The Radio Amateur's Hand Book
by A. Frederick Collins · English · Gutenberg #6935 · 412,670 chars · public domain (US)
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Title: The Radio Amateur's Hand Book
Author: A. Frederick Collins
Release date: November 19, 2004 [eBook #6935]
Most recently updated: December 30, 2020
Language: English
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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
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