cotton covered
magnet wire_, in which case you will have to shellac the tube and the
wire after you get it on.

[Illustration: Fig. 97.--How the Tuning Coil is Made.]

As you wind on the wire take off a tap at every 15th turn, that is,
scrape the wire and solder on a piece about 7 inches long, as shown in
Fig. 99; and do this until you have 6 taps taken off. Instead of
leaving the wires outside of the tube bring them to the inside of it
and then out through one of the open ends. Now buy a _round wood-base
switch_ with 7 contact points on it as shown at B in Fig. 97. This
will cost you 25 or 50 cents.

The Headphone.--An ordinary Bell telephone receiver is of small use
for wireless work as it is wound to too low a resistance and the
diaphragm is much too thick. If you happen to have a Bell phone you
can rewind it with _No. 40_ single covered silk magnet wire, or
enameled wire of the same size, when its sensitivity will be very
greatly improved. Then you must get a thin diaphragm and this should
_not_ be enameled, as this tends to dampen the vibrations of it. You
can get a diaphragm of the right kind for 5 cents.

The better way, though, is to buy an earphone made especially for
wireless work. You can get one wound to 1000 ohms resistance for $1.75
and this price includes a cord. [Footnote: This is Mesco, No. 470
wireless phone. Sold by the Manhattan Electrical Supply Co., Park
Place, N.Y.C.] For $1.00 extra you can get a head-band for it, and
then your phone will look like the one pictured in Fig. 98.

[Illustration: Fig. 98.--Mesco 1000 Ohm Head Set.]

How to Mount the Parts.--Now mount the coil on a wood base, 1/2 or 1
inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect
one end of the coil to one of the end points on the switch, and
connect each succeeding tap to one of the switch points, as shown
schematically in Fig. 99 and diagrammatically in Fig. 100. This done,
screw the switch down to the base. Finally screw the detector to the
base and screw two binding posts in front of the coil. These are for
the earphone.

[Illustration: Fig. 99.--Schematic Layout of $5.00 Receiving Set.]

[Illustration: Fig. 100.--Wiring Diagram for $5.00 Receiving Set.]

The Condenser.--You do not have to connect a condenser across the
earphone but if you do you will improve the receiving qualities of the
receptor.

How to Connect Up the Receptor.--Now connect up all the parts as shown
in Figs. 99 and 100, then connect the leading-in wire of the aerial
with the lever of the switch; and connect the free end of the tuning
coil with the _ground_. If you have no aerial wire try hooking it up
to a rain pipe that is _not grounded_ or the steel frame of an
umbrella. For a _ground_ you can use a water pipe, an iron pipe driven
into the ground, or a hydrant. Put on your headphone, adjust the
detector and move the lever over the switch contacts until it is in
adjustment and then, if all your connections are properly made, you
should be able to pick up messages.

[Illustration: Wireless Set made into a Ring, designed by Alfred G.
Rinehart, of Elizabeth, New Jersey. This little Receptor is a
Practical Set; it will receive Messages, Concerts, etc., Measures 1"
by 5/8" by 7/8". An ordinary Umbrella is used as an Aerial.]




APPENDIX


USEFUL INFORMATION

ABBREVIATIONS OF UNITS

Unit                   Abbreviation

ampere                 amp.
ampere-hours           amp.-hr.
centimeter             cm.
centimeter-gram-second c.g.s.
cubic centimeters      cm.^3
cubic inches           cu. in.
cycles per second      ~
degrees Centigrade     °C.
degrees Fahrenheit     °F.
feet                   ft.
foot-pounds            ft.-lb.
grams                  g.
henries                h.
inches                 in.
kilograms              kg.
kilometers             km.
kilowatts              kw.
kilowatt-hours         kw.-hr.
kilovolt-amperes       kv.-a.
meters                 m.
microfarads            [Greek: mu]f.
micromicrofarads       [Greek: mu mu]f.
millihenries           mh.
millimeters            mm.
pounds                 lb.
seconds                sec.
square centimeters     cm.^2
square inches          sq. in.
volts                  v.
watts                  w.

PREFIXES USED WITH METRIC SYSTEM UNITS

Prefix          Abbreviation          Meaning

micro           [Greek: mu].          1 millionth
milli           m.                    1 thousandth
centi           c.                    1 hundredth
deci            d.                    1 tenth
deka            dk.                   10
hekto           h.                    1 hundred
kilo            k.                    1 thousand
mega            m.                    1 million




SYMBOLS USED FOR VARIOUS QUANTITIES


Quantity                 Symbol

capacitance              C

conductance              g

coupling co-efficient    k

current, instantaneous   i

current, effective value I

decrement                [Greek: delta]

dielectric constant      [Greek: alpha]

electric field intensity [Greek: epsilon]

electromotive force,
instantaneous value      E

electromotive force,
effective value          F

energy                   W

force                    F

frequency                f

frequency x 2[Greek: pi] [Greek: omega]

impedance                Z

inductance, self         L

inductance, mutual       M

magnetic field intensity A

magnetic flux            [Greek: Phi]

magnetic induction       B

period of a complete
oscillation              T

potential difference     V

quantity of electricity  Q

ratio of the
circumference of a
circle to its diameter
=3.1416                  [Greek: pi]

reactance                X

resistance               R

time                     t

velocity                 v

velocity of light        c

wave length              [Greek: lambda]

wave length in meters    [Greek: lambda]m

work                     W

permeability             [Greek: mu]

Square root              [Math: square root]




TABLE OF ENAMELED WIRE

  No. of   Turns     Turns      Ohms per
  Wire,     per       per      Cubic Inch
  B.& S.  Linear    Square        of
  Gauge    Inch      Inch       Winding

  20        30         885         .748

  22        37        1400        1.88

  24        46        2160        4.61

  26        58        3460       11.80

  28        73        5400       29.20

  30        91        8260       70.90

  32       116      21,000     7547.00

  34       145      13,430     2968.00

  36       178      31,820     1098.00

  38       232      54,080      456.00

  40       294      86,500      183.00




TABLE OF FREQUENCY AND WAVE LENGTHS


  W. L.--Wave Lengths in Meters.
  F.--Number of Oscillations per Second.
  O. or square root L. C. is called Oscillation Constant.
  C.--Capacity in Microfarads.
  L.--Inductance in Centimeters.
  1000 Centimeters = 1 Microhenry.


    W.L.     F          O       L.C.
      50  6,000,000     .839       .7039
     100  3,000,000    1.68       2.82
     150  2,000,000    2.52       6.35
     200  1,500,000    3.36      11.29
     250  1,200,000    4.19      17.55
     300  1,000,000    5.05      25.30
     350    857,100    5.87      34.46
     400    750,000    6.71      45.03
     450    666,700    7.55      57.00
     500    600,000    8.39      70.39
     550    545,400    9.23      85.19
     600    500,000   10.07     101.41
     700    428,600   11.74     137.83
     800    375,000   13.42     180.10
     900    333,300   15.10     228.01
   1,000    300,000   16.78     281.57
   1,100    272,730   18.45     340.40
   1,200    250,000   20.13     405.20
   1,300    230,760   21.81     475.70
   1,400    214,380   23.49     551.80
   1,500    200,000   25.17     633.50
   1,600    187,500   26.84     720.40
   1,700    176,460   28.52     813.40
   1,800    166,670   30.20     912.00
   1,900    157,800   31.88   1,016.40
   2,000    150,000   33.55   1,125.60
   2,100    142,850   35.23   1,241.20
   2,200    136,360   36.91   1,362.40
   2,300    130,430   38.59   1,489.30
   2,400    125,000   40.27   1,621.80
   2,500    120,000   41.95   1,759.70
   2,600    115,380   43.62   1,902.60
   2,700    111,110   45.30   2,052.00
   2,800    107,140   46.89   2,207.00
   2,900    103,450   48.66   2,366.30
   3,000    100,000   50.33   2,533.20
   4,000     75,000   67.11   4,504.00
   5,000     60,000   83.89   7,038.00
   6,000     50,000  100.7   10,130.00
   7,000     41,800  117.3   13,630.00
   8,000     37,500  134.1   18,000.00
   9,000     33,300  151.0   22,820.00
  10,000     30,000  167.9   28,150.00
  11,000     27,300  184.8   34,150.00
  12,000     25,000  201.5   40,600.00
  13,000     23,100  218.3   47,600.00
  14,000     21,400  235.0   55,200.00
  15,000     20,000  252.0   63,500.00
  16,000     18,750  269.0   72,300.00




PRONUNCIATION OF GREEK LETTERS


Many of the physical quantities use Greek letters for symbols. The
following is the Greek alphabet with the way the letters are
pronounced:

  a   alpha
  b   beta
  g   gamma
  d   delta
  e   epsilon
  z   zeta
  ae  eta
  th  theta
  i   iota
  k   kappa
  l   lambda
  m   mu
  n   nu
  x   Xi(Zi)
  o   omicron
  p   pi
  r   rho
  s   sigma
  t   tau
  u   upsilon
  ph  phi
  ch  chi
  ps  psi
  o   omega




TABLE OF SPARKING DISTANCES

In Air for Various Voltages between Needle Points


  Volts               Distance
	       Inches         Centimeter
  5,000         .225            .57
  10,000        .470           1.19
  15,000        .725           1.84
  20,000       1.000           2.54
  25,000       1.300           3.30
  30,000       1.625           4.10
  35,000       2.000           5.10
  40,000       2.450           6.20
  45,000       2.95            7.50
  50,000       3.55            9.90
  60,000       4.65           11.8
  70,000       5.85           14.9
  80,000       7.10           18.0
  90,000       8.35           21.2
  100,000      9.60           24.4
  110,000     10.75           27.3
  120,000     11.85           30.1
  130,000     12.95           32.9
  140,000     13.95           35.4
  150,000     15.00           38.1


FEET PER POUND OF INSULATED MAGNET WIRE

  No. of    Single     Double     Single     Double
  B.& S.    Cotton,    Cotton,    Silk,      Silk,      Enamel
  Gauge     4-Mils     8-Mils     1-3/4-Mils 4-Mils

  20           311        298       319         312       320
  21           389        370       408         389       404
  22           488        461       503         498       509
  23           612        584       636         631       642
  24           762        745       800         779       810
  25           957        903     1,005         966     1,019
  26         1,192      1,118     1,265       1,202     1,286
  27         1,488      1,422     1,590       1,543     1,620
  28         1,852      1,759     1,972       1,917     2,042
  29         2,375      2,207     2,570       2,435     2,570
  30         2,860      2,534     3,145       2,900     3,240
  31         3,800      2,768     3,943       3,683     4,082
  32         4,375      3,737     4,950       4,654     5,132
  33         5,590      4,697     6,180       5,689     6,445
  34         6,500      6,168     7,740       7,111     8,093
  35         8,050      6,737     9,600       8,584    10,197
  36         9,820      7,877    12,000      10,039    12,813
  37        11,860      9,309    15,000      10,666    16,110
  38        14,300     10,636    18,660      14,222    20,274
  39        17,130     11,907    23,150      16,516    25,519
  40        21,590     14,222    28,700      21,333    32,107




INTERNATIONAL MORSE CODE AND CONVENTIONAL SIGNALS

TO BE USED FOR ALL GENERAL PUBLIC SERVICE RADIO COMMUNICATION


1. A dash is equal to three dots.

2. The space between parts of the same letter is equal to one dot.

3. The space between two letters is equal to three dots.

4. The space between two words is equal to five dots.

[Note: period denotes Morse dot, hyphen denotes Morse dash]

A .-

B -...

C -.-.

D -..

E .

F ..-.

G --.

H ....

I ..

J .---

K -.-

L .-..

M --

N -.

O ---

P .--.

Q --.-

R .-.

S ...

T -

U ..-

V ...-

W .--

X -..-

Y -.--

Z --..

Ä (German) .-.-

Á or Å (Spanish-Scandinavian) .--.-

CH (German-Spanish) ----

É (French) ..-..

Ñ (Spanish) --.--

Ö (German) ---.

Ü (German) ..--

1 .----

2 ..---

3 ...--

4 ....-

5 .....

6 -....

7 --...

8 ---..

9 ----.

0 -----

Period .. .. ..

Semicolon -.-.-.

Comma -.-.-.

Colon ---...

Interrogation ..--..

Exclamation point --..--

Apostrophe .----.

Hyphen -....-

Bar indicating fraction -..-.

Parenthesis -.--.-

Inverted commas .-..-.

Underline ..--.-

Double dash -...-

Distress Call ...---...

Attention call to precede every transmission -.-.-

General inquiry call -.-. --.-

From (de) -.. .

Invitation to transmit (go ahead) -.-

Warning--high power --..--

Question (please repeat after ...)--interrupting long messages ..--..

Wait .-...

Break (Bk.) (double dash) -...-

Understand ...-.

Error ........

Received (O.K.) .-.

Position report (to precede all position messages) - .-.

End of each message (cross) .-.-.

Transmission finished (end of work) (conclusion of correspondence) ...-.-




INTERNATIONAL RADIOTELEGRAPHIC CONVENTION

LIST OF ABBREVIATIONS TO BE USED IN RADIO COMMUNICATION

ABBREVIATION      QUESTION                ANSWER OR REPLY

PRB   Do you wish to communicate          I wish to communicate by means
        by means of the International       of the International Signal Code.
        Signal Code?

QRA   What ship or coast station is       This is....
      that?

QRB   What is your distance?              My distance is....

QRC   What is your true bearing?          My true bearing is....

QRD   Where are you bound for?            I am bound for....

QRF   Where are you bound from?           I am bound from....

QRG   What line do you belong to?         I belong to the ... Line.

QRH   What is your wave length in         My wave length is ... meters.
        meters?

QRJ   How many words have you to send?    I have ... words to send.

QRK   How do you receive me?              I am receiving well.

QRL   Are you receiving badly?            I am receiving badly. Please
        Shall I send 20?                    send 20.
                   ...-.                               ...-.
                   for adjustment?                     for adjustment.

QRM   Are you being interfered with?      I am being interfered with.

QRN   Are the atmospherics strong?        Atmospherics are very strong.

QRO   Shall I increase power?             Increase power.

QRP   Shall I decrease power?             Decrease power.

QRQ   Shall I send faster?                Send faster.

QRS   Shall I send slower?                Send slower.

QRT   Shall I stop sending?               Stop sending.

QRU   Have you anything for me?           I have nothing for you.

QRV   Are you ready?                      I am ready. All right now.

QRW   Are you busy?                       I am busy (or: I am busy with...).
                                            Please do not interfere.

QRX   Shall I stand by?                   Stand by. I will call you when
                                            required.

QRY   When will be my turn?               Your turn will be No....

QRZ   Are my signals weak?                You signals are weak.

QSA   Are my signals strong?              You signals are strong.

QSB   Is my tone bad?                     The tone is bad.
      Is my spark bad?                    The spark is bad.

QSC   Is my spacing bad?                  Your spacing is bad.

QSD   What is your time?                  My time is....

QSF   Is transmission to be in            Transmission will be in
       alternate order or in series?        alternate order.

QSG                                       Transmission will be in a
                                            series of 5 messages.

QSH                                       Transmission will be in a
                                            series of 10 messages.

QSJ   What rate shall I collect for...?   Collect....

QSK   Is the last radiogram canceled?     The last radiogram is canceled.

QSL   Did you get my receipt?             Please acknowledge.

QSM   What is your true course?           My true course is...degrees.

QSN   Are you in communication with land? I am not in communication with land.

QSO   Are you in communication with       I am in communication with...
        any ship or station                 (through...).
        (or: with...)?

QSP   Shall I inform...that you are       Inform...that I am calling him.
        calling him?

QSQ   Is...calling me?                    You are being called by....

QSR   Will you forward the radiogram?     I will forward the radiogram.

QST   Have you received the general       General call to all stations.
        call?

QSU   Please call me when you have        Will call when I have finished.
        finished (or: at...o'clock)?

QSV  Is public correspondence being       Public correspondence is being
       handled?                             handled. Please do not interfere.

[Footnote: Public correspondence is any radio work, official or
private, handled on commercial wave lengths.]

QSW   Shall I increase my spark           Increase your spark frequency.
        frequency?

QSX   Shall I decrease my spark           Decrease your spark frequency.
        frequency?

QSY   Shall I send on a wavelength        Let us change to the wave length
        of ... meters?                        of ... meters.

QSZ                                       Send each word twice. I have
                                            difficulty in receiving you.

QTA                                       Repeat the last radiogram.


When an abbreviation is followed by a mark of interrogation, it refers
to the question indicated for that abbreviation.




Useful Information

Symbols Used For Apparatus

alternator

ammeter

aerial

arc

battery

buzzer

condenser

variable condenser

connection of wires

no connection

coupled coils

variable coupling

detector

gap, plain

gap, quenched

ground

hot wire ammeter

inductor

variable inductor

key

resistor

variable resistor

switch s.p.s.t.

" s.p.d.t.

" d.p.s.t.

" d.p.d.t.

" reversing

phone receiver

" transmitter

thermoelement

transformer

vacuum tube

voltmeter

choke coil




DEFINITIONS OF ELECTRIC AND MAGNETIC UNITS


The _ohm_ is the resistance of a thread of mercury at the temperature
of melting ice, 14.4521 grams in mass, of uniform cross-section and a
length of 106.300 centimeters.

The _ampere_ is the current which when passed through a solution of
nitrate of silver in water according to certain specifications,
deposits silver at the rate of 0.00111800 of a gram per second.

The _volt_ is the electromotive force which produces a current of 1
ampere when steadily applied to a conductor the resistance of which is
1 ohm.

The _coulomb_ is the quantity of electricity transferred by a current
of 1 ampere in 1 second.

The _ampere-hour_ is the quantity of electricity transferred by a
current of 1 ampere in 1 hour and is, therefore, equal to 3600
coulombs.

The _farad_ is the capacitance of a condenser in which a potential
difference of 1 volt causes it to have a charge of 1 coulomb of
electricity.

The _henry_ is the inductance in a circuit in which the electromotive
force induced is 1 volt when the inducing current varies at the rate
of 1 ampere per second.

The _watt_ is the power spent by a current of 1 ampere in a resistance
of 1 ohm.

The _joule_ is the energy spent in I second by a flow of 1 ampere in 1
ohm.

The _horse-power_ is used in rating steam machinery. It is equal to
746 watts.

The _kilowatt_ is 1,000 watts.

The units of capacitance actually used in wireless work are the
_microfarad_, which is the millionth part of a farad, because the
farad is too large a unit; and the _C. G. S. electrostatic unit of
capacitance_, which is often called the _centimeter of capacitance_,
which is about equal to 1.11 microfarads.

The units of inductance commonly used in radio work are the
_millihenry_, which is the thousandth part of a henry; and the
_centimeter of inductance_, which is one one-thousandth part of a
microhenry.

Note.--For further information about electric and magnetic units get
the _Bureau of Standards Circular No. 60_, called _Electric Units and
Standards_, the price of which is 15 cents; also get _Scientific Paper
No. 292_, called _International System of Electric and Magnetic
Units_, price 10 cents. These and other informative papers can be had
from the _Superintendent of Documents, Government Printing Office_,
Washington, D. C.




WIRELESS BOOKS


The Admiralty Manual of Wireless Telegraphy. 1920. Published by His
Majesty's Stationery Office, London.

Ralph E. Batcher.--Prepared Radio Measurements. 1921. Wireless Press,
Inc., New York City.

Elmer E. Bucher.--Practical Wireless Telegraphy. 1918. Wireless
Press, Inc., New York City.

Elmer E. Bucher.--Vacuum Tubes in Wireless Communication. 1919.
Wireless Press, Inc., New York City.

Elmer E. Bucher.--The Wireless Experimenter's Manual. 1920. Wireless
Press, Inc., New York City.

A. Frederick Collins.--Wireless Telegraphy, Its History, Theory, and
Practice. 1905. McGraw Pub. Co., New York City.

J. H. Dellinger.--Principles Underlying Radio Communication. 1921.
Signal Corps, U. S. Army, Washington, D. C.

H. M. Dorsett.--Wireless Telegraphy and Telephony. 1920. Wireless
Press, Ltd., London.

J. A. Fleming.--Principles of Electric Wave Telegraphy. 1919.
Longmans, Green and Co., London.

Charles B. Hayward.--How to Become a Wireless Operator. 1918.
American Technical Society, Chicago, Ill.

G. D. Robinson.--Manual of Radio Telegraphy and Telephony. 1920.
United States Naval Institute, Annapolis, Md.

Rupert Stanley.--Textbook of Wireless Telegraphy. 1919. Longmans,
Green and Co., London.

E. W. Stone.--Elements of Radio Telegraphy. 1919. D, Van Nostrand Co.,
New York City.

L. B. Turner.--Wireless Telegraphy and Telephony. 1921. Cambridge
University Press. Cambridge, England.

Send to the _Superintendent of Documents, Government Printing Office_,
Washington, D. C., for a copy of _Price List No. 64_ which lists the
Government's books and pamphlets on wireless. It will be sent to you
free of charge.

The Government publishes; (1) _A List of Commercial Government and
Special Wireless Stations_, every year, price 15 cents; (2) _A List of
Amateur Wireless Stations_, yearly, price 15 cents; (3) _A Wireless
Service Bulletin_ is published monthly, price 5 cents a copy, or 25
cents yearly; and (4) _Wireless Communication Laws of the United
States_, the _International Wireless Telegraphic Convention and
Regulations Governing Wireless Operators and the Use of Wireless on
Ships and Land Stations_, price 15 cents a copy. Orders for the above
publications should be addressed to the _Superintendent of Documents,
Government Printing Office, Washington, D. C._




Manufacturers and Dealers in Wireless Apparatus and Supplies:

Adams-Morgan Co., Upper Montclair, N. J.

American Hard Rubber Co., 11 Mercer Street, New York City.

American Radio and Research Corporation, Medford Hillside, Mass.

Brach (L. S.) Mfg. Co., 127 Sussex Ave., Newark, N. J.

Brandes (C.) Inc., 237 Lafayette St., New York City.

Bunnell (J. H.) Company, Park Place, New York City.

Burgess Battery Company, Harris Trust Co. Bldg., Chicago, Ill.

Clapp-Eastman Co., 120 Main St., Cambridge, Mass.

