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Wireless Telegraph Construction For Amateurs 
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       :PG.Title: Wireless Telegraph Construction For Amateurs
       :PG.Id: 64174
       :PG.Rights: Public Domain
       :PG.Producer: James Simmons
       :PG.Credits: This file was produced from page images at the Internet Archive.
       :DC.Creator: Alfred Powell Morgan
       :DC.Title: Wireless Telegraph Construction For Amateurs 
       :DC.Language: en
       :DC.Created: 1914
       :PG.Released: 2020-12-30
       :coverpage: images/CoverImage.jpg

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.. topic:: Transcriber's Note

    This book was transcribed from scans of the original found at the Internet Archive. Tables are represented as images.
    The index of the original book has been removed, but the catalog of books from the publisher has been included.
    There was no book cover image in the scans so I created one.
        
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   :alt: Frontispiece. Plate I. Electrical Conventions. 
   
   *Frontispiece.* **Plate I. Electrical Conventions.**

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       WIRELESS TELEGRAPH 

       CONSTRUCTION FOR 

       AMATEURS 

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       BY 

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       ALFRED POWELL MORGAN 

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       EDITOR MECHANICAL AND ELECTRICAL DEPARTMENT OF THE "BOYS' MAGAZINE"
        
       AUTHOR OF "WIRELESS TELEGRAPHY AND TELEPHONY" 

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       *WITH 167 ILLUSTRATIONS*

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       **Third Edition, Revised and Enlarged**

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       WITH A COMPLETE DESCRIPTION OF THE
 
       NEW WIRELESS LAW 

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       NEW YORK: 

       \D. VAN NOSTRAND COMPANY 

       25 PARK PLACE
 
       1914 

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   Copyright, 1910, 1913, by 

   \D. VAN NOSTRAND COMPANY 

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   *Stanhope Press*

   \F. H. GILSON COMPANY
 
   BOSTON. U.S.A. 

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PREFACE. 
--------

In this work, the author has endeavored to present a 
book embracing practical information for those who may 
wish to build for private or experimental use a set of 
wireless instruments which are more than toys but yet not so 
expensive as the commercial apparatus. 

Many books have been published on the subject of 
wireless telegraphy, but in them the interests of the novice 
have been rather neglected and in order to build an outfit 
he has been forced to rely upon a series of disconnected 
articles published in the amateur periodicals. 

It is the object of this book to show the construction of 
simple, efficient instruments by means of clear drawings, 
and to give enough elementary theory and practical hints 
to enable the experimenter to build a size and type in 
keeping with his needs and resources. 

The tiresome "how to make" style has been avoided as 
far as possible. History and all unimportant details are 
omitted to give in their place a concise explanation of the 
parts played by the different instruments and the 
influence of developing their various factors. 

A small lathe and a set of taps and dies are necessary to 
produce apparatus having a good appearance, but a little 
ingenuity displayed in adapting screws and parts of old 
electrical instruments oftentimes at hand will make these 
tools unnecessary. 

Ordinary precaution and plenty of time should be used in 
the work. It is obvious that if a large coil is to be made, 
it is well to insure its successful completion by painstaking 
care and the use of proper materials. Neither is it wise to 
strain an instrument through becoming impatient and using 
it before it is properly completed and adjusted. 

Wherever possible instructions have been given regarding 
the adjustment of the apparatus, but it is only by actual 
practice that the operator will acquaint himself with the 
most efficient manipulation. 

Extracts from articles contributed by the Author to 
*Popular Electricity* have been used in the chapters on 
Spark Gaps, Oscillation Detectors and Telephone 
Receivers, through the courtesy of the editor, Mr. H. W. Young. 

In conclusion, the writer wishes to express his thanks to 
the United Wireless Telegraph Company for views of their 
apparatus and to the other firms who have loaned 
electrotypes and supplied information. To those who have 
assisted in the preparation of the book, more especially to 
Mr. Safford Adams, for numerous suggestions and criticisms, 
the Author desires to express his full acknowledgments. 

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ALFRED POWELL MORGAN. 

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UPPER MONTCLAIR, N.J.

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*June*, 1910. 

PREFACE TO THE THIRD EDITION. 
-----------------------------

The success of the previous editions of this book has 
made a new and third one necessary. 

There have not been any startling changes or new 
discoveries made in the field of wireless telegraphy since the 
first edition was published, but the art has undergone a 
number of small changes and improvements which have 
increased the efficiency and selectivity of the apparatus. 

Since then a federal law restricting and controlling 
wireless telegraphy has been passed. Its effect has been 
to place wireless telegraphy upon a more certain basis, 
and to give a recognized standing to the amateur 
experimenter. 

This new law has been included in this edition in the 
form of an appendix. The amateur will do well to read 
it carefully. Compliance with its regulations will prove 
beneficial rather than a hindrance. 

A fully illustrated chapter explaining exactly how to 
comply with the law and how to build the apparatus 
required has been added. Complete descriptions of several 
new types of detectors are also included. 

All old matter has been thoroughly revised and several 
illustrations replaced by ones more up-to-date and of 
direct interest. 

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ALFRED P. MORGAN. 

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UPPER MONTCLAIR, N.J.
 
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*May*, 1913. 

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CHAPTER I. INTRODUCTORY.
------------------------

Being desirous of keeping this book as far as possible 
within the limits prescribed by the title, it is not possible to 
go deeply into the theory of the propagation of electric waves, 
but at the same time it is not deemed advisable to plunge 
suddenly into the construction of wireless apparatus 
without giving some explanation of the underlying principles. 

If the reader desires information upon this subject he is 
referred to Fleming's "Electric Wave Telegraphy" or the 
same author's "Elementary Manual of Radio-telegraphy 
and Radio-telephony." 

The explanations given in this chapter do not involve 
any actual theory of the transmission and reception of 
electric waves. They are merely intended to show the 
train of actions which take place and may be observed in 
a physical sense. With this purpose in view, several 
references have been made to simple hydraulic apparatus and
an analogy drawn to render the explanation clearer. 