Connecticut Telephone and Telegraph Co., Meriden, Conn.

Continental Fiber Co., Newark, Del.

Coto-Coil Co., Providence, R. I.

Crosley Mfg. Co., Cincinnati, Ohio.

Doolittle (F. M.), 817 Chapel St., New Haven, Conn.

Edelman (Philip E.), 9 Cortlandt St., New York City.

Edison Storage Battery Co., Orange, N. J.

Electric Specialty Co., Stamford, Conn.

Electrose Mfg. Co., 60 Washington St., Brooklyn, N. Y.

General Electric Co., Schenectady, N. Y.

Grebe (A. H.) and Co., Inc., Richmond Hill, N. Y. C.

International Brass and Electric Co., 176 Beekman St., New York City.

International Insulating Co., 25 West 45th St., New York City.

King Amplitone Co., 82 Church St., New York City.

Kennedy (Colin B.) Co., Rialto Bldg., San Francisco, Cal.

Magnavox Co., Oakland, Cal.

Manhattan Electrical Supply Co., Park Place, N. Y.

Marshall-Gerken Co., Toledo, Ohio.

Michigan Paper Tube and Can Co., 2536 Grand River Ave., Detroit, Mich.

Murdock (Wm. J.) Co., Chelsea, Mass.

National Carbon Co., Inc., Long Island City, N. Y.

Pittsburgh Radio and Appliance Co., 112 Diamond St., Pittsburgh, Pa,

Radio Corporation of America, 233 Broadway, New York City.

Riley-Klotz Mfg. Co., 17-19 Mulberry St., Newark, N. J.

Radio Specialty Co., 96 Park Place, New York City.

Roller-Smith Co., 15 Barclay St., New York City.

Tuska (C. D.) Co., Hartford, Conn.

Western Electric Co., Chicago, Ill.

Westinghouse Electric Co., Pittsburgh, Pa.

Weston Electrical Instrument Co., 173 Weston Ave., Newark, N. J.

Westfield Machine Co., Westfield, Mass.




ABBREVIATIONS OF COMMON TERMS


A. ..............Aerial

A.C. ............Alternating Current

A.F. ............Audio Frequency

B. and S. .......Brown & Sharpe Wire Gauge

C. ..............Capacity or Capacitance

C.G.S. ..........Centimeter-Grain-Second

Cond. ...........Condenser

Coup. ...........Coupler

C.W. ............Continuous Waves

D.C. ............Direct Current

D.P.D.T. ........Double Point Double Throw

D.P.S.T. ........Double Point Single Throw

D.X. ............Distance

E. ..............Short for Electromotive Force (Volt)

E.M.F. ..........Electromotive Force

F. ..............Filament or Frequency

G. ..............Grid

Gnd. ............Ground

I. ..............Current Strength (Ampere)

I.C.W. ..........Interrupted Continuous Waves

KW. .............Kilowatt

L. ..............Inductance

L.C. ............Loose Coupler

Litz. ...........Litzendraht

Mfd. ............Microfarad

Neg. ............Negative

O.T. ............Oscillation Transformer

P. ..............Plate

Prim. ...........Primary

Pos. ............Positive

R. ..............Resistance

R.F. ............Radio Frequency

Sec. ............Secondary

S.P.D.T. ........Single Point Double Throw

S.P.S.T. ........Single Point Single Throw

S.R. ............Self Rectifying

T. ..............Telephone or Period (time) of Complete
                    Oscillation

Tick. ...........Tickler

V. ..............Potential Difference

Var. ............Variometer

Var. Cond. ......Variable Condenser

V.T. ............Vacuum Tube

W.L. ............Wave Length

X. ..............Reactance




GLOSSARY


A BATTERY.--See Battery A.

ABBREVIATIONS, CODE.--Abbreviations of questions and answers used in
wireless communication. The abbreviation _of a question_ is usually in
three letters of which the first is Q. Thus Q R B is the code
abbreviation of "_what is your distance?_" and the answer "_My
distance is_..." See Page 306 [Appendix: List of Abbreviations].

ABBREVIATIONS, UNITS.--Abbreviations of various units used in wireless
electricity. These abbreviations are usually lower case letters of the
Roman alphabet, but occasionally Greek letters are used and other
signs. Thus _amperes_ is abbreviated _amp., micro_, which means _one
millionth_, [Greek: mu], etc. See Page 301 [Appendix: Useful
Abbreviations].

ABBREVIATIONS OF WORDS AND TERMS.--Letters used instead of words and
terms for shortening them up where there is a constant repetition of
them, as _A.C._ for _alternating current; C.W._ for _continuous waves;
V.T._ for _vacuum tube_, etc. See Page 312 [Appendix: Abbreviations of
Common Terms].

AERIAL.--Also called _antenna_. An aerial wire. One or more wires
suspended in the air and insulated from its supports. It is the aerial
that sends out the waves and receives them.

AERIAL, AMATEUR.--An aerial suitable for sending out 200 meter wave
lengths. Such an aerial wire system must not exceed 120 feet in length
from the ground up to the aerial switch and from this through the
leading-in wire to the end of the aerial.

AERIAL AMMETER.--See _Ammeter, Hot Wire_.

AERIAL, BED-SPRINGS.--Where an outdoor aerial is not practicable
_bed-springs_ are often made to serve the purpose.

AERIAL CAPACITY.--See _Capacity, Aerial._

AERIAL COUNTERPOISE.--Where it is not possible to get a good ground an
_aerial counterpoise_ or _earth capacity_ can be used to advantage.
The counterpoise is made like the aerial and is supported directly
under it close to the ground but insulated from it.

AERIAL, DIRECTIONAL.--A flat-top or other aerial that will transmit
and receive over greater distances to and from one direction than to
and from another.

AERIAL, GROUND.--Signals can be received on a single long wire when it
is placed on or buried in the earth or immersed in water. It is also
called a _ground antenna_ and an _underground aerial._

AERIAL, LOOP.--Also called a _coil aerial, coil antenna, loop aerial,
loop antenna_ and when used for the purpose a _direction finder_. A
coil of wire wound on a vertical frame.

AERIAL RESISTANCE.--See _Resistance, Aerial._

AERIAL SWITCH.--See _Switch Aerial._

AERIAL WIRE.--(1) A wire or wires that form the aerial. (2) Wire that
is used for aerials; this is usually copper or copper alloy.

AERIAL WIRE SYSTEM.--An aerial and ground wire and that part of the
inductance coil which connects them. The open oscillation circuit of
a sending or a receiving station.

AIR CORE TRANSFORMER.--See _Transformer, Air Core._

AMATEUR AERIAL OR ANTENNA.--See _Aerial, Amateur._

ALTERNATOR.--An electric machine that generates alternating current.

ALPHABET, INTERNATIONAL CODE.--A modified Morse alphabet of dots and
dashes originally used in Continental Europe and, hence, called the
_Continental Code_. It is now used for all general public service
wireless communication all over the world and, hence, it is called the
_International Code_. See page 305 [Appendix: International Morse
Code].

ALTERNATING CURRENT (_A.C._)--See _Current._

ALTERNATING CURRENT TRANSFORMER.--See _Transformer_.

AMATEUR GROUND.--See _Ground, Amateur_.

AMMETER.--An instrument used for measuring the current strength, in
terms of amperes, that flows in a circuit. Ammeters used for measuring
direct and alternating currents make use of the _magnetic effects_ of
the currents. High frequency currents make use of the _heating
effects_ of the currents.

AMMETER, HOT-WIRE.--High frequency currents are usually measured by
means of an instrument which depends on heating a wire or metal strip
by the oscillations. Such an instrument is often called a _thermal
ammeter_, _radio ammeter_ and _aerial ammeter_.

AMMETER, AERIAL.--See _Ammeter, Hot Wire_.

AMMETER, RADIO.--See _Ammeter, Hot Wire_.

AMPERE.--The current which when passed through a solution of nitrate
of silver in water according to certain specifications, deposits
silver at the rate of 0.00111800 of a gram per second.

AMPERE-HOUR.--The quantity of electricity transferred by a current of
1 ampere in 1 hour and is, therefore, equal to 3600 coulombs.

AMPERE-TURNS.--When a coil is wound up with a number of turns of wire
and a current is made to flow through it, it behaves like a magnet. B
The strength of the magnetic field inside of the coil depends on (1)
the strength of the current and (2) the number of turns of wire on the
coil. Thus a feeble current flowing through a large number of turns
will produce as strong a magnetic field as a strong current flowing
through a few turns of wire. This product of the current in amperes
times the number of turns of wire on the coil is called the
_ampere-turns_.

AMPLIFICATION, AUDIO FREQUENCY.--A current of audio frequency that is
amplified by an amplifier tube or other means.

AMPLIFICATION, CASCADE.--See _Cascade Amplification_.

AMPLIFICATION, RADIO FREQUENCY.--A current of radio frequency that is
amplified by an amplifier tube or other means before it reaches the
detector.

AMPLIFICATION, REGENERATIVE.--A scheme that uses a third circuit to
feed back part of the oscillations through a vacuum tube and which
increases its sensitiveness when used as a detector and multiplies its
action as an amplifier and an oscillator.

AMPLIFIER, AUDIO FREQUENCY.--A vacuum tube or other device that
amplifies the signals after passing through the detector.

AMPLIFIER, MAGNETIC.--A device used for controlling radio frequency
currents either by means of a telegraph key or a microphone
transmitter. The controlling current flows through a separate circuit
from that of the radio current and a fraction of an ampere will
control several amperes in the aerial wire.

AMPLIFIERS, MULTI-STAGE.--A receiving set using two or more
amplifiers. Also called _cascade amplification_.

AMPLIFIER, VACUUM TUBE.--A vacuum tube that is used either to amplify
the radio frequency currents or the audio frequency currents.

AMPLITUDE OF WAVE.--The greatest distance that a point moves from its
position of rest.

AMPLIFYING TRANSFORMER, AUDIO.--See _Transformer, Audio Amplifying_.

AMPLIFYING MODULATOR VACUUM TUBE.--See _Vacuum Tube, Amplifying
Modulator_.

AMPLIFYING TRANSFORMER RADIO.--See _Transformer, Radio Amplifying_.

ANTENNA, AMATEUR.--See _Aerial, Amateur_.

ANTENNA SWITCH.--See _Switch, Aerial_.

APPARATUS SYMBOLS.--See _Symbols, Apparatus_.

ARMSTRONG CIRCUIT.--See _Circuit, Armstrong_.

ATMOSPHERICS.--Same as _Static_, which see.

ATTENUATION.--In Sending wireless telegraph and telephone messages the
amplitude of the electric waves is damped out as the distance
increases. This is called _attenuation_ and it increases as the
frequency is increased. This is the reason why short wave lengths
will not carry as far as long wave lengths.

AUDIO FREQUENCY AMPLIFIER.--See _Amplifier, Audio Frequency_.

AUDIO FREQUENCY AMPLIFICATION.--See _Amplification, Audio Frequency_.

AUDIBILITY METER.--See _Meter, Audibility_.

AUDIO FREQUENCY.--See _Frequency, Audio_.

AUDIO FREQUENCY CURRENT.--See _Current, Audio Frequency_.

AUDION.--An early trade name given to the vacuum tube detector.

AUTODYNE RECEPTOR.--See _Receptor, Autodyne_.

AUTO TRANSFORMER.--See _Transformer, Auto_.

BAKELITE.--A manufactured insulating compound.

B BATTERY.--See _Battery B_.

BAND, WAVE LENGTH.--See _Wave Length Band_.

BASKET WOUND COILS.--See _Coils, Inductance_.

BATTERY, A.--The 6-volt storage battery used to heat the filament of a
vacuum tube, detector or amplifier.

BATTERY, B.--The 22-1/2-volt dry cell battery used to energize the
plate of a vacuum tube detector or amplifier.

BATTERY, BOOSTER.--This is the battery that is connected in series
with the crystal detector.

BATTERY, C.--A small dry cell battery sometimes used to give the grid
of a vacuum tube detector a bias potential.

BATTERY, EDISON STORAGE.--A storage battery in which the elements are
made of nickel and iron and immersed in an alkaline
_electrolyte_.

BATTERY, LEAD STORAGE.--A storage battery in which the elements are
made of lead and immersed in an acid electrolyte.

BATTERY POLES.--See _Poles, Battery_.

BATTERY, PRIMARY.--A battery that generates current by chemical
action.

BATTERY, STORAGE.--A battery that develops a current after it has been
charged.

BEAT RECEPTION.--See _Heterodyne Reception_.

BED SPRINGS AERIAL.--See _Aerial, Bed Springs_.

BLUB BLUB.--Over modulation in wireless telephony.

BROAD WAVE.--See _Wave, Broad_.

BRUSH DISCHARGE.--See _Discharge_.

BUZZER MODULATION.--See _Modulation, Buzzer_.

BLUE GLOW DISCHARGE.--See _Discharge_.

BOOSTER BATTERY.--See _Battery, Booster_.

BROADCASTING.--Sending out intelligence and music from a central
station for the benefit of all who live within range of it and who
have receiving sets.

CAPACITANCE.--Also called by the older name of _capacity_. The
capacity of a condenser, inductance coil or other device capable of
retaining a charge of electricity. Capacitance is measured in terms
of the _microfarad_.

CAPACITIVE COUPLING.--See _Coupling, Capacitive_.

CAPACITY.--Any object that will retain a charge of electricity; hence
an aerial wire, a condenser or a metal plate is sometimes called a
_capacity_.

CAPACITY, AERIAL.--The amount to which an aerial wire system can be
charged. The _capacitance_ of a small amateur aerial is from
0.0002 to 0.0005 microfarad.

CAPACITY, DISTRIBUTED.--A coil of wire not only has inductance, but
also a certain small capacitance. Coils wound with their turns
parallel and having a number of layers have a _bunched capacitance_
which produces untoward effects in oscillation circuits. In honeycomb
and other stagger wound coils the capacitance is more evenly
distributed.

CAPACITY REACTANCE.--See _Reactance, Capacity_.

CAPACITY UNIT.--See _Farad_.

CARBON RHEOSTATS.--See _Rheostat, Carbon_.

CARBORUNDUM DETECTOR.--See _Detector_.

CARRIER CURRENT TELEPHONY.--See _Wired-Wireless_.

CARRIER FREQUENCY.--See _Frequency, Carrier_.

CARRIER FREQUENCY TELEPHONY.--See _Wired-Wireless_.

CASCADE AMPLIFICATION.--Two or more amplifying tubes hooked up in a
receiving set.

CAT WHISKER CONTACT.--A long, thin wire which makes contact with the
crystal of a detector.

CENTIMETER OF CAPACITANCE.--Equal to 1.11 _microfarads_.

CENTIMETER OF INDUCTANCE.--Equal to one one-thousandth part of a
_microhenry_.

CELLULAR COILS.--See _Coils, Inductance_.

C.G.S. ELECTROSTATIC UNIT OF CAPACITANCE.--See _Centimeter of
Capacitance_.

CHARACTERISTICS.--The special behavior of a device, such as an aerial,
a detector tube, etc.

CHARACTERISTICS, GRID.--See _Grid Characteristics_.

CHOKE COILS.--Coils that prevent the high voltage oscillations from
surging back into the transformer and breaking down the insulation.

CHOPPER MODULATION.--See _Modulation, Chopper_.

CIRCUIT.--Any electrical conductor through which a current can flow. A
low voltage current requires a loop of wire or other conductor both
ends of which are connected to the source of current before it can
flow. A high frequency current will surge in a wire which is open at
both ends like the aerial.

Closed Circuit.--A circuit that is continuous.

Open Circuit.--A conductor that is not continuous.

Coupled Circuits.--Open and closed circuits connected together
by inductance coils, condensers or resistances. See _coupling_.

Close Coupled Circuits.--Open and closed circuits connected
directly together with a single inductance coil.

Loose Coupled Circuits.--Opened and closed currents connected
together inductively by means of a transformer.

Stand-by Circuits.--Also called _pick-up_ circuits. When listening-in
for possible calls from a number of stations, a receiver is used which
will respond to a wide band of wave lengths.

Armstrong Circuits.--The regenerative circuit invented by Major E. H.
Armstrong.

CLOSE COUPLED CIRCUITS.--See _Currents, Close Coupled_.

CLOSED CIRCUIT.--See _Circuit, Closed_.

CLOSED CORE TRANSFORMER.--See _Transformer, Closed Core_.

CODE.--

Continental.--Same as _International_.

International.--On the continent of Europe land lines use the
_Continental Morse_ alphabetic code. This code has come to be used
throughout the world for wireless telegraphy and hence it is now
called the _International code_. It is given on Page 305. [Appendix:
International Morse Code].

Morse.--The code devised by Samuel F. B. Morse and which is used on
the land lines in the U. S.

National Electric.--A set of rules and requirements devised by the
_National Board of Fire Underwriters_ for the electrical installations
in buildings on which insurance companies carry risks. This code also
covers the requirements for wireless installations. A copy may be had
from the _National Board of Fire Underwriters_, New York City, or from
your insurance agent.

National Electric Safety.--The Bureau of Standards, Washington, D. C.,
have investigated the precautions which should be taken for the safe
operation of all electric equipment. A copy of the _Bureau of
Standards Handbook No. 3_ can be had for 40 cents from the
_Superintendent of Documents_.

COEFFICIENT OF COUPLING.--See _Coupling, Coefficient of_.

COIL AERIAL.--See _Aerial, Loop_.

COIL ANTENNA.--See _Aerial, Loop_.

COIL, INDUCTION.--An apparatus for changing low voltage direct
currents into high voltage, low frequency alternating currents. When
fitted with a spark gap the high voltage, low frequency currents are
converted into high voltage, high frequency currents. It is then also
called a _spark coil_ and a _Ruhmkorff coil_.

COIL, LOADING.--A coil connected in the aerial or closed oscillation
circuit so that longer wave lengths can be received.

COIL, REPEATING.--See _Repeating Coil_.

COIL, ROTATING.--One which rotates on a shaft instead of sliding as in
a _loose coupler_. The rotor of a _variometer_ or _variocoupler_ is a
_rotating coil_.

COILS, INDUCTANCE.--These are the tuning coils used for sending and
receiving sets. For sending sets they are formed of one and two coils,
a single sending coil is generally called a _tuning inductance coil_,
while a two-coil tuner is called an _oscillation transformer_.
Receiving tuning coils are made with a single layer, single coil, or a
pair of coils, when it is called an oscillation _transformer_. Some
tuning inductance coils have more than one layer, they are then called
_lattice wound_, _cellular_, _basket wound_, _honeycomb_,
_duo-lateral_, _stagger wound_, _spider-web_ and _slab_ coils.

COMMERCIAL FREQUENCY.--See _Frequency, Commercial_.

CONDENSER, AERIAL SERIES.--A condenser placed in the aerial wire
system to cut down the wave length.

CONDENSER, VERNIER.--A small variable condenser used for receiving
continuous waves where very sharp tuning is desired.

CONDENSER.--All conducting objects with their insulation form
capacities, but a _condenser_ is understood to mean two sheets or
plates of metal placed closely together but separated by some
insulating material.

Adjustable Condenser.--Where two or more condensers can be coupled
together by means of plugs, switches or other devices.

Aerial Condenser.--A condenser connected in the aerial.

Air Condenser.--Where air only separates the sheets of metal.

By-Pass Condenser.--A condenser connected in the transmitting currents
so that the high frequency currents cannot flow back through the power
circuit.

Filter Condenser.--A condenser of large capacitance used in
combination with a filter reactor for smoothing out the pulsating
direct currents as they come from the rectifier.

Fixed Condenser.--Where the plates are fixed relatively to one
another.

Grid Condenser.--A condenser connected in series with the grid lead.

Leyden Jar Condenser.--Where glass jars are used.

Mica Condenser.--Where mica is used.

Oil Condenser.--Where the plates are immersed in oil.

Paper Condenser.--Where paper is used as the insulating material.

Protective.--A condenser of large capacity connected across the low
voltage supply circuit of a transmitter to form a by-path of kick-back
oscillations.

Variable Condenser.--Where alternate plates can be moved and so made
to interleave more or less with a set of fixed plates.

Vernier.--A small condenser with a vernier on it so that it can be
very accurately varied. It is connected in parallel with the variable
condenser used in the primary circuit and is used for the reception of
continuous waves where sharp tuning is essential.

CONDENSITE.--A manufactured insulating compound.

CONDUCTIVITY.--The conductance of a given length of wire of uniform
cross section. The reciprocal of _resistivity_.

CONTACT DETECTORS.--See _Detectors, Contact_.

CONTINENTAL CODE.--See _Code, Continental_.

COULOMB.--The quantity of electricity transferred by a current of 1
ampere in 1 second.

CONVECTIVE DISCHARGE.--See _Discharge_.

CONVENTIONAL SIGNALS.--See _Signals, Conventional_.

COUNTER ELECTROMOTIVE FORCE.--See _Electromotive Force, Counter_.

COUNTERPOISE. A duplicate of the aerial wire that is raised a few feet
above the earth and insulated from it. Usually no connection is made
with the earth itself.

COUPLED CIRCUITS.--See _Circuit, Coupled_.

COUPLING.--When two oscillation circuits are connected together either
by the magnetic field of an inductance coil, or by the electrostatic
field of a condenser.

COUPLING, CAPACITIVE.--Oscillation circuits when connected together by
condensers instead of inductance coils.

COUPLING, COEFFICIENT OF.--The measure of the closeness of the
coupling between two coils.

COUPLING, INDUCTIVE.--Oscillation circuits when connected together by
inductance coils.

COUPLING, RESISTANCE.--Oscillation circuits connected together by a
resistance.

CRYSTAL RECTIFIER.--A crystal detector.

CURRENT, ALTERNATING (A.C.).--A low frequency current that surges to
and fro in a circuit.

CURRENT, AUDIO FREQUENCY.--A current whose frequency is low enough to
be heard in a telephone receiver. Such a current usually has a
frequency of between 200 and 2,000 cycles per second.

CURRENT, PLATE.--The current which flows between the filament and the
plate of a vacuum tube.

CURRENT, PULSATING.--A direct current whose voltage varies from moment
to moment.

CURRENT, RADIO FREQUENCY.--A current whose frequency is so high it
cannot be heard in a telephone receiver. Such a current may have a
frequency of from 20,000 to 10,000,000 per second.

CURRENTS, HIGH FREQUENCY.--(1) Currents that oscillate from 10,000 to
300,000,000 times per second. (2) Electric oscillations.

CURRENTS, HIGH POTENTIAL.--(1) Currents that have a potential of more
than 10,000 volts. (2) High voltage currents.

CYCLE.--(1) A series of changes which when completed are again at the
starting point. (2) A period of time at the end of which an
alternating or oscillating current repeats its original direction of
flow.

DAMPING.--The degree to which the energy of an electric oscillation is
reduced. In an open circuit the energy of an oscillation set up by a
spark gap is damped out in a few swings, while in a closed circuit it
is greatly prolonged, the current oscillating 20 times or more before
the energy is dissipated by the sum of the resistances of the circuit.

DECREMENT.--The act or process of gradually becoming less.

DETECTOR.--Any device that will (1) change the oscillations set up by
the incoming waves into direct current, that is which will rectify
them, or (2) that will act as a relay.

Carborundum.--One that uses a _carborundum_ crystal for the sensitive
element. Carborundum is a crystalline silicon carbide formed in the
electric furnace.

Cat Whisker Contact.--See _Cat Whisker Contact_.

Chalcopyrite.--Copper pyrites. A brass colored mineral used as a
crystal for detectors. See _Zincite_.

Contact.--A crystal detector. Any kind of a detector in which two
dissimilar but suitable solids make contact.

Ferron.--A detector in which iron pyrites are used as the sensitive
element.

Galena.--A detector that uses a galena crystal for the rectifying
element.

Iron Pyrites.--A detector that uses a crystal of iron pyrites for its
sensitive element.

Molybdenite.--A detector that uses a crystal of _sulphide of
molybdenum_ for the sensitive element.

Perikon.--A detector in which a _bornite_ crystal makes contact with a
_zincite_ crystal.

Silicon.--A detector that uses a crystal of silicon for its sensitive
element.

Vacuum Tube.--A vacuum tube (which see) used as a detector.

Zincite.--A detector in which a crystal of _zincite_ is used as the
sensitive element.

DE TUNING.--A method of signaling by sustained oscillations in which
the key when pressed down cuts out either some of the inductance or
some of the capacity and hence greatly changes the wave length.

DIELECTRIC.--An insulating material between two electrically charged
plates in which there is set up an _electric strain_, or displacement.

DIELECTRIC STRAIN.--The electric displacement in a dielectric.

DIRECTIONAL AERIAL.--See _Aerial, Directional_.

DIRECTION FINDER.--See _Aerial, Loop_.

DISCHARGE.--(1) A faintly luminous discharge that takes place from the
positive pointed terminal of an induction coil, or other high
potential apparatus; is termed a _brush discharge_. (2) A continuous
discharge between the terminals of a high potential apparatus is
termed a _convective discharge_. (3) The sudden breaking-down of the
air between the balls forming the spark gap is termed a _disruptive
discharge_; also called an _electric spark_, or just _spark_ for
short. (4) When a tube has a poor vacuum, or too large a battery
voltage, it glows with a blue light and this is called a _blue glow
discharge_.

DISRUPTIVE DISCHARGE.--See _Discharge_.

DISTRESS CALL. [Morse code:] ...---... (SOS).

DISTRIBUTED CAPACITY.--See _Capacity, Distributed_.

DOUBLE HUMP RESONANCE CURVE.--A resonance curve that has two peaks or
humps which show that the oscillating currents which are set up when
the primary and secondary of a tuning coil are closely coupled have
two frequencies.

DUO-LATERAL COILS.--See _Coils, Inductance_.

DUPLEX COMMUNICATION.--A wireless telephone system with which it is
possible to talk between both stations in either direction without the
use of switches. This is known as the _duplex system_.

EARTH CAPACITY.--An aerial counterpoise.

EARTH CONNECTION.--Metal plates or wires buried in the ground or
immersed in water. Any kind of means by which the sending and
receiving apparatus can be connected with the earth.

EDISON STORAGE BATTERY.--See _Storage Battery, Edison_.

ELECTRIC ENERGY.--The power of an electric current.

ELECTRIC OSCILLATIONS.--See _Oscillations, Electric_.

ELECTRIC SPARK.--See _Discharge, Spark_.

ELECTRICITY, NEGATIVE.--The opposite of _positive electricity_.
Negative electricity is formed of negative electrons which make up the
outside particles of an atom.

ELECTRICITY, POSITIVE.--The opposite of _negative electricity_.
Positive electricity is formed of positive electrons which make up the
inside particles of an atom.

ELECTRODES.--Usually the parts of an apparatus which dip into a liquid
and carry a current. The electrodes of a dry battery are the zinc and
carbon elements. The electrodes of an Edison storage battery are the
iron and nickel elements, and the electrodes of a lead storage battery
are the lead elements.

ELECTROLYTES.--The acid or alkaline solutions used in batteries.

ELECTROMAGNETIC WAVES.--See _Waves, Electric_.

ELECTROMOTIVE FORCE.--Abbreviated _emf_. The force that drives an
electric current along a conductor. Also loosely called
_voltage_.

ELECTROMOTIVE FORCE, COUNTER.--The emf. that is set up in a direction
opposite to that in which the current is flowing in a conductor.

ELECTRON.--(1) A negative particle of electricity that is detached
from an atom. (2) A negative particle of electricity thrown off from
the incandescent filament of a vacuum tube.

ELECTRON FLOW.--The passage of electrons between the incandescent
filament and the cold positively charged plate of a vacuum tube.

ELECTRON RELAY.--See _Relay, Electron_.

ELECTRON TUBE.--A vacuum tube or a gas-content tube used for any
purpose in wireless work. See _Vacuum Tube_.

ELECTROSE INSULATORS.--Insulators made of a composition material the
trade name of which is _Electrose_.

ENERGY, ELECTRIC.--See _Electric Energy_.

ENERGY UNIT.--The _joule_, which see, Page 308 [Appendix: Definitions
of Electric and Magnetic Units].

FADING.--The sudden variation in strength of signals received from a
transmitting station when all the adjustments of both sending and
receiving apparatus remain the same. Also called _swinging_.

FARAD.--The capacitance of a condenser in which a potential difference
of 1 volt causes it to have a charge of 1 coulomb of electricity.

FEED-BACK ACTION.--Feeding back the oscillating currents in a vacuum
tube to amplify its power. Also called _regenerative action_.

FERROMAGNETIC CONTROL.--See _Magnetic Amplifier_.

FILAMENT.--The wire in a vacuum tube that is heated to incandescence
and which throws off electrons.

FILAMENT RHEOSTAT.--See _Rheostat, Filament_.

FILTER.--Inductance coils or condensers or both which (1) prevent
troublesome voltages from acting on the different circuits, and (2)
smooth out alternating currents after they have been rectified.

FILTER REACTOR.--See _Reactor, Filter_.

FIRE UNDERWRITERS.--See _Code, National Electric_.

FIXED GAP.--See _Gap_.

FLEMING VALVE.--A two-electrode vacuum tube.

FORCED OSCILLATIONS.--See _Oscillations, Forced_.

FREE OSCILLATIONS.--See _Oscillations, Free_.

FREQUENCY, AUDIO.--(1) An alternating current whose frequency is low
enough to operate a telephone receiver and, hence, which can be heard
by the ear. (2) Audio frequencies are usually around 500 or 1,000
cycles per second, but may be as low as 200 and as high as 10,000
cycles per second.

Carrier.--A radio frequency wave modulated by an audio frequency wave
which results in setting of _three_ radio frequency waves. The
principal radio frequency is called the carrier frequency, since it
carries or transmits the audio frequency wave.

Commercial.--(1) Alternating current that is used for commercial
purposes, namely, light, heat and power. (2) Commercial frequencies
now in general use are from 25 to 50 cycles per second.

Natural.--The pendulum and vibrating spring have a _natural frequency_
which depends on the size, material of which it is made, and the
friction which it has to overcome. Likewise an oscillation circuit has
a natural frequency which depends upon its _inductance_, _capacitance_
and _resistance_.

Radio.--(1) An oscillating current whose frequency is too high to
affect a telephone receiver and, hence, cannot be heard by the ear.
(2) Radio frequencies are usually between 20,000 and 2,000,000 cycles
per second but may be as low as 10,000 and as high as 300,000,000
cycles per second.

Spark.--The number of sparks per second produced by the discharge of a
condenser.

GAP, FIXED.--One with fixed electrodes.

GAP, NON-SYNCHRONOUS.--A rotary spark gap run by a separate motor
which may be widely different from that of the speed of the
alternator.

GAP, QUENCHED.--(1) A spark gap for the impulse production of
oscillating currents. (2) This method can be likened to one where a
spring is struck a single sharp blow and then continues to set up
vibrations.

GAP, ROTARY.--One having fixed and rotating electrodes.

GAP, SYNCHRONOUS.--A rotary spark gap run at the same speed as the
alternator which supplies the power transformer. Such a gap usually
has as many teeth as there are poles on the generator. Hence one spark
occurs per half cycle.

GAS-CONTENT TUBE.--See _Vacuum Tube._

GENERATOR TUBE.--A vacuum tube used to set up oscillations. As a
matter of fact it does not _generate_ oscillations, but changes the
initial low voltage current that flows through it into oscillations.
Also called an _oscillator tube_ and a _power tube._

GRID BATTERY.--See _Battery C._

GRID CHARACTERISTICS.--The various relations that could exist between
the voltages and currents of the grid of a vacuum tube, and the values
which do exist between them when the tube is in operation. These
characteristics are generally shown by curves.

GRID CONDENSER.--See _Condenser, Grid._

GRID LEAK.--A high resistance unit connected in the grid lead of both
sending and receiving sets. In a sending set it keeps the voltage of
the grid at a constant value and so controls the output of the aerial.
In a receiving set it controls the current flowing between the plate
and filament.

GRID MODULATION.--See _Modulation, Grid._

GRID POTENTIAL.--The negative or positive voltage of the grid of a
vacuum tube.

GRID VOLTAGE.--See _Grid Potential._

GRINDERS.--The most common form of _Static,_ which see. They make a
grinding noise in the headphones.

GROUND.--See _Earth Connection._

GROUND, AMATEUR.--A water-pipe ground.

GROUND, WATERPIPE.--A common method of grounding by amateurs is to use
the waterpipe, gaspipe or radiator.

GUIDED WAVE TELEPHONY.--See _Wired Wireless._

HARD TUBE.--A vacuum tube in which the vacuum is _high,_ that is,
exhausted to a high degree.

HELIX.--(1) Any coil of wire. (2) Specifically a transmitter tuning
inductance coil.

HENRY.--The inductance in a circuit in which the electromotive force
induced is 1 volt when the inducing current varies at the rate of 1
ampere per second.

HETERODYNE RECEPTION.--(1) Receiving by the _beat_ method. (2)
Receiving by means of superposing oscillations generated at the
receiving station on the oscillations set up in the aerial by the
incoming waves.

HETERODYNE RECEPTOR.--See _Receptor, Heterodyne._

HIGH FREQUENCY CURRENTS.--See _Currents, High Frequency._

HIGH FREQUENCY RESISTANCE.--See _Resistance, High Frequency._

HIGH POTENTIAL CURRENTS.--See _Currents, High Potential._

HIGH VOLTAGE CURRENTS.--See _Currents, High Potential._

HONEYCOMB COILS.--See _Coils, Inductance._

HORSE-POWER.--Used in rating steam machinery. It is equal to 746
watts.

HOT WIRE AMMETER.--See _Ammeter, Hot Wire._

HOWLING.--Where more than three stages of radio amplification, or more
than two stages of audio amplification, are used howling noises are
apt to occur in the telephone receivers.

IMPEDANCE.--An oscillation circuit has _reactance_ and also
_resistance,_ and when these are combined the total opposition to the
current is called _impedance._

INDUCTANCE COILS.--See _Coils, Inductance._

INDUCTANCE COIL, LOADING.--See _Coil, Loading Inductance._

INDUCTIVE COUPLING.--See _Coupling, Inductive._

INDUCTIVE REACTANCE.--See _Reactance, Inductive._

INDUCTION COIL.--See _Coil, Induction._

INDUCTION, MUTUAL.--Induction produced between two circuits or coils
close to each other by the mutual interaction of their magnetic
fields.

INSULATION.--Materials used on and around wires and other conductors
to keep the current from leaking away.

INSPECTOR, RADIO.--A U. S. inspector whose business it is to issue
both station and operators' licenses in the district of which he is in
charge.

INTERFERENCE.--The crossing or superposing of two sets of electric
waves of the same or slightly different lengths which tend to oppose
each other. It is the untoward interference between electric waves
from different stations that makes selective signaling so difficult a
problem.

INTERMEDIATE WAVES.--See _Waves._

IONIC TUBES.--See _Vacuum Tubes._

INTERNATIONAL CODE.--See Code, International.

JAMMING.--Waves that are of such length and strength that when they
interfere with incoming waves they drown them out.

JOULE.--The energy spent in 1 second by a flow of 1 ampere in 1 ohm.

JOULE'S LAW.--The relation between the heat produced in seconds to the
resistance of the circuit, to the current flowing in it.

KENOTRON.--The trade name of a vacuum tube rectifier made by the
_Radio Corporation of America._

KICK-BACK.--Oscillating currents that rise in voltage and tend to flow
back through the circuit that is supplying the transmitter with low
voltage current.

KICK-BACK PREVENTION.--See _Prevention, Kick-Back._

KILOWATT.--1,000 watts.

LAMBDA.--See Pages 301, 302. [Appendix: Useful Abbreviations].

LATTICE WOUND COILS.--See _Coils, Inductance._

LIGHTNING SWITCH.--See _Switch, Lightning._

LINE RADIO COMMUNICATION.--See _Wired Wireless._

LINE RADIO TELEPHONY.--See _Telephony, Line Radio._

LITZENDRAHT.--A conductor formed of a number of fine copper wires
either twisted or braided together. It is used to reduce the _skin
effect._ See _Resistance, High Frequency._

LOAD FLICKER.--The flickering of electric lights on lines that supply
wireless transmitting sets due to variations of the voltage on opening
and closing the key.

LOADING COIL.--See _Coil, Loading._

LONG WAVES.--See _Waves._

LOOP AERIAL.--See _Aerial, Loop._

LOOSE COUPLED CIRCUITS.--See _Circuits, Loose Coupled._

LOUD SPEAKER.--A telephone receiver connected to a horn, or a
specially made one, that reproduces the incoming signals, words or
music loud enough to be heard by a room or an auditorium full of
people, or by large crowds out-doors.

MAGNETIC POLES.--See _Poles, Magnetic._

MEGOHM.--One million ohms.

METER, AUDIBILITY.--An instrument for measuring the loudness of a
signal by comparison with another signal. It consists of a pair of
headphones and a variable resistance which have been calibrated.

MHO.--The unit of conductance. As conductance is the reciprocal of
resistance it is measured by the _reciprocal ohm_ or _mho._

MICA.--A transparent mineral having a high insulating value and which
can be split into very thin sheets. It is largely used in making
condensers both for transmitting and receiving sets.

MICROFARAD.--The millionth part of a _farad._

MICROHENRY.--The millionth part of a _farad._

MICROMICROFARAD.--The millionth part of a _microfarad._

MICROHM.--The millionth part of an _ohm._

MICROPHONE TRANSFORMER.--See _Transformer, Microphone._

MICROPHONE TRANSMITTER.--See _Transmitter, Microphone._

MILLI-AMMETER.--An ammeter that measures a current by the
one-thousandth of an ampere.

MODULATION.--(1) Inflection or varying the voice. (2) Varying the
amplitude of oscillations by means of the voice.

MODULATION, BUZZER.--The modulation of radio frequency oscillations by
a buzzer which breaks up the sustained oscillations of a transmitter
into audio frequency impulses.

MILLIHENRY.--The thousandth part of a _henry._

MODULATION, CHOPPER.--The modulation of radio frequency oscillations
by a chopper which breaks up the sustained oscillations of a
transmitter into audio frequency impulses.

MODULATION, GRID.--The scheme of modulating an oscillator tube by
connecting the secondary of a transformer, the primary of which is
connected with a battery and a microphone transmitter, in the grid
lead.

MODULATION, OVER.--See _Blub Blub._

MODULATION, PLATE.--Modulating the oscillations set up by a vacuum
tube by varying the current impressed on the plate.

MODULATOR TUBE.--A vacuum tube used as a modulator.

MOTION, WAVE.--(1) The to and fro motion of water at sea. (2) Waves
transmitted by, in and through the air, or sound waves. (3) Waves
transmitted by, in and through the _ether,_ or _electromagnetic
waves,_ or _electric waves_ for short.

MOTOR-GENERATOR.--A motor and a dynamo built to run at the same speed
and mounted on a common base, the shafts being coupled together. In
wireless it is used for changing commercial direct current into direct
current of higher voltages for energizing the plate of a vacuum tube
oscillator.

MULTI-STAGE AMPLIFIERS.--See _Amplifiers, Multi-Stage._

MUTUAL INDUCTION.--See _Induction, Mutual._

MUSH.--Irregular intermediate frequencies set up by arc transmitters
which interfere with the fundamental wave lengths.

MUSHY NOTE.--A note that is not clear cut, and hence hard to read,
which is received by the _heterodyne method_ when damped waves or
modulated continuous waves are being received.

NATIONAL ELECTRIC CODE.--See _Code, National Electric._

NATIONAL ELECTRIC SAFETY CODE.--See _Code, National Electric
Safety._

NEGATIVE ELECTRICITY.--See _Electricity, Negative._

NON-SYNCHRONOUS GAP.--See _Gap, Non-Synchronous._

OHM.--The resistance of a thread of mercury at the temperature of
melting ice, 14.4521 grams in mass, of uniform cross-section and a
length of 106.300 centimeters.

OHM'S LAW.--The important fixed relation between the electric current,
its electromotive force and the resistance of the conductor in which
it flows.

OPEN CIRCUIT.--See _Circuit, Open._

OPEN CORE TRANSFORMER.--See _Transformer, Open Core._

OSCILLATION TRANSFORMER.--See _Transformer, Oscillation._

OSCILLATIONS, ELECTRIC.--A current of high frequency that surges
through an open or a closed circuit. (1) Electric oscillations may be
set up by a spark gap, electric arc or a vacuum tube, when they have
not only a high frequency but a high potential, or voltage. (2) When
electric waves impinge on an aerial wire they are transformed into
electric oscillations of a frequency equal to those which emitted the
waves, but since a very small amount of energy is received their
potential or voltage is likewise very small.

Sustained.--Oscillations in which the damping factor is small.

Damped.--Oscillations in which the damping factor is large.

Free.--When a condenser discharges through an oscillation circuit,
where there is no outside electromotive force acting on it, the
oscillations are said to be _free._

Forced.--Oscillations that are made to surge in a circuit whose
natural period is different from that of the oscillations set up in
it.

OSCILLATION TRANSFORMER.--See _Transformer._

OSCILLATION VALVE.--See _Vacuum Tube._

OSCILLATOR TUBE.--A vacuum tube which is used to produce electric
oscillations.

OVER MODULATION.--See _Blub Blub._

PANCAKE OSCILLATION TRANSFORMER.--Disk-shaped coils that are used for
receiving tuning inductances.

PERMEABILITY, MAGNETIC.--The degree to which a substance can be
magnetized. Iron has a greater magnetic permeability than air.

PHASE.--A characteristic aspect or appearance that takes place at the
same point or part of a cycle.

PICK-UP CIRCUITS.--See _Circuits, Stand-by._

PLATE CIRCUIT REACTOR.--See _Reactor, Plate Circuit._

PLATE CURRENT.--See _Current, Plate._

PLATE MODULATION.--See _Modulation, Plate._

PLATE VOLTAGE.--See _Foliage, Plate._

POLES, BATTERY.--The positive and negative terminals of the elements
of a battery. On a storage battery these poles are marked + and -
respectively.

POLES, MAGNETIC.--The ends of a magnet.

POSITIVE ELECTRICITY.--See _Electricity, Positive._

POTENTIAL DIFFERENCE.--The electric pressure between two charged
conductors or surfaces.

POTENTIOMETER.--A variable resistance used for subdividing the voltage
of a current. A _voltage divider._

POWER TRANSFORMER.--See _Transformer, Power._

POWER TUBE.--See _Generator Tube._

PRIMARY BATTERY.--See _Battery, Primary._

PREVENTION, KICK-BACK.--A choke coil placed in the power circuit to
prevent the high frequency currents from getting into the transformer
and breaking down the insulation.

Q S T.--An abbreviation used in wireless communication for (1) the
question "Have you received the general call?" and (2) the notice,
"General call to all stations."

QUENCHED GAP.--See _Gap, Quenched._

RADIATION.--The emission, or throwing off, of electric waves by an
aerial wire system.

RADIO AMMETER.--See _Ammeter, Hot Wire._

RADIO FREQUENCY.--See _Frequency, Radio._

RADIO FREQUENCY AMPLIFICATION.--See _Amplification, Radio Frequency._

RADIO FREQUENCY CURRENT.--See _Current, Radio Frequency._

RADIO INSPECTOR.--See _Inspector, Radio_.

RADIOTRON.--The trade name of vacuum tube detectors, amplifiers,
oscillators and modulators made by the _Radio Corporation of America_.

RADIO WAVES.--See _Waves, Radio_.

REACTANCE.--When a circuit has inductance and the current changes in
value, it is opposed by the voltage induced by the variation of the
current.

REACTANCE, CAPACITY.--The capacity reactance is the opposition offered
to a current by a capacity. It is measured as a resistance, that is,
in _ohms_.

RECEIVING TUNING COILS.--See _Coils, Inductance_.

RECEIVER, LOUD SPEAKING.--See _Loud Speakers_.

RECEIVER, WATCH CASE.--A compact telephone receiver used for wireless
reception.

REACTANCE, INDUCTIVE.--The inductive reactance is the opposition
offered to the current by an inductance coil. It is measured as a
resistance, that is, in _ohms_.

REACTOR, FILTER.--A reactance coil for smoothing out the pulsating
direct currents as they come from the rectifier.

REACTOR, PLATE CIRCUIT.--A reactance coil used in the plate circuit of
a wireless telephone to keep the direct current supply at a constant
voltage.

RECEIVER.--(1) A telephone receiver. (2) An apparatus for receiving
signals, speech or music. (3) Better called a _receptor_ to
distinguish it from a telephone receiver.

RECTIFIER.--(1) An apparatus for changing alternating current into
pulsating direct current. (2) Specifically in wireless (_a_) a
crystal or vacuum tube detector, and (_b_) a two-electrode vacuum
tube used for changing commercial alternating current into direct
current for wireless telephony.

REGENERATIVE AMPLIFICATION.--See _Amplification, Regenerative_.

RECEPTOR.--A receiving set.

RECEPTOR, AUTODYNE.--A receptor that has a regenerative circuit and
the same tube is used as a detector and as a generator of local
oscillations.

RECEPTOR, BEAT.--A heterodyne receptor.

RECEPTOR, HETERODYNE.--A receiving set that uses a separate vacuum
tube to set up the second series of waves for beat reception.

REGENERATIVE ACTION.--See _Feed-Back Action._

REGENERATIVE AMPLIFICATION.--See _Amplification, Regenerative._

RELAY, ELECTRON.--A vacuum tube when used as a detector or an
amplifier.

REPEATING COIL.--A transformer used in connecting up a wireless
receiver with a wire transmitter.

RESISTANCE.--The opposition offered by a wire or other conductor to
the passage of a current.

RESISTANCE, AERIAL.--The resistance of the aerial wire to oscillating
currents. This is greater than its ordinary ohmic resistance due to
the skin effect. See _Resistance, High Frequency._

RESISTANCE BOX.--See _Resistor._

RESISTANCE COUPLING.--See _Coupling, Resistance._

RESISTANCE, HIGH FREQUENCY.--When a high frequency current oscillates
on a wire two things take place that are different than when a direct
or alternating current flows through it, and these are (1) the current
inside of the wire lags behind that of the current on the surface, and
(2) the amplitude of the current is largest on the surface and grows
smaller as the center of the wire is reached. This uneven distribution
of the current is known as the _skin effect_ and it amounts to the
same thing as reducing the size of the wire, hence the resistance is
increased.

RESISTIVITY.--The resistance of a given length of wire of uniform
cross section. The reciprocal of _conductivity._

RESISTOR.--A fixed or variable resistance unit or a group of such
units. Variable resistors are also called _resistance boxes_ and more
often _rheostats._

RESONANCE.--(1) Simple resonance of sound is its increase set up by
one body by the sympathetic vibration of a second body. (2) By
extension the increase in the amplitude of electric oscillations when
the circuit in which they surge has a _natural_ period that is the
same, or nearly the same, as the period of the first oscillation
circuit.

RHEOSTAT.--A variable resistance unit. See _Resistor._

RHEOSTAT, CARBON.--A carbon rod, or carbon plates or blocks, when used
as variable resistances.

RHEOSTAT, FILAMENT.--A variable resistance used for keeping the
current of the storage battery which heats the filament of a vacuum
tube at a constant voltage.

ROTATING COIL.--See _Coil._

ROTARY GAP.--See _Gap._

ROTOR.--The rotating coil of a variometer or a variocoupler.

RUHMKORFF COIL.--See _Coil, Induction._

SATURATION.--The maximum plate current that a vacuum tube will take.

SENSITIVE SPOTS.--Spots on detector crystals that are sensitive to the
action of electric oscillations.

SHORT WAVES.--See _Waves._

SIDE WAVES.--See _Wave Length Band._

SIGNALS, CONVENTIONAL.--(1) The International Morse alphabet and
numeral code, punctuation marks, and a few important abbreviations
used in wireless telegraphy. (2) Dot and dash signals for distress
call, invitation to transmit, etc. Now used for all general public
service wireless communication.

SKIN EFFECT.--See _Resistance, High Frequency._

SOFT TUBE.--A vacuum tube in which the vacuum is low, that is, it is
not highly exhausted.

SPACE CHARGE EFFECT.--The electric field intensity due to the pressure
of the negative electrons in the space between the filament and plate
which at last equals and neutralizes that due to the positive
potential of the plate so that there is no force acting on the
electrons near the filament.

SPARK.--See _Discharge._

SPARK COIL.--See _Coil, Induction._

SPARK DISCHARGE.--See _Spark, Electric._

SPARK FREQUENCY.--See _Frequency, Spark._

SPARK GAP.--(1) A _spark gap,_ without the hyphen, means the apparatus
in which sparks take place; it is also called a _spark discharger._
(2) _Spark-gap,_ with the hyphen, means the air-gap between the
opposed faces of the electrodes in which sparks are produced.

Plain.--A spark gap with fixed electrodes.

Rotary.--A spark gap with a pair of fixed electrodes and a number of
electrodes mounted on a rotating element.

Quenched.--A spark gap formed of a number of metal plates placed
closely together and insulated from each other.

SPIDER WEB INDUCTANCE COIL.--See _Coil, Spider Web Inductance._

SPREADER.--A stick of wood, or spar, that holds the wires of the
aerial apart.

STAGGER WOUND COILS.--See _Coils, Inductance._

STAND-BY CIRCUITS.--See _Circuits, Stand-By._

STATIC.--Also called _atmospherics, grinders, strays, X's,_ and, when
bad enough, by other names. It is an electrical disturbance in the
atmosphere which makes noises in the telephone receiver.

STATOR.--The fixed or stationary coil of a variometer or a
variocoupler.

STORAGE BATTERY.--See _Battery, Storage._

STRAY ELIMINATION.--A method for increasing the strength of the
signals as against the strength of the strays. See _Static._

STRAYS.--See _Static_.

STRANDED WIRE.--See _Wire, Stranded_.

SUPER-HETERODYNE RECEPTOR.--See _Heterodyne, Super_.

SWINGING.--See _Fading_.

SWITCH, AERIAL.--A switch used to change over from the sending to the
receiving set, and the other way about, and connect them with the
aerial.

SWITCH, LIGHTNING.--The switch that connects the aerial with the
outside ground when the apparatus is not in use.

SYMBOLS, APPARATUS.--Also called _conventional symbols_. These are
diagrammatic lines representing various parts of apparatus so that
when a wiring diagram of a transmitter or a receptor is to be made it
is only necessary to connect them together. They are easy to make and
easy to read. See Page 307 [Appendix: Symbols Used for Apparatus].

SYNCHRONOUS GAP.--See _Gap, Synchronous_.

TELEPHONY, LINE RADIO.--See _Wired Wireless_.

THERMAL AMMETER.--See _Ammeter, Hot Wire_.

THREE ELECTRODE VACUUM TUBE.--_See Vacuum Tube, Three Electrode_.

TIKKER.--A slipping contact device that breaks up the sustained
oscillations at the receiving end into groups so that the signals can
be heard in the head phones. The device usually consists of a fine
steel or gold wire slipping in the smooth groove of a rotating brass
wheel.

TRANSFORMER.--A primary and a secondary coil for stepping up or down a
primary alternating or oscillating current.

A. C.--See _Power Transformer_.

Air Cooled.--A transformer in which the coils are exposed to the air.

Air Core.--With high frequency currents it is the general practice not
to use iron cores as these tend to choke off the oscillations. Hence
the core consists of the air inside of the coils.

Auto.--A single coil of wire in which one part forms the primary and
the other part the secondary by bringing out an intermediate tap.

Audio Amplifying.--This is a transformer with an iron core and is used
for frequencies up to say 3,000.

Closed Core.--A transformer in which the path of the magnetic flux is
entirely through iron. Power transformers have closed cores.

Microphone.--A small transformer for modulating the oscillations set
up by an arc or a vacuum tube oscillator.

Oil Cooled.--A transformer in which the coils are immersed in oil.

Open Core.--A transformer in which the path of the magnetic flux is
partly through iron and partly through air. Induction coils have open
cores.

Oscillation.--A coil or coils for transforming or stepping down or up
oscillating currents. Oscillation transformers usually have no iron
cores when they are also called _air core transformers._

Power.--A transformer for stepping down a commercial alternating
current for lighting and heating the filament and for stepping up the
commercial a.c., for charging the plate of a vacuum tube oscillator.

Radio Amplifying.--This is a transformer with an air core. It does not
in itself amplify but is so called because it is used in connection
with an amplifying tube.

TRANSMITTER, MICROPHONE.--A telephone transmitter of the kind that is
used in the Bell telephone system.

TRANSMITTING TUNING COILS.--See _Coils, Inductance._

TUNING.--When the open and closed oscillation circuits of a
transmitter or a receptor are adjusted so that both of the former will
permit electric oscillations to surge through them with the same
frequency, they are said to be tuned. Likewise, when the sending and
receiving stations are adjusted to the same wave length they are said
to be _tuned._

Coarse Tuning.--The first adjustment in the tuning oscillation
circuits of a receptor is made with the inductance coil and this tunes
them coarse, or roughly.

Fine Tuning.--After the oscillation circuits have been roughly tuned
with the inductance coil the exact adjustment is obtained with the
variable condenser and this is _fine tuning._

Sharp.--When a sending set will transmit or a receiving set will
receive a wave of given length only it is said to be sharply tuned.
The smaller the decrement the sharper the tuning.

TUNING COILS.--See _Coils, Inductance._

TWO ELECTRODE VACUUM TUBE.--See _Vacuum Tube, Two Electrode._

VACUUM TUBE.--A tube with two or three electrodes from which the air
has been exhausted, or which is filled with an inert gas, and used as
a detector, an amplifier, an oscillator or a modulator in wireless
telegraphy and telephony.

Amplifier.--See _Amplifier, Vacuum Tube._

Amplifying Modulator.--A vacuum tube used for modulating and
amplifying the oscillations set up by the sending set.

Gas Content.--A tube made like a vacuum tube and used as a detector
but which contains an inert gas instead of being exhausted.

Hard.--See _Hard Tube._

Rectifier.--(1) A vacuum tube detector. (2) a two-electrode vacuum
tube used for changing commercial alternating current into direct
current for wireless telephony.

Soft.--See _Soft Tube._

Three Electrode.--A vacuum tube with three electrodes, namely a
filament, a grid and a plate.

Two Electrode.--A vacuum tube with two electrodes, namely the filament
and the plate.

VALVE.--See _Vacuum Tube._

VALVE, FLEMING.--See _Fleming Valve._

VARIABLE CONDENSER.--See _Condenser, Variable._

VARIABLE INDUCTANCE.--See _Inductance, Variable._

VARIABLE RESISTANCE.--See _Resistance, Variable._

VARIOCOUPLER.--A tuning device for varying the inductance of the
receiving oscillation circuits. It consists of a fixed and a rotatable
coil whose windings are not connected with each other.

VARIOMETER.--A tuning device for varying the inductance of the
receiving oscillation currents. It consists of a fixed and a rotatable
coil with the coils connected in series.

VERNIER CONDENSER.--See _Condenser, Vernier._

VOLT.--The electromotive force which produces a current of 1 ampere
when steadily applied to a conductor the resistance of which is one
ohm.

VOLTAGE DIVIDER.--See _Potentiometer._

VOLTAGE, PLATE.--The voltage of the current that is used to energize
the plate of a vacuum tube.

VOLTMETER.--An instrument for measuring the voltage of an electric
current.

WATCH CASE RECEIVER.--See _Receiver, Watch Case._

WATER-PIPE GROUND.--See _Ground, Water-Pipe._

WATT.--The power spent by a current of 1 ampere in a resistance of 1
ohm.

WAVE, BROAD.--A wave having a high decrement, when the strength of the
signals is nearly the same over a wide range of wave lengths.

WAVE LENGTH.--Every wave of whatever kind has a length. The wave
length is usually taken to mean the distance between the crests of two
successive waves.

WAVE LENGTH BAND.--In wireless reception when continuous waves are
being sent out and these are modulated by a microphone transmitter the
different audio frequencies set up corresponding radio frequencies and
the energy of these are emitted by the aerial; this results in waves
of different lengths, or a band of waves as it is called.

WAVE METER.--An apparatus for measuring the lengths of electric waves
set up in the oscillation circuits of sending and receiving sets.

WAVE MOTION.--Disturbances set up in the surrounding medium as water
waves in and on the water, sound waves in the air and electric waves
in the ether.

WAVES.--See _Wave Motion_.

WAVES, ELECTRIC.--Electromagnetic waves set up in and transmitted by
and through the ether.

Continuous. Abbreviated C.W.--Waves that are emitted without a break
from the aerial. Also called _undamped waves_.

Discontinuous.--Waves that are emitted periodically from the aerial.
Also called _damped waves_. Damped.--See _Discontinuous Waves_.

Intermediate.--Waves from 600 to 2,000 meters in length.

Long.--Waves over 2,000 meters in length.

Radio.--Electric waves used in wireless telegraphy and telephony.

Short.--Waves up to 600 meters in length.

Wireless.--Electric waves used in wireless telegraphy and telephony.

Undamped.--See _Continuous Waves_.

WIRELESS TELEGRAPH CODE.--See _Code, International_.

WIRE, ENAMELLED.--Wire that is given a thin coat of enamel which
insulates it.

WIRE, PHOSPHOR BRONZE.--A very strong wire made of an alloy of copper
and containing a trace of phosphorus.

WIRED WIRELESS.--Continuous waves of high frequency that are sent over
telephone wires instead of through space. Also called _line radio
communication; carrier frequency telephony, carrier current telephony;
guided wave telephony_ and _wired wireless._

X'S.--See _Static._

ZINCITE.--See _Detector._




WIRELESS DON'TS

AERIAL WIRE DON'TS

_Don't_ use iron wire for your aerial.

_Don't_ fail to insulate it well at both ends.

_Don't_ have it longer than 75 feet for sending out a 200-meter wave.

_Don't_ fail to use a lightning arrester, or better, a lightning
switch, for your receiving set.

_Don't_ fail to use a lightning switch with your transmitting set.

_Don't_ forget you must have an outside ground.

_Don't_ fail to have the resistance of your aerial as small as
possible. Use stranded wire.

_Don't_ fail to solder the leading-in wire to the aerial.

_Don't_ fail to properly insulate the leading-in wire where it goes
through the window or wall.

_Don't_ let your aerial or leading-in wire touch trees or other
objects.

_Don't_ let your aerial come too close to overhead wires of any kind.

_Don't_ run your aerial directly under, or over, or parallel with
electric light or other wires.

_Don't_ fail to make a good ground connection with the water pipe
inside.

TRANSMITTING DON'TS

_Don't_ attempt to send until you get your license.

_Don't_ fail to live up to every rule and regulation.

_Don't_ use an input of more than 1/2 a kilowatt if you live within 5
nautical miles of a naval station.

_Don't_ send on more than a 200-meter wave if you have a restricted or
general amateur license.

_Don't_ use spark gap electrodes that are too small or they will get
hot.

_Don't_ use too long or too short a spark gap. The right length can be
found by trying it out.

_Don't_ fail to use a safety spark gap between the grid and the
filament terminals where the plate potential is above 2,000 volts.

_Don't_ buy a motor-generator set if you have commercial alternating
current in your home.

_Don't_ overload an oscillation vacuum tube as it will greatly shorten
its life. Use two in parallel.

_Don't_ operate a transmitting set without a hot-wire ammeter in the
aerial.

_Don't_ use solid wire for connecting up the parts of transmitters.
Use stranded or braided wire.

_Don't_ fail to solder each connection.

_Don't_ use soldering fluid, use rosin.

_Don't_ think that all of the energy of an oscillation tube cannot be
used for wave lengths of 200 meters and under. It can be if the
transmitting set and aerial are properly designed.

_Don't_ run the wires of oscillation circuits too close together.

_Don't_ cross the wires of oscillation circuits except at right
angles.

_Don't_ set the transformer of a transmitting set nearer than 3 feet
to the condenser and tuning coil.

_Don't_ use a rotary gap in which the wheel runs out of true.

RECEIVING DON'TS

_Don't_ expect to get as good results with a crystal detector as with
a vacuum tube detector.

_Don't_ be discouraged if you fail to hit the sensitive spot of a
crystal detector the first time--or several times thereafter.

_Don't_ use a wire larger than _No. 80_ for the wire electrode of a
crystal detector.

_Don't_ try to use a loud speaker with a crystal detector receiving
set.

_Don't_ expect a loop aerial to give worthwhile results with a crystal
detector.

_Don't_ handle crystals with your fingers as this destroys their
sensitivity. Use tweezers or a cloth.

_Don't_ imbed the crystal in solder as the heat destroys its
sensitivity. Use _Wood's metal,_ or some other alloy which melts at or
near the temperature of boiling water.

_Don't_ forget that strong static and strong signals sometimes destroy
the sensitivity of crystals.

_Don't_ heat the filament of a vacuum tube to greater brilliancy than
is necessary to secure the sensitiveness required.

_Don't_ use a plate voltage that is less or more than it is rated for.

_Don't_ connect the filament to a lighting circuit.

_Don't_ use dry cells for heating the filament except in a pinch.

_Don't_ use a constant current to heat the filament, use a constant
voltage.

_Don't_ use a vacuum tube in a horizontal position unless it is made
to be so used.

_Don't_ fail to properly insulate the grid and plate leads.

_Don't_ use more than 1/3 of the rated voltage on the filament and on
the plate when trying it out for the first time.

_Don't_ fail to use alternating current for heating the filament where
this is possible.

_Don't_ fail to use a voltmeter to find the proper temperature of the
filament.

_Don't_ expect to get results with a loud speaker when using a single
vacuum tube.

_Don't_ fail to protect your vacuum tubes from mechanical shocks and
vibration.

_Don't_ fail to cut off the A battery entirely from the filament when
you are through receiving.

_Don't_ switch on the A battery current all at once through the
filament when you start to receive.

_Don't_ expect to get the best results with a gas-content detector
tube without using a potentiometer.

_Don't_ connect a potentiometer across the B battery or it will
speedily run down.

_Don't_ expect to get as good results with a single coil tuner as you
would with a loose coupler.

_Don't_ expect to get as good results with a two-coil tuner as with
one having a third, or _tickler_, coil.

_Don't_ think you have to use a regenerative circuit, that is, one
with a tickler coil, to receive with a vacuum tube detector.

_Don't_ think you are the only amateur who is troubled with static.

_Don't_ expect to eliminate interference if the amateurs around you
are sending with spark sets.

_Don't_ lay out or assemble your set on a panel first. Connect it up
on a board and find out if everything is right.

_Don't_ try to connect up your set without a wiring diagram in front
of you.

_Don't_ fail to shield radio frequency amplifiers.

_Don't_ set the axes of the cores of radio frequency transformers in a
line. Set them at right angles to each other.

_Don't_ use wire smaller than _No. 14_ for connecting up the various
parts.

_Don't_ fail to adjust the B battery after putting in a fresh vacuum
tube, as its sensitivity depends largely on the voltage.

_Don't_ fail to properly space the parts where you use variometers.

_Don't_ fail to put a copper shield between the variometer and the
variocoupler.

_Don't_ fail to keep the leads to the vacuum tube as short as
possible.

_Don't_ throw your receiving set out of the window if it _howls_. Try
placing the audio-frequency transformers farther apart and the cores
of them at right angles to each other.

_Don't_ use condensers with paper dielectrics for an amplifier
receiving set or it will be noisy.

_Don't_ expect as good results with a loop aerial, or when using the
bed springs, as an out-door aerial will give you.

_Don't_ use an amplifier having a plate potential of less than 100
volts for the last step where a loud speaker is to be used.

_Don't_ try to assemble a set if you don't know the difference between
a binding post and a blue print. Buy a set ready to use.

_Don't_ expect to get Arlington time signals and the big cableless
stations if your receiver is made for short wave lengths.

_Don't_ take your headphones apart. You are just as apt to spoil them
as you would a watch.

_Don't_ expect to get results with a Bell telephone receiver.

_Don't_ forget that there are other operators using the ether besides
yourself.

_Don't_ let your B battery get damp and don't let it freeze.

_Don't_ try to recharge your B battery unless it is constructed for
the purpose.

STORAGE BATTERY DON'TS

_Don't_ connect a source of alternating current direct to your storage
battery. You have to use a rectifier.

_Don't_ connect the positive lead of the charging circuit with the
negative terminal of your storage battery.

_Don't_ let the electrolyte get lower than the tops of the plates of
your storage battery.

_Don't_ fail to look after the condition of your storage battery once
in a while.

_Don't_ buy a storage battery that gives less than 6 volts for heating
the filament.

_Don't_ fail to keep the specific gravity of the electrolyte of your
storage battery between 1.225 and 1.300 Baume. This you can do with a
hydrometer.

_Don't_ fail to recharge your storage battery when the hydrometer
shows that the specific gravity of the electrolyte is close to 1.225.

_Don't_ keep charging the battery after the hydrometer shows that the
specific gravity is 1.285.

_Don't_ let the storage battery freeze.

_Don't_ let it stand for longer than a month without using unless you
charge it.

_Don't_ monkey with the storage battery except to add a little
sulphuric acid to the electrolyte from time to time. If anything goes
wrong with it better take it to a service station and let the expert
do it.

EXTRA DON'TS

_Don't_ think you have an up-to-date transmitting station unless you
are using C.W.

_Don't_ use a wire from your lightning switch down to the outside
ground that is smaller than No. _4_.

_Don't_ try to operate your spark coil with 110-volt direct lighting
current without connecting in a rheostat.

_Don't_ try to operate your spark coil with 110-volt alternating
lighting current without connecting in an electrolytic interrupter.

_Don't_ try to operate an alternating current power transformer with
110-volt direct current without connecting in an electrolytic
interruptor.

_Don't_--no never--connect one side of the spark gap to the aerial
wire and the other side of the spark gap to the ground. The Government
won't have it--that's all.

_Don't_ try to tune your transmitter to send out waves of given length
by guesswork. Use a wavemeter.

_Don't_ use _hard fiber_ for panels. It is a very poor insulator where
high frequency currents are used.

_Don't_ think you are the only one who doesn't know all about
wireless. Wireless is a very complex art and there are many things
that those experienced have still to learn.




THE END.