The Transmission and Reception of Electric Waves.
`````````````````````````````````````````````````

Wireless telegraphy by means of electromagnetic waves 
may be divided into four distinct operations, namely: 

1. The generation of electrical oscillations. 

2. The transformation of electrical oscillations into electrical waves. 

3. The transformation of electrical waves into electrical oscillations. 

4. The detection of the electrical oscillations. 

The first two operations comprise those taking place at 
the transmitter, while the last two, which are the converse 
of the first, are in evidence only when receiving. 

.. figure:: images/Image1.jpg
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   :alt: Fig 1. Hertz Oscillator and Resonator.
   
   Fig 1. Hertz Oscillator and Resonator.

Fig. 1 illustrates the original Hertz oscillator and 
resonator, which is the simplest form a wireless installation may 
take. *T* represents the 
transmitting apparatus 
and *R* the receptor. At 
the transmitting station a 
telegraph key is placed in 
series with a battery and 
an induction coil. Two 
large metal plates, *t* and *t'*, 
are connected to the opposite sides of the spark gap, which in turn is connected to 
the secondary of the induction coil. When the key is 
pressed the electrical circuit is completed and the voltage 
of the battery is raised sufficiently by the induction coil to 
charge the metal plates *t* and *t'*. 

The key serves to break the current into periods 
corresponding to the dots and dashes of the telegraph code. 
When the high voltage of the induction coil is impressed 
upon the plates they become charged, and being of opposite 
polarity, when at a maximum the energy rushes across the 
gap and produces a disruptive spark. Each discharge, 
although appearing like a single spark passing in one 
direction, is in reality made up of a large number of rapid 
oscillations or surgings. The first passage of current serves to 
more than discharge the plates and they become charged 
in the opposite direction. A reverse discharge then occurs 
which also oversteps itself, and thus the oscillations go on, 
but gradually become weaker and weaker until they die 
completely or are damped out. The heated air of the 
spark gap becomes a conductor during the passage of the 
spark, and the oscillations are enabled to surge back and 
forth at the rate of 15,000 to 1,000,000 per second, although 
the actual discharge may take only a fraction of a second. 

.. figure:: images/Image2.jpg
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   :alt: Fig. 2. Hydraulic Oscillator. 
   
   Fig. 2. Hydraulic Oscillator. 

The generation of electrical oscillations may perhaps be 
made more clear by reference to the hydraulic apparatus 
illustrated in Fig. 2. *T* and *T'* are 
communicating tubes divided by an elastic 
membrane M. The tubes may be likened 
to the metal plates *t* and *t'* or the arms of 
the oscillator. The membrane may be 
likened to the layer of air between the 
knobs which separates the opposite arms 
of the oscillator. *P* is a pump connected 
to the two tubes *T* and *T'*, and the 
broken lines in the apparatus represent water. The 
pump corresponds to the induction coil in Fig. 1, and 
the water to the secondary currents of the induction 
coil. When the pump is set in operation, the water is drawn 
from the tube *T* and injected into *T'*. The pump valves 
prevent it from flowing back. When the level becomes 
very high in *T'*, the great pressure distends the 
membrane in the direction shown by the dotted line until 
finally it bursts and the water is allowed to flow with a rush 
into the tube T. But the inertia of the water causes it 
to rise higher in the tube than its final position of 
equilibrium, while in returning and endeavoring to seek its level 
its inertia carries it below this position. Thus the water 
oscillates back and forth until finally it comes to rest. 

Similarly the difference of potential of the oscillator arms 
is not immediately equalized upon the breaking down of 
the air gap, and the apparatus becomes the seat of extremely 
rapid electrical oscillations, as explained above. 

All space is supposed to be filled with a highly 
attenuated, invisible and weightless medium called ether. 
When the electrical oscillations surge back and forth 
through the arms of the oscillator, portions of the energy 
are thrown off from the apparatus and travel in enlarging 
circles like the ripples on a pond. These consist of lines 
of dielectric stress or electrostatic flux which pass through 
the ether and constitute electromagnetic waves. 

The receptor or resonator *R*, Fig. 1, consists of a circle 
of wire having in it a small spark gap capable of minute 
adjustment. Two metal plates *r* and *r'* are sometimes 
attached to the opposite sides of the spark gap. When 
the key is pressed at the transmitting station and waves 
are sent out through the ether, they strike the resonator 
and set up therein electrical oscillations which pass across 
the gap in the shape of sparks. 

.. figure:: images/Image3.jpg
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   :alt: Fig. 3. "Hydraulic" Transmitter and Receptor. 
   
   Fig. 3. "Hydraulic" Transmitter and Receptor. 

To make the explanation clearer, let us consider Fig. 3 
in which two floats or blocks of wood are represented as 
resting on the surface of a tank or pool of water. One 
float, *A*, is connected by a rope and pulley so that by 
jerking the rope the float may be made to *oscillate* and cause 
little ripples or waves to pass outwards in a gradually 
enlarging circle. When the waves reach the float, *B*, they 
cause it to rise and fall with each wave or to oscillate and 
reproduce the movements of the float, *A*. Likewise the 
oscillations set up by a wireless transmitter are sent out 
into space to be caught and duplicated at the receiving 
station. Of course this analogy to the propagation and 
reception of electric waves is not the same as the true 
electrical actions, but is merely a graphical, representation. 

.. figure:: images/Image4.jpg
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   :alt: Fig. 4. Simple Wireless Telegraph Transmitter and Receptor. 
   
   Fig. 4. Simple Wireless Telegraph Transmitter and Receptor. 

The wireless telegraph outfit illustrated in Fig. 1 would 
not serve for more than short distances of a few feet, and 
so a somewhat similar but more efficient apparatus is 
employed in practice. Fig. 4 shows such a system in its 
simplest form. In this case the secondary or high 
potential leads of the induction coil are connected, one to an 
earth and the other to an aerial or antenna composed of 
a number of bare copper wires insulated and suspended 
from a mast. 

All electrically charged bodies are surrounded by an 
electrostatic field of force, the nature of which in theory 
is a state of strain. 

The action of an induction coil connected as in Fig. 4 
is to charge the upper part of the aerial above the spark 
gap, say with negative electricity and establish a field of 
force in its vicinity varying in area from a few feet to 
several miles. When the charge reaches a certain 
potential it is sufficient to puncture the layer of air in the gap 
and a spark takes place, setting up electrical oscillations. 

.. figure:: images/Image5.jpg
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   :alt: Fig. 5. Electric Waves and Lines of Strain.
   
   Fig. 5. Electric Waves and Lines of Strain.

Previous to the rupture of the spark gap, *lines of electric 
strain or force* stretch from the aerial to the earth on all 
sides as in the center of Fig. 5. A line of force may be 
defined as a curve drawn in the electric field so that the 
direction of the curve is the same as that of the electric 
intensity at that point. 

The aerial and the earth act like the two metal plates 
in Fig. 1 or like the opposite plates of a condenser. As 
soon as the air gap is punctured it becomes conductive 
and the aerial charge rushes down into the earth. With 
the discharge, the strain in the electrostatic field is released 
and the aerial charge rushes down into the earth, but in 
so relaxing produces a new current and builds up a strain 
around the antenna opposite in direction to the first. This 
process repeats itself very rapidly and electrical oscillations 
are thus set up in the antenna. Every oscillation changes 
the direction of the magnetic flux or dielectric strain and 
causes the imaginary lines which originally stretched from 
the aerial to the earth to be displaced and the ends 
terminating at the aerial to run down it and form semi-loops 
or inverted "U's" standing with their ends on the earth 
in a circular ripple around the aerial and moving away 
from it with the speed of light. In Fig. 5 three 
oscillations are supposed to have taken place. The shortest 
distance between two adjacent points at which the electric 
strain is at a maximum in the same direction and period 
of time is the *wave length* emitted by the aerial. The 
separate standing groups of dielectric strain moving away 
from the antenna are electromagnetic waves. In the 
figure, the adjacent groups are separated by half a wave 
length. These waves are emitted at right angles to the 
transmitting aerial, whence they pass through the ether to 
the other station. When they reach the receiving aerial 
they set up electrical oscillations therein which are *too weak 
to be perceptible in the shape of sparks* as in the original 
Hertz oscillator and resonator because of the great 
distance separating the stations, so they are made to flow 
through a *detector*, which in Fig. 4 is represented as being a 
crystal of a mineral called silicon. When the high 
frequency currents strike the silicon, they set up a weak 
pulsating direct current. This action is due to a peculiar 
rectifying property of the mineral. The direct current 
flows through the telephone receiver and produces an 
audible sound. If the aerial and ground were connected 
directly to the terminals of the telephone receiver, 
without the silicon, the oscillations would not pass because of 
the impeding or choking action of the electro-magnets in 
the telephone receivers. 

**Tuning.**—It is sometimes desirable that messages 
should be made selective or secretive. It is obvious that if 
there were several large stations in the same neighborhood 
they could not all operate at the same time unless some 
means of preventing the stations from receiving more than 
one message at a time were possible. This is the object 
in view of the so-called "tuning" of wireless telegraphy. 
It also accomplishes a second purpose which is perhaps 
considered more important than the first. The length of the 
aerial may be too great or too short for the amount of 
energy and the length of the waves which it emits or 
receives. When this is the case, the oscillations are quickly 
damped out and do not generate very powerful waves or 
produce strong signals at the receiving station and thus by 
properly adjusting the circuit all undesirable messages may 
be cut out as well as the signaling range greatly increased. 
Every electrical circuit has a definite period or electrical 
length, determined by its inductance and capacity. A 
circuit emits waves of only one length for given values of 
inductance and capacity, and must also be of a certain 
length before it will respond to waves sent out by another 
transmitter. The careful adjustment of a circuit to emit 
or receive a given wave constitutes *tuning*. 

.. figure:: images/Image6.jpg
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   :alt: Fig. 6. Resonance Tube.
   
   Fig. 6. Resonance Tube.

This may be made more clear by the comparison of an 
electrical circuit with a column of air. Fig. 6 represents a 
cross section of a glass tube, *T*, lying 
in a horizontal position and 
containing a cork, *C*, which can be slid to 
various positions. By adjusting the 
cork we are able to obtain various 
depths of air in the tube from its 
open end, *M*, to the cork, *C*. 

When a vibrating tuning fork, *F*, is held opposite the 
open mouth and the cork slid back and forth it is found 
that the sound of the tuning fork is greatly increased in 
volume at a certain position of the cork. If the cork is 
then removed from this position the sound decreases in 
intensity. When the cork is in such a position that the 
sound of the fork is reenforced, we have secured resonance. 
When in this condition and the prong of the vibrating 
fork is moving toward the open mouth of the tube a 
"condensed" pulse of air travels down the tube and back again, 
having been reflected at the cork and reaching *M* just as 
the prong of the fork begins its excursion away from the 
open mouth of the tube. When the prong of the fork is 
moving away from *M* a "rarefied" pulse of air moves from 
*M* to *C* and back again by the time the prong is ready to 
begin its next vibration. When the tube is not in resonance, 
the successive condensations and rarefactions passing up 
and down the air column interfere with one another and 
decrease instead of increase the sound of the tuning fork. 

If we substitute the sound waves emitted by the tuning 
fork for high frequency oscillations and the air column for 
the electrical circuit we may readily see that by adjusting 
its length, resonance can be produced. If the length of 
the air column is measured it will be found that the 
reenforcing of the sound of the fork reaches a maximum when 
the depth of the air column is *one-fourth* of the sound wave 
length given by the fork. Likewise resonance is produced 
in wireless telegraphy when the length of the circuit is 
*approximately one-fourth* the length of the waves. Vice 
versa, the wave emitted from an ordinary closed circuit 
transmitter is *approximately four times* the length of the 
aerial wire. For example, an aerial 25 meters long will 
emit waves having a length in the neighborhood of 100 
meters. 

As stated above, tuning is accomplished and resonance or 
syntony established by varying the inductance and capacity 
of the circuit. The capacity of a circuit may be defined 
as its relative ability to retain an electrical charge, while 
inductance is the property of an electric circuit by virtue 
of which lines of force are developed around it. 

Capacity and inductance are opposite or reactive in their 
effects upon a circuit. If the value of one is decreased the 
influence of the other in increased. Fig. 7 and the 
following explanation will serve to illustrate this. 

.. figure:: images/Image7.jpg
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   :alt: Fig. 7. Lag and Lead. 
   
   Fig. 7. Lag and Lead. 

Alternating currents do not always keep step with the 
voltage impulses of a circuit. If there is inductance in the 
circuit, the current will lag behind the voltage, and if there 
is capacity, the impulses of the current will lead. Fig. 7 *A* 
illustrates the lag produced by inductance and *B* the lead 
produced by capacity. In *A* the impulses of the current, 
represented by the full line, occur a little *later* than those of 
the volts as represented by the dotted line. In *B* the effect 
is just the opposite and the current leads. These reactive 
effects of inductance and capacity are very pronounced 
with the high frequency currents of wireless telegraphy, and, 
as stated before, are the factors which determine the period 
of the circuit. 

.. figure:: images/Image8.jpg
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   :alt: Fig. 8. Tuned Hydraulic Transmitter and Receptor. 
   
   Fig. 8. Tuned Hydraulic Transmitter and Receptor. 

Tuning is represented graphically in Fig. 8. The two 
floats *A* and *B* are not only resting on the surface of a pool of 
water as in Fig. 3 but are also suspended from the springs *S* 
and *S'*. The springs will have, like a pendulum, a definite 
time of rising and falling, or period of oscillation, depending 
upon their length. If we strike the float *A* the spring will 
cause the float to rise and fall at a definite rate and send 
out a little wave or ripple with every oscillation. If the 
springs *S* and *S'* are of the same length, the float *B* will be 
caused to oscillate with every wave sent out by *A*, for, the 
periods of the springs being equal, *B* will be permitted to 
rise with a wave and fall again just in time to be raised 
by the next oncoming ripple. On the other hand, if the 
springs are of different lengths, *B* may only rise slightly and 
in falling meet an oncoming wave which will cause it to rise 
before it has reached its lowest point and so dampen or 
weaken its oscillations that they either do not become very 
strong or are entirely obliterated. Thus several floats 
having different periods of oscillation might be sending out 
ripples in the same pool, and the float *B* could be made to 
respond to any of them by adjusting the length of the 
spring. 

We may also see in this illustration the part that tuning 
plays in causing the apparatus to emit or receive more 
powerful impulses. When the rope in the untuned 
apparatus illustrated in Fig. 3 is jerked, the block *A* oscillates 
only once or twice before a new jerk is required to keep it 
in motion. In Fig. 8 it is quite the contrary, for when an 
impulse has been given to the float *A* it will oscillate much 
longer than the untuned float before it requires to be set 
in motion again. Likewise the float *B* in Fig. 8 will 
oscillate longer and more powerfully than the float *B* in Fig. 3, 
when once it has been set in motion. 

.. figure:: images/Image9.jpg
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   :alt: Fig. 9. Tuned Wireless Telegraph Transmitter and Receptor 
   
   Fig. 9. Tuned Wireless Telegraph Transmitter and Receptor 

Fig. 9 shows a diagram of a simple wireless telegraph 
system employing an inductance and capacity for tuning 
the circuits. When the induction coil is in operation it 
charges a condenser. The condenser discharges through 
the sending helix and across the spark gap. The sending 
helix is merely a spiral coil of wire of large diameter, and 
constitutes the greater part of the inductance in the 
circuit. Two movable contacts, *A* and *B*, make connections 
with the helix. The spark gap, condenser and lower portion 
of the helix up to the movable contact *A* are known as the 
closed circuit. By shifting *A*, more or less inductance may 
be included in the closed circuit until resonance is secured. 
The aerial, the inductance from the contact *B* down, the 
condenser and the ground compose the open circuit. By 
varying the contact *B* more or less inductance may be 
included in the open circuit and its period altered until the 
oscillatory currents of both circuits flow in the same period 
of time. The closed and open portions of the transmitting 
helix form an auto transformer, and the voltages of the open 
circuit are raised above those of the closed circuit. 

The tuned receptor shown in Fig. 9 is the simplest form 
possible and is known as the single slide system. The 
tuning coil or helix is much longer in proportion to its diameter 
than the sending helix, and is made of finer wire, since it 
does not carry such heavy currents. When the contact 
is slid up or down on the tuning coil, the inductance of 
the circuit is varied. Since the oscillating currents in the 
receiving aerial have the same frequency as those in the 
radiating aerial, the receptor must have the same relative 
values of inductance and capacity. This condition is 
obtained by varying the slider until the signals in the 
telephone receivers are the loudest. 

In practice more than one sliding contact is used, and these 
together with adjustable condensers make the circuit more 
complicated. These devices are necessary because 
oscillations may be forced on a receptor by a near-by transmitter 
unless other precautions than the "single slider" are taken. 
Such circuits are illustrated in Plates IV and V. With 
them it is possible to obtain a considerable degree of 
selectivity and "tune out" an undesirable message. 

CHAPTER II. THE APPARATUS. 
--------------------------

It is generally the receiving apparatus which first attracts 
the attention of the amateur operator, and so it will be 
considered first here. An efficient receiving set consists of some 
form of *Detector, Tuning Coil, Telephone Receivers*, and 
*Condenser*. 

Other accessories such as adjustable condensers, 
potentiometer, battery and testing buzzer improve the outfit 
and make it more complete. 

The choice of the type of instruments must be left entirely 
to the person who is constructing them. His resources 
will determine whether he is to use 1,000 ohm telephone 
receivers built especially for wireless work or ordinary ones 
having a resistance of only 75 ohms. It is therefore best 
to read carefully the chapters devoted to the different 
pieces of receiving apparatus and select the type of detector, 
tuning coil, etc., which it is desirable to use before 
commencing the construction of any. 

For beginners, I would recommend an outfit consisting 
of a silicon detector, a double slide tuning coil, a condenser 
of fixed capacity and 75-ohm telephone receivers. Such an 
outfit with a 50-foot aerial will receive messages about 
150 miles. If 1,000 ohm telephone receivers are used, 
messages may be read up to 400 miles. Much depends 
upon the location of the station and the ability of the 
operator. 

A more elaborate and efficient set consists of an 
electrolytic or "Perikon" detector, a transforming tuner, two 
adjustable condensers, a potentiometer and a pair of 
1,000 ohm telephone receivers. This outfit and a 75-foot aerial 
could be made to receive 500 to 1,000 miles by a careful 
operator. 

Several cuts of wireless apparatus built for private 
installation are shown both in this chapter and further 
through the book, to give an idea of how the better 
instruments of this type are constructed and finished. 

.. figure:: images/Image10.jpg
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   :alt: Fig. 10. Long-distance Receiving Set. 
   
   Fig. 10. Long-distance Receiving Set. 

Fig. 10 illustrates a selective receiving set built by the 
Long Distance Wireless Company. The set is mounted on 
a mahogany base and the instruments are finished in 
polished hard rubber and lacquered brass. They comprise a 
detector stand so arranged that any of the sensitive minerals 
used in wireless work may be used. The tuning coil is of 
the double slide type. The condenser is sealed up in a 
square lacquered brass tube fitted with hard rubber ends 
and binding posts. The arrangement and construction of 
the outfit may be readily understood from the cut. 

.. figure:: images/Image11.jpg
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   :alt: Fig. 11. Murdock Receiving Set. 
   
   Fig. 11. Murdock Receiving Set. 

Fig. 11 illustrates a receiving set manufactured by the 
Wm. J. Murdock Company. The tuning coil is fitted with 
hard rubber composition ends and is wound on a special 
core which is not affected by temperature changes. The 
detector is of the crystal type and is of rather unique 
construction, since the small fixed 
condenser is mounted in the base 
of the detector itself. 

The Clapp-Eastham set in Fig. 
12 employs a receiving 
transformer which makes great 
selectivity possible. The detector is 
mounted at the left-hand side 
of the outfit. A very sensitive 
mineral called "Ferron" is used 
in the detector. The fixed 
condenser is enclosed in a brass tube fitted with hard rubber 
ends and is located on the front of the base, directly in 
the center. A variable condenser of the rotary type is 
placed at the right-hand corner. 

.. figure:: images/Image12.jpg
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   :scale: 85 %
   :alt: Fig. 12. Clapp-Eastham Receiving Set. 
   
   Fig. 12. Clapp-Eastham Receiving Set. 

The Prague Electric Company manufacture the 
apparatus shown in Fig. 13. The cabinet is mahogany and is 
fitted with a hard rubber cover. A fixed condenser and a 
double slide tuning coil are mounted within the cabinet. 
The sliders of the tuning coil project through two long slots 
in the cabinet. A universal detector mounted on top of 
the cabinet is so designed that any material may be 
experimented with or tested. 

.. figure:: images/Image13.jpg
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   :alt: Fig. 13. Prague Receiving Set. 
   
   Fig. 13. Prague Receiving Set. 

Fig. 14 shows a receiving set built up from apparatus 
described in this book. The cabinet is 12 x 16 inches and 
4 inches deep. The wood should be 1/2 inch thick, and in 
order to present a good appearance is preferably of 
mahogany. As mahogany is sometimes very hard to procure 
and expensive, some may find red birch an excellent 
substitute. When stained with a mahogany stain it presents 
a fine appearance. 

.. figure:: images/Image14.jpg
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   :alt: Fig. 14. Receiving Set. 
   
   Fig. 14. Receiving Set. 

Varnishing and polishing are wasted time when applied 
to the average amateur's instruments in view of the rough 
handling and scratching which they receive. The best 
plan is to stain the wood with an oil stain and give it a 
wax finish. An oil stain contains no varnish but is merely 
coloring matter and oil. A good coat should be applied 
with a wide brush and the surplus stain immediately wiped 
off by rubbing the whole surface with a piece of cheesecloth. 
As soon as the stain is thoroughly dry the wood is waxed. 

Cut up some beeswax into fine shreds and place it in a 
jar. Pour some turpentine over the beeswax and let the 
mixture stand for five or six hours, giving it an occasional 
stir. Allow it to stand further if necessary until the wax 
melts and then add enough turpentine to give the mixture 
a consistency similar to that of thick cream. Apply the 
preparation to the wood with a rag, and then rub with a 
piece of clean cheesecloth until the finish is hard and 
dry. Waxing produces a gloss which is not so bright as a 
French polish but yet is more durable and not so easily 
scratched or marred. 

A double slide tuning coil made as described in Chapter 
XIV is mounted on top of the cabinet in the rear. A 
"universal" detector is mounted in the center, directly in 
front of the tuning coil. A tubular condenser of fixed 
capacity is placed on the left-hand side of the detector, and a 
potentiometer on the opposite side. A double point switch 
placed directly in front of the detector enables the 
potentiometer to be brought into play when a battery is used. 
Four binding posts are mounted on the front of the cabinet. 
The ground and aerial are connected to the left-hand pair 
and the telephone receivers to those on the right hand. 
The wiring diagram is shown also in Fig. 14. By placing 
the switch *A* on contact 1, the potentiometer is brought into 
use. When on contact 2, the potentiometer is cut out. 
The switch *B* must be opened when the detector is not in 
use so as not to run down the battery. 

.. figure:: images/Image15.jpg
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   :alt: Fig. 15. Receiving Set. 
   
   Fig. 15. Receiving Set. 

Fig. 15 shows a receiving set somewhat similar to that 
shown in Fig. 14 but more elaborate and efficient. The 
cabinet in this case measures 14 x 22 inches and is 6 inches 
deep. A loosely coupled or transforming tuning coil is 
used in place of the closely coupled double slide type. Two 
variable condensers are mounted on either side of the 
tuning coil. The detector and potentiometer occupy the 
space directly in front of the tuning coil, while a fixed 
condenser is placed at their right. The two switches for 
breaking the battery circuit and disconnecting the potentiometer 
are in front of the detector. The aerial, ground and 
telephone receiver leads are connected to binding posts mounted 
on the front of the cabinet. 

The batteries, in both cases, are placed inside the cabinet. 
The details and construction of all the separate instruments 
will be found in the respective chapters as denoted by the 
titles. 

**Transmitting Range.**—A simple transmitting outfit 
capable of sending about two miles consists of the necessary 
batteries, a one-inch spark induction coil, a small zinc spark 
gap and a key. The connections of such a transmitting 
outfit are shown in Fig. 4. 

If the same coil is used with a transmitting helix and a 
condenser, the range may be increased from 3 to 5 miles. 

A 1 1/2-inch spark induction coil using a condenser and a 
transmitting helix will send about 10 miles, and a 3-inch 
coil under the same conditions about 20 miles. A 4 and a 
6 inch coil will transmit about 30 and 40 miles respectively. 

.. figure:: images/Image16.jpg
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   :alt: Fig. 16. Murdock Transmitting and Receiving Set. 
   
   Fig. 16. Murdock Transmitting and Receiving Set. 

The one quarter kilowatt transformer with a helix and 
four two-quart leyden jars or an equivalent condenser will 
transmit at least 50 miles with a suitable aerial. Used as a 
one half kilowatt transformer with a helix and eight 
two-quart leyden jars, it will send about 100 miles. 

Of course, as in the case of the receiving outfits, these 
distances are approximate and depend upon the location 
of the station, the nature of the ground over which the 
messages are transmitted, the kind of receptor used at the 
receiving station and the efficiency of the operator himself. 

Fig. 16 illustrates a complete Murdock transmitting and 
receiving set. The transmitting outfit consists of a 15-watt 
induction coil giving about a one-inch spark, a sending 
helix, oscillation condenser, a key and a double pole double 
throw switch for changing the antenna and ground from 
the transmitting to the receiving instruments or vice versa. 
The spark gap is mounted on top of the coil. The 
receiving outfit is the same as that illustrated in Fig. 11. 

**A complete wireless station**—outside of the aerial consists 
primarily of a source of electrical energy, a transformer or 
induction coil for charging the oscillation condenser, an 
oscillation condenser, a transmitting helix, a key for 
breaking the primary current, a spark gap, an aerial switch, a 
hot wire ammeter for tuning the transmitting circuits, a 
detector, a receiving tuner, auxiliary tuning apparatus such 
as fixed and variable condensers, a potentiometer and 
battery, and a pair of telephone receivers with a headband. 

Other apparatus such as switches, insulators, anchor 
gaps, testing buzzers, reactance coils, grounding switches, 
etc., have been described in various places throughout 
the book and their use suggested whenever it is of any 
advantage. 

The choice of transmitting instruments, as with the 
receiving apparatus, is left entirely with the experimenter 
so that he may suit his ideas and means. Wherever possible 
the range and power of the instruments have been given 
and suggestions made as to the other apparatus which 
should be used in connection with them so that the 
completed outfit will bear some sense of proportion. 

.. figure:: images/Image17.jpg
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   :alt: Fig. 17. United Wireless Portable Outfit. 
   
   Fig. 17. United Wireless Portable Outfit. 

Fig. 17 illustrates the portable wireless telegraph set 
manufactured by the United Wireless Telegraph Company 
for army service and exploring expeditions or isolated 
camps. The aerial and the mast can be unloaded, erected, 
and all parts be ready for operation in fifteen minutes. 
The mast is made of interchangeable wooden sections. 
The current for the transmitter is furnished by a portable 
storage battery. The whole outfit is capable of furnishing 
efficient service for distances of 25 to 30 miles. 

CHAPTER III. AERIALS AND EARTH CONNECTIONS. 
-------------------------------------------

The aerial or antenna ordinarily consists of a number 
of wires elevated in the air to emit or intercept the 
Hertzian waves. In fitting up a wireless station the location 
and erection of an aerial are of prime importance, and the 
successful reception and transmission of wireless messages 
will depend largely upon its condition. 

A few years ago the wireless antenna consisted of a metal 
plate high in the air and having a wire suspended from it, 
but to-day usually exists in one of the forms illustrated in 
Plate II. 

The higher an aerial is placed above the surface of the 
earth, the wider will be its electrostatic field, and 
consequently more powerful electrical waves will be developed. 
But after a height of 180-200 feet is attained, the 
engineering difficulties and the expenses increase so rapidly that 
few stations exceed it. Other things being equal, the 
increased range in transmitting varies as the square of the 
height of the radiating wires. For example, a 25-foot 
aerial capable of transmitting one mile theoretically will 
send waves 16 miles if made 100 feet high. The actual 
ratio is often greater, but much is dependent upon the many 
meteorological conditions. 

After the limit in a vertical direction has been reached, 
the only remaining possibilities are to increase the surface 
and spread out horizontally. 

The flat top aerials are used on shipboard or wherever 
it is an advantage to suspend the wires between two masts. 

They are especially recommended for amateur use, since 
they need not be so high as the other aerials, to be efficient. 
The flat top aerials are *directive*, that is, they receive or 
radiate waves better in certain directions. The bent or 
inverted L type is one of these and exhibits a preference 
for waves coming from a direction opposite to that in which 
its free end points. This directive action of an inverted 
L antenna may be somewhat lessened if the leads are taken 
off at the center and it is made a T aerial. This is the 
most common form of flat top aerial in use on ships. 

The inverted U type is not used extensively because the 
two opposite leads or rat-tails make a centrally located 
operating room necessary. The loop aerial is used by the 
United Wireless Company, in both their ship and land 
stations. This type of aerial is well adapted to long waves 
and close tuning. 

The Lodge-Muirhead capacity aerial does not make use 
of a ground and is rarely seen in this country. Lately the 
United States Signal Corps have applied it to their balloons 
where an earth connection would be impossible. The upper 
part of the balloon is covered with a network of wires which 
serves as the upper aerial, and a second system of wires is 
suspended below the balloon to take the place of the ground. 
By this means they have had little difficulty in establishing 
successful communication between the balloons and the 
earth. 

The pyramid aerial is the type used by Marconi in 
long-distance ultra-powerful stations, but is debarred 
from extensive installation on account of the large cost of 
erection. 

The cage and grid aerials are of the vertical type and are 
excellent where a high support to elevate them can be 
secured. They are at present used principally by the Massie 
and Stone Companies. 

.. figure:: images/Plate2.jpg
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   :alt: Plate II. Aerial Systems. 
   
   **Plate II. Aerial Systems.**

The desirable feature of an aerial is a quantity known as 
its electrostatic capacity and is measured by the charge 
required to raise its potential one unit. An increase in 
capacity enables more energy to be accumulated in the 
antenna, and consequently greater radiation results. The 
capacity of an aerial may be increased by adding wires, but 
must not be carried too far or the transmitting apparatus 
will not be able to raise its potential sufficiently. Owing 
to an effect caused by mutual induction between the wires, 
the lines of strain are not distributed symmetrically, and the 
capacity will not vary directly but rather approximately 
as the square root of the number of wires. In order to 
decrease this action and use the surface most efficiently, 
the wires should not be placed nearer than one-fiftieth of 
their length and preferably farther apart. 

The materials used for the insulation and suspension of 
an aerial must be reliable, so that in event of bad weather 
the station will not lose energy or be put out of working 
order because the aerial blew down. 

Porcelain cleats or a string of porcelain insulating knobs 
make inexpensive insulators. The standard insulator for 
wireless telegraph work is the "Electrose" insulator. These 
are made of a molded composition, and have iron rings set 
firmly in the ends so that they can withstand a very heavy 
strain. Hard rubber is undesirable for an aerial insulator 
because it becomes carbonized and covered with a 
conducting layer. 

.. figure:: images/Image18.jpg
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   :alt: Fig. 18. Electrose Insulators. 
   
   Fig. 18. Electrose Insulators. 

High frequency currents permeate copper wire only about 
one three-hundredth of an inch, and so, in order to increase 
the surface and decrease the resistance, it is best to make 
the aerial of stranded wire. A phosphor bronze wire for 
this purpose which is very flexible but still does not sag or 
stretch, is composed of 7 strands of No. 20 B. S. gauge. 
Such a wire 150 feet long suspended vertically and insulated 
from the earth will have a capacity of from 0.0003 to 0.0004 
of a microfarad. 

The aerial must receive very particular attention if the 
station is one kilowatt or over in power. In that case 
stranded wire is necessary. The insulation of the aerial 
must be as thorough as possible, and proximity to large 
conductors such as smokestacks, telephone lines, etc., 
avoided. Rope stays and guys are advisable in order to 
prevent dissipation of energy. If wire stays must be used 
they should be divided up at frequent intervals by 
insulators. 

Fig. 19 illustrates a guy insulator used by the United 
Wireless Telegraph Company. It is made of two strips 
of well paraffined wood separated by two porcelain knob 
insulators. 

.. figure:: images/Image19.jpg
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   :alt: Fig. 19. Guy Insulator. 
   
   Fig. 19. Guy Insulator. 

Copper wire is the most desirable for an aerial. Iron 
wire must never be used unless it is very heavily galvanized, 
and even then it is not to be recommended. Aluminum 
wire is undesirable except for kite sustained aerials. When 
used on an aerial and exposed to smoke and other fumes it 
becomes quickly coated with a layer of oxide. All 
connections made in aluminum wire must be soldered. This 
necessity may be better understood when it is explained 
that electro-magnets on dynamos, etc., are sometimes 
wound with bare aluminum wire and that the natural 
coating of oxide on the wire is sufficient insulation to separate 
the turns. 

.. figure:: images/Image20.jpg
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   :alt: Fig. 20. Insulating Tube. 
   
   Fig. 20. Insulating Tube. 

Where the aerial enters the building in which the 
instruments are located it must be very carefully insulated. The 
simplest method is to bore a hole through the wall and 
push a porcelain tube through it. The rat-tail or 
leading-in wire is then passed through and the interstices between 
it and the tube poured full of melted paraffin. 

The best method is to bore a hole in the window pane and 
pass the wire through a hard rubber insulating tube. Fig. 
20 shows such a tube. It is three-quarters of an inch in 
outside diameter and has an internal bore of three-eighths 
of an inch. The tube is threaded throughout its entire 
length. Two hard rubber flanges \ inch thick and 2 inches 
in diameter are threaded to screw on the tube. The tube 
is inserted in the hole in the window pane and the flanges 
screwed on either side. If a soft rubber washer is placed 
between the hard rubber flanges and the pane there will 
be less likelihood of cracking the glass. The leading-in 
wire is then passed through the tube. The hole in the 
window pane may be bored by using a copper tube having an 
external diameter equal to that of the required hole. The 
tube is set in a brace and used like an ordinary bit, but must 
be kept well smeared with emery and oil or else it will 
not cut. 

This method of leading in the rat-tail is the only one to 
be recommended if the transmitter is one-quarter kilowatt 
or over in power. 

.. figure:: images/Image21.jpg
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   :alt: Fig. 21. High-tension Cable and Insulator. 
   
   Fig. 21. High-tension Cable and Insulator. 

The lead-in should be anchored just outside of the 
window so as to relieve the glass pane and the tube from all 
strain. Pirelli cable or the high-tension cable which is 
used for the secondary wiring of an automobile is the best 
conductor to use for the aerial in the interior of a building. 
The way to lead it over the ceiling is to support it on a 
porcelain cleat similar to that shown in Fig. 21. 

Many are under the erroneous impression that four times 
the length of the aerial is the wave length which the station 
will emit. This is only at the best a very rough 
approximation, for many undeterminable factors such as the nature 
and location of surrounding objects, trees, etc., so affect 
the capacity and inductance of the aerial that the wave 
length must be determined empirically after the aerial is in 
operation. 

The standard wave length of the United States Navy for 
ship installations is 425 meters. An inverted L aerial, 
calculated before erection to have a wave length as near 
as possible to this, has the following dimensions: Four 
horizontal stranded phosphor bronze wires (7 strands No. 20 
\B. S.) each 160 feet long and spaced 5 feet apart, four 
vertical wires 85 feet long and a 35-foot rat-tail. 

It is always desirable that the wave length should be as 
long as possible, for the waves will then travel farther and 
are not absorbed to such an extent by trees, etc. The 
absorption due to trees is said to vary as the fourth power 
of the frequency. 

It is sometimes very convenient to calculate the strain 
on insulators or masts caused by a horizontal antenna. 
This is easily found by the following equation: 

*P* equals L² x W/8S

where *P* is the required strain in lbs., *W* the weight in lbs. 
per foot of aerial, *L* the length of the aerial and *S* the sag 
of the wire in feet. 

When erecting an aerial, it is best to fasten a pulley at 
the top of the supporting mast and hoist the aerial up after 
the pole is in position. Then in case the wires become 
twisted or broken they may be lowered and repaired 
without any difficulty. 

**Erection of an Aerial.**—The average amateur aerial is 
generally from 40 to 60 feet high and supported at one end by 
a short pole placed on the house and at the other end by a 
mast set in the ground or lashed to a tree. Fig. 22 
illustrates such an arrangement whereby a flat-top T aerial is 
supported at one end by a short pole fastened to the house 
and at the other end by a pole set in the ground. 

.. figure:: images/Image22.jpg
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   :alt: Fig. 22. Flat-top T Aerial. 
   
   Fig. 22. Flat-top T Aerial. 

The flat-top loop aerial is preferred by some amateurs 
and it is to be recommended for receiving but is an inefficient 
radiator. When this type of aerial is used the two 
leading-in wires should be connected to a switch so that when the 
switch is closed they are connected. The aerial may then 
be used as a straight-away aerial for transmitting, and by 
opening the switch, as a loop aerial for receiving. This 
precaution is advised when a loop aerial is to be used with 
a low-powered induction coil as a transmitter, for 
otherwise there will be a loss of energy at the anchor gap. 

A large aerial is of no advantage when used with a small 
transformer or induction coil because it cannot become 
properly charged. 

To erect a flat-top T aerial, first select its location. If 
possible take advantage of two trees and lash a short pole 
in the top of each, so that the aerial may be raised up clear 
of the leaves. Another good plan is to erect a pole at each 
end of the house. In any case, the distance separating the 
poles must not be greater than three times the height above 
ground or the directive action of the aerial will be very 
pronounced. An aerial 50 to 60 feet high should have a length 
of from 80 to 100 feet. Stranded wire is no advantage for 
receiving, but must be used if the transmitter is other than 
a small induction coil. 

Secure two spruce sticks about 2 inches in diameter and 
10 feet long. Fasten an insulator 6 inches from each end 
of the spars and two more each 3 J feet from the ends. This 
arrangement will separate each of the four wires which 
compose the aerial by three feet. 

The two spars are then laid on the ground at a distance 
apart equal to the desired length of the aerial. Four 
wires, either stranded or No. 12 B. S. gauge copper, are cut 
to equal lengths and fastened to the corresponding 
insulators. The middle of each wire is found and a long copper 
wire soldered to it. These four wires constitute the 
rat-tail or lead-in. They should be of the same length, and are 
not connected together until they are about to enter the 
building. A short rope tied to each end of the spars and 
fastened to the rope which passes over the pulley on the 
top of the pole, serves as a bridle to prevent the aerial from 
twisting. The aerial is then hoisted up but allowed to hang 
slightly slack. 

There is considerable difference of opinion among experts 
as to whether or not the ends of the horizontal wires should 
be connected, and it is impossible to say with good reason 
which method is better. However, when erecting a flat 
top aerial, exercise every care to make all the wires of 
exactly the same length. 

An aerial of the size and type just described will send and 
receive the following distances. 

.. figure:: images/Table1.jpg
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   :alt: Sending and Receiving Range Tables

These distances are only approximate and will vary with 
the efficiency of the operator and the location of the station. 

When any of the transformers described later are used, 
the aerial should be 80 to 100 feet high. In this case the 
last named receiving outfit will have a range of from 500 to 
1,000 miles. 

**Ground Connections.**—The importance of a good earth 
or ground connection can hardly be overestimated. 
Whenever possible commercial stations are located on moist 
ground or near a body of water so that a good ground may 
be secured by imbedding zinc or copper plates in the earth 
or water. A ground on shipboard is easily secured by 
fastening a conductor to one of the ship's plates. 

If the ground connection is poor, the natural period of 
the oscillation circuit is made irregular and short, so that 
the currents are choked in passing in and out of the earth. 
The result is an undesirable rise of potential at the lower 
end of the aerial and often harmful sparking at the ground 
connection. The transmitting and receiving ranges of a 
station are very considerably reduced through a poor earth. 

Ground connection can often be obtained in the country 
by immersing metal plates in a well or a cistern. Where 
connection is made to a water supply pipe some sort of a 
ground clamp should be used to insure a good contact. 

.. figure:: images/Image23.jpg
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   :alt: Fig. 23. Ground Clamp. 

   Fig. 23. Ground Clamp. 

An efficient earth for portable outfits may be quickly 
formed by spreading a large area of wire netting over the 
ground. 

Proper precautions for protection against lightning by 
grounding the aerial outside of the building should be 
taken. 

The wisest plan is to install a heavy single pole double 
throw switch outside of the building where the rat-tail 
enters. The knife of the switch should be connected to 
the aerial, one contact to the house lead and the other to 
a heavy wire grounded on the outside of the building as 
in Fig. 24. When the apparatus is not in use the aerial 
should be grounded by throwing the switch on the grounded 
contact. 

.. figure:: images/Image24.jpg
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   :alt: Fig. 24. Switch for Lightning Protection. 

   Fig. 24. Switch for Lightning Protection. 

The rulings of the National Board of Fire Underwriters 
governing this class of work are appended below. 

"1. Aerial conductors to be permanently and effectively 
grounded at all times when the station is not in operation 
by a conductor not smaller than No. 4 B. S. gauge copper 
wire, run in a direct line as possible to water pipe on street 
side of said water pipe within the premises or to some other 
equally satisfactory earth connection. 

"2. Aerial conductors when grounded as above specified 
must be effectually cut off from all apparatus within the 
building. 

"3. Or the aerial to be permanently connected at all 
times to earth in the manner specified above, through a 
short gap lightning arrester; said arrester to have a gap of 
not over .015 of an inch between brass or copper plates not 
less than 2 1/2 inches in length, parallel to the gap, and 1 1/2 
inches the other way, with a thickness of not less than 
one-eighth of an inch, mounted on non-combustible, 
non-absorptive insulating material of such dimensions as to 
give ample strength. Other approved arresters of equally 
low resistance and equally substantial construction may be 
used. 

"4. In cases where the aerial is grounded as specified in 
paragraph 1, the switch employed to join the aerial to the 
ground connection shall not be smaller than a standard 
100-ampere jack-knife switch. 

"Notice of wiring done for these installations should be 
sent to the Board, the same as for all other work." 

CHAPTER IV. INDUCTION COILS. 
----------------------------

Some means of charging the condenser which produces 
the oscillatory discharge is necessary. An induction coil 
is the most practical for the amateur. 

The induction coil consists of a primary coil of wire 
wound around a central iron core and surrounded by a 
secondary coil consisting of many thousand turns of 
carefully insulated wire. The primary coil is connected to a 
source of direct current which also includes an interrupter 
to "make" and "break" the current in rapid succession. 
Every "make" of the circuit and consequent 
magnetization of the core induces a momentary inverse current in 
the secondary, and every "break" and corresponding 
demagnetization a momentary direct current. Normally, 
the induced currents would be equal, but by means of a 
condenser shunted across the interrupter the circuit when 
"made" requires considerable time for the current and 
magnetization of the core to reach a maximum value, while 
when broken the demagnetization and current drop are 
nearly instantaneous. The value of the induced 
electromotive force in a circuit varies as the speed at which the 
magnetic lines of force cut the circuit, and so the induced 
\e.m.f. at "break" is thus rendered high enough to leap 
across a gap in the shape of sparks. 

The formulas connected with induction coils depend upon 
conditions which are never met in actual practice and 
cannot be relied upon. To construct a coil of a given size, it 
is necessary to use dimensions obtained empirically. 
Therefore it is well for the amateur to stick closely to lines and 
hints which are given here or which appear in some *up to 
date* book on induction coil building. 

.. figure:: images/Image25.jpg
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   :alt: Fig. 25. Diagram of an Induction Coil. 

   Fig. 25. Diagram of an Induction Coil. 

For a long time the induction coil was an expensive, 
inefficient instrument, until wireless telegraphy demanded 
of it more rigid and efficient design and construction. It 
was the aim of manufacturers to produce the longest possible 
spark length with a minimum amount of secondary wire. 
As a result of this demand, wireless coils are now made 
with a core of large diameter and give heavier and thicker 
sparks. The secondary in this case is short and uses wire 
of large cross section in order to reduce the resistance and 
minimize the heating. 

No one part of an induction coil may be developed to 
its maximum efficiency without seriously influencing and 
lowering the efficiency of the other parts. The following 
suggestions regarding the construction are given that they 
may prove a useful guide to the amateur coil builder. 
The parts will be considered in their natural order of 
construction. 

**Core.**—Some experimenters not quite familiar with the 
principles of magnetism reason that if an induction coil 
were provided with a closed core as the transformer, the 
efficiency of the coil would be materially increased. But 
this is not so, for the magnetization and demagnetization 
of the iron cannot take place rapidly enough in a closed 
core when an interrupted direct current is employed in place 
of an alternating current. 

The core of an induction coil is therefore always straight. 
For the same reason, it is never solid but is made up of a 
bundle of soft iron wires in order that rapid changes in 
magnetism may take place. The wires are always of 
as high a permeability [#]_ as possible so as to create a 
strong magnetic field. Swedish or Russian iron of a good 
quality is the best, as its hysteresis [#]_ losses are small. 
The smaller the diameter of the wire the less will be the 
eddy current losses and heating, but the permeability is 
also rendered less and the core will not be so effective, as 
the amount of iron is thereby decreased and the oxidized 
surface increased. No. 22 B. S. gauge wire is the best size 
for the average core. 

Wires of a good quality may be purchased already cut 
to various lengths. To buy them in this form will save a 
great deal of the labor required in building a core. If the 
wires are not quite straight they may be straightened by 
rolling them, one at a time, between two boards. It is best 
to reanneal the wires in the following manner. Place 
them in an iron pipe and plug the ends of the pipe with clay. 
Then lay it in a coal fire until the whole mass attains a red 
heat. The fire is then allowed to die out gradually with 
the pipe and wires remaining in the ashes until cool. When 
cool remove them from the pipe and rub each one with 
emery paper until bright. After this cleaning, the wires 
are dipped in hot water and dried. They are then dipped 
in a good quality of varnish and allowed to dry again. 

.. figure:: images/Image26.jpg
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   :alt: Fig. 26. Induction Coil Core. 

   Fig. 26. Induction Coil Core. 

The varnish serves to interpose resistance to the eddy 
currents generated in the core and renders the losses due 
to this cause much less. A strong 
paper tube having an internal 
diameter equal to the diameter of the 
finished core is made by rolling the 
paper on a form and cementing with 
shellac. When perfectly dry. the tube is removed and the 
wires tightly packed in it. The following table gives the 
core dimensions for practical coils of different sizes. 

.. figure:: images/Table2.jpg
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   :alt: Core Dimensions Table.

**Primary Winding.**—The ratio of the number of primary 
turns of an induction coil to the number of secondary turns 
bears no relation to the ratio of the primary and the 
secondary currents. It has been found in practice that two layers 
of wire wound tightly on the core constitute the best 
primary. The primary should always be thoroughly shellacked 
or covered with insulating varnish. Since there is almost 
no ventilation in the primary the wire must be large enough 
to avoid all heating. A table containing the various sizes 
of primary wires is given below. 

In large coils, the inductance of the primary causes a 
"kick back" and sparks are liable to pass between the 
adjacent turns. For this reason, it is always well to use double 
cotton covered wire and to further thoroughly insulate it by 
soaking the primary and core in a pan of melted paraffin 
and allowing them to harden therein. Afterwards the pan 
is slightly warmed to loosen the cake of paraffin and the 
excess of wax removed by scraping with a blunt instrument 
so as not to injure the wires. Paraffin contracts upon 
hardening, and the proper method to impregnate a porous 
substance is to allow it to soak and become set in it upon 
cooling. 

A good method of reducing the "kick back" and also the 
size of the condenser shunted across the interrupter is to 
form the primary of a number of turns of smaller wire in 
parallel, the effect being to give a conductivity equal to a 
single wire of large diameter and at the same time to make 
a more compact winding of the primary on the core. This 
method of winding is very desirable in large coils, as it 
reduces the cross section of the primary and allows the 
secondary to be placed nearer the core, where the magnetic 
field is the strongest.

.. figure:: images/Table3.jpg
   :align: center
   :scale: 85 %
   :alt: Primary Windings Table.

The primary winding ought to occupy nearly the whole 
length of the core, since there is no gain in carrying the end 
of the core very far beyond the end of the primary, for most 
of the magnetic lines of force bend at the end of the primary 
and return without passing through the extreme ends of 
the core. 

**Insulating Tube.**—The successful operation of an 
induction coil without breaking down when under strain 
depends largely upon the insulating tube which 
separates the primary and secondary. Hard rubber tubes 
are perhaps the best. A tube may be easily built up of 
several layers of 1/2-inch sheet hard rubber by steaming 
it so as to soften it and then wrapping it around a form. 
The tube should fit the primary tightly and be about 
one inch shorter than the core. After the tube is in place 
it is poured full of beeswax and rosin in order to fill all 
interstices and prevent sparks due to the condenser effect 
of the windings from jumping from the inside of the tube 
to the primary. 

**Secondary.**—A coil used as a wireless telegraph 
transmitter must have wire of large cross section in its secondary 
so as to obtain a heavy disruptive discharge. Numbers 34 
and 32 B. S. are generally used for small coils and numbers 
30 and 28 B. S. for large coils. Silk covered wire is the usual 
practice, but enameled wire is coming into use. Cotton 
covered wire takes up too much space and has poorer 
insulating qualities. 

Enameled wire is insulated by a coating of cellulose 
acetate, which has a dielectric strength of about twice that of 
cotton and takes up much less room than silk. There is, 
then, with enameled wire a great saving in space, and a 
greater number of turns may be placed on the secondary 
without increasing its mean distance from the core. The 
following table shows the comparative diameters of silk and 
enamel covered wires suitable in size for use on the 
secondaries of induction coils. 

.. figure:: images/Table4.jpg
   :align: center
   :scale: 85 %
   :alt: Silk and Enameled Wires Table.

In winding enameled wire it must be taken into 
consideration that the insulation of enameled wire is rigid and has 
no give. Consequently, to allow for expansion, enameled 
wire must be more loosely wound than fiber or silk 
covered wire. The occasional 
insertion of a layer of paper in 
winding will give room for 
expansion and at the same time 
not add greatly to the diameter. 

.. figure:: images/Image27.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 27. Theoretical and practical form of secondary. 
   
   Fig. 27. Theoretical and practical form of secondary. 

The length of the secondary is 
generally not much more than 
one-half the length of the core. 
Coils giving sparks up to 2 inches 
in length may be wound in two 
sections or in layer windings, but the layer winding is not 
recommended for coils giving sparks over one inch. It is 
best in a coil of this kind to insert an occasional layer of 
paper. The paper should be well shellacked or paraffined 
and be of a good grade of linen. It should project about 
one-quarter of an inch from the ends of the secondary 
as shown by the sectional drawing in Fig. 28.
 
This insertion of paper increases the insulation and renders 
the liability of sparks jumping from layer to layer much less, 
as is the case when the layers are very long. 

.. figure:: images/Image28.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 28. Layer Winding for Small Coils. 
   
   Fig. 28. Layer Winding for Small Coils. 

The secondaries of large coils are made up of "pies" or 
"pancakes" from one-eighth to three-eighths of an inch in 
thickness. The "pies" are separated from each other by a 
triple thickness of blotting paper which has been thoroughly 
dried and then soaked in melted paraffin. In cutting the 
blotting paper, much labor may be saved if a metal template 
of the required size is first cut from sheet brass and then 
laid on the blotting paper, which is cut by scoring around 
the edge of the template with a sharp knife. 

.. figure:: images/Image29.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 29. Section Winder.
   
   Fig. 29. Section Winder.

The "pies" are wound in a bobbin or form such as is 
shown in Fig. 29. 

The disks or flanges are made of sheet brass and mounted 
on an arbor so that the form may be placed in a lathe or 
some other contrivance for revolving it. The core is beveled 
in order to facilitate the removal of a completed "pie" from 
the winder. The flanges of the winder are clamped against 
the core by two nuts placed on either side. The "pie" is 
removed by unscrewing one of the nuts and removing one 
of the flanges. 

In winding silk covered wire it is first passed through a 
mixture of beeswax and rosin or a bath of melted paraffin. 
The excess of wax is removed by passing the wire through a 
slit made in a pad of paper or by rubbing against a piece of 
felt. Fig. 30 shows such a contrivance. 

.. figure:: images/Image30.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 30. Impregnator for Silk Covered Wire. 
   
   Fig. 30. Impregnator for Silk Covered Wire. 

The wire passes from the reel over an ordinary spool 
down into the pan of paraffin, out of the paraffin, over 
another spool, and rubs against a piece of felt to remove the 
surplus paraffin. The spools are mounted with a screw and 
a washer so that they will turn without friction. 

The wire is guided, when winding, by the fingers. If it is 
wrapped with a piece of felt and held between the thumb 
and forefinger it will run without friction and not cut the 
fingers. It is necessary that the wire should be closely 
watched for kinks, etc. which would cause the wire to 
break. Oftentimes the wire is broken but is held together 
by the insulation. Therefore each "pie" should be tested 
for continuity when completed. This is best accomplished 
by means of a galvanometer and battery. All imperfect 
"pies" should be rejected, as one of them would cause serious 
trouble if embodied in the coil. In soldering the secondary 
wires, acid *must not be used* as it soon corrodes the fine wires. 
Rosin is the best flux for this purpose. When building a 
small coil with a "layer" winding it is absolutely necessary 
that the wire should be wound on in smooth even layers. In 
a built-up secondary having "pies" not greater than 1/4 inch 
in thickness such great care is not necessary. 

.. figure:: images/Image31.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 31. Methods of Connecting the Secondary Sections. 
   
   Fig. 31. Methods of Connecting the Secondary Sections. 

Fig. 31 shows the methods of connecting up the pies or 
pancakes. In *A*, the inside of one section is connected to 
the outside of the next, and so on. The maximum voltage 
which can exist between the adjacent sections in this case 
is equal to the e.m.f. generated by one "pie" and is equal 
throughout. In *B*, the coils are connected alternately inside 
and out. The voltage ranges from zero at the points where 
they are connected, to a value equal to twice the e.m.f. 
developed by one section. It would seem that there would 
be a saving in insulation space of one-half in the first case, 
but it is not so since the connecting wire passes between the 
"pies" and therefore the insulation must be twice as thick 
or exactly equal to that in the second case. The latter 
method (Fig. 31 B) is the best and most convenient. When 
the "pies" are connected in this manner the current must 
flow through alternate sections in opposite directions. To 
accomplish this it is not necessary to wind every alternate 
coil in an opposite direction, but merely to turn them around 
and connect them with the direction of their windings 
reversed as shown by the arrows and the bevels in Fig. 31. 
The connections between the sections must be very 
carefully soldered. 

After the secondary is assembled the coil should be 
placed in a tight receptacle or tank containing melted 
paraffin. The tank is then connected to an air pump or 
aspirator and the air exhausted. The diminution of 
pressure causes any air bubbles in the windings to expand and 
be pumped out. After standing a while, the pressure of 
the atmosphere is readmitted and the place of the bubbles 
will be occupied by paraffin which has been forced in under 
pressure. 

.. figure:: images/Table5.jpg
   :align: center
   :scale: 85 %
   :alt: SECONDARY DIMENSIONS TABLE.

**Mounting.**—A coil for wireless work is best mounted 
as shown in Fig. 32 and used with an independent 
interrupter. The coil may then be placed under the operating 
table or on the wall, out of harm's way, and the 
interrupter on the table, where it is handy to the adjustment of 
the operator. 

.. figure:: images/Image32.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 32. Coil Case. 
   
   Fig. 32. Coil Case. 

The case is simply a rectangular hardwood box large 
enough to contain the completed coil. Two binding posts 
mounted on the side of the box connect with the primary 
winding and two on the top of the box lead to the secondary 
terminals. The box is filled with boiled oil or melted 
paraffin and sealed up by screwing on the lid. If desirable, the 
secondary binding posts may be mounted on the top of a 
short piece of hard rubber rod as illustrated in the drawing. 

.. [#] Magnetic permeability is the conducting power for lines of magnetic force. 

.. [#] See *hysteresis* under Magnetic Detector. 

CHAPTER V. INTERRUPTERS. 
------------------------

We now come to what is the greatest source of trouble 
and annoyance in an induction coil, namely the interrupter. 
Too much importance cannot be attached to this 
instrument, for upon it depends largely the satisfactory working 
of the coil. The operation of an induction coil and the 
part played by the interrupter were fully explained in the 
chapter on induction coils. 

An adjustable interrupter is necessary for large coils, that 
is, one not only whose speed may be governed, but also the 
time and duration of the break. 

.. figure:: images/Image33.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 33. Simple Interrupter.  
   
   Fig. 33. Simple Interrupter. 

The rapidity of oscillation of a 
mechanical interrupter is a 
very different thing from the 
speed of break. The ideal 
speed of break is instantaneous. 
In wireless telegraphy, very 
faint signals are heard more distinctly in telephone 
receivers if the rate of interruption at the station sending 
them is high. The human ear is somewhat more sensitive 
to sounds higher than those ordinarily produced in the 
telephone receivers of a wireless receptor. This seems to 
argue the use of a high-speed interrupter to make and break 
the current. But the effect on the coil must also be 
considered. 

In the first place, where a condenser is shunted across 
the terminals of the secondary as is the case with a wireless 
transmitter, a high-speed interrupter would be very likely 
to set up harmful oscillations in the secondary of the coil 
itself. 

Second, if too fast, the rise and fall of the secondary 
currents will be caused to run into each other, since the break 
will occur before the primary current has reached a 
maximum and the reverse secondary current has died away. 

Third, the diameter of the core of a wireless coil is 
generally much larger than that of the ordinary coil, and if a very 
rapid interrupter is employed there is not time enough to 
properly magnetize the core before the current is broken. 

Fourth, the strength of the losses in the core caused by 
the eddy currents and hysteresis are proportional to the 
interruptions in the primary circuit and therefore a low 
speed will be the most efficient. A rapid interrupter 
requires a higher voltage and amperage than the same 
interrupter run at a lower speed. 

These are some of the reasons why it is very desirable to 
use an atomic interrupter or one so adjustable that the rate 
of the time and duration of the "make" and "break" may 
be closely regulated. An ideal interrupter is designed to 
give the longest time possible after contact is established 
and before the "break" occurs. 

It does not pay to construct an interrupter for an 
induction coil giving sparks up to 2 inches in length. The type 
of interrupter in use on automobile coils is perfectly well 
adapted to small coils, and may be purchased complete with 
the platinum points for as low a price as $1.50. 

The mechanical break described below is designed so 
that various adjustments are possible and it may be adapted 
to almost any coil. Since it is independent, it need not 
be mounted directly on the coil, but may be placed in the 
position most convenient to the operator for adjustment. 
The interrupter will not operate coils well on an 
electromotive force above 30 volts, for the excessive voltage causes 
a spark at the contacts when the circuit is broken and 
prolongs the decadence of the primary current. 

.. figure:: images/Image34.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 34. Independent Interrupter. 
   
   Fig. 34. Independent Interrupter. 

**Independent Atomic Interrupter.**—Fig. 34 illustrates 
two views of the interrupter. Current is furnished to the 
electromagnets by a six volt battery independent of the 
source supplying the coil. The interrupter is set in 
operation by closing the circuit breaker on the aerial switch. 
When the primary circuit of the transmitter is then 
completed by pressing the key, the coil will respond immediately 
because the interrupter is already in vibration. 

The electromagnets (Fig. 35) are a pair of four ohm 
telegraph sounder magnets. A hole is bored in the center of 
the top of each magnet core and threaded with an 8-32 tap 
so that the pole pieces may be fastened thereto, The shape 
and dimensions of these projections, which must be made 
of soft iron, are illustrated in Fig. 35. 

.. figure:: images/Image35.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 35. Details of Magnets. 
   
   Fig. 35. Details of Magnets. 

A soft iron yoke *Y*, 2 1/2 x 7/8 x 1/4 inches, connects the 
bottom of the magnets and supports them in an upright 
position. An 8-32 machine screw passing upward through 
the base and yoke holds them firmly. The base is 
preferably of hard rubber 4 x 3 1/4 x 3/4 inches. 

.. figure:: images/Image36.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 36. Details of Moving Parts. 
   
   Fig. 36. Details of Moving Parts.

The moving parts are illustrated in Fig. 36. The main 
spring, *D*, is a strip of spring steel, 2 1/8 inches long, 1/2 inch 
wide, and 1/32 inch thick. The soft iron armature, *A*, is 
fastened to the spring by means of two small 4-36 machine 
screws. *M* is a piece of brass rod, 1 1/2 inches long, bent in 
the form of a hook and threaded with a 4-36 die to screw 
in a similarly threaded hole in the back of the armature *A*. 
The hooked portion of *M* is fitted with a small piece of hard 
rubber rod, *R*, to insulate it where it comes into contact 
with the spring, *G*. The spring, *D*, carries a second hook, 
*E*, riveted to the center of the spring 1 5/8 inches from the 
lower end. The hook, which is about 3/8 inch long, passes 
through a hole in the top of the spring, *F*, and engages it so 
that it is set in operation by the vibratory motion of the 
spring, *D*. The spring, *F*, is 1 3/4 inches long, 5/16 inch wide, 
and ir 1/64 inch thick. It carries a platinum rivet 3/4 inch from 
its lower end. The spring, *G*, is 2 1/2 inches long, 5/16 inch wide 
and 1/64 inch thick. A heavy platinum rivet is fastened 
2 1/4 inches from the lower end. An elongated hole, 1/4 inch 
long and 3/16 inch wide, permits the hook, *M*, to pass through 
the opening. A 5/32 inch hole, 1 1/4 inches from the bottom, 
allows the adjusting screw to pass through and make 
contact with the platinum rivet on the spring, *F*. 

Two rectangular pieces of brass, *O*, 1 1/4 x 1/2 x 5/16 inches 
are fastened to the base to support the springs. 

.. figure:: images/Image37.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 37. Details of Standard and Screws. 
   
   Fig. 37. Details of Standard and Screws. 

The standard, *U*, supporting the adjusting thumbscrews 
is a piece of 3/8-inch brass, 2 1/2 inches high. It tapers from 
1 1/2 inches at the bottom to 3/4 inch at the top. A hole 2 1/4
inches from the bottom is threaded with a 10-32 tap to 
receive the thumbscrew, *B*. A second hole 1 1/4 inches from 
the base is threaded with an 8-32 tap to fit the adjusting 
screw, *S*. 

Both of the adjusting thumbscrews carry heavy platinum 
points. The standard is held upright to the base by means 
of two machine screws passing through the base. 

A 3/32 inch brass rod 1 3/4 inches long is threaded to fit a hole 
in the top of the armature. A sliding weight, *W*, may be 
clamped in any position on the rod by means of a 
thumb-screw. Raising or lowering the position of the weight 
decreases or increases the natural period of vibration of 
the interrupter. Screwing the hook, *M*, in or out so as to 
shorten or lengthen it, decreases or increases the ratio of 
the make to the break. 

.. figure:: images/Image38.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 38. Diagram of Connections for an Independent Interrupter. 
   
   Fig. 38. Diagram of Connections for an Independent Interrupter. 

Fig. 38 shows a diagram of the connections of the 
interrupter. The standard, the thumbscrew, *B*, and the spring, 
*G*, form part of the primary circuit of the induction coil. 
The standard, the thumbscrew, *S*, the spring, *F*, and the 
electromagnets are placed in series with a six-volt battery 
and connected to the circuit breaker on the aerial switch, 
so that when the switch is thrown in position for 
transmitting, the interrupter will be set in operation. 

A condenser must be shunted across the larger contacts 
of the interrupter in order to hasten the demagnetization 
of the core of the induction coil and create a higher e.m.f. 
in the secondary. The condenser must be suited in size 
to the induction coil with which the interrupter is to be used 
and so the following table is appended to serve as a guide. 

.. figure:: images/Table6.jpg
   :align: center
   :scale: 85 %
   :alt: CONDENSERS TABLE.

The condensers are built up of alternate sheets of tin foil 
and paraffined paper. Connections are made to the sheets 
by means of tin foil strips which project out alternately 
from opposite sides as in the illustration. 

The paper should be about two inches larger each way 
so as to leave a one inch margin on all sides of the tin foil. 

.. figure:: images/Image39.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 39. Construction of a Paper Condenser. 
   
   Fig. 39. Construction of a Paper Condenser. 

When the alternate sheets of 
tin foil and paper have all been 
assembled, the condenser is 
warmed so as to soften the 
paraffin. It is then placed 
between two flat boards and subjected to great pressure 
in a letter press or a vice. The capacity of a pressed 
condenser is often several times that of a condenser of the 
same dimensions but not pressed. 

**Mercury Interrupters.**—The mercury turbine interrupter is 
one of the most convenient and successful breaks 
in use. The construction is such that a stream of mercury 
is made to play against a number of saw shaped metal teeth. 
A spiral worm terminating in a nozzle at the top is rapidly 
revolved by an electric motor. The lower end of the 
tubular worm dips in a mercury reservoir, so that when the 
spiral is revolved the mercury is caused by centrifugal 
action to rise in the tube and be thrown out in the form of 
a jet at the upper end. When the revolving jet strikes 
one of the metal teeth, the circuit is closed and the current 
flows from the mercury jet into the teeth. When the 
mercury jet passes between the openings between the teeth, 
the circuit is interrupted. By raising and lowering the saw 
teeth so that the mercury strikes either the lower or upper 
part of them, the ratio between the make and break may be 
made smaller or larger. By regulating the speed of the 
motor driving the jet, the number of interruptions may be 
varied from 10 to 10,000 per second. The bottom and 
sides of the mercury reservoir are ribbed to prevent the 
mercury from attaining a rotary motion. 

A somewhat simpler and more easily constructed type 
of mercury interrupter consists of a hard rubber disk 
having a brass rod running through from the periphery to 
the center, where it connects with the shaft. The lower 
edge of the disk dips at an angle in a mercury bath and 
is rapidly revolved by an electric motor. When the rod 
is under the surface of the mercury, the circuit is made 
through the mercury to the rod. The circuit is broken 
when the rod is above the surface. The mercury is covered 
with a layer of alcohol, which prevents excessive sparking 
and makes a quicker break. An interrupter of this kind 
when run by a motor of the magnetic attraction type is 
exceedingly simple. 

The break of any of the mercury type interrupters when 
properly adjusted is much quicker than the hammer spring 
break and gives thicker sparks. 

After the mercury has been in use awhile it becomes 
churned up into small globules of a black color, but may be 
easily cleaned and restored for use by shaking up with some 
strong sulphuric acid. Care must be taken that the 
mercury is perfectly dry and free from acid before replacing 
in the interrupter. 

**Electrolytic Interrupters.**—Fig. 40 shows a diagram 
of a Wehnelt interrupter. The cathode or negative 
electrode is a lead plate immersed in dilute sulphuric acid. The 
anode is a piece of platinum wire placed in a porcelain 
tube and projecting through a small hole in the bottom, so 
that only a very small surface of the wire is exposed to the 
liquid. When a strong electrical current is passed through 
the acid electrolyte, the current is very rapidly interrupted 
by the formation of gases on the small platinum electrode. 
The speed of the interrupter is variable through great 
ranges by moving the platinum electrode up or down and 
changing the amount of surface 
exposed to the liquid. The only 
disadvantage of this interrupter is 
that the electrolyte soon becomes 
heated, and unless the interrupter 
is provided with a water jacket or 
some device for cooling, the bubbles of gas do not form 
freely. A potential of at least 40 volts is required to 
operate a Wehnelt or other electrolytic break. 

.. figure:: images/Image40.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 40. Wenhelt and Simon Electrolytic Interrupters.
   
   Fig. 40. Wenhelt and Simon Electrolytic Interrupters.

A Wehnelt interrupter may easily be made by sealing a 
platinum wire in a glass tube. It is well to make several 
such tubes with the platinum projecting from one-sixteenth 
to one-quarter of an inch. The different tubes will each 
have a different speed of interruption, and one should be 
picked out which seems to be most suitable for the coil 
upon testing. Connection to the platinum wire is 
established by filling the tube with mercury and dipping a wire 
in it. 

Fig. 40 also shows a diagram of a Simon electrolytic 
interrupter. It consists of a vessel containing dilute 
sulphuric acid and divided into two parts by a thin 
porcelain diaphragm having a small hole in the center. A lead 
electrode dips into each of the divisions. The 
interruption is caused by exceeding a certain current density 
in the small hole at the diaphragm. Upon the passage 
of the current the liquid is so heated that it becomes 
vaporized. The vapor is a poor conductor to low voltages and 
so the current is broken. Immediately upon the cessation 
of the current, the vapor condenses and the circuit is 
established again. This cycle repeats itself with a speed 
depending upon the size of the aperture and the amount of 
current flowing. 

A crude form of this type of interrupter may be made 
by heating the end of a test tube in a pin flame, and then 
blowing on the open end of the tube so as to burst the soft 
glass and form a small hole. Several such test tubes should 
be prepared having holes varying from 1/32 to 1/8 of an inch in 
diameter. The one which gives the best results upon trial 
is selected for use. A number of holes in a single tube, if 
not too many or too large in diameter, increases the 
efficiency and the speed of interruption. The tube should 
be immersed in a glass jar containing dilute sulphuric acid. 
One lead electrode is placed inside of the test tube and the 
other outside. It makes no difference which way the 
current flows through this interrupter. 

The Caldwell interrupter is a modification of the Simon 
type in which the size of the aperture is made adjustable 
by means of a pointed glass rod which may be raised or 
lowered in the hole and the speed of interruption varied. 
An interrupter of the test tube type as described above 
may be modified to this form by locating the hole directly 
in the center of the bottom of the tube and inserting 
in it a hard glass rod which has been drawn out to a 
point. 

Electrolytic interrupters do not require any condenser 
connected across the break. 

.. figure:: images/Image41.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 41. Construction of Electrolytic Interrupters. 
   
   Fig. 41. Construction of Electrolytic Interrupters. 

Fig. 41 shows in section more substantial forms of both 
the Wehnelt and Simon-Caldwell interrupters. The 
containers are ordinary 5 x 7 inch battery jars. They are 
fitted with covers made of two thicknesses, *C* and *B*, of 
3/4-inch wood. The upper piece, *C*, is 6 inches in diameter, 
while the under one should fit snugly into the interior of 
the jar. The wood must be boiled in paraffin to protect 
it from the action of the acid. A slit is made in the 
left-hand side of both covers for the passage of a lead 
electrode, *L*, 1 inch wide and 1/4 inch thick. The upper end 
of the electrode is bent over and fitted with a binding 
post. 

.. figure:: images/Image42.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 42. Details of Electrolytic Interrupters. 
   
   Fig. 42. Details of Electrolytic Interrupters. 

The mechanism for adjusting the interrupters is the same 
in both cases. The dimensions are indicated in Fig. 42. 
A brass yoke, *Y*, is mounted on the cover in the position 
shown. A 1/2-inch hole is bored through the upper part of 
the yoke and a piece of brass tubing, *S*, 1 inch long soldered 
in a vertical position in the hole. A 1/4-inch threaded brass 
rod passes through the tube, 5. A groove is milled in A 
along its entire length and engages a pin in the wall of *S*. 
The rod is thus enabled to slide up and down in the tube 
but is prevented from revolving. A fiber head, *H*, is fitted 
with a brass sleeve or bushing in its center. The bushing 
should fit tightly into the fiber head and is threaded to fit 
the rod, *A*. The electrode may then be carefully raised or 
lowered by revolving the head. The tube, *V*, for the 
Simon-Caldwell interrupter is a hard glass test tube. A 1/8-inch 
hole is blown in the bottom of the tube. A hard glass rod, 
*G*, is drawn out to a point and fastened to the lower end of 
the rod, *A*, by means of a short length of flexible rubber 
tubing, *R*. 

The tube, N, for the Wehnelt break is made from a piece 
of hard rubber tubing 6 inches long, having a bore of J inch. 

.. figure:: images/Image43.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 43. Electrolytic Interrupter. 
   
   Fig. 43. Electrolytic Interrupter. 

The lower end is fitted with a 
spark plug porcelain. The 
porcelain must fit the tube tightly and 
not leak. The electrode, *P*, is a 
piece of brass wire which will just 
pass through the hole in the 
porcelain. The upper end of the 
electrode, *P*, is soldered or fastened 
otherwise to the lower end of the 
rod, *A*. 

A small hole, *h*, should be made 
in the tubes, *N* and *V*, above the 
level of the electrolyte in the jar. 
When the interrupter is in 
operation the electrolyte gradually rises 
in the tubes, and would corrode the 
lower end of *A* if it were not able to 
pass out through the vents. 

In the Simon-Caldwell 
interrupter, a strip of lead passes 
from the binding post mounted on the foot of the yoke 
down inside of the test tube. The size of the hole in the 
tube is regulated by revolving the fiber head so that 
the glass pointed rod will be inserted in or withdrawn from 
the hole. 

The frequency of the interruption will also depend 
somewhat on the concentration of the acid solution. It is 
therefore best to start with a weak solution and add acid slowly 
until it is of the proper strength. 

CHAPTER VI. TRANSFORMERS. 
-------------------------

Where alternating current is available in commercial 
wireless telegraph stations, the induction coil has been 
gradually superseded by the more modern transformer for 
charging the oscillation condenser. Since the transformer 
is less expensive to construct than an induction coil capable 
of transmitting the same distance, it is favored by many 
amateur experimenters. A one quarter kilowatt 
transformer has a sending range of over 50 miles when used with 
a properly constructed aerial about 80 feet high. This is 
probably the size best suited to the average private 
installation. 

The secondary of a wireless transformer seldom develops 
potentials exceeding 15,000 to 20,000 volts, while those of an 
induction coil range from 1 5,000 to 300,000 volts. However, 
the strength of the secondary current of a transformer is so 
much greater than that of an induction coil, that more 
powerful and penetrating waves are developed. For these 
reasons a transformer is always rated by its output in watts 
or kilowatts rather than by the spark length produced at 
the secondary terminals. The spark of a one quarter 
kilowatt transformer is only 0.25 to 0.50 of an inch, while the 
spark of a one half kilowatt transformer may be the same 
length but still represent more energy. 

There are two distinct types of transformers in use, known 
as the "open" and "closed," accordingly whether the core 
is straight like the core of an induction coil or in the form 
of a hollow rectangle. The open core type is used in the 
government stations and by the United Wireless Telegraph 
Co. It is the simpler and more easily constructed of the 
two, but is also less efficient and requires that more material 
be expended to bring it up to a definite rating. In principle 
it is simply an induction coil operated on alternating 
current minus the interrupter and condenser. In view of 
the greater currents employed, the windings must be larger 
and heavier than those of the induction coil to prevent 
heating. 

Before commencing the construction of a transformer one 
should read the chapter on induction coils and use the same 
care emphasized there in regard to building coils. 

**Open Core Transformer.**—The transformer described 
below will transmit from 20 to 75 miles and consume about 
300 watts on the no volt 60 cycle alternating current. 

The core is 16 inches long and 2 inches in diameter. It 
is built up of soft iron wires in the same manner as if it 
were the core of an induction coil. 

The primary is composed of two layers of No. 14 double 
cotton covered B. S. gauge magnet wire. The primary is 
14 inches long and is wrapped with a layer of micanite cloth 
3/8 inch thick to separate it from the secondary winding. 

It is never advisable to use shellacked cotton cloth as 
insulation. When cotton is dried and shellacked, it is at 
first a good insulator, but soon becomes capable of 
absorbing moisture. Shellac carbonizes at a low temperature, and 
if a transformer or coil having any of this sort of insulation 
entering into its construction is overheated, the insulation 
is liable to become a conductor. Micanite cloth is the 
best insulation for transformers. The dielectric strengths 
of the different forms of micanite are shown by the 
following table. 

.. figure:: images/Table7.jpg
   :align: center
   :scale: 85 %
   :alt: VOLTS PER MILLIMETER TABLE 

The secondary is wound in ten sections over the micanite 
insulation. Each section is 6 inches in diameter and 1 1/4
inches thick and is wound with No. 30 B. S. single silk 
covered wire. The sections are separated by disks of 
blotting paper 1/8 inch thick and 7 inches in diameter, treated as 
described in Chapter IV. The completed transformer 
should be placed in a box and covered with oil. 

**A One Quarter Kilowatt Closed Core Transformer.**
The simplest form of a closed core transformer consists of 
two independent coils of insulated wire wound upon an iron 
ring. When an alternating current is passed through one 
of the coils, known as the primary, it generates a magnetic 
flux in the iron core. The lines of force passing through 
the core induce in the secondary coil an electromotive force 
the magnitude of which is in nearly the same ratio to the 
primary inducing electromotive force as the number of turns 
of wire in the secondary is to the number of turns in the 
primary. For example, if it is desired to raise the potential 
of the no volt alternating current to 22,000 volts, the 
number of turns in the secondary of the transformer must be at 
least 200 times the number in the primary. 

A circular ring of iron wire presents several theoretical 
advantages as a transformer core but it would be difficult to 
form and afterwards place the windings in position. The 
core is therefore usually in the form of a hollow rectangle, 
built up of very thin sheets or laminations of soft iron 
carefully insulated from one another by a coat of varnish. If 
the core were solid or the separate laminations not 
insulated from one another, heavy currents, known as eddy 
currents, would be set up in the iron and cause heating. A 
considerable loss in the efficiency of the transformer would 
also result. 

One half of both the secondary and the primary windings 
of a properly designed transformer are placed on opposite 
sides or "legs" of the core in order to reduce the magnetic 
leakage and increase the efficiency. The only difficulty 
involved in such construction is the proper insulation of 
the primary from the secondary, but if careful attention is 
given to this point no difficulty will be experienced. 

**Core.**—The dimensions and method of assembling the 
core laminations are indicated by Fig. 44. Long strips are 
cut from soft Russian or Swedish stovepipe iron. The strips, 
which are 1 3/4 inches wide are then cut up into short lengths, 
one half of which are 7 3/4 inches long and the other half 4 3/4 
inches. Enough are cut to form two piles of each size 1 3/4 
inches high when compressed. The completed core will then 
form a hollow rectangle 9 1/2 x 6 1/2 x 1 3/4 inches. 

.. figure:: images/Image44.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 44. Assembly and Dimensions of Core. 
   
   Fig. 44. Assembly and Dimensions of Core. 

The strips must be dipped in some good insulating 
varnish such as P. & B. compound and thoroughly dried before 
they are assembled. Both "legs" (the longest sides) are laid 
on a table with the alternate ends overlapping as shown by 
*A* and *B* in Fig. 44. After the short pieces *C* and *D* have 
been slipped between the overlapping ends the whole core is 
squared up. The strips *D* are then carefully removed and 
one end of the core thus left open until all the windings are 
in place. Three or four layers of well varnished linen cloth 
are wound tightly over the "legs" preparatory to winding 
on the primary. 

**Primary.**—Four fiber heads, *H*, 4 3/4 inches square, 1/2 inch 
thick and having a square hole 1 7/8 x 1 7/8 inches cut in the 
center are required. One of the fiber heads is placed on each 
end of the assembled "leg" as shown in Fig. 48. 

.. figure:: images/Image45.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 45. Fiber Head and Separator. 
   
   Fig. 45. Fiber Head and Separator. 

The primary winding is wound in six layers, 4 1/2 inches 
long, three layers on each "leg." About three pounds of 
No. 16 B. S. gauge double cotton covered magnet wire are 
required for the winding. The terminals of the two halves 
of the primary are led through the fiber heads at the same 
end of the transformer. The windings are not to be carried 
close up to the fiber heads but begin and end about 1/4 inch 
from them, so that the remaining space may be filled by 
winding in a strip of micanite cloth 1/4 inch wide. The 
primary and secondary windings are separated by a strip of 
micanite cloth 5 inches wide, wound over both of the 
primary windings close up to the heads until a layer 1/2 inch 
thick is formed. 

**Secondary.**—The form on which the secondary sections 
are wound is illustrated in Fig. 46. All the parts are cut 
out of wood except the shaft and are made of the 
dimensions indicated. If the center of the form is slightly tapered 
it will greatly facilitate the removal of the completed 
sections. Sixteen sections are required. When removed 
from the winder they will be in the form of hollow squares 
4 1/2 x 4 1/2 x 7/16 inches. 

.. figure:: images/Image46.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 46. Section Form. 
   
   Fig. 46. Section Form. 

About ten pounds of No. 34 B. S. gauge silk covered 
wire are required to wind the sections. Cotton covered wire 
must not be used to avoid expense, because with it a 
sufficient number of secondary turns cannot be secured to bring 
the secondary current up to the proper voltage. By 
observing explicitly the instructions and precautions given below 
no trouble will be experienced in handling enameled wire 
and forming the sections. The form should be placed in a 
lathe chuck or some other machine which is convenient and 
whereby the form may be rapidly revolved under the 
control of the operator. 

Saw slots are cut in the wooden flanges and the center of 
the form as shown in the illustration so that silk threads 
may be passed under and around the completed section and 
tied so that a possible "cave in" of the wire is prevented. 
After tying up the section should be removed from the form 
by unscrewing the nut and taking off the flange. 

.. figure:: images/Image47.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 47. Methods of Connecting Sections. 
   
   Fig. 47. Methods of Connecting Sections. 

When winding the wire it must be very carefully watched 
for loops or kinks and only be laid on in even layers. It 
must also be borne in mind that enameled wire cannot be as 
tightly wound as fiber covered wire for reasons heretofore 
explained. In case the wire becomes broken, it must be 
smoothly spliced and soldered. Do not under any 
consideration use acid as a flux or heat the wire with a flame. Acid 
will corrode the fine wire, and the flame will badly oxidize 
or melt it. Use a short piece of No. 8 B. S. gauge tinned 
copper wire set in a small file handle as a soldering iron, 
and rosin as a flux. Paraffin some silk binding tape such 
as dressmakers use and wrap the joint with a small piece. 
The sections as they are removed from the winder must 
be taped and then carefully marked with an arrow which 
points in the direction of the winding. 

Fig. 47 illustrates the two methods of connecting up the 
sections. It will be noticed in the second method that the 
arrow denoting the direction of winding points down on 
every alternate section. This does not indicate necessarily 
that every alternate section is wound in an opposite 
direction from the other, but that they have merely been turned 
around so that the arrows come on a reverse side of the core 
and point in an opposite direction. This precaution must 
be taken in order that the current will flow through all the 
sections, and is made necessary because the inside terminal 
of one section is connected to the inside terminal of the 
adjacent section and the outside terminal of that section is 
connected to the outside terminal of the next adjacent section. 
The first method, *A*, illustrated in Fig. 44, is less 
complicated and does not require this reversal, but for various 
reasons is not to be recommended in place of *B*. 

Eight of the completed and taped sections are placed on 
each "leg" of the transformer, with one of the fiber 
separators between each pair as in Figs. 48 and 49. When each 
"leg" has been completely assembled, solder all the 
secondary terminals together so as to connect as in Fig. 47. 

.. figure:: images/Image48.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 48. Assembly of Leg. 
   
   Fig. 48. Assembly of Leg. 

Then place the remaining fiber head, *S*, on each of the 
"legs" and finish assembling the core by slipping in the end 
strips *D*. 

Square the core up perfectly true and fasten by four fiber 
strips *M*, Fig. 49, 9 3/4 inches long, 1 3/4 inches wide and 1/2-inch 
thick. The strips are placed in the position shown in Fig. 
46 and a hole *P* bored in the end of each. Four 1/4-inch 
bolts, two of which are 3 inches long and two 3 1/2 inches, pass
through the holes in the strips, so that when the nuts are 
screwed on the core is clamped firmly. The two longer 
bolts are placed at the same end of the transformer. 

.. figure:: images/Image49.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 49. Transformer with One Secondary removed. 
   
   Fig. 49. Transformer with One Secondary removed. 

The terminals of the primary lead out to four binding 
posts mounted on the fiber strips. The pillars which 
support the secondary binding posts are fiber rods, 1 inch in 
diameter and 2 inches long. The lower end of each is bored 
and tapped to fit the upper ends of the longer bolts which 
clamp the fiber strips together. An insulating shield must 
be placed between the two secondary windings to prevent 
sparks from jumping across. A piece of fiber 5 x 5 x 1/8 
inches will serve nicely for this purpose. If the primary 
windings are placed in series the transformer will consume 
about 300 watts. When the transformer is placed in a box 
and the box filled with some boiled amber petroleum, the 
windings may be connected in parallel and the transformer 
will consume about 500 watts. It will then transmit over 
100 miles providing the aerial is at least 100 feet high. 

The wiring connections are diagramed in Fig. 50. 
A variable inductance or reactance coil is connected in 
series with the primary circuit to steady the current, as 
explained in the paragraph under reactance. A reactance 
suitable for this transformer may be constructed by winding 
two layers of No. 12 B. S. gauge cotton covered wire, six 
inches long, around a hollow wooden tube made of cigar box 
wood. The core is built up of soft sheet iron to form a 
rectangle 8 x 1 3/4 x 1 3/4 inches which will just slide in and out 
of the tube. The windings should be about six inches long. 

.. figure:: images/Image50.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 50. Wiring Diagram. 
   
   Fig. 50. Wiring Diagram. 

Five half-gallon Leyden jars form about the right capacity 
for the secondary of the transformer when the windings are 
in series. Twice that number must be used when the 
windings are in parallel. 

The secondary sections must always be kept in series, as 
otherwise the voltage would not be high enough to properly 
charge the condenser. 

Construction of a 2-K.W. Transformer.
````````````````````````````````````` 

**Core.**—Strips 2 1/2 inches wide are cut from soft sheet 
iron. One half of them should be 11 1/2 inches long and the
other half 6 1/2 inches. Enough are cut to make two piles of 
each size 2 1/2 inches high. Both sides (the longest strips) of 
the core are built up with the ends overlapping as in Fig. 41. 

The ends (the short pieces) are then slipped between the 
overlapping ends of the long strips and the whole core 
squared up. The completed core should have a cross 
section of 2 1/2 inches square and form a hollow rectangle 8 x 14 
inches. The strips of iron must be dipped in P. & B. 
insulating varnish and dried before they are assembled. 

**Primary.**—Four fiber heads 6 inches square, 1/2 inch 
thick and having a hole 2 1/2 inches square are made. One of 
these is placed on the core legs as shown by Fig. 48. Two 
or three layers of well varnished linen are wound over the 
core preparatory to winding the primary. Room must be 
left for the other head to be placed on the opposite end after 
the windings are all in place. The primary consists of 100 
double turns of No. 12 B. S. gauge double cotton covered 
magnet wire. Fifty of the double turns are wound on each 
leg. The four terminals of the primary are led out through 
the fiber heads. Care should be taken to distinguish them 
from each other so that they may be identified when the 
transformer is completed. The primary is then wound with 
a strip of micanite or empire cloth 8 inches wide until it 
measures 4 inches square over all. 

**Secondary.**—The secondary coils, which are eight in 
number, are wound on a form 4 inches square and 1 1/2 inches 
between the flanges. The construction of the form is similar 
to that shown in Fig. 46 but is larger. The slots are also 
necessary here so that the completed section may be tied up. 

About ten pounds of No. 30 B. S. gauge single silk covered 
wire are required to wind the secondary. The sections are 
wound in smooth even layers until they are six inches in 
outside diameter. They are then tied up and removed from 
the winder. The sections are separated by sheets of fiber 
6 1/2 inches square on the outside, 1/2 inch thick, having a hole 
4 inches square cut in the center. The sections are all 
connected in series and the terminals soldered to strips of 
copper. 

After the secondary coils are all in place and connected, 
the fiber head is slipped on the end of the leg. Then the 
short lengths of the core, which had been pulled out again 
after squaring the core up, are slipped into place. The 
core is squared up again and fastened together by boring 
a 3/8-inch hole completely through the core at each corner. 
Two strips of fiber 12 x 2 1/2 x 1/2 inches are bored with 
corresponding holes in their ends. These strips are placed 
at the end of the transformer, on top of the core, and 1/4-inch 
bolts passed through the holes in the fiber and the core. 
The bolts are wrapped with micanite cloth where they pass 
through the core, and an insulating washer is placed under 
the nuts, so that the iron core laminations are not electrically 
connected. The nuts are tightened until the core is held 
firmly together. 

The fiber strips also serve as insulated supports for the 
binding posts. The copper terminals of the secondary lead 
to two binding posts mounted on two fiber or hard rubber 
pillars 1 inch diameter and 4 inches high. The rods are 
arranged as explained in the section under the heading of 
a 1/4-K.W. transformer. 

The transformer is designed for use on a 60-cycle 
110-volt current. It may be used on 220 volts if the two 
primary coils are connected in series. When the primaries 
are in series, and the transformer is used on the 110-volt 
current, it will deliver a voltage of about 12,000 at the 
secondary. With either primary alone the voltage will 
be about 12,000, and with both in parallel about 25,000. 
It will then deliver a very heavy current at the secondary 
and draw from the line about 20 amperes in the primary. 
If used with a proper tuning helix, condenser and aerial, the 
transformer is capable of sending about 300 miles under 
favorable conditions. 

If the transformer is to be used for long periods at a time, 
it is best to place it in a tight wooden box 18 inches square 
and 12 inches deep. The box is then filled with boiled 
linseed oil or amber petroleum. 

A rheostat or impedance and reactance coil should be 
placed in series with the transformer to regulate the current 
and also to prevent arcing across the spark gap. 

**Reactance.**—In Chapter I, the lag and lead of a circuit 
were explained in connection with tuning. This is a 
property of every alternating circuit and is brought to our 
notice again in the transformer which charges the condenser. 
The current developed by a transformer is a leading current, 
since the instantaneous values of the current do not 
correspond to the proportionate values of the voltage supplying 
the current. In order to force the current values of the 
charging current to correspond with the voltage it is 
necessary to produce a "lag." This is accomplished by means 
of an adjustable reactance in series with the primary of the 
transformer. 

A reactance or inductance suitable for the 2-K.W. 
transformer may be made by building up a coil in the same 
manner as described under the heading of the J-K.W. 
transformer. The reactance will have to be somewhat 
larger on account of the heavier currents. The core is 
built up of sheet iron to measure 2 1/2 x 2 1/2 x 10 inches when 
completed. The coil is wound around a wooden form and 
is composed of about 100 turns of No. 8 B. S. gauge double 
cotton covered magnet wire. By varying the amount of 
core inserted in the hollow coil the energy may be adjusted 
as desired. 

.. figure:: images/Image51.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 51. Clapp-Eastham 1/4-K.W. Transformer.
   
   Fig. 51. Clapp-Eastham 1/4-K.W. Transformer.

Fig. 51 illustrates the 1/4-K.W. transformer manufactured 
by the Clapp-Eastham Company. The core is so 
constructed that a small metal tongue of soft iron projects 
from one side of the core towards the opposite side between 
the windings, but is separated from the opposite side by a 
small air gap. Several objects are accomplished by this 
tongue, which gives rise to magnetic leakage; the 
inductance of the primary is increased thereby to such an 
extent that the transformer is self-controlling, so that it 
may be connected directly to the source of alternating 
current supply of ordinary commercial frequencies and 
potential, and the current flowing in this circuit be regulated by 
varying the number of turns in the primary coil. As this 
magnetic leakage gives rise to a loose coupling effect, the 
primary and secondary circuits may be brought into 
resonance by placing a suitable capacity across the secondary 
terminals. This condition of resonance brings the power 
factor to a materially higher percentage. While the power 
factor of the open or closed core transformer is seldom 
above 50%, this type of transformer has a power factor of 
80 to 90% when used with a suitable condenser. 

.. figure:: images/Image52.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 52. United Wireless Motor-Generator set for supplying Alternating Current to the Transformer. 
   
   Fig. 52. United Wireless Motor-Generator set for supplying Alternating Current to the Transformer. 

Another point of considerable advantage is the almost 
entire freedom from arcing at the spark gap when this type 
of transformer is used. The spark gap is connected directly 
across the secondary terminals of the transformer and the 
condenser. The primary turns of the helix and the spark 
gap are connected in series. When the transformer is in 
operation, this condenser being across the secondary, the 
transformer is in resonance and the condenser is charged 
to such a point that it will jump the spark gap. At the 
instant that the spark passes, the secondary of the 
transformer is practically short circuited through the spark gap. 
As this circuit is now closed and the condenser out of circuit, 
the secondary circuit of the transformer is no longer in 
resonance and the energy immediately drops off, destroying 
at once the tendency for an arc to form. As soon as the 
spark has passed, the condenser of course comes in to play and 
the condition of resonance being reestablished the same 
process is repeated. The Clapp-Eastham Company have made 
application for a patent on any transformer employing this 
or any similar construction for use in charging a condenser. 

CHAPTER VII. OSCILLATION CONDENSERS AND LEYDEN JARS. 
----------------------------------------------------

A condenser consists of two conducting surfaces 
separated by an insulator or dielectric. Fig. 53 shows a 
diagram of a simple condenser in which *A* and *B* are two 
tinfoil sheets separated by a sheet of glass, *C*. 

.. figure:: images/Image53.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 53. Simple Condenser.
   
   Fig. 53. Simple Condenser.

If *A* is connected by means of a wire to a static machine 
a positive charge will collect on the glass at *A* and induce 
a negative charge at *B*, so that if *A* and *B* are connected to a 
small spark gap the charge will leap the gap in the form of 
a spark. 

When a condenser discharges through a coil of wire, the 
discharge consists of a large number of exceedingly rapid 
oscillations or surgings. The first passage of current more 
than empties the condenser and it becomes charged in the 
opposite direction, that is, the conducting coatings change 
their polarity. A reverse discharge then occurs which also 
oversteps itself and the oscillations thus go on but become 
rapidly weaker until they die completely. The time 
consumed in the discharge may have been only a fraction of a 
second, but during that short period the current perhaps 
oscillated several thousand times. 

If a condenser is discharged through a conductor of high 
resistance the discharge passes out slowly, and dies away 
gradually in one direction without oscillating. One of the 
fundamental equations of wireless telegraphy is therefore 
that there will be oscillations in a circuit if the resistance in 
ohms is not greater than the square root of four times the 
inductance in henries divided by the capacity of the 
condenser in microfarads. 

The capacity or the ability of a condenser to store 
electricity depends upon the area and form of the conducting 
surfaces, the thickness of the dielectric between them, and 
a factor known as the specific inductive capacity of the 
dielectric. The unit of capacity is called the farad and is 
defined as the condenser which would be raised to a potential 
of one volt by a charge of one ampere flowing for one second. 
A condenser of such a capacity is, because of its enormous 
size, impractical to construct, and the unit ordinarily used 
is therefore the microfarad, or one millionth of a farad. 

Capacity may be calculated from the following formula: 

Capacity equals K(A/D),

where *K* equals a constant depending upon the specific 
inductive capacity of the dielectric, *A* the total area of 
tinfoil and *D* the thickness of the dielectric. 

.. figure:: images/Table8.jpg
   :align: center
   :scale: 85 %
   :alt: TABLE OF SPECIFIC INDUCTIVE CAPACITIES. 

**Leyden Jars.**—Transmitting condensers in a wireless 
telegraph station usually take the convenient form of a 
jar, coated inside and out with tinfoil and known as a 
Leyden jar. 

The jars should be of good Bohemian or Jena hard glass 
and coated with tinfoil only for about three-quarters of 
their height, as otherwise the discharge is liable to pass over 
the top. The tinfoil must be thick to avoid blistering, 
and is stuck to the glass with shellac varnish. The 
blistering of Leyden jars is a serious fault, for when this condition 
exists, the capacity is thereby altered to such an extent that 
the period of the closed circuit may be sufficiently altered 
to throw the system out of tune and decrease the radiation 
of energy. 

Considerable expense may be saved if the glass jars are 
purchased and coated by the amateur. The best jars are 
those imported from Germany, which have wide mouths 
so that they may be easily coated inside with tinfoil. 

.. figure:: images/Image54.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 54. Leyden Jar. 

   Fig. 54. Leyden Jar. 

The jars must be *thoroughly* cleaned and dried before they 
are coated. Give the inside a thorough brushing over with 
shellac varnish, and before it is dry, carefully insert the 
tinfoil and press it smoothly against the glass. The outside 
of the jar is treated and coated in the same manner. The 
inside and outside of the bottom are also coated by cutting 
the tinfoil in circular pieces and shellacking them on. 

.. figure:: images/Image55.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 55. "Aerial Switch."

   Fig. 55. "Aerial Switch."

The whole upper part of the jar is given one or two 
coats of shellac in order to prevent the collection of 
moisture and brush discharging. 
A wooden plug fitted in the top 
of the jar supports a brass rod, 
terminating at the lower end in 
a chain or spiral spring which 
connects with the inner coating. 
When trouble is experienced 
because of an imperfect contact 
between the coating and the chain or rod, a layer of brass 
filings an inch or two deep placed in the bottom of 
the jar will remedy the difficulty. The upper end of 
the rod usually terminates in a small brass ball or a 
binding post. 

The wooden plug or cover is dried in an oven to expel all 
moisture and then boiled in paraffin. 

Small Leyden jars may be very conveniently made from 
six-inch test tubes and mounted in a rack so that the 
capacity of the condenser will be adjustable by removing one or 
more of the tubes. An ordinary test tube rack such as is 
used in chemical laboratories serves very well for this 
purpose. The tubes should be connected in parallel, that is, 
all the outside coatings together and all the inside coatings 
together. 

Figs. 55 and 56 illustrate condensers of this type which 
are on the market. The tubes are all separately removable 
so that the capacity may be adjusted. 

.. figure:: images/Image56.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 56. Amco Oscillation Condenser. 

   Fig. 56. Amco Oscillation Condenser. 

**Glass Plate Condensers.**—Glass plate condensers offer 
several advantages over Leyden jars and are coming into 
wide use. They are not so bulky or expensive and, above 
all, do not blister. 

Plate condensers are often placed in a rack and made 
adjustable by means of movable contacts. Much the 
better plan is to place the plates in oil, as this eliminates all 
corona or brush discharges and much sharper tuning is 
rendered possible. The container is usually a tight wooden 
box filled with oil or paraffin after the plates are in place. 

It is impossible to state the size of condenser suitable for 
induction coils of a given power or spark length, because 
many factors such as inductance, length of aerial, etc., 
which differ in various stations, influence the capacity. A 
condenser of convenient size suitable for coils or small 
transformers consuming from 250 to 300 watts is that described 
below. It is about the proper size for the small open core 
and 1/4-K.W. closed core transformers, described in the last 
chapter. 

.. figure:: images/Image57.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 57. Clapp-Eastham Oscillation Condenser. 

   Fig. 57. Clapp-Eastham Oscillation Condenser. 

The glass plates may be secured by removing the emulsion 
from old 8 x 10 inch photograph plates. Hot water will 
soften the gelatin on the plates so that it may be very easily 
scraped off. Twenty-four plates of this size are required. 
The tinfoil is cut 8 x 8 inches, so that an inch margin is left 
on all sides. The alternate sheets are connected together 
by heavy tinfoil or thin copper foil strips. The condenser 
should be placed in a convenient sized wooden box and 
poured full of paraffin. 

The plate condenser shown in Fig. 57 is of .02 microfarad 
capacity. The condenser is mounted in a plain wooden 
box with several binding posts brought out, so that the 
capacity may be varied by connecting in various sections. 
The condenser is manufactured and designed by the 
Clapp-Eastham Company for use with the transformer illustrated 
in Fig. 51. 

It is very necessary to have the transmitting condenser 
adjustable so that its capacity may be varied, for the proper 
value depends upon the wave length, spark frequency, 
power and persistency of the wave train. 

When the condenser capacity is too small the spark will 
be somewhat flaming like an arc, and the potential to which 
the aerial is charged will be low. If too much capacity is 
used the spark will be very irregular and intermittent. 

.. figure:: images/Image58.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 58. Methods of Varying Capacity. 

   Fig. 58. Methods of Varying Capacity. 

Fig. 58 shows condensers connected in series and in 
parallel and a combination of the two. Two condensers of 
equal capacity connected in parallel have twice the capacity 
of one, while in series they will have only one-half the 
capacity of either. This may be otherwise stated as the capacity 
in series is equal to the reciprocal of the sum of the 
reciprocals of their capacities separately. By this means of 
connecting either in series or in parallel almost any desired 
adjustment of capacity may be brought about. 

Oftentimes a high voltage may be divided between two 
condensers by placing them in series and thus using them 
safely on a voltage which would rupture either one alone. 
For example, two condensers built for 20,000 volts and to 
be used on 30,000 volts could be made to perform this duty 
safely and only undergo a potential of 15,000 volts, which 
is a large margin of safety. 

It is obvious that if the capacity of the circuit were to 
remain constant, four condensers connected up in 
series-parallel would be necessary. 

In case of several Ley den jars or condensers connected 
up in a transmitting circuit, the leads or conducting wires 
connecting the various units should all be of as nearly the 
same length as it is possible to have them. 

The resistance of metallic conductors to high frequency 
currents is several times their normal resistance to constant 
currents. The larger the diameter of the wire the greater 
is this ratio. This increase of resistance is due to the fact 
that the high frequency currents permeate wires only a very 
short distance. In the case of copper, the depth is only 
about one three-hundredth of an inch and with other metals 
much less. Therefore it is advisable to use as leads and 
conductors of large condensers, stranded wires or flat 
ribbons of sheet copper in order to present more surface and 
offer less resistance than solid conductors of an equal cross 
sectional area. 

Iron must never be used, as its resistance to these currents 
is over fifty times that of copper. 

After connections are once established between the jars 
or the condenser units, they cannot be altered nor the 
capacity changed without re tuning the circuits afterwards. 

CHAPTER VIII. SPARK GAPS OR OSCILLATORS. 
----------------------------------------

The oscillator or spark gap is one of the most important 
yet often the most poorly adjusted part of a wireless 
station. 

To obtain a good oscillatory discharge with little damping 
it is necessary that the resistance of the circuit should be 
kept low, and since the greatest part of the resistance is in 
the spark gap it would appear as if this must be very short. 
While there are reasons for keeping it short there are on the 
other hand very good reasons why it should not be made too 
short, and the proper length should be a sort of compromise 
to be determined by experiment. 

If the gap is too short, the discharge will form an arc and 
the only oscillations taking place will be those corresponding 
to the frequency of the charging current. Power 
consumption is also in favor of a long gap, since it causes the 
induction coil or transformer to draw less current from the line. 
Another argument in favor of a long gap is the fact that 
the condenser is charged to a higher voltage and more 
energy stored up, which makes a greater distance of 
transmission possible. But as stated above (and there always is 
a tendency for the amateur operator to open out his gap as 
long as the sparks will continue to jump steadily) the 
discharge will not oscillate but will merely set up a 
unidirectional current. 

There exists a proper gap length for a given circuit which 
will cause that circuit to emit a maximum amount of energy 
and which may be determined accurately only by means of 
a hot-wire ammeter placed in the aerial circuit. The proper 
gap length is then indicated by the maximum deflection of 
the meter. 

The correct adjustment of the gap may be approximated 
by the experienced operator. If too short, the spark will be 
hissing and flaming and is in extreme cases red or yellow 
colored. It should be lengthened out until it is thick and 
white and a slight increase in sound is noted. The spark 
should not be, as commonly thought, stringy and crackling. 

Arcing is often caused by insufficient condenser capacity 
in the circuit. But if the capacity is increased to remedy the 
arcing, the gap length should also be increased or otherwise 
the potential of the condenser may not be sufficiently raised 
to permit a disruptive discharge to take place. 

.. figure:: images/Image59.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 59. Spark Gaps. 

   Fig. 59. Spark Gaps. 

The best spark gap for use with a small untuned 
transmitter, making use of neither tuning helix nor condenser, is 
shown at the left in Fig. 59. It consists of two brass balls 
supported on suitable double binding posts. The balls tend 
to thicken the spark and make it more disruptive than if it 
passed between rods or points. The balls also increase the 
potential required to leap the gap without increasing its 
length and permit the aerial to become more highly charged 
before a discharge takes place. For this reason the balls or 
knobs must always be kept free from small rough spots or 
points by frequent polishing. 

Silver has some peculiar property which makes it the 
most efficient material for a spark gap, but its cost 
prohibits its use and so brass or zinc, which are next in order, 
is generally used. 

The type of gap illustrated at the right in Fig. 59 is 
very convenient and efficient for small tuned transmitters 
employing coils of low power. 

.. figure:: images/Image60.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 60. Spark Gap. 

   Fig. 60. Spark Gap. 

The zinc tips are pieces of 3/8-inch zinc battery rod 3/4 inch 
long. They are bored and threaded to fit a pair of brass 
rods 1/8 inch diameter and 2 1/2 inches long. The rods are 
supported by two double binding posts and are fitted with two 
pieces of hard rubber rod 1/2 inch diameter and 1 inch long to 
serve as handles. If desirable one of the rods and binding 
posts may be threaded so that the adjustment of the gap 
can be accomplished by revolving the handle and screwing 
the gap in or out. 

A gap of the size and type just described would not be 
suitable in connection with a large transformer or an 
induction coil. The heavy discharge of such powerful 
instruments would very rapidly heat the small brass parts and 
corrode or even melt the zinc. The spark gap such as is 
shown in Fig. 59 may be used with a very large coil or the 
two kilowatt transformer if the same proportions are kept 
and it is made one-half again as large. Using the 
dimensions shown in the figure, the spark gap is suited to either 
the open core or the 1/4 and 1/2 kilowatt transformers. 

Two pieces of hard rubber rod, 3/4 inch diameter and 2 
inches long serve as the standards. Three grooves 1/8 inch 
wide, 1/8 inch deep and 1/8 inch apart better the appearance 
and reduce the liability of leakage but are not necessary. 
Two holes 2 inches apart are bored in *S*, a strip of brass 
3 x 3/4 x 1/4 inches. Two screws pass through these holes into 
the rubber standards *BB* and hold *S* firmly in position. 
The end of *S* is bent down at right angles and bored to 
receive a binding post. A hole is bored in *S* halfway 
between the standards and tapped to receive a threaded brass 
rod 2 inches long and 1/4 inch diameter. The lower ends of 
the hard rubber standards are each bored and tapped to 
receive a screw which fastens them to the base. The 
electrodes are zinc or brass cylinders 3/4 inch diameter and 5/8 inch 
long. The upper electrode is adjustable by means of a 
knurled hard rubber head 2 inches diameter and 1/2 inch thick. 
The lower one is fastened to a brass plate 2 inches long, 
1 inch wide and 1/8 inch thick. One end of the plate is fitted 
with a binding post. The base is a piece of hard rubber 
5 1/2 x 3 inches x 3/4 inch. 

CHAPTER IX. TRANSMITTING HELIXES. 
---------------------------------

The transmitting helix or tuning coil supplies the greater 
part of the inductance which is so necessary for the 
production of electrical oscillations in the transmitting circuit. 
It consists merely of a few turns of heavy copper or brass 
wire wound in a helix around a form. Two or more 
movable contacts permit various amounts of the 
inductance to be inserted in the open or closed circuits. 

The tuning helixes described in this chapter are offered 
principally to serve as guides. They have been designed as 
carefully as possible to suit the transmitters for which they 
are recommended. 

There are factors, such as the aerial, etc., which vary 
greatly in stations of the same rated power and make it 
best to determine the length of the helix by actual 
experiment. 

A certain amount of inductance is necessary in the closed 
circuit for the production of electrical oscillations and to 
transfer energy to the open circuit. Inductance beyond that 
necessary to receive energy from the closed circuit lessens 
the radiation and makes it necessary to increase the period 
of the open circuit by adding wires to the aerial. 

The open and closed circuits of a tuning helix constitute 
an oscillation transformer, and the two circuits if they are 
very close together or intertwined are said to be *closely 
coupled*. When separated or far apart they are *loosely 
coupled*. 

**Closely Coupled Helix.**—Fig. 61 illustrates a closely 
coupled tuning helix, suitable for ordinary induction coils 
giving sparks up to 3 or 4 inches in length. 

The heads of the helix are circular pieces of hard wood 
1 inch thick and 12 inches in diameter. Six rectangular 
notches are made at equal distances along the edges of the 
heads. Six uprights 3/4 x 1/2 inch and 8 3/4 inches long are 
fastened in the notches with small round headed brass 
screws so that the heads are separated a distance of 6 3/4
inches. Grooves are cut in the outside face of each of the 
uprights at a distance of 7/8 inch apart. The wire forming 
the helix is 1/4 inch brass. Brass wire is springy and retains 
its shape better than copper. About twenty-two feet will 
be required. The wire is wound in the grooves in the 
uprights and held in place by a few double pointed tacks 
placed judiciously. The adjacent turns of wire will then 
have a separation of about 5/8 inch. 

.. figure:: images/Image61.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 61. Closely Coupled Helix. 

   Fig. 61. Closely Coupled Helix. 

The helix is raised above the level of the operating bench 
or table by three small feet fastened to the under head, 120 
degrees apart. 

.. figure:: images/Plate3.jpg
   :align: center
   :scale: 85 %
   :alt: Plate III. Transmitting Circuits. 

   **Plate III. Transmitting Circuits.**

If it is desired to use this helix with the one quarter K.W. 
transformer, the diameter of the wire should be increased to 
5/16 inch. The two K.W. transformer will require seven 
turns of 1/2-inch hard drawn brass wire two feet in diameter. 

.. figure:: images/Image62.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 62. Prague Transmitting Helix.

   Fig. 62. Prague Transmitting Helix.

When setting up a transmitting 
station, it is a good plan to coil 
up a long piece of the wire to be 
used on the helix around a rough 
form. The adjacent turns should 
be the same distance apart as 
they are to be on the finished 
instrument. Tune up the station 
with this improvised helix and 
ascertain the amount of 
inductance required. It is then easy 
to design a helix containing the 
proper amount of wire. Four or 
five feet extra should be 
included to allow plenty of range in case it is ever necessary 
to make any changes in the aerial or condenser. 

.. figure:: images/Image63.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 63. Closely Coupled Tuning Circuit. 

   Fig. 63. Closely Coupled Tuning Circuit. 

Plate III illustrates the transmitting circuits of the 
various commercial systems. The circuit used will determine 
the number of binding posts and movable clips necessary. 
Fig. 63 gives the diagram of a very good circuit. 

**Loosely Coupled Helix**. The heads of the primary 
coil of the loosely coupled helix illustrated in Fig. 64 are 
circular pieces of hard wood 1 inch thick and 18 inches in 
diameter. Six uprights 3/4 x 1/2 inch and 11 inches long are 
set into notches in the upper head and fastened to the base 
so that the space between the heads for winding the wire is 
10 inches. 

.. figure:: images/Image64.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 64. Loosely Coupled Transmitting Helix and Contact Clip. 

   Fig. 64. Loosely Coupled Transmitting Helix and Contact Clip. 

A square wooden pillar 1 1/2 x 1 1/2 inches and 32 inches 
long passes through a square hole 1 1/2 x 1 1/2 inches in the 
center of the heads and projects 20 inches above the upper 
one. The heads of the secondary coil are each 12 inches 
in diameter. The distance between them is also 12 inches. 
A square hole 1 1/2 inches x 1 1/2 inches in the center of each of 
the heads permits the whole secondary coil to slide up and 
down on the pillar. Several 1/4 inch holes bored 1 inch apart 
in the pillar admit a small peg of the same diameter. The 
coupling between the two coils is varied by changing the 
height of *S* above *P* and inserting the peg to hold the 
upper coil in position. 

The primary winding of the transformer should consist of 
about 20 turns 15 inches in diameter, and may range in size 
of wire from No. 2 to No. 8 B. S. gauge. 

The secondary is 10 inches in diameter and will require 
about 40 turns of No. 10 to No. 16 B. S. gauge. 

The largest sizes of wire are for the one-quarter and 
one-half K.W. transformers while the smaller sizes are best 
suited to small induction coils. 

Fig. 64 also illustrates a clip for making connections to 
the turns of the helix. The handle is a piece of hard rubber 
rod 2 1/2 inches long and 5/8 inch in diameter. A saw slot 1 inch 
deep is cut down the center of one end. Two strips of spring 
brass 2 inches long, 5/8 inch wide and 3/64 inch thick are bent 
as shown in the illustration. The straight ends are slipped 
in the slot in the handle and clamped together by boring 
a hole and passing a machine screw through. The upper 
end may be fitted with a nut or a binding post to 
facilitate connection. Flexible copper ribbons or stranded wire 
should be the only conductor used for the tuning leads. 

.. figure:: images/Image65.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 65. Loosely Coupled Transmitting Circuit. 

   Fig. 65. Loosely Coupled Transmitting Circuit. 

**Tuning a Transmitter.**—Fig. 62 shows a complete 
wiring diagram of a transmitter with a hot wire ammeter 
inserted in the aerial circuit. 

To tune such a transmitter place both contacts *A* and *B* 
together on a turn of wire near the center of the helix. Set 
the transmitter in operation by pressing the key and move 
both contacts together along the various turns of wire until 
the meter shows a maximum reading. Then vary *B* alone 
until the reading is still higher. Shifting *A* varies the 
inductance in the closed circuit and *B* that of the open circuit. 

Fig. 65 illustrates the circuit of a loosely coupled 
transmitter. To tune such a circuit it is necessary to connect a 
small needle spark gap between the aerial and the ground. 

.. figure:: images/Image66.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 66. United Wireless Helix, Spark Gap and Condenser.

   Fig. 66. United Wireless Helix, Spark Gap and Condenser. 

A suitable spark gap for 
this purpose may be made 
of two darning needles 
mounted in double binding 
posts. 

Set the clips, *A* and *B*, at 
the center turns of their 
respective coils. Press the 
key to operate the 
transmitter and adjust the clip, 
*A*, until the best spark is 
obtained in the small 
needle gap. Then adjust 
*B* until the spark is still 
better. 

If several wires seem to 
give the same results, move 
the secondary a little 
further away from the primary and try again. After securing 
the best spark it is possible to obtain, remove the needle 
gap, which is only used in testing. The hot wire ammeter 
should then be placed in series with the aerial. By slowly 
and carefully adjusting the clips and varying the coupling, 
the hot wire ammeter will indicate the proper "tune." 

The secondary of the loosely coupled tuning coil produces 
a "kick back" effect on the primary, due to induction, and 
unless the two coils are somewhat separated, the wave 
emitted from the transmitter will have more than one "hump" 
and a person receiving the wave will be able to tune it in 
on two places on his tuning coil. 

A loosely coupled tuning coil does not radiate so much 
energy as a closely coupled helix, but will, when properly 
tuned, emit a wave which is not so highly damped. 
Therefore as far as distance is concerned the loosely coupled type 
is perhaps the most efficient. 

CHAPTER X. KEYS. 
----------------

THE keys used in wireless work differ from those used 
in commercial wire telegraphy in being much heavier and 
stronger, so as to conduct and break the heavier 
currents without heating. Where very powerful currents must 
be broken the contacts of the key usually operate under oil 
or in the magnetic field of a pair of electromagnets. In 
other cases a small key is used to operate a heavy relay. 
In the former type a metal arm projects downward from 
the lever of an ordinary Morse telegraph key into a 
compartment filled with oil. The arm is provided with a 
platinum point which makes contact with another similar point 
on the bottom of the compartment, so that the break is 
made under oil and the key remains cool and does not arc. 
In the second form the same result is accomplished by a 
magnetic "blowout." The "blowout" is merely an 
electromagnet connected in series with the key and its poles at 
right angles to the contacts of the key. When the circuit 
is broken the magnetic field extinguishes the arc which tends 
to form between the contacts of the key. 

An ordinary Morse key may be used with coils operated 
on batteries if they do not give more than a four-inch spark. 
Larger coils or transformers, especially if they are operated 
on the 110-volt current, require a heavier key. Where an 
ordinary Morse key is used with a 3-inch or 4-inch coil it 
is a very good plan to provide an auxiliary conductor, one 
end of which is fastened to the metal base and the other 
end to the adjusting screw on the back of the lever. A 
piece of flexible lamp cord is suitable for this purpose. 
This precaution saves the pivots of the key from heating 
and possible burning by heavy currents. 

.. figure:: images/Image67.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 67. Morse Key fitted with Extension Lever. 

   Fig. 67. Morse Key fitted with Extension Lever. 

The most convenient method is to fit up an old Morse 
key in the manner shown in Fig. 67. The lever is extended 
by a piece of aluminum or brass 6 inches long and 5/16 inch 
thick. The exact shape and the dimensions are indicated 
in the illustration. 

The extension lever is provided with a 1/2-inch round brass 
or nickel steel contact 7/8 inch long. The lower end of the 
contact is bored and tapped to receive a short machine 
screw. The other contact is a similar piece projecting 
downwards from a small arm fastened to the top of a 
standard 1/2 inch diameter and 2 inches long. The arm is a strip 
of brass 1/2 inch wide, 1/4 inch thick, and 1 1/2 inches long, 
fastened to the top of the standard with a machine screw. 
The brass standard is held in an upright position by means 
of a small machine screw which passes through the base. 
A wire connects with this screw to a heavy binding post 
mounted on the base. Connection is made with contact 
on the extension lever by means of a piece of heavy flexible 
lamp cord, which also runs to a binding post mounted on 
the base. The contact is insulated from the extension lever 
by means of two mica insulating washers and a bushing. 
Avoid running the connection to the base of the key so that 
the current must pass through the bearings. The contacts 
should be filed until they are perfectly flat and square across 
and make contact over their entire surface. When 
carefully constructed a key of this type will carry without 
heating almost any currents in reach of the amateur operator 
and which his induction coil or transformer will stand. 

.. figure:: images/Image68.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 68. Wireless Key. 

   Fig. 68. Wireless Key. 

The plans and dimensions for a heavier key are shown in 
Fig. 68. A wooden pattern of the base and bearings is 
made and taken to a brass foundry where a casting in brass 
may be secured. The pattern should be of the same shape 
and size as the finished article represented in the figure. 
It is given a slight taper so that it may be easily withdrawn 
from the sand mold. The brass casting is finished up square 
and smooth by grinding on an emery wheel or by careful 
filing. The lever is a piece of brass rod 1/2 inch square and 
6 1/2 inches long. One end is fitted with an ordinary hard 
rubber Morse key knob. The knurled nuts and 
thumbscrews are of the same size as those used on an ordinary 
key, and may be purchased from an electrical supply house. 

.. figure:: images/Image69.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 69. "United Wireless Type Key." 

   Fig. 69. "United Wireless Type Key." 

The pivot is a piece of 3/16 inch round steel 1 inch long, and 
passes through the lever 1 1/2 inches from the rear end. The 
ends are ground or turned to sharp points and rest in 
bearings formed by boring a recess in the ends of the 
thumbscrews. The thumbscrews pass through the center of the 
bearing, standards 3/4 inch above the base. The lever is 
clamped to the center of the pivot by means of a small 
machine screw. A heavy piece of spring brass, *S*, 1/2 inch 
wide and 3 inches long, is fastened to the base at one end 
with a short 8-32 screw. The other end is bent upward so 
that it presses hard against the lower end of an adjusting 
screw, which passes through the lever 1 1/4 inches forward of 
the pivot. This spring serves as an auxiliary conductor 
and saves the key from carrying an excessive current 
through its bearings. By adjusting the thumbscrew, the 
tension of the key may be regulated to suit the operator. 
The contacts of the key are 1/8-inch round nickel steel alloy 
or pure silver, set in short 1/4-inch machine screws which 
fit into correspondingly threaded holes in the base and 
the lever. This makes the contacts easily removable for 
renewal. The lower contact is set in a longer screw than 
the upper one so that connection may be made to it. It 
is insulated from the base by a hard rubber brushing. 

The contacts must be directly above one another and 
in perfect alignment or else they will pit and stick. 

CHAPTER XI. AERIAL SWITCHES AND ANCHOR GAPS. 
--------------------------------------------

Some form of switch for quickly connecting the aerial 
and ground to either the transmitting or receiving 
apparatus is necessary. 

Low powered stations using an induction coil as a 
transmitter will find a 250-volt double pole, double throw 
porcelain base switch to be suitable. Such a switch is 
connected up according to the diagram shown in Fig. 70. As 
clearly illustrated, the receiving apparatus is in use when 
the switch is thrown to the right, and the transmitter is ready 
for operation when the switch is in the left-hand position. 
The ease and speed with which such a switch may be thrown 
from right to left or vice versa may be much facilitated by 
fitting it with a larger and longer handle than the one 
usually provided. 

.. figure:: images/Image70.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 70. Connections for Aerial Switch. 

   Fig. 70. Connections for Aerial Switch. 

An ordinary double pole, double throw switch should be 
mounted on the wall within easy reach of the operator, 
while the two types of switch about to be described are 
best situated directly on the operating table alongside of the 
transmitting key. 

All insulated parts of an aerial switch such as the base, 
insulating bar, handle, etc., should be made of some good 
insulating material, as porcelain, hard rubber or ebonite. 
All insulation which is used in power switches such as slate, 
wood, marble, etc., is worthless and should not be used. 

If a loop aerial system is used, a switch is necessary, which 
will break the primary transmitting current so that in case 
of an accidental touch of the key while receiving, the high 
voltage discharge will not pass across the anchor gap into the 
receptor and badly damage the same or shock the operator. 
The connections of such a switch and the loop aerial are 
shown in the wiring diagram of the De Forest system. 

.. figure:: images/Image71.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 71. Aerial Switches. 

   Fig. 71. Aerial Switches. 

A switch may be easily constructed from a 50 ampere, 
single throw, triple pole, fuseless power switch. If it is 
mounted on a slate base remove it and set it up on a base 
of the same size made of fiber or porcelain. Flat unglazed 
tiles of various sizes are obtainable from tile setters at a 
very low cost. They may be easily bored with an ordinary 
steel twist drill. Such tiles are excellent insulators when 
not exposed to moisture and are useful for bases, etc., in 
many cases. A heavy coat of shellac varnish will make 
the tile impervious to moisture. 

A hard rubber rod, *S*, 3 inches long and 5/8 inch diameter, 
is mounted on both sides of the base in alignment with the 
contacts. A strip of hard rubber, *Y*, 1 inch wide, 1/2 inch 
thick and 6 1/2 inches long is fitted with two contacts similar 
to those mounted on the base of the switch. The contacts 
are mounted at a distance apart equal to the distance 
between the outside knife blades of the switch. A 1/8-inch hole 
is bored through the strip at both ends, through the axis 
of the rods along their entire length and through the base. 
A piece of brass rod 4 inches long and threaded at both 
ends with an 8-32 die is passed through the holes and yoke, 
so that the rods may be held firmly to the base and the 
strip to the tops of the rods by two nuts screwed on the 
ends of the brass rod. 

.. figure:: images/Image72.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 72. Detail of Contacts.

   Fig. 72. Detail of Contacts.

The upper contacts should be directly over the two 
outside lower ones. They are made from a strip of brass 1/2 inch 
wide, 3 1/2 inches long and 1/16 inch thick (bent as in Fig. 72).
A binding post is mounted on the yoke directly above and 
connecting with each one of the contacts. 

The middle pole of the switch is connected to the primary 
of the coil or transformer, so that when the switch is down, 
the primary circuit is completed, and when it is up it is 
broken. 

.. figure:: images/Image73.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 73. Details of Switch Parts.

   Fig. 73. Details of Switch Parts.

Some may prefer to make the complete switch, and in 
that case the dimensions given in Fig. 73 may be of aid. 
The knife blades are 6 inches long, 5/8 inch wide and 1/8 inch 
thick. Three are required. A 1/8-inch hole is bored 3/8 inch 
from one end, and the other end is cut out in the shape 
shown in the illustration. An insulating bar 5 x 3/4 x 5/8 
inches is made of hard rubber and three notches are cut in 
the back face, one directly in the center and one 2 inches 
on either side. 

.. figure:: images/Image74.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 74. Method of Fastening Knife. 

   Fig. 74. Method of Fastening Knife. 

Three 1/8-inch holes are bored one in the center of each 
groove and at right angles to it. An 8-32 machine screw 
3/4 inch long is placed in the notch in the end of the knife 
blade and the screw passed through the hole in the 
insulating bar. The blade may then be clamped tightly in place 
by putting a nut on the end of the screw. The screw 
which holds the middle knife blade in place is longer than 
the other two so that a handle may be fitted on. 

The bearings are made the same size and shape as the 
contacts illustrated in Fig. 72, with the exception that a 
1/8-inch hole is bored through near the top so that a small 
bolt may be slipped in to hold the knife blades in place. 

The base of the switch measures 8 x 9 x 3/4 inches. The 
parts are assembled as in Fig. 71. 

Another type of aerial switch called a "T" switch is 
illustrated in the same figure. A piece of 3/4-inch hard rubber 
is sawed in the shape of a T, 3 1/2 inches high and 6 1/2 inches 
wide at the top. The upper contacts are mounted on arms 
of the "T" and connected to binding posts placed 
immediately above them, A slot, 1/2 inch wide and 3 inches long, 
sawed in the center of the leg of the T, permits the middle 
knife blade to move without obstruction. 

.. figure:: images/Image75.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 75. "T" Aerial Switch. 

   Fig. 75. "T" Aerial Switch. 

A double pole, double throw switch may be easily 
adapted to form a "T" switch. Two knives are cut from sheet 
brass, of the same shape as those already on the switch but 
twice as long. The contacts at one end of the porcelain 
base are removed and the bearings of the knife blade 
fastened there in their stead. This forms a single throw, 
double pole switch having knife blades twice the length of 
the original double pole, double throw switch. A "T" 
shaped support for the upper contacts may be sawed out 
of 1/2-inch hard rubber and smoothed up with a file. The 
support is fastened upright by means of two screws which 
pass through holes in the center of the base where the 
knife bearings originally were. The two contacts which 
were removed from the base are fastened to the support 
directly over the knife blades so that they make a good 
contact when the switch is up. Two binding posts mounted 
above the contacts make connection with them. 

If desirable the switch may be fitted with a third knife 
blade and contact so that when the switch is up in position 
for receiving, the primary circuit of the induction coil or 
small transformer is open. 

It is obvious that the dimensions, etc., need not be the 
same as those given here but may be adapted to suit the size 
and design of the switch which is to be altered. The knives 
should always be as long as convenient and the contacts 
separated by a wide space. 

.. figure:: images/Image76.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 76. "United" Wireless Lightning Switch. 

   Fig. 76. "United" Wireless Lightning Switch. 


.. figure:: images/Image77.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 77. Shoemaker Tuning Coil and Aerial Switch. 

   Fig. 77. Shoemaker Tuning Coil and Aerial Switch. 

Figs. 76 and 77 illustrate the aerial switches used in the 
installations of the United Wireless Telegraph Company.
These illustrations give a good idea of the long knife blades 
employed. The lightning switch is fitted with a 
micrometer spark gap on top of the switch which is in service 
when the handle is up. The small spark gap affords a path 
for the lightning to jump into the ground, but cannot be 
bridged by the receiving currents. 

**Anchor Gaps.**—When a loop aerial system is employed 
for both transmitting and receiving, a device known as an 
anchor gap becomes necessary. 

.. figure:: images/Image78.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 78. "United" Wireless Anchor Gaps. 

   Fig. 78. "United" Wireless Anchor Gaps. 

The construction and connection of a simple anchor gap 
are shown in Fig. 79. A ring 1 3/4 inches outside and 1 1/4 inches 
inside is cut out of 5/8-inch hard rubber or fiber and smoothed 
up. Three 1/8-inch holes are bored in the periphery of the 
ring at 120 degrees to each other. The holes are threaded 
with a 10-24 tap. Three small binding posts are each 
fitted with a 3/16-inch brass rod 7/8 inch long, having a 10-24 
thread so that they may be screwed into the holes in the 
ring. 

.. figure:: images/Image79.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 79. Anchor Gap. 

   Fig. 79. Anchor Gap. 

The gap between the ends of the two rods connected to 
the aerial and the receiving apparatus is adjusted until it 
is about 1/8 inch long. The third point is screwed in until 
it all but touches the other two. 

CHAPTER XII. HOT WIRE AMMETER. 
------------------------------

When a current passes through a conductor, it generates 
heat in proportion to the resistance offered and the amount 
of current flowing. Heat causes metals to expand 
sufficiently so that these two properties may be applied to the 
construction of a hot wire ammeter for the measurement 
of alternating currents of high frequency and potential. 

The hot wire ammeter is placed in series with the aerial, 
so that by noting the deflection of the pointer, the 
inductance, capacity and spark gap may be adjusted until the 
meter gives a maximum reading. 

.. figure:: images/Image80.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 80. Simple Hot Wire Meter. 

   Fig. 80. Simple Hot Wire Meter. 

A simple and crude form of meter which is sufficiently 
sensitive for most experimental work is illustrated in Fig. 
\80. A piece of No. 36 B. S. platinum wire is sealed in the 
bulb of an ordinary air thermometer. When the wire 
becomes heated by a passing current of electricity, it causes 
the air in the bulb to expand and change the height of the 
colored liquid in the tube. 

An air-thermometer is simply a glass tube of fine bore 
having a bulb blown at the upper end and the free end 
immersed in a reservoir of ink or some other colored liquid. 
The instrument is put in working order by grasping the 
bulb in the palm of the hand, so that the warmth of the 
hand will expand the air and cause some of it to escape 
from the lower end of the tube. Upon removing the hand, 
the air will contract and suck some of the liquid up into the 
tube. It should rise only about half way to the bulb, and 
the tube should be about 18 inches long so as to leave room 
for changes in the position of the column due to variations 
in the outside atmosphere. A cardboard scale graduated in 
inches and reading downward is fastened in back of the 
tube. 

The tube should have a fine bore so as to make the 
instrument as sensitive as possible. The best liquid to use is 
alcohol, colored with a little aniline dye. Alcohol has a 
lower specific gravity than water, and the column will be 
more sensitive to small changes of pressure. The same 
figure shows a form of meter devised and used with success 
by the author. 

Two tubes are fitted to the bulb, a large one having a 
bore of about 0.1 of an inch and another about 0.04 inch. 
Connection is established by the aid of two corks and a 
short length of glass tubing one inch in diameter. The 
tubes are bent U shaped, and a little colored alcohol is placed 
in each, so that the bottle reservoir is unnecessary. The 
tube of large bore is fitted at the top with an ordinary glass 
stopcock such as that used in chemical laboratories. 

The stopcock is left open and the transmitter is set in 
operation by holding down the key. The helix, etc., are adjusted 
until the larger tube shows a maximum reading. The 
stop-cock is then closed and the instruments further adjusted by 
noting the reading in the finer tube which corresponds to 
much smaller changes in current. The finer bore cannot at 
first be used alone because the large changes of current 
would blow the liquid out of the tube. In lieu of a glass 
stopcock, a piece of rubber tubing may be placed over the 
end of the tube and closed, when necessary, with a pinch 
cock. 

.. figure:: images/Image81.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 81. Meter with Case Removed. 

   Fig. 81. Meter with Case Removed. 

Fig. 81 shows a more elaborate and sensitive form of 
meter which is not only suitable for experimental outfits but 
may be used with good results for more careful work. The 
advantage of the form of meter here described is that it is 
"pivotless" so to speak, and contains no bearings which 
require jewels to eliminate friction. 

The "hot wire" is platinum, and in order to compensate 
for external changes of the atmospheric temperature, is 
mounted on a strip of glass. Glass and platinum expand at 
nearly the same rate, and the wire is thus kept taut and 
prevented from changing the position of the pointer except 
when the current passes. 

.. figure:: images/Image82.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 82. Glass Compensating Strip. 

   Fig. 82. Glass Compensating Strip. 

Drill four 1/8-inch holes in a piece of window glass 6 inches 
long and 1 inch wide. The location of the holes is shown in 
Fig. 82. The two at the ends serve to mount the standards, 
*A* and *B*, and those at the center to fasten down the strip 
to the base. The holes are drilled with a small 
three-cornered file which has been broken off and set in a breast drill. 
The broken end should be used to drill the glass and be 
kept thoroughly lubricated with camphor and turpentine. 
With a little care and patience the holes may be drilled 
without breaking the glass. 

.. figure:: images/Image83.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 83. Details of "Hot Wire" Supports. 

   Fig. 83. Details of "Hot Wire" Supports. 

Two brass standards are fastened on each end of the glass. 
They are bent out of sheet brass and are 3/4 inch high and 
3/8 inch wide. A brass spring of the same width and 1 1/4 inches 
long is clamped under one standard. The standard which 
holds the spring in position is tapped for a small 
thumbscrew which may be secured from a binding post. Solder a 
small brass pin to the top of the spring and another one to 
the top of the standard which is fastened at the opposite 
end of the glass strip. Some paper or rubber washers must 
be placed between the feet of the standards and the glass 
strip to prevent it from cracking when the screws are 
tightened. 

For a station up to one-half K.W. in power the hot wire 
must be No. 40 B. S. gauge platinum. For larger stations 
a single No. 36 wire may be used or three No. 40 wires in 
parallel. The wire must be about 7 inches long. Stretch 
it between the standard, *A*, and the spring, *C*. Wrap the 
ends around the pins and solder them there, using as small 
amount of solder as possible. The tension of the wire, which 
should be taut, is adjusted with the thumbscrew. 

Take a piece of the platinum wire about 1/2 inch long and 
make a little eyelet at one end. Wrap the straight end 
around the center of the long hot wire and tie a piece of 
silk in the eyelet. 

.. figure:: images/Image84.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 84. Details of Movement. 

   Fig. 84. Details of Movement. 

The glass strip and its standards supporting the hot wire 
may then be fastened to the baseboard of the instrument by 
means of two round headed brass wood screws. Two rubber 
washers must be interposed between the glass and the wood. 
A piece of 3/32 inch brass 1/2 inch wide and 3 1/4 inches long is 
bent in the shape shown by *F* in Fig. 84. The upper end is 
bored and tapped to receive a thumbscrew similar to the 
one in the standard on the glass strip. Two brass springs 
1/64 inch thick, 3/8 inch wide and 1 1/4 inches long are soldered or 
riveted at opposite ends of *F* in the positions shown in Fig. 
\85. The springs should project one inch from the upright. 
A small hook made from an ordinary pin is soldered to the 
outside end of each. 

.. figure:: images/Image85.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 85. Complete Movement. 

   Fig. 85. Complete Movement. 

The movement is shown in perspective by Fig. 85. *G* is 
a rectangle of very thin copper, 1/2 inch long and 1/4 inch wide, 
having a little projection 1/4 inch long bent in a curve so that 
it forms a sextant of a circle, of which the intersection of the 
diagonals of *G* would be the center. 

The pointer is a piece of steel wire 5 inches long. It is 
slightly flattened by hammering so that it will retain its 
shape and not curl. About 1/2 inch is allowed to project 
through *G* and is weighted with a lead shot so as to partly 
counterbalance its weight. 

Two loops of wire are fastened to the corners of *G* by 
tying them in holes which are bored there for that purpose. 
The wire is fine phosphor bronze .003-.005 of an inch in 
diameter, which is used for suspending the movements of 
delicate galvanometers. Pass the loops over the hooks on 
the springs and adjust until the pointer moves horizontally. 
Then fasten the wires permanently to the hooks by means 
of a small drop of solder. 

.. figure:: images/Image86.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 86. Side View of Hot Wire and Movement. 

   Fig. 86. Side View of Hot Wire and Movement. 

The movement is mounted in the position shown by Fig. 
\86. The silk thread tied to the eyelet runs to the little 
sextant and is cemented at the further end by means of a 
small drop of sealing wax. The scale is a piece of sheet 
copper or brass, covered with white paper and calibrated in 
degrees or made to read in amperes by connecting it in 
series with an ammeter and a source of direct current. A 
rheostat should be included in the circuit and the current 
varied so that various values may be marked off. All the 
different points must be located by sending an actual 
current of that value through the meter. An error is liable to 
result if any of the points are marked by guesswork, for the 
divisions grow smaller and smaller as they become farther 
away from zero. For example a position of the pointer 
corresponding to 0.1 of an ampere will not be half way between 
zero and 0.2 but will be nearer the 0.2 division. 

The resistance of wires to high frequency currents is much 
higher than their resistance to constant currents. This 
would seem at first to indicate that our meter will give a 
higher reading for an equal current value, when used with 
a high frequency current after being calibrated with a direct 
current. But with wires of very small diameter such as No. 
40 B. S. gauge there is almost no perceptible difference and 
consequently no error unless the frequency of the 
oscillations exceeds 1,000,000 per second, which is very unlikely 
with the "spark" method of wireless telegraphy. 

Fig. 87 illustrates the form of hot wire ammeter used by 
the United Wireless Telegraph Co. for tuning their 
installations. 

.. figure:: images/Image87.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 87. United Wireless Hot Wire Ammeter. 

   Fig. 87. United Wireless Hot Wire Ammeter. 

The pivotless meter just described should be fitted with 
heavy binding posts which are connected to the brass 
standards mounted on the glass strip by means of stranded 
copper wire. 

The meter should be fitted with a case and glass cover to 
exclude dust and prevent injury to the working parts. It 
should be mounted in such a position that the weight of the 
pointer is sufficient to keep the silk thread taut so that when 
the wire expands the pointer which is normally at zero will 
fall of its own weight. When the wire cools after the current 
has ceased to flow, it will contract and draw the pointer up 
again. 

Platinum wire will give good results, but for more accurate 
work an alloy known as platinoid is most suitable. 

Detailed instructions for tuning the transmitting circuits 
by means of a hot wire ammeter are given in the chapter on 
Transmitting Helixes. 

CHAPTER XIII. OSCILLATION DETECTORS. 
------------------------------------

"UNIVERSAL" DETECTOR. 
`````````````````````

The purpose and position of the detector in a wireless 
telegraph system has already received some notice in 
the first chapter, but its operation and adjustment are so 
important that this chapter deserves the most careful 
consideration. The receiving range of a station is not as 
much dependent upon the aerial system as it is upon the 
adjustment of the tuning circuits and the detector itself. 

It is suggested that the amateur experimenter not confine 
his work to receiving only with a single type of detector but 
rather accustom himself to the different instruments. 

During the past few years many wireless telegraph 
detectors have been invented which lend themselves readily to 
amateur construction. It is somewhat of a convenience to 
have a "universal" detector which with a little 
manipulation may be used as more than one type and thus save 
unnecessary expense and much labor. 

The "universal" detector shown in Fig. 88 has been so 
designed as to present a good appearance and at the same 
time be successfully operated as an electrolytic, tantalum, 
peroxide of lead, silicon, carborundum or any of the crystal 
type detectors. 

.. figure:: images/Image88.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 88. Universal Detector.

   Fig. 88. Universal Detector.

.. figure:: images/Image89.jpg
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   :scale: 85 %
   :alt: Fig. 89. Details of Universal Detector. 

   Fig. 89. Details of Universal Detector. 

The standard, *R*, is a 3/4-inch hard rubber rod, 1 1/4 inches 
long, with a 3/16 inch hole bored through its axis. A spring, 
*S*, is made after the plan shown in Fig. 86. It is 2 inches 
long and 1/16 inch thick. A brass collar 1/8 inch thick and 
3/8 inch diameter is soldered on the smaller end of the spring 
in order to so reenforce it that it may be bored and threaded 
with an 8-32 tap to receive a thumbscrew. The brass 
standard, *D*, is a small cylinder 3/8 inch high and 1/2 inch in diameter. 
A 3/16 inch hole is bored through its axis. The arm, *A*, is brass 
and measures 1 1/2 x 1/2 x 1/4 inches. The ends are rounded 
by filing or grinding so that they coincide with the 
semi-circumference of a circle having a diameter of 1/2 inch. Two 
holes are bored on the center line 1/4 inch from each end. 

One is a 1/8-inch hole and the other is threaded with a 10-32 
tap to fit the large adjusting screw. The adjusting screw, 
*H*, is 1 1/4 inches long and has a 10-32 thread. A hard rubber 
head 1 inch thick and 1 1/4 inches in diameter is clamped to 
the upper end by means of two hexagonal brass nuts. A 
small brass washer should be placed between the head and 
each of the nuts to give it a more finished appearance and 
prevent the nuts from marring the rubber. 

.. figure:: images/Image90.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 90. Parts of Universal Detector. 

   Fig. 90. Parts of Universal Detector. 

The brass bed plate, *B*, is 1/8 inch thick, 3 inches long and 
2 inches wide. Two holes are drilled on the center line 9/16 
inch and 7/8 inch from either end. One is 3/8 inch in diameter 
and the other is threaded with an 8-32 tap. An insulating 
bushing in the shape of a hard rubber washer on the lower 
end of *R*, 1/8 inch thick and 3/8 inch in diameter, has a 3/16-inch 
hole bored in its center and is fitted in the larger hole in the 
bedplate. The whole detector is assembled and mounted 
on a hard rubber base 4 x 5 x 4 inches. A brass binding 
rod, *M*, 3 1/4 inches long and having an 8-32 thread, is passed 
successively through the arm, the brass standard, the spring, 
the hard rubber standard and the bedplate. A hexagonal 
brass nut on the under side of the base and a thumb nut 
on the brass arm serves to bind the whole tightly together. 
Four binding posts are mounted on the four corners of the 
base. Two are connected to the brass binding rod and two 
to the bedplate. This completes the universal part of the 
detector. The remaining parts are each described under the 
headings of the respective detectors to which they belong. 

ELECTROLYTIC DETECTORS. 
```````````````````````

**"Bare Point" Type.**—Although the electrolytic is the 
oldest of a long line of very sensitive detectors, [#]_ it still 
holds first rank when in the hands of an experienced and 
skillful operator. It exists in two different forms, but the 
more favored is that known as the Fessenden "bare point" 
type, which consists of a very fine Woolaston platinum wire 
(.001-.00002 of an inch in diameter) dipping in a small cup 
of dilute acid. The acid is either 20 per cent chemically 
pure nitric or sulphuric. 

.. figure:: images/Image91.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 91. Bare Point Electrolytic Detector. 

   Fig. 91. Bare Point Electrolytic Detector. 

A large electrode of platinum wire or foil dips into or is 
sealed in the bottom of the cup so as to make an electrical 
connection with the liquid. The fine Woolaston wire is 
clamped over the cup in a holder which permits of vertical 
adjustment, by means of a thumbscrew, so that the depth 
of immersion in the acid may be regulated. 

.. figure:: images/Image92.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 92. Effect of Exposing too much Wire. 

   Fig. 92. Effect of Exposing too much Wire. 

Woolaston wire is covered with a comparatively thick 
coating of silver, which before using must be removed from 
the end for about 1/32 inch by dipping it in strong nitric acid, 
which will dissolve the silver and expose the almost invisible 
platinum core. Too much of the fine platinum core must 
not be exposed or else the surface tension of the acid will 
cause the wire to curl over and present a large flat surface 
instead of a fine point. This is a very necessary and 
important precaution, for the detector is more sensitive as 
the area of contact between the fine wire and the liquid is 
smaller. 

Whenever this condition is reached the end of the wire 
should be cut off with a pair of sharp scissors and a new 
point exposed. 

.. figure:: images/Image93.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 93. Electrolytic Detector Circuits. 

   Fig. 93. Electrolytic Detector Circuits. 

The detector circuit is shown in Fig. 93. The fine "bare 
point" is always made the positive or anode of the battery 
circuit. Otherwise the detector will not operate. A 
potentiometer must be shunted across the terminals of the battery 
to reduce the voltage to a value just below that which is 
required to break down the thin film of oxygen gas which 
collects on the "bare point" and polarizes it or insulates 
it from the liquid so that little or no battery current can 
flow. This film of gas is caused by the electrolysis of the 
acid solution and the decomposition of the water into 
hydrogen and oxygen gas. 

When oscillations are set up in the receiving aerial and 
they surge through the detector, a sufficient e.m.f. is 
generated to break down the film of gas and permit the battery 
current to flow again. The passage of current causes the 
signals in the telephone receivers. 

The electrolytic cup for the universal detector is 
illustrated in Fig. 90. It is made of a piece of hard rubber rod 
3/4 inch in diameter and 3/4 inch high. A recess 1/2 inch in 
diameter and 3/8 inch deep is cut in the top to contain the acid. 
A small hole 1/4 inch deep is bored in the under side and 
threaded with an 8-32 tap. A brass pin 1/2 inch long, 
having a corresponding thread, is fitted in the hole. The 
pin may then be screwed into the small hole in the 
bedplate. A piece of No. 30 B. S. gauge platinum wire or a 
strip of platinum foil is clamped between the bottom of 
the cup and the bedplate and then bent over the top of the 
cup into the liquid. 

.. figure:: images/Image94.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 94. Electrolytic Detector. 

   Fig. 94. Electrolytic Detector. 

A 1/16-inch hole 1/4 inch deep is bored in the lower end of a 
thumbscrew having an 8-32 thread. A piece of Woolaston 
wire 1/2 inch long is placed in the center of the hole and 
tinfoil packed into the surrounding space with the head of a 
sewing needle until the wire is held firmly in position. The 
free end of the wire must then be dipped in some strong 
nitric acid to remove the silver. The thumbscrew is placed 
in the collar on the end of the spring of the universal 
detector and lowered until the "bare point" almost touches the 
surface of the electrolyte in the cup beneath. Pressure 
must then be applied to the spring by turning the large 
adjusting screw until the "bare point" touches the liquid 
and a click is heard in the telephone receivers and a faint 
bubbling sound is also audible. The adjusting screw must 
then be slowly and carefully turned in the opposite 
direction so as to raise the point until the bubbling changes to a 
hissing sound. The point is then above the level of the 
electrolyte in the cup but is still in contact with it because 
of the capillary action of the fine wire and the liquid. 

By using the large adjusting screw as much as possible, 
instead of the small thumbscrew, the point is raised or 
lowered without giving it a circular motion and much finer 
adjustment is made possible. The potentiometer is 
adjusted until the hissing noise caused by excessive battery 
voltage just disappears. The detector is then in its most 
sensitive condition for receiving signals. 

When the detector is in use for long periods, the 
potentiometer must be frequently readjusted to compensate the 
gradual loss in voltage of the battery. It is well to provide 
a small switch which will disconnect the battery from the 
potentiometer when the detector is not in use. In the same 
case the acid should be removed and placed in a tightly 
stoppered bottle. A pipette or fountain pen filler furnishes 
the most convenient means for filling or emptying the cup. 
The acid must be kept perfectly pure and out of contact 
with all metals other than platinum. Great care should 
be exercised in filling the cup, for the acid, if spilled, will 
not only badly corrode the metal fittings, but will also 
provide a current leak and seriously weaken the signals. 

**Shoemaker and Stone Detectors.**—These two types of 
detectors make use of "glass points," so called because the 
fine platinum wire is sealed in a glass tube and the end of 
the tube is then ground down on a fine oilstone until the 
platinum wire is exposed. This results in a very fine 
contact area and insures constant immersion of the point 
without readjustment. 

.. figure:: images/Image95.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 95. Forming "Glass" Point. 

   Fig. 95. Forming "Glass" Point. 

The fine platinum wire for a glass point may be secured 
from one of the flaming pocket cigar lighters making use of 
spongy platinum. The center of a thick walled glass tube 
is softened by heat and contracted as shown at *A-B* in 
Fig. 95. After cooling, the tube is cut in half at the point 
indicated by the dotted line. The platinum wire is placed 
in the contracted end of the tube and carefully fused in so 
that about one-half of the wire, which is about 1/2 inch long, 
is embedded in the glass. The contracted end of the tube 
containing the wire should be closed. Connection is 
established to the upper end of the fine platinum wire by filling 
the tube with mercury and dipping a piece of flexible 
conductor in the mercury. The upper end of the tube is closed 
and the mercury prevented from escaping by a small dab 
of sealing wax. 

The "point" is slowly and carefully rubbed on a fine 
oilstone kept well wet with water. The tube must be held in 
a vertical position so that the glass will be ground away at 
right angles. When it is thought that the platinum wire 
has been exposed by the grinding, connect the flexible 
conductor to one pole of a battery. The other pole of the 
battery is connected to a pair of sensitive telephone 
receivers and the telephone receivers to a vessel containing 
dilute acid. If the platinum wire is exposed, a sharp click 
will be heard in the telephone receivers when the "point" 
is dipped in the acid. Do not confuse the sharp click with 
the sound which may be occasioned because the outside of 
the glass tube is damp or wet. 

After the point has been sufficiently ground, disconnect 
the testing apparatus and connect the free end of the 
flexible conductor to a binding post placed on the end of the 
detector spring, *S*. The detector circuit is similar to that 
of the "bare point" type. 

.. figure:: images/Image96.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 96. Shoemaker Detector. 

   Fig. 96. Shoemaker Detector. 

The illustration shows what is sometimes called a 
"primary cell" detector because it furnishes its own current and 
does not require a battery. A Stone detector may be very 
easily changed to one of the Shoemaker type by 
substituting an amalgamated zinc rod for the platinum wire anode 
which makes connection with the liquid in the cup. This 
combination of platinum and zinc results in an 
electromotive force of about 0.7 volt, and the telephone receivers 
are connected directly to the terminals of the detector 
without any local battery or potentiometer. The 
electrolyte in the cup must be a 20 per cent solution of pure 
sulphuric acid, as nitric acid would dissolve the zinc in a very 
few minutes. The zinc must be kept well amalgamated 
with mercury. 

.. figure:: images/Image97.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 97. Shoemaker Detector Circuits. 

   Fig. 97. Shoemaker Detector Circuits. 

The Shoemaker system makes use of a loop aerial, and the 
circuits with a single and double coil tuner are illustrated 
in Fig. 97. It is not necessary to use these, and the detector 
will operate just exactly as well on a "straightaway" 
aerial. 

**Lamp Detector.**—All electrolytic detectors, more 
especially those of the "glass point" type, are subject to the 
annoyance of "burn-outs." That is, the fine platinum wire 
melts when receiving strong signals from a near-by station. 

In such case, the "bare point" must be lowered until it 
again makes contact with the liquid, and the "glass point" 
reground until the wire is again exposed. 

When this trouble comes often it is very convenient to 
have at hand a simple detector which will not burn out 
and which may be substituted for the 
usual one when great sensitiveness is not 
required. 

.. figure:: images/Image98.jpg
   :align: center
   :scale: 50 %
   :alt: Fig. 98. Lamp Detector. 

   Fig. 98. Lamp Detector. 

Such an instrument is made by 
snipping off the tip of a small incandescent 
electric lamp and removing the filament 
with a wire. One of the leading-in 
wires is broken off as close as possible to 
the glass stub and the globe half filled 
with a 20 per cent acid solution. The 
broken wire must be made the negative or 
cathode and connected like a Fessenden 
or Stone detector. This lamp detector 
though crude will give good service 
without burning out when used to receive from near-by stations. 

In place of a lamp detector, a glass point having a larger 
wire than that of the cigar lighter may be used instead of 
the usual point, but it will not be so sensitive. 

Fig. 99 illustrates a simple form of electrolytic detector 
which is not so sensitive as that shown in Fig. 100 but is 
still very serviceable. 

The cup is made from the carbon of an old dry cell, the 
brass connecting cap serving very well to make the 
connections to. It has a recess about 1/2 inch in diameter and 
1/4 inch deep cut in the top to contain the electrolyte. The 
cup should be about one inch high. A file will smooth up 
any rough edges and give it a good appearance. 

.. figure:: images/Image99.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 99. Simple Electrolytic Detector. 

   Fig. 99. Simple Electrolytic Detector. 

The yoke is made of a piece of 1/8-inch sheet brass about 
3/4 inch wide, bent in the shape shown in the illustration. 
Two small holes are drilled in the feet, to serve to fasten 
the yoke firmly to the base and also to make connection to. 

The adjusting screw may be made from the screw taken 
from the carbon of an old dry cell. To permit of accurate 
adjustment, it should be fitted with a large head made from 
a piece of 1/4-inch hard rubber or fiber cut in a circle about 
1 1/4 inches in diameter. Bore a small hole about 1/8 inch in 
diameter through the center of the head and force it on 
the screw. A nut screwed on the under side will then 
clamp it tightly against the brass head. A hole is bored 
in the center of the yoke and a battery nut which will fit 
the adjusting screw soldered directly under it. 

The platinum wire may be either soldered to the 
adjusting screw or fastened with tinfoil in the method which has 
been described. 

The cup and yoke are best mounted on a piece of hard 
rubber 1/2 inch thick, 3 inches wide and 4 inches long. A 
binding post is placed near each of the four corners. 

It is possible to do extremely fine and long distance work 
with the detector illustrated in Fig. 100. It is so arranged 
that the "bare point" need not necessarily be revolved when 
making an adjustment, and so it is possible to place it in a 
very sensitive condition. 

A brass standard, *U*, 1 1/4 inches long is cut from a piece 
of 1/2-inch rod. A hole bored in the top and bottom of the 
standard is threaded with an 8-32 tap. A brass rod, *R*, 
2 inches long is threaded with an 8-32 die throughout its 
entire length. One end is screwed in the top of *U*. 

A piece of brass tubing, *P*, 1 1/4 inches long and having an 
internal bore of 1/2 inch is slipped over *U*. A slot cut in *P* 
fits over a small pin set in *U* and permits *P* to be slid up and 
down but not to turn around. 

.. figure:: images/Image100.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 100. Electrolytic Detector. 

   Fig. 100. Electrolytic Detector. 

A head in the form of a circular brass washer, *E*, 1/8 inch 
thick, 1/2 inch in diameter and having a 5/32-inch hole bored 
in the center is soldered in the top of the tube, *P*. 

A circular piece of hard rubber, *H*, 2 inches in diameter 
and 1/2 inch thick is fitted with a brass bushing having a hole 
in the center with an 8-32 thread to screw on the rod, *R*. 

A spiral spring is placed around *R* between *U* and the 
head *E*. A small brass washer should be placed between 
*H* and *E* in order to eliminate friction. When *H* is turned 
in one direction, the spring will cause *P* to rise, and when 
turned in the other direction it will be lowered. 

A brass arm, *A*, 1/4 x 1/4 x 1 1/2 inches carries a small 
thumbscrew, *r*, at one end, while the other end is soldered to *P* 
as shown in Fig. 96. The Woolaston wire is soldered to *T*. 

.. figure:: images/Image101.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 101. Details of Electrolytic Detector. 

   Fig. 101. Details of Electrolytic Detector. 

A small carbon cup 3/4 x 3/4 inch serves to hold the 
electrolyte. A 3/8-inch hole is bored 1/4 inch deep in the bottom 
of the cup and poured full of melted lead. The lead is then 
bored and tapped to fit a machine screw which fastens the 
cup to the base. Connection is made from a binding post 
to the machine screw. A second binding post is connected 
to the screw which fits into the bottom of *U* and holds 
it to the base. 

If desirable a circular piece of hard wood, *F*, may be 
turned out and glued to the base around the cup in order 
to give it a more finished appearance. 

The thumbscrew, *T*, is used to lower the "bare point" 
until it almost touches the liquid, and then the large head, 
*H*, is brought into play to make the finer adjustment. 

**Increasing the Sensitiveness of an Electrolytic Detector.**
The sensitiveness of an electrolytic detector may be 
increased in three ways, viz., by connecting two detectors 
in series, by warming the electrolyte and by agitating it. 

The first method is clearly apparent. 

The second is accomplished by placing the detector over 
a sand bath and gently warming it. It will then show a 
marked increase in the strength of the signals at a 
temperature of about 30 C. This increase will continue to 
rise with the temperature until it reaches a maximum at 
about 60 C. 

.. figure:: images/Image102.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 102. Increasing the Sensitiveness of an Electrolytic Detector. 

   Fig. 102. Increasing the Sensitiveness of an Electrolytic Detector. 

Branly discovered that a fine stream of gas passed through 
the electrolyte in order to agitate it increases the strength 
of the signals in the phones. He devised a detector 
provided with two extra platinum terminals sealed in the cup. 
When connected in series with a battery and an adjustable 
resistance, these terminals cause electrolysis of the water, 
and a fine stream of oxygen and hydrogen gas flows through 
the acid electrolyte. The stream of gas agitates the liquid 
just sufficiently so that when oscillations strike the detector 
they augment the breaking down of the film of gas which 
collects on the fine platinum point. This results in an 
increase in the battery current flowing through the telephone 
receivers of from two to four times and a corresponding 
increase in the volume of sound. The adjustable resistance 
is used to regulate the decomposition of the electrolyte and 
formation of gas, for if this proceeds too rapidly an 
undesirable rumbling noise will be produced in the telephone 
receivers. 

TANTALUM DETECTOR.
``````````````````

The tantalum detector is especially suitable for the 
amateur experimenter because its change in resistance when 
struck by oscillations is so great that high resistance 
telephone receivers are not necessary. Its normal resistance 
is about 1000-2000 ohms, and this sometimes drops as low 
as 125-100 ohms when struck by oscillations of ordinary 
strength. It is not nearly so sensitive as the electrolytic 
or crystal detectors, but gives very much louder tones 
in the telephone receivers when used for short distance 
work. 

.. figure:: images/Image103.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 103. Tantalum Detector. 

   Fig. 103. Tantalum Detector. 

The detector is easily made by substituting a piece of 
tantalum wire for the Woolaston wire of an ordinary 
electrolytic detector. The dilute acid solution is removed from the 
cup and replaced by some pure mercury. The 
connections remain the same as for the "bare point." The 
potentiometer is adjusted until the potential of the battery is in 
the neighborhood of 0.2-0.4 volt. 

The tantalum wire may be easily secured by breaking the 
globe of a tantalum lamp and using a piece of the filament. 
It is best to snip off the lamp tip before breaking the globe. 
This precaution admits the air and prevents an explosion 
which would shatter the glass and scatter the filament in 
fragments. 

If the universal detector is used with a tantalum point, 
turn the small thumbscrew until the wire almost touches 
the surface of the mercury. Then lower it with the large 
adjusting screw until the tantalum touches the surface and 
a sharp click is heard in the telephone receivers. Adjust the 
potentiometer until the signals are the loudest. 

CRYSTAL DETECTORS.
`````````````````` 

Certain minerals and crystals, principally members of the 
carbon and sulphur groups, possess the peculiar property of 
rectifying electrical oscillations and converting them into a 
pulsating direct current. These crystals conduct the current 
better in one direction than in the other. In the case of a 
current having a potential of ten volts and applied to the 
ends of a carborundum crystal, the current may be one 
hundred times greater when flowing in one direction than 
when flowing in the other. This ratio decreases as the 
voltage is raised, for with 25 volts it may be only about 
forty times greater. The crystals when properly inserted 
in the aerial circuit are enabled to rectify the oscillations 
and produce sounds in the telephone receivers without the 
aid of a battery. 

The following is a partial list of the minerals and crystals 
exhibiting these properties to a sufficient extent that they 
are of value as oscillation detectors in wireless telegraphy. 

.. figure:: images/Table9.jpg
   :align: center
   :scale: 85 %
   :alt: Common and Chemical Names. 

In the case of iron pyrites the writer has found that a 
specimen of this mineral containing very little or no copper 
as an impurity does not exhibit these properties to an 
appreciable extent. 

.. figure:: images/Image104.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 104. United Wireless Carborundum Detector (horizontal type). 
   
   Fig. 104. United Wireless Carborundum Detector (horizontal type). 

In order to use the universal detector for minerals, a 
special contact similar to that shown in Fig. 90 must be 
made. The contact is bored and threaded on its under side 
to fit a brass pin 3/4 inch long and having an 8-32 thread. 
The other end of the pin screws into the hole in the 
bedplate. The large knurled portion of the contact permits 
it to be raised or lowered without the fingers coming in 
contact with the crystal. The crystal is clamped between 
the contact and the spring, *S*. The position is varied until 
a sensitive spot is found and then the pressure is carefully 
regulated by means of the large adjusting screw until the 
signals in the telephone receivers are the loudest. If 
possible avoid touching the crystals with the fingers, as the oil 
and dirt, even though it cannot always be seen, spoils their 
value for long distance work. Use instead a pair of steel 
forceps. 

.. figure:: images/Image105.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 105. United Wireless Carborundum Detector (vertical type). 
   
   Fig. 105. United Wireless Carborundum Detector (vertical type). 

The United Wireless Telegraph Co. makes use of 
carborundum in the detectors shown in Figs. 104 and 105. The 
principal advantage of carborundum over such substances 
as silicon, etc., is that it is not affected by the heavy discharge 
of the transmitting apparatus and does not require a new 
adjustment after each period of sending. All the crystals 
will not work, and so a large cake should be purchased and 
the desired crystals selected. The dark blue portions of the 
mass, which are the hardest, will give the clearest tones in 
the telephone receivers, and are preferable to the lighter 
colored crystals. Since the crystals conduct better in one 
direction than in the other, as explained above, the 
adjustment must be made with the view of determining in which 
position the particular crystal will work the best. 

Carborundum will produce sounds in the telephone 
receivers without the aid of any battery, but for careful work 
a battery and a potentiometer are necessary. 

The other crystals given in the column merely require that 
the telephone receivers be connected to the detector 
terminals as in the wiring diagram in Fig. 108. 

The Clapp-Eastham detector makes use of a crystal of 
iron pyrites held in a brass retaining cup beneath the metal 
contact point. It is not affected by strong signals and 
requires no battery or potentiometer. When adjusted it will 
remain in a sensitive condition for a long time without 
further attention. 

.. figure:: images/Image106.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 106. Clapp-Eastham Ferron Detector. 
   
   Fig. 106. Clapp-Eastham Ferron Detector. 

**Silicon Detector.**—While the silicon and "perikon" 
detectors are classed as mineral or crystal detectors they 
deserve special attention. 

.. figure:: images/Image107.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 107. Silicon Crystal in Cup.
   
   Fig. 107. Silicon Crystal in Cup.

Silicon gives fair results if a crystal is placed between two 
metal electrodes as, for instance, between the contact and 
spring of the "universal" detector, but is much more 
sensitive when properly mounted. A brass cup such as that 
shown in Fig. 90 is made and the interior brightened by 
scraping with a file. The cup is then poured full of a molten 
fusible alloy and the silicon pressed in it until it cools and 
becomes set. It should then present an appearance similar 
to that shown by *A* in Fig. 107. The silicon is ground down 
by rubbing on the surface of a clean oilstone kept well wet 
with water, until the surface is flat and shows a polish. 

.. figure:: images/Image108.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 108. Silicon Detector Circuits. 
   
   Fig. 108. Silicon Detector Circuits. 

The cup containing the silicon is placed over the hole in 
the bedplate of the universal detector. A knurled brass 
thumbscrew having a point on its lower end is screwed into 
the collar on the spring, *S*, and brought to bear on the 
polished surface of the silicon. The pressure may be easily 
regulated by means of the large adjusting screw until the 
signals in the telephone receivers are the loudest. It is not 
advisable to fasten the cup to the bedplate but merely to 
brighten the bottom so as to insure a good contact. The 
cup may then be moved around so that different portions of 
the polished surface of the silicon may be brought into play 
when desirable. 

If the knurled brass thumbscrew is fitted with a 
platinum point which can be brought to bear on the surface of 
the silicon, the efficiency of the detector will be materially 
increased. 

When mounting silicon or other crystals some careless 
experimenters use lead or a metal having a high melting 
point instead of a fusible alloy. This is poor policy because 
the high temperature coats the surface of the crystals and 
the interior of the cup with a non-conducting layer which 
destroys the sensitiveness and makes it unfit for long 
distance work. A fusible alloy melting at about the boiling 
point of water or even lower should be used. Such alloys are 
usually composed of tin, lead and bismuth. The addition 
of a little cadmium serves to make the fusing point 
considerably lower in each case. The alloys may be prepared 
by the experimenter from the following formulae, or are 
obtainable from a firm manufacturing fire plugs for 
automatic fire extinguishers. 

.. figure:: images/Table10.jpg
   :align: center
   :scale: 85 %
   :alt: Fusing Point Table.

The lead should be melted first and then the bismuth, 
tin and cadmium added in the order named. 

**Perikon Detector.**—The Perikon detector is one of the 
latest types to come into extensive use. It consists of two 
crystals, zincite and chalcopyrites, [#]_ set in cups in the 
manner just described and placed in contact with each other. 
The minerals are mounted similar to those in Fig. 105. The 
zincite should present a rather flat surface with the grain of 
the crystal parallel to the sides of the cup so that the top 
surface corresponds to the end of a stick of wood sawed at 
right angles to the grain. More than one crystal of zincite 
is usually set in the same cup. The chalcopyrites should 
present a rather blunt point. The cup containing the 
chalcopyrites is the smaller and is bored and threaded to fit a 
thumbscrew which passes through the collar in the spring, 
S, of the "universal" detector. The bottom of the cup 
containing the zincite is brightened so as to insure a good 
contact and then placed on the bed plated under the cup 
containing the chalcopyrites which is fastened to the 
thumbscrew. The zincite may then be moved around until the 
most sensitive portion is found. The chalcopyrites is 
lowered until it comes into contact with the zincite and then 
the pressure regulated by means of the large adjusting 
screw. 

.. figure:: images/Image109.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 109. Perikon Detector Elements. 
   
   Fig. 109. Perikon Detector Elements. 

The Perikon detector gives excellent results without a 
battery and is preferably used in that manner. If a battery 
is used, a potentiometer to lower the voltage is necessary. 

When adjusting this or the carborundum detector where 
a battery is used, the pressure must be very carefully 
regulated until it is found to be the best. When the pressure is 
light the signals in the phones are due to an imperfect 
contact, and when it is slightly increased the rectifying 
properties of the crystal are brought into play. 

The Perikon detector illustrated in Fig. 110 is somewhat 
similar to that used for commercial work. 

The standards or posts supporting the cups which 
contain the elements are brass rods 1/2 inch square and 1 1/2 inches 
high. A hole is bored in the bottom of each and threaded 
with an 8-32 tap to receive a machine screw which passes 
through the base and holds them in an upright position. A 
hole is bored 1 1/8 inches from the bottom, in the face of one 
standard and threaded with an 8-32 tap. A brass rod 1 1/4
inches long, carrying at one end a cup 1 inch in diameter 
and 3/8 inch deep, is threaded to fit in the hole in the standard. 
The zincite is mounted in this cup. 

.. figure:: images/Image110.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 110. Perikon Detector. 
   
   Fig. 110. Perikon Detector. 

The other standard is cut in half with a hack saw and a 
1/8-inch hole bored 1/4 inch deep in the axis of each piece. A 
pin, 1/2 inch long, is set in the lower half by soldering it in the 
hole. The upper half of the standard is placed over the pin 
and left free to move when twisted. A 1/8-inch brass tube, 
1 inch long, passes through the upper part of the standard. 
A 1/8-inch brass rod, 1 3/4 inches long, passes through the tube. 

The small cup containing the zincite is mounted on one 
end of the rod and a hard rubber handle on the other. 

A brass spring is placed between the cup and the standard 
in order to press the chalcopyrites against the zincite. The 
cup is mounted out of center so that by revolving it and 
twisting the standard at the same time the chalcopyrites 
may be brought into contact with any portion of the zincite. 
By screwing the rod supporting the zincite cup in or out of 
the standard the pressure with which the two elements are 
pressed together may be regulated. 

The base of the detector is hard rubber of the dimensions 
indicated in the illustration. Four binding posts on each 
corner of the base are necessary. The detector is connected 
in a similar manner to the silicon detector shown in Fig. 
\108. If a battery is used the circuit should be like that of 
the "bare point" electrolytic, and the current must flow 
from the zincite to the chalcopyrites. 

LEAD PEROXIDE DETECTOR.
``````````````````````` 

The peroxide of lead detector makes use of no liquids, but 
still may be classed as an electrolytic since its action is of 
that nature. 

.. figure:: images/Image111.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 111. Peroxide of Lead Detector. 
   
   Fig. 111. Peroxide of Lead Detector. 

It consists of a pellet of lead peroxide held between an 
electrode of lead and one of platinum. Contrary to most 
other detectors, the resistance is increased upon the passage 
of electrical oscillations. The oscillations stimulate 
chemical action and increase a counter-electromotive force 
sufficiently so that a decrease in the current sent through the 
phones by the local battery takes place. The action may 
be outlined more in detail as follows. The current of the 
local battery decomposes part of the lead peroxide into its 
components, lead and oxygen. The lead ions are 
positively electrified and so they tend to pass upward toward 
the lead electrode which is negative. The negative ions of 
oxygen gas tend to pass downwards towards the platinum. 
But the lead and platinum electrodes with the intervening 
lead peroxide constitute a small cell acting independently 
of the local battery and sending a current in the opposite 
direction. This counter-electromotive force tends to send 
the ions in an opposite direction to that in which they are 
sent by the battery current. Upon the passage of electrical 
oscillations this counter electromotive force is increased 
and sufficient ions sent out in opposition to those of the 
battery current so that an appreciable drop in the current 
flowing through the telephone receivers takes place. The 
sudden current drop produces a sound in the receivers. 

The lead pellets may be secured from a druggist who can 
mold them in his tablet press. They should be subjected 
to as great a pressure as possible in order to reduce 
resistance and prevent crumbling. 

A piece of platinum foil about 1/2 inch square is placed 
beneath the pellet on the crystal electrode. A piece of 
clean, bright sheet lead 3/8 inch in diameter and 1/8 inch thick 
is laid on the pellet and the whole clamped together by 
tightening the thumbscrew passing through the collar on 
the spring, *S*. The detector is connected up similar to 
the "bare point," The platinum is made the positive of 
the local battery. Adjustment is secured by regulating the 
pressure. 

It is very necessary that the pellets be kept dry, as 
otherwise a loud singing and hissing noise, due to the 
decomposition of the water, will render the reception of signals very 
difficult. 

THE MARCONI MAGNETIC DETECTOR.
`````````````````````````````` 

When an oscillatory discharge takes place through a coil 
of wire surrounding a needle, it magnetizes the needle in 
a totally different manner from a voltaic current. The 
needle will have several poles throughout its length, many 
of them reversed. Rutherford applied this phenomenon to 
the detection of electrical oscillations, but it remained for 
Marconi to improve it and give the magnetic detector its 
existing form. This type of detector is very sensitive, free 
from all adjustment and is not made inoperative by the 
heavier discharge of the transmitter during each period of 
sending. 

.. figure:: images/Image112.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 112. Marconi Magnetic Detector. 
   
   Fig. 112. Marconi Magnetic Detector. 

A small transformer is provided with a core composed 
of a band or cord of iron wires in the form of an endless 
belt which passes around two pulleys kept in motion by 
a clockwork motor. The band revolves in the field of a 
strong horseshoe magnet and passes directly over the poles 
after issuing from the transformer bobbin, so that the 
portion approaching the bobbin are constantly in a state of 
increasing magnetism. The actual operation is based upon 
the property of iron called hysteresis, for the magnetism 
of the core lags behind that of the permanent magnet and 
is of a different degree from what it ought to be, in view of 
its position in the vicinity of the permanent magnet. The 
moment the oscillations pass through the primary coil of 
the transformer, this lag is set free and the magnetism 
assumes its full value. The change in magnetism induces 
a current in the secondary, which registers as a sound in 
the telephone receivers. 

.. figure:: images/Image113.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 113. Details of Transformer. 
   
   Fig. 113. Details of Transformer. 

The primary coil is made up of a single layer of No. 
36 B. S. gauge silk covered wire wound on a thin walled 
glass or hard rubber tube. The ends of the tube, which is 
2 inches long and 1/4 inch external diameter, are slightly 
flared so as not to chafe the band. The primary is 
thoroughly shellacked and covered with a single layer of paper. 

The secondary is also of No. 36 B. S. silk covered wire 
and is wound between two disks of hard rubber, 1/4 inch 
thick and 1 1/2 inches in diameter, placed 3/8 inch apart in the 
center of the secondary and the intervening space wound 
full of wire. 

The terminals of both the primary and secondary are 
extended to binding posts mounted on the case of the 
instrument. 

.. figure:: images/Image114.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 114. Method of Joining Ends of Band. 
   
   Fig. 114. Method of Joining Ends of Band. 

The core or revolving band is made by winding 100 
strands of No. 36 silk covered soft iron wire between two 
small pegs, placed a distance apart, equal to twice the 
circumference of the oval formed by the two pulleys. The 
wire is all wound in the same direction. It should be 
carefully removed from the pegs and kept taut while it is 
slightly twisted, doubled, and then further twisted into a 
rope or cord. The ends are threaded together with a 
separate piece of insulated wire, into a link which will pass 
easily through the primary tube. 

.. figure:: images/Image115.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 115. Pulley. 
   
   Fig. 115. Pulley. 

The pulleys around which the band revolves are made of 
hard wood. They are 4 inches in diameter and 3/8 inch thick 
and have a V-shaped groove cut in the edge. In order to 
minimize friction and wear, it is advisable to fit them with 
a bearing which may be made out of brass tubing and a 
couple of washers. One of the pulleys is geared to a 
clockwork motor so that the band makes a complete revolution 
about once every two minutes. An old eight day clock 
may be adapted for this purpose, or, what is much better, 
the motor from an old phonograph. 

.. figure:: images/Image116.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 116. Pulley Bearings. 
   
   Fig. 116. Pulley Bearings. 

The horseshoe magnet is mounted with its north pole 
pointing towards and nearly touching the middle of the 
outside of the secondary. The south pole is placed 
opposite the end of the primary tube which is on the side towards 
which the band is revolving, that is, the band in revolving 
passes first over the north pole and then over the south. 
Two magnets are sometimes used with their north poles 
together in the center of the secondary, and a south pole 
opposite each end of the primary tube. 

.. figure:: images/Image117.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 117. Circuit of Magnetic Detector. 
   
   Fig. 117. Circuit of Magnetic Detector. 

The commercial instrument is placed in a glass covered 
case which protects it from dust and injury. The 
clockwork motor is concealed in the lower part of the case. This 
is a good plan but an experimental detector may be merely 
mounted on a flat wooden base as illustrated in Fig. 112. 

The secondary terminals are connected directly to the 
telephone receivers while the primary leads to the aerial 
and the ground. When the detector is started up it should 
make a very slight hissing sound in the telephone receivers 
as the band passes slowly through the coils. This shows 
the instrument to be in good working order and ready for 
the reception of signals. 

**The Audion.**—Dr. Lee DeForest was led by the 
flickering of a sensitive gas flame to investigate whether or not it 
would respond to Hertzian vibrations as well as to those of 
heat and sound. His experiments led to the invention of 
the audion, a peculiar instrument making use of ionized 
gas for its operation. 

The audion consists of an incandescent lamp having a 
metallic filament, on either side of which are a grid and a 
plate made of nickel. When the filament is lighted it 
throws off ions which act as a relay to high frequency 
oscillations passing between the plate and the grid. A 
properly constructed audion is exceedingly sensitive and 
produces very loud tones in the telephone receivers. It has 
the further advantages of entire absence of adjustment 
except the governing of the battery voltage, and is capable 
of extremely fine tuning. 

.. figure:: images/Image118.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 118. Fleming Oscillation Valve. 
   
   Fig. 118. Fleming Oscillation Valve. 

Fleming originated the oscillation valve illustrated in 
Fig. 118. It consists of an ordinary incandescent lamp 
with a carbon filament, having a metal cylinder, *C*, placed 
around the filament, but attached to an independently 
insulated platinum wire sealed in the glass. When the lamp 
is lighted by passing a current through the filament, the 
incandescent carbon liberates negative ions. If 
oscillations are then set up in a circuit which includes a pair of 
sensitive telephone receivers and is formed by connecting 
the negative terminal of the filament with the platinum 
cylinder, negative electricity will be enabled to pass from 
the filament to the cylinder but not in the opposite direction, 
and so sounds will be produced in the telephone receivers. 
High frequency oscillations themselves could not be made 
to pass through the telephone receivers because of the 
choking action of the iron cores of the electromagnets. 

.. figure:: images/Image119.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 119. Flame Audion. 
   
   Fig. 119. Flame Audion. 

The simple but sensitive form of detector illustrated in 
Fig. 119 is not of practical value for commercial work, but 
is very interesting as the progenitor of the audion, and 
provides a good field for amateur investigation. Its only 
drawback is that the gas flame is very difficult to keep 
steady and every flicker registers as a sound in the telephone 
receivers. 

A Bunsen burner using coal gas furnishes the flame, and 
a salt of an alkaline metal heated in the flame, the ions. 
The hydroxides of caesium, potassium and sodium give the 
best results in the order named. 

The salt is contained in a piece of trough-shaped platinum 
foil, about 3/8 inch long and 1/16 inch wide. This trough is 
made the cathode or negative of the telephone circuit and 
placed in the outer oxidizing flame just above its juncture 
with the interior reducing flame and must be kept 
incandescent. The upper electrode or anode is a piece of 
platinum wire about 1/16 inch above the trough. 

.. figure:: images/Image120.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 120. Circuit of Flame Audion. 
   
   Fig. 120. Circuit of Flame Audion. 

The arrangement and construction of the detector is 
clearly indicated by the drawing so that it is unnecessary 
to go into details. The block, *E*, which fits on the tube of 
the Bunsen burner, is made of fiber. Two double binding 
posts, *D*, are fastened to *E* to support the rods, *R*, which 
are fitted at the tops with binding posts, *B*, into which the 
electrodes may be clamped. 

Twelve dry cells are connected with a multiple point 
switch so that an electromotive force of 6-18 volts, varying 
in steps of one cell at a time, may be secured. The flame 
is best provided with a mica chimney to protect it from 
drafts. By keeping plenty of salt in the trough and 
carefully adjusting the voltage, this detector may be made 
marvelously sensitive. 

.. [#] The different detectors in order of their sensitiveness are electrolytic, perikon, magnetic, silicon, carborundum. 

.. [#] Peacock ore or bornite, which consists of about 60 parts of copper, 14 parts of iron and 26 parts of sulphur, may be substituted for the chalcopyrites with excellent results. 


CHAPTER XIV. TUNING COILS AND TRANSFORMERS. 
-------------------------------------------

A tuning coil is merely a variable inductance wound in 
single layer on a suitable form. 

Fig. 121 illustrates a double slide tuner. The base is a 
piece of hard wood, 12 inches long, 1 inch thick and 5 1/2 
inches wide. Two wooden heads 4 x 4 x 3/4 inches support 
the form upon which the coil is wound. 

.. figure:: images/Image121.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 121. Double-slide Tuning Coil. 
   
   Fig. 121. Double-slide Tuning Coil. 

The form is a piece of wooden curtain pole, 9 inches long 
and 3 inches in diameter. Some may prefer to use a 
cardboard tube in place of the curtain pole. A tube can be 
made by winding a long strip of cardboard 9 inches wide 
around a suitable form and cementing the layers together 
with shellac. The liberal use of shellac will stiffen the tube 
and cause it to better retain its shape. The tube is held 
tightly between the two heads by means of a brass rod 
which passes through the center and is clamped by two 
nuts. 

A square brass rod 10 1/2 inches long is fastened to the 
center of the top of the heads and a similar rod to the center 
of the front face. 

.. figure:: images/Image122.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 122. Sliders. 
   
   Fig. 122. Sliders. 

Fig. 122 shows two forms of sliders. The first one is the 
better and to be preferred. A short square brass tube, *S*, fits 
snugly upon the square brass rod, *R*. It cannot turn around 
but is free to slide back and forth. A strip of spring brass, 
*C*, is soldered to the lower face of the square tube. It is 
bent in a double turn and a punch mark made near the lower 
end as shown in the illustration. The indentation is made 
with a center punch, but should not be deep enough to 
break through the metal. 

.. figure:: images/Image123.jpg
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   :alt: Fig. 123. Double-slide Tuning Coil Circuits. 
   
   Fig. 123. Double-slide Tuning Coil Circuits. 

The little projection on the under side of *C* caused by the 
punch mark is the only part of the slider which should make 
contact with the wire on the tuning coil. It should slide 
easily but firmly along the wires and touch only one at a 
time. Long distance signals will be considerably weakened 
if the slider touches more than one wire at a time and 
short-circuits a turn. 

.. figure:: images/Plate4.jpg
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   :scale: 85 %
   :alt: Plate IV. Receiving Circuits. (Straightaway Aerial.) 
   
   **Plate IV. Receiving Circuits. (Straightaway Aerial.)**

The slider, *B*, is similar to *A* except that it has a short 
length of brass tubing, *T*, soldered to the under side of *S* 
in place of the brass strip, *C*. A small ball bearing which 
just fits the bore of the tube is pushed down into contact 
with the wire by means of a small spiral spring inside of the 
tube. Both sliders are fitted with a hard rubber handle 
so that they may be adjusted without the ringers coming 
into contact with the metal. 

.. figure:: images/Image124.jpg
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   :alt: Fig. 124. Murdock Double-slide Tuning Coil. 
   
   Fig. 124. Murdock Double-slide Tuning Coil. 

.. figure:: images/Image125.jpg
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   :alt: Fig. 125. United Wireless Receiving Set. 
   
   Fig. 125. United Wireless Receiving Set. 

Two good circuits employing the double slide tuner are 
given in Fig. 123. Plates IV and V illustrate the 
oscillation or tuning circuits of the most prominent receptor 
systems.

If a loop aerial is used, more than one tuning coil is 
necessary as shown by the loop aerial oscillation circuits in 
Plate V. 

Figs. 125 and 126 illustrate the instruments employed 
for receiving by the United Wireless Company. 

.. figure:: images/Image126.jpg
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   :alt: Fig. 126. United Wireless Portable Receiving Set. 
   
   Fig. 126. United Wireless Portable Receiving Set. 

In Fig. 125 the handles which are attached to the sliders 
of the tuning coils project through long slots cut in the top 
and one side of the cabinet. 

The tuning coils in the portable outfit are mounted in 
a vertical position in back of the aerial switch. 

**Loosely Coupled Tuning Coil.**—By the use of a loosely 
coupled receiving tuner or transformer, the range of a station 
is considerably increased, as is also the strength of the 
signals, and much finer tuning and selectivity made possible. 

Fig. 127 illustrates the construction of such an oscillation 
transformer. 

The base is wood and measures 14 x 5 1/2 x 1 inches. The 
primary winding is wound on a cardboard or fiber tube 4 1/4 
inches long, having an internal diameter of 2 3/4 inches and 
an external diameter of 3 inches. The heads, *L* and *M*, are 
the same size as those of the double slide tuning coil. The 
head, *L*, has a circular hole 2 3/4 inches in diameter cut in the 
center in order to permit the secondary coil to slide in and 
out of the primary. 

.. figure:: images/Image127.jpg
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   :alt: Fig. 127. Oscillation Transformer. 
   
   Fig. 127. Oscillation Transformer. 

The secondary coil is a piece of round curtain pole 2 1/2 
inches in diameter and 3 inches long. A 5/16-inch hole is 
bored through its axis. The head, *K*, of the secondary coil 
is 3 3/4 x 3 3/4 x 3/4 inches. A ten-point switch on *K* is so 
connected that it divides the secondary into ten equal parts 
and permits any number of the divisions to be used as 
desired. 

.. figure:: images/Image128.jpg
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   :alt: Fig. 128. United Wireless Receiving Transformer. 
   
   Fig. 128. United Wireless Receiving Transformer. 

A wooden post, *J*, 2 1/2 inches high and 1 1/4 inches wide, 
supports one end of a 1/4-inch brass rod upon which the 
secondary slides back and forth. 

.. figure:: images/Image129.jpg
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   :alt: Fig. 129. Details of Receiving Transformer. 
   
   Fig. 129. Details of Receiving Transformer. 

No. 24 B. S. gauge copper wire may be used for winding 
both the primary and secondary. It is also the proper size 
to use on the double slide tuner. The best method is to use 
bare wire, wound with a thread so that a thread is 
interposed between adjacent turns of the winding. Give the 
whole winding one or two coats of thick shellac and allow it 
to harden. Then use a strip of sandpaper to remove the 
shellac in a long narrow path immediately below the sliders 
so that they may make contact with the wire. 

.. figure:: images/Image130.jpg
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   :alt: Fig. 130. Slider for Loose Coupler.
   
   Fig. 130. Slider for Loose Coupler.

Some may prefer to make a loosely coupled tuner in which 
the inductance of both coils is adjustable by means of a 
sliding contact. In such a case the slider on the secondary coil 
must be constructed as illustrated in Fig. 130. The contact 
is long and narrow so that it can touch the innermost turns, 
when placed within the primary. By slipping the slider off 
the end of the rod and reversing it, the contact can be made 
to touch the turns next to the head. The square brass rod 
is set in a notch cut in the coil head so that the rod is flush 
with the top. 

When tuning a receiving transformer, place both variable 
condensers in a halfway position and adjust the sliding 
contacts, first on the primary and then on the secondary, until 
the signals are the loudest. Then adjust the condensers. 

.. figure:: images/Image131.jpg
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   :alt: Fig. 131. Loosely Coupled Tuning Circuits. 
   
   Fig. 131. Loosely Coupled Tuning Circuits. 

To cut out an undesirable station, vary the coupling 
between the two coils by sliding the secondary away from the 
primary. When several turns on the secondary seem to 
give the same results also vary the coupling. 

.. figure:: images/Image132.jpg
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   :alt: Fig. 132. Combination Loosely and Closely Coupled Tuner. 
   
   Fig. 132. Combination Loosely and Closely Coupled Tuner. 

Fig. 132 illustrates the wiring diagram of a combination 
loosely and closely coupled tuner. Two sliding contacts are 
placed on the primary coil of the receiving transformer and 
connected with a double pole double throw switch as in the 
diagram. When the switch is thrown on contacts 1 and 2, 
the primary is connected to the detector as a double slide 
tuner, and when on 3 and 4 both the primary and secondary 
are brought into use as a transformer. 

This arrangement may seem cumbersome and is 
recommended only as a convenience in experimenting. A loosely 
coupled tuning coil is capable of exact tuning, and unless one 
understands how to use it, he may not hear a station 
because the tuner is not properly adjusted. By using the 
double slide tuner first and then throwing the switch so as 
to tune in on the transformer, this difficulty may be 
eliminated. 

.. figure:: images/Image133.jpg
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   :alt: Fig. 133. Clapp-Eastham Loose Coupler. 
   
   Fig. 133. Clapp-Eastham Loose Coupler. 

**Potentiometer.**—A potentiometer is not properly classed 
under the heading of tuning coils, but the construction may 
be made so similar that it well appears here. 

The potentiometer is merely a variable resistance shunted 
across the terminals of the detector battery in the manner 
illustrated in the numerous detector circuits. It is used to 
reduce the voltage of the battery to a value slightly below 
the critical voltage of the detector. The critical voltage of 
a detector is the voltage at which its action commences. In 
the case of an electrolytic detector, it is the voltage required 
to break down the thin film of gas which collects on the 
"bare point." 

.. figure:: images/Image134.jpg
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   :alt: Fig. 134. A Highly Efficient Form of Loose Coupler. 
   
   Fig. 134. A Highly Efficient Form of Loose Coupler. 

In construction, the potentiometer illustrated in Fig. 135 
is in reality a small edition of a double slide tuning coil. It 
is wound with No. 28 B. S. gauge German silver wire. Three 
binding posts are mounted on the base, two of them 
connecting with the ends of the coil and one with the sliding 
contact. 

.. figure:: images/Image135.jpg
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   :alt: Fig. 135. Potentiometer. 
   
   Fig. 135. Potentiometer. 

In a finely balanced circuit where long distance work 
and close tuning are desired, the potentiometer must be 
non-inductive. 

.. figure:: images/Image136.jpg
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   :alt: Fig. 136. Amco Potentiometer. 
   
   Fig. 136. Amco Potentiometer. 

This may be accomplished by using two potentiometers 
wound in opposite directions from one another and 
connected in series. The two terminals of the windings are 
then connected across the battery and the sliding contacts 
led to the detector. 

.. figure:: images/Plate5.jpg
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   :scale: 85 %
   :alt: Plate V. Receiving Circuits.
   
   **Plate V. Receiving Circuits.**

CHAPTER XV. RECEIVING CONDENSERS. 
---------------------------------

Condensers play an important part in tuning and 
adjusting the receiving circuits of a wireless telegraph 
station. They are inserted in the circuits for various 
purposes. In some places a small condenser shunts the 
detector to somewhat equalize any small changes in 
capacity which might occur in the detector and throw the 
circuit out of tune. In other cases where selectivity is 
desired they provide a path for undesirable oscillations and 
allow them to flow into the ground without passing through 
the detector. Wherever the double slide tuner or the 
Fessenden single slider circuit is used, a condenser must be 
inserted in the circuit to prevent the wire of the tuning coil 
from short-circuiting the telephone receivers and battery. 

.. figure:: images/Image137.jpg
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   :alt: Fig. 137. Tuning Circuit with and without an Adjustable Condenser. 
   
   Fig. 137. Tuning Circuit with and without an Adjustable Condenser. 

The value of a condenser may be readily appreciated by 
the following experiment. Connect up a detector according 
to the diagram shown by *A* of Fig. 137. This circuit will 
give good results and the signals will be clear. But change 
it to that shown in *B*, by connecting one side of a variable 
condenser to the upper contact of the tuning coil and 
leading the other side to the ground. Considerable selectivity 
may now be attained and the signals will be 50 per cent 
louder. 

To be of any value for a receiving circuit the capacity of 
the condenser must be adjustable, but there are many places 
where a fixed condenser is of service. 

The average capacity of such condensers generally ranges 
around .003 of a microfarad, but cannot be predetermined, as 
it depends upon many factors which vary greatly in 
different stations. Even if specific dimensions were given for 
the construction of a paper condenser of stated capacity, 
the experimenter would very seldom succeed in constructing 
his condenser and have it of this value when finished. The 
paper used as the dielectric and the pressure applied to the 
condenser would make the difference. 

The best plan is to build one up in the form of a roll as 
follows. Three thin tin foil strips 3 1/2 inches wide and four 
feet long are separated by strips of thin paraffined paper 
4 inches wide and four and one-half feet long. The two 
outside strips of tin foil are connected together and form one 
terminal of the condenser. The middle strip of tin foil is the 
other. The outside strips of tin foil are covered with 
paraffined paper and the whole rolled up. If thin paper and 
tin foil are used the condenser will form a roll 4 inches long 
and less than an inch in diameter. 

Two or three such condensers should be constructed, and 
one of them connected up in the circuit where it is desirable 
to use it. By unrolling a little of the condenser and cutting 
one or two inches off at a time the proper size may be 
determined. 

As explained in Chapter VII, two equal condensers 
connected in series have one-half the capacity of either. By 
connecting them in parallel the capacity is the sum of the 
two. In this manner it is not hard to first find the 
approximate capacity, which gives the best results before cutting 
the condenser. 

.. figure:: images/Image138.jpg
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   :alt: Fig. 138. Tubular Condenser. 
   
   Fig. 138. Tubular Condenser. 

When the proper value is found, place the condenser in 
a brass tube about 5 inches long and 1 inch in diameter. 
The tube is fitted with hard rubber flanges to close the ends. 
A binding post is mounted on each flange, and connects with 
the terminal of the condenser to which it is nearest. 

Mounting a condenser in this manner gives it a much 
better appearance and it occupies less space than otherwise. 
Fixed condensers are used in two cases only, to shunt the 
condenser and to prevent the tuning coil from 
short-circuiting the telephone receivers. In any other position they are 
worthless. 

**Variable Condensers.**—A simple form of adjustable 
condenser which may be quickly made for a special 
experiment is constructed in the following manner. A wooden 
curtain pole 2 inches in diameter and 18 inches long is 
covered with a layer of tin foil. The tin foil must be laid on 
smoothly and cemented with shellac. A layer of paraffined 
paper is then placed over the tin foil. A piece of sheet 
copper or tin 6 3/4 inches wide and 18 inches long is rolled up 
in a cylinder to fit over the rod with its tin foil and paper. 
The rod is fastened at one end to a base board about 20 
inches long and 4 inches wide, by means of a bracket, or it 
may be mounted on a smaller base in a vertical position. 

Connections are made to the tin foil and to the outside 
metal tube. By sliding the tube back and forth on the rod 
the condenser may be given a variable capacity. 

.. figure:: images/Image139.jpg
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   :alt: Fig. 139. Variable Condenser. 
   
   Fig. 139. Variable Condenser. 

The best variable condensers are constructed so that the 
dielectric between the two plates is formed by air. There 
are consequently no losses of energy in the condenser, for 
this mode of construction eliminates all dielectric hysteresis. 

Fig. 139 shows such a variable condenser and Fig. 140 
the details. It is possible to do very close, selective tuning 
with this instrument. The efficiency of the receiving circuit 
may be considerably improved if one is used wherever a 
condenser is required. 

A rectangular box is built up in the manner shown in 
Fig. 135. The sides, *D*, are 6 inches long, 4 11/16 inches wide 
and 1/2 inch thick. The top, *A*, is 6 inches long, 1 13/16 inches 
wide and 1/2 inch thick. The bottom, *B*, has the same width 
and thickness but is 11 inches long. Eleven grooves are 
cut in *A* and *B* as shown in the cross section. The grooves 
are 1/16 inch wide, 3/16 inch deep and 1/16 inch apart. They are 
formed by setting the blade of a circular saw so that it 
projects 3/16 inch above the table or bed. After cutting one 
groove, the guide is moved 1/8 inch and another cut made. 

.. figure:: images/Image140.jpg
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   :alt: Fig. 140. Details of Variable Condenser. 
   
   Fig. 140. Details of Variable Condenser. 

Eleven metal plates, *P*, are required, six fixed and five 
movable. They are made of No. 22 gauge sheet brass and 
measure 4 x 6 inches. Six of them are placed in the grooves 
in the box in such a manner that an empty groove is left 
between each one. The six plates are then electrically 
connected together by soldering a strip of brass across their 
rear ends. 

.. figure:: images/Image141.jpg
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   :alt: Fig. 141. Sliding Plate Variable Condenser. 
   
   Fig. 141. Sliding Plate Variable Condenser.  

Five slots each 1/4 inch deep and 1/4 inch apart are made 
with a hack saw in a piece of brass, *C*, 1 1/2 inches long, 
3/4 inch wide and 1/2 inch thick. A small pin 1/2 inch long is 
set in the center of *C* on the opposite side from the saw 
cuts. A fiber handle 1/2 inch in diameter and 1 1/2 inches long 
is fastened to the pin. 

The five movable brass plates are set in the grooves 
between the six fixed plates. They are allowed to project 
three or four inches out of the box. The yoke, *C*, is then 
soldered across the ends so that each one of the movable 
plates fits into its corresponding saw cut. 

The capacity of the condenser is varied by sliding the 
movable plates back and forth between the fixed plates. 

A binding post is soldered to the yoke, *C*, and another 
one to the strip which holds the fixed plates together. 
Connections are made to the binding posts with lamp cord or 
some other flexible conductor which will not interfere with 
the movement of the plates. 

The instrument is finished by staining the woodwork and 
giving it a coat of varnish or shellac. 

CHAPTER XVI. TELEPHONE RECEIVERS AND HEADBANDS. 
-----------------------------------------------

A pair of high resistance telephone receivers in nice 
adjustment constitute one of the most sensitive electrical 
instruments in existence and will detect an exceedingly 
weak current. 

The only type of receiver of much service in wireless 
telegraphy is that known as a watch case or pony receiver. It 
is small and compact so that it may be attached to a 
headband and clamped against the ear. 

.. figure:: images/Image142.jpg
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   :alt: Fig. 142. Types of Permanent Magnets. 
   
   Fig. 142. Types of Permanent Magnets. 

The permanent magnets of a watch-case receiver are 
usually in the form of either a ring or a horseshoe as shown 
by Fig. 142. The first form has "consequent" poles and 
is considered somewhat superior to the horseshoe, since the 
lines of force are not so liable to pass across the pole pieces 
before they pass through the electromagnets and the 
diaphragm. 

The ordinary low resistance telephone receiver is 
perfectly well suited to the telephone work for which it was 
designed and adjusted, and will give good service on a 
wireless receptor for short distances, but can be considerably 
improved by following the suggestions and instructions 
given below. 

The principal objection to the ordinary receiver is that 
it does not contain enough turns of wire on its bobbins. 
This is easily remedied by carefully rewinding them with a 
very fine silk covered, pure copper magnet wire no larger 
than No. 40 B. S. gauge. This will increase the number 
of turns and also the resistance, but it must not be inferred 
that resistance is to be desired. This is a common 
impression of amateurs who do not understand the underlying 
principle, that the strength of an electromagnet varies 
directly as the number of turns of wire, multiplied by the 
amperes flowing through the magnet. When a telephone 
receiver is wound with a finer wire the resistance is increased, 
cutting down both the current and the strength of the 
magnet. But if pure copper wire is used, and the winding 
not carried beyond the point where the circumference of 
the outside layer becomes twice as great as the 
circumference of the first layer, the number of turns increases faster 
than the resistance and the magnet strength is considerably 
greater than before the receiver was rewound. 

No. 40 B. S. gauge silk covered wire is often used for this 
purpose, but the best results are obtained with enameled 
covered wire of the same size. It is possible to wind almost 
three times as much of the enameled wire on a telephone 
bobbin as silk wire of the same size. The difference is due 
to the thickness of the insulation. An ordinary double pole 
watch-case receiver will have a resistance of 800-1,000 
ohms when wound with silk covered wire and 1,500-1,800 
ohms when wound with enameled wire. 

To rewind a telephone receiver, first unscrew the cap and 
remove the diaphragm, then remove the bobbins by 
unloosening the screws with the aid of a screw driver. 
Unwind the old wire and examine the empty bobbins to see 
that wherever the wire is liable to come into contact with 
the metal that it is well insulated with paraffined paper 
or some other equally good material. Then wind the new 
wire on in smooth even layers and when it is completed 
fasten the bobbins back on the permanent magnets and 
connect them up. The current should flow through in 
opposite directions so that the north pole of one and the 
south pole of the other is on top. Do not trust splice 
connections but solder them using acid as a flux. 

The Navy Department specifies that its wireless receivers 
shall be wound with copper wire of not less than 0.0015 
inch in diameter and the diaphragm to have a diameter 
of 1 3/4 inches and a thickness of 0.004 inch. The 
resistance of the coils is specified at 1,000-1,100 ohms. 
There is not much advantage in greatly exceeding the 
number of turns possible with this winding, for to obtain 
them a much finer wire than No. 40 B. S. gauge is 
necessary and the ratio between resistance and turns becomes 
greater. 

The second objection to the ordinary receiver is that the 
diaphragms are very often too thick. A receiver having a 
thin diaphragm is preferable because when a weak current 
is sent through the coils, the change in magnet strength is 
greater. But this may be carried to excess and the 
diaphragm made so thin that it cannot absorb sufficient lines 
of force to properly play its part. The best thickness then 
for a diaphragm can only be determined experimentally 
and depends much upon the diameter. The distance from 
the poles and the strength of the magnets will also have 
considerable bearing on the thickness. The ordinary phone 
will be very sensitive and give clear tones with diaphragms 
ranging from .01-.004 inch. 

The relation between the thickness and the diameter is 
shown by the following: If the diaphragm of a receiver is 
increased in diameter, the tones will become more distinct, 
but if the increase is carried too far they will become 
indistinct and the only remedy is to thicken the diaphragm. 
Likewise if after clearness is secured the diaphragm is 
thickened so that the tones again become indistinct, the 
diameter must be increased. 

.. figure:: images/Image143.jpg
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   :alt: Fig. 143. Grinding Tool. 
   
   Fig. 143. Grinding Tool. 

The third objection is that such receivers are not 
carefully and properly adjusted. The adjustment is also a 
matter of experiment and is accomplished by comparison 
of the receiver in question with one which is known to be 
in a sensitive condition. The adjusting may be done by 
means of the tool shown in Fig. 143. 

This tool is made from an ordinary file by grinding off 
the teeth on one side save for a distance of about 3/4 inch in 
the middle. The grinding may be done on an emery wheel. 
The part (*a*) is used for filing the pole pieces and thus 
making the distance between them and the diaphragm greater. 
The tool has the advantage over an ordinary file of 
permitting the poles to be filed without removal from the 
receiver and without grooving the diaphragm bed or the 
receiver case. 

To lessen the distance between the poles and the 
diaphragm, lay the receiver bed downward on a piece of fine 
emery paper and rub with a circular scouring motion. If 
the emery paper is placed on a perfectly flat surface no 
trouble will be experienced in grinding the bed down evenly. 

When filing the pole pieces rub with the same circular 
motion so as to grind off all sides evenly. Test from time 
to time by passing a straight edge over the bed in all 
directions while holding to the light and looking between the 
straight edge and the poles. In this manner the distance 
separating the diaphragm and the poles may be gauged and 
whether or not it is the same on all sides. Bear in mind 
that if the diaphragm is thin, the attraction of the 
permanent magnets will cause it to bend in towards the poles. 

In case you have a pair of receivers built for wireless work, 
which appear to be in good condition but do not give 
their former results, the last thing to do is to tamper with 
the adjustment. The most common cause, when the tones 
are impaired, is dirt or dust accumulated on the poles or 
diaphragm and damping its vibration. The cap should 
be carefully unscrewed and the diaphragm examined to see 
if it is bent. If so, replace with a new one of the same size. 
Remove any dirt or filings, and if the diaphragm is rusty 
clean it by laying it on a flat surface and rubbing it with a 
piece of fine emery paper. Then give it a thin coat of 
colorless lacquer. Examine the magnets and pole pieces to see 
if they have become loosened and if so tighten them. 

Or the trouble may be that the permanent magnets have 
lost part of their magnetism, and almost any receiver which 
has been in use for some length of time will bear having its 
magnets strengthened. If they are found to be weak they 
should be removed and remagnetized. This is 
accomplished by winding a coil of No. 18 B. S. gauge wire around 
them and sending a heavy direct current through for a few 
minutes. 

.. figure:: images/Image144.jpg
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   :alt: Fig. 144. Parts of a Holtzer Cabot Receiver. 
   
   Fig. 144. Parts of a Holtzer Cabot Receiver. 

In carrying out any of these suggestions remember to 
work with one receiver at a time, keeping the other for 
comparison, so that by repeated tests you may tell whether 
or not an improvement is being made and when well enough 
is reached, let it alone. 

Fig. 144 shows the construction of a telephone receiver 
manufactured by the Holtzer Cabot Co. of Brookline, Mass. 
The permanent magnets and bobbins are mounted in a 
metal cup, *B*, which supports the diaphragm, *A*. The metal 
cup is enclosed in a hard rubber shell, *C*, and fitted with a 
cap, *D*. 

The complete receivers are mounted on an adjustable 
headband and fitted with pneumatic ear cushions which 
make them set more comfortably and shut out extraneous 
noise. These receivers are wound to all resistances used in 
the wireless field but, for the experimenter, those having a 
resistance of 1000 ohms apiece will give the best all around 
results. 

.. figure:: images/Image145.jpg
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   :alt: Fig. 145. Holtzer Cabot Head Set. 
   
   Fig. 145. Holtzer Cabot Head Set. 

It is very desirable that the receivers should be fitted 
with a comfortable headband which will hold the telephones 
in close adjustment to the ears. Fig. 146 shows the 
construction of such a band. 

.. figure:: images/Image146.jpg
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   :alt: Fig. 146. Adjustable Head Band. 
   
   Fig. 146. Adjustable Head Band. 

Two brass straps, 1 inch wide, 12 inches long and 1/16 inch 
thick are necessary. Two 1/8-inch holes, *mm*, are bored in 
them 3/16 inch from one end and the end bent up at an angle 
along a line 3/8 inch from the end as shown by the drawing. 
A cover is made for the straps, by sewing two strips of 
leather 1 1/4 inches wide and 12 inches long, together along 
their edges. The covers may then be slipped over the 
straps. Two 1/16-inch brass strips, 3/8 inch wide and a little 
longer than one-half the circumference of the watch-case 
receiver to be fitted to the head band, are bent into stirrups 
as shown in the illustration by *Y*. The ends of the stirrups 
are fitted with two pivots, *PP*, which are riveted in a hole. 
Two holes or recesses are bored in the shell of each receiver, 
on the sides 180 degrees apart. The pivots, *PP*, fit into 
these holes and form bearings in which the receivers can 
turn and adjust themselves to the ears. The stirrup has 
two small holes, *hh*, bored 3/8 inch apart at the top and 
tapped to receive a small screw. The screws pass through 
the holes, *mm*, and hold the stirrups at the end of their 
respective strap. 

The leather-covered straps are bound together by means 
of two clamps which permit the head band to be adjusted 
to suit the wearer. The clamps, *C*, are made from 1/16-inch 
brass 3/8 inch wide. Their form and construction may be 
best understood from the drawing. A small screw eye is 
cut in half and soldered to the center of the upper side of 
the clamp so that the receiver cord may be passed through 
the eyelet, *E*. 

The telephone receivers should be connected in series by 
means of a flexible telephone cord. 

CHAPTER XVII. OPERATION. 
------------------------

The first essential in order to manage a wireless station, 
after learning the construction and handling of the 
instruments, is to acquire a thorough knowledge of the telegraph 
codes. 

The two codes in use in wireless service are the Morse and 
the Continental. They are given below. 

In some cases, the intending wireless operator has had 
some experience with a Morse sounder and then it is merely 
a matter of transition and of accustoming the ear to a new 
sound. However it is always best to learn the Morse code 
first as Continental is merely an adaptation in which no 
space characters appear. 

A beginner may learn to receive most easily by 
communicating with another person to whom it is also new. They 
should first memorize all the letters of the code and practice 
transmitting before commencing any communication. 

It is a great mistake for a beginner to start by writing 
down the dots and dashes as he receives them on paper. 
He should make an effort to translate them and set the 
characters and words down directly. This at first will 
sacrifice speed but will make a better operator and enable one 
to become proficient sooner than if he begins otherwise. 

In case two complete sets of wireless apparatus are not 
convenient, one may learn to read from a buzzer connected 
to a key and a battery. The signals may be read directly 
from the sound of the buzzer itself, but if a pair of telephone 
receivers are connected across the terminals, a sound will 
be produced in the phones similar to that of a wireless 
receptor. 

In sending, avoid a short, choppy or jerky style and 
handle the key with a light but firm touch. Keep the dots 
and dashes firm and of the proper relative length, as also 
the spaces between letters and words. 

.. figure:: images/Table11.jpg
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   :alt: MORSE ALPHABET. 
   
The following suggestions and instructions adapted from 
the Rules and Regulations governing Naval Wireless 
Telegraph Stations may be of value and service to many in 
operating their instruments. 

.. figure:: images/Table12.jpg
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   :alt: CONTINENTAL ALPHABET. 
   
"The operating room should be well lighted and free from 
vibration. The room should have a well insulated entrance 
for the aerial and should be fitted with an operating table 
about two and one-half feet wide, not less than seven feet 
long and of a convenient height for working the sending key. 

The table should be of dry, well-seasoned wood and the 
instruments should be mounted on the table at safe sparking 
distances from each other. 

"The connections should all be as direct as possible and 
well insulated. High potential leads should be kept away 
from low potential leads and where they cross it should be 
at nearly right angles. 

"Sending key contacts must be kept clean and flat with 
surfaces parallel to each other. 

"All sliding contacts, especially in the receiving tuning 
coils, should be kept clean and bright and free from foreign 
matter. A sending set working at low power with all 
connections good, closed and open circuits in resonance, no 
sparking from edge of condenser, jar or plates, no glow from 
aerial and no sparking to rigging, is utilizing its power much 
more efficiently than the same set pushed to the limit with 
high resistance connections, sparking at all points and out 
of resonance." 

.. figure:: images/Image147.jpg
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   :alt: Fig. 147. Marconi Station at Siasconset, Mass. 
   
   Fig. 147. Marconi Station at Siasconset, Mass. 
   
It is a good plan for any amateur to keep a note book in 
which he can record the various distances he has been able 
to receive and transmit. He should try more than one 
circuit and jot down the results. It is then possible to bring 
a station up to an efficiency which cannot be reached in 
any other manner. 

ELECTRICAL TERMS AND DEFINITIONS.
`````````````````````````````````

*Accumulator:*
    A cell whose positive and negative 
    electrodes are formed or deposited by a current flowing from 
    a separate source. 

*Aerial:*
    A network or a number of wires insulated from 
    surrounding objects and suspended in the air to emit or 
    intercept electromagnetic waves. 

*Alternating Current:*
    An electric current, of which the 
    direction of flow reverses a number of times per second. 

*Ampere:*
    The quantity of current which will flow 
    through a resistance of one ohm under a potential of one 
    volt. The unit of current. 

*Ampere Hour:*
    The quantity of electricity passed when 
    flowing at the rate of one ampere for one hour. 

*Anode:*
    The positive terminal of a broken circuit or a 
    source of electricity. It is the carbon of a cell or the pole 
    at which a current enters a solution. 

*Capacity:*
    The relative ability of a conductor to receive 
    and retain an electric charge. 

*Circuit:*
    An unbroken conducting path for an electric 
    current. 

*Condenser:*
    A device for receiving and storing up electrostatic energy. 

*Cycle:*
    The full period of reversal of an alternating 
    current. A 60-cycle current is one making 60 complete 
    reversals per second. 

*Detector, Wireless:*
    An instrument for detecting 
    oscillations in the aerial of a receiving station. It either varies 
    its own internal resistance or generates a weak intermittent 
    direct current similar in time and duration with the signals 
    emitted by the transmitting station. 

*Dielectric:*
    A non-conductor or insulator. It usually 
    refers to the material interposed between the oppositely 
    charged coatings of a condenser. 

*Direct Current:*
    A current flowing in one direction only. 

*Electrode:*
    The terminal of an open electric circuit or a 
    conductor carrying a current and immersed in an electrolyte. 

*Electrolysis:*
    The separation of a chemical compound 
    into its elements by the action of an electric current. 

*Electrolyte:*
    A solution which will conduct a current of 
    electricity. 

*Electromagnet:*
    A mass of iron which is magnetized by 
    the passage of a current of electricity through a coil of wire 
    wound around the mass and insulated therefrom. 

*Farad:*
    The unit of electrical capacity. A condenser 
    having a capacity of one farad would be raised to a potential 
    of one volt by one ampere flowing for one second. 

*Field of Force:*
    The space which is under magnetic stress 
    in the neighborhood of a magnet or a wire carrying a current. 

*Helix, Transmitting:*
    A coil of heavy wire which furnishes 
    the inductance for the closed oscillation circuit of a wireless 
    transmitter and acts as an auto-transformer to raise the 
    voltage of the high frequency currents. 

*Henry:*
    The unit of induction. It is the induction in a 
    circuit when the electromotive force induced in this circuit 
    is one volt, while the inducing current varies at the rate of 
    one ampere per second. 

*Inductance:*
    The property of an electric circuit whereby 
    lines of force are developed around it. 

*Induction Coil:*
    An instrument or device consisting of 
    two independent coils of wire wound around an iron core, 
    and which by magnetic induction steps up an intermittent 
    direct current from a low to a high voltage. 

*Insulator:*
    A non-conductor or a substance impervious to 
    the passage of electricity. 

*Key:*
    A device for making and breaking a current into 
    periods corresponding to the dots and dashes of the telegraph code. 

*Kilowatt:*
    1,000 watts. See watt. 

*Leyden Jar:*
    A static condenser which will store up 
    static electricity and is cylindrical in form. So-called 
    because it was originated in Leyden, Holland. 

*Multiple:*
    The term expressing the connection of several 
    pieces of electrical apparatus in parallel with each other so 
    that the current is divided between them. 

*Ohm:*
    The unit of resistance. It is arbitrarily taken as 
    the resistance of a column of mercury, one square millimeter 
    in cross sectional area and 106 centimeters in height. 

*Parallel:*
    The same meaning as multiple. Parallel 
    circuits are those which start at a common point and end at 
    a common point. 

*Polarization:*
    The collection of hydrogen upon the 
    positive electrode of a primary cell with a consequent loss of 
    voltage. 

*Potential:*
    Voltage or electrical force. 

*Resistance:*
    The quality of an electrical conductor 
    whereby it opposes the passage of an electric current. The unit 
    of resistance is the ohm. 

*Rheostat:*
    A variable resistance to regulate the strength 
    of an electric current. 

*Series:*
    Opposed to parallel or multiple. Instruments 
    in series are so connected that the current passes from one 
    to the other and does not divide. 

*Spark Gap:*
    An air gap or open space between two electrodes for the passage of a high voltage discharge. 

*Storage Battery:*
    See accumulator. 

*Transformer:*
    A device for stepping up or stepping down 
    the voltage of an alternating current by means of magnetic 
    induction. 

*Tuning Coil:*
    A variable inductance for changing the 
    period of the receptor circuit. 

*Volt:*
    The unit of electrical force or potential. The 
    electromotive force which, if steadily applied to a conductor 
    whose resistance is one ohm, will produce a current of one 
    ampere. 

*Voltmeter:*
    An instrument for measuring voltage. 

*Watt:*
    Unit of work. It is the rate of work of one ampere 
    flowing under a potential of one volt. Seven hundred and 
    forty-six watts represent one electrical horsepower. 

.. figure:: images/Plate6.jpg
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   :alt: Plate VI. DeForest and Marconi Systems.
   
   **Plate VI. DeForest and Marconi Systems.**
   
CHAPTER XVIII. THE AMATEUR AND THE WIRELESS LAW. WHAT IT IS; HOW TO COMPLY; HOW TO SECURE A LICENSE.
----------------------------------------------------------------------------------------------------

On August 13, 1912, Congress enacted a "Wireless Law" 
to regulate radio communication. The whole law may be 
found in the appendix of this book, but briefly as far as 
the amateur is concerned it is as follows: 

An amateur may not use transmitting apparatus which 
is sufficiently powerful to send radio signals across any of 
the boundaries of the state in which he is located and 
which can be detected by a sensitive receiving set located 
just beyond the state boundary, nor can he use apparatus 
which is powerful enough to interfere with the reception of 
signals by others from beyond the state boundaries unless 
he has a *license*.

An amateur may receive messages from anywhere at 
any time without a license provided that his station is not 
also fitted with transmitting apparatus. 

In other words if the amateur possesses a receiving 
outfit only which is in working order or if he has both 
transmitter and receptor and the former is not powerful enough 
to send signals out of the state in which he lives, or to 
interfere with the reception of messages by another when 
the messages come from beyond the state boundary a 
*license* is unnecessary. 

This is of course somewhat unfair for those living near 
the center of large states for they may operate almost as 
they please with ordinary instruments with no fear of the 
signals going beyond the border, while those living within 
a few miles of another state must secure a license. 

If an amateur has a license he may transmit messages 
beyond the state border, but he must not employ a wave 
length greater than 200 meters or a power input into the 
transmitter of more than 1 K.W. without special 
permission. 

.. figure:: images/Image148.jpg
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   :alt: Fig. 148. Experimental Amateur Station of W. Haddon, Brooklyn, N. Y. 
   
   Fig. 148. Experimental Amateur Station of W. Haddon, Brooklyn, N. Y. 
   
If the amateur is within five nautical miles of an army 
or navy station equipped with radio apparatus his power 
input must not be more than 1 K.W. 

**Complying with Law.**—After a license is secured, or 
rather as a matter of fact in order to secure it, the wave 
length must not be greater than 200 meters. In order to 
secure such a wave length the effective portion of the 
aerial cannot usually be made greater than 115 feet in 
consideration of the amount which the lead-in, helix and 
ground wire add. 

.. figure:: images/Image149.jpg
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   :alt: Fig. 149. Complete Receiving Outfit Consisting of Receiving Transformer, Detector, Fixed Condenser, Loading Coil, Two Variable Condensers, Potentiometer, Battery, Switches, etc. 
   
   Fig. 149. Complete Receiving Outfit Consisting of Receiving Transformer, Detector, Fixed Condenser, Loading Coil, Two Variable Condensers, Potentiometer, Battery, Switches, etc. 
   
Such an aerial will serve well for transmitting purposes, 
but is too short for receiving very long distances. If the 
amateur desires to pick up long distance messages he must 
employ two aerials, a short one for transmitting and a 
long one for receiving. If it is desirable to use the long 
aerial for both transmitting and receiving its wave length 
may be brought down to 200 meters or under, while 
transmitting by placing a large glass plate condenser of the 
proper capacity in series with the aerial. It may be 
short-circuited with a suitable switch when receiving. 

The law also says that the transmitting wave must be 
pure, and must be sharply tuned, which means that the 
wave must be of one length and not, as is very often 
the case, composed of two or more waves of different 
lengths. 

In order to comply with this restriction, the use of an 
oscillation helix or loosely coupled helix is necessary. A 
rotary or quenched gap is also necessary in place of the 
ordinary spark gap. 

The construction of all three of these instruments is 
described farther on. 

**How to Obtain a License.**—In order to obtain a license 
send to the nearest Radio Inspector; Radio Inspectors are 
stationed at the Custom Houses at the following cities: 
Boston, Mass.; New York, N. Y.; Savannah, Ga.; 
Baltimore, Md.; Cleveland, Ohio; Chicago, Ill.; Seattle, 
Wash.; New Orleans, La.; San Francisco, Cal.; and 
obtain a copy of The Wireless Law, 8-6412, The 
Regulations Governing Radio Communication, The Berlin 
International Radio-telegraphic Convention, and the 
necessary Application Forms. 

Look over the Wireless Law, the Regulations and the 
Berlin Convention pamphlet, then fill out Form 756. 
This is an application for an operator's license. 

.. figure:: images/Image150.jpg
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   :alt: Fig. 150. Receiving Outfit Consisting of Receiving Transformer, Fixed Condenser and Detector.
   
   Fig. 150. Receiving Outfit Consisting of Receiving Transformer, Fixed Condenser and Detector.
   
If the amateur is not already in possession of a certificate 
of skill as an operator it will be necessary to find out, from 
the commandant at the nearest one of the stations, listed on 
page 4 of the Regulations as being the places where 
examinations are given, on what days the examinations are held. 
If the amateur is able to pass the examination, an 
*operator's license* will be issued. Then fill out Form 757 and 
forward it to the Radio Inspector. If he thinks your 
station conforms to the regulations without inspection the 
license will be issued; if not, the license will be issued 
after inspection. 

There are no fees to pay in connection with securing 
any of the licenses. 

APPARATUS REQUIRED IN MANY INSTANCES IN ORDER TO COMPLY WITH THE WIRELESS LAW.
`````````````````````````````````````````````````````````````````````````````` 

**OSCILLATION HELIX**

The oscillation helix has almost become a necessity in 
order to comply with the regulations of the Wireless Law 
regarding wave form, except in those stations where a 
quenched gap is used. 

.. figure:: images/Image151.jpg
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   :alt: Fig. 151. Amco Oscillation Helix. 
   
   Fig. 151. Amco Oscillation Helix. 
   
The wave emitted by many stations is not pure. It is 
composed usually of two or three separate waves of 
different lengths instead of all the energy being confined to 
oscillations of one period. It is possible to tune such a 
wave in two or more places or "humps," as they are called, 
on the tuning coil. It is obvious that a wave possessing 
such humps cannot be closely tuned and is liable to 
interfere with the signals of another station. This is one of 
the principal causes of interference. 

The reason for this phenomenon is simple. The action 
of a transmitter is to first charge a condenser. When the 
potential of the condenser rises to sufficient value it 
discharges across the spark gap and sets up oscillations in 
the *closed* circuit. These oscillations immediately induce 
oscillations in the *open* circuit or aerial system and part of 
the energy passes off into the ether as electro-magnetic 
waves. However, the oscillations in the *aerial* system do 
not immediately die away after the oscillations in the 
closed circuit cease during the interim until the next 
condenser discharge, but continue to surge and react upon the 
dosed circuit to sufficient extent to induce therein currents 
which surge back and forth long after the current from 
the condenser discharge has died away. 

We might call the oscillations due to the condenser 
discharge *primary oscillations* and those induced in the 
aerial thereby *secondary oscillations*. Those which are 
then set up in the closed circuit by the reaction of the 
*secondary* currents are *tertiary*. This third train of 
oscillations persist after the secondary currents have died away, 
and induce another set of oscillations in the aerial which 
send out a second set of electromagnetic waves differing 
in length from the first. 

The oscillations which take place after the initial surge 
in the closed and open circuits are naturally somewhat 
weak. By using an oscillation helix in which the primary 
and secondary are separated from each other it is possible 
to eliminate the third and fourth trains of oscillations and 
all others having a tendency to follow, by placing the 
circuits apart so that the weak oscillations are not strong 
enough* to react across the intervening space. The 
immediate oscillations set up by the condenser discharge are 
strong enough to act across the space and set up powerful 
oscillations in the aerial. 

.. figure:: images/Image152.jpg
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   :alt: Fig. 152. Details of Oscillation Helix Construction. 
   
   Fig. 152. Details of Oscillation Helix Construction. 
   
A hot wire ammeter placed in the aerial circuit of a 
transmitter employing an oscillation transformer will not 
indicate as much current as if placed in the same position 
in a circuit using an ordinary helix; but in spite of the fact, 
a transmitter using an oscillation helix will send farther 
because the energy is concentrated in waves of one 
length. 

The construction of one type of oscillation helix has 
already been outlined on page 92. The form shown in 
Fig. 152 has no special advantages over the other but is 
preferred by many experimenters. 

It is of the "pancake" type, so-called because of the 
flat form of the windings which are made in the shape of 
a spiral of brass ribbon set in a slotted frame. 

The dimensions of the helix are clearly apparent from 
the drawing. The primary is composed of seven turns of 
brass ribbon 1/2 inch wide and 1/16 inch thick. The 
secondary should have from 10 to 15 turns of ribbon 3/8 x 1/16.
The coils may be slid back and forth on the brass rod so 
that the distance between them is variable. Connection 
is made to the coils by means of suitable clips. A clip 
similar to that shown on page 92, but made to snap on a 
flat ribbon instead of a round wire, will serve the purpose. 

**QUENCHED SPARK GAP.**

A "quenched" gap is made up of a number of brass 
or copper disks accurately turned to a true surface and 
separated by mica or rubber rings about .01 inch thick. 
The spark discharge takes place in the air-tight space at 
the center of the disks, inside of the mica rings. 

The quenched gap has several advantages over other 
forms. It is practically noiseless and the nuisance of a 
crashing discharge may be avoided by its use. 

The large surface offered to the spark by the disks cools 
the spark and quickly stops the oscillations in the closed 
circuit, and thereby leaves the open circuit and aerial 
system free to vibrate in its own period and therefore 
radiates *pure* waves. By pure wave a wave of one length 
is meant. 

A quenched gap cannot be used on a set of over 1 K.W. 
power without artificial cooling by an air blast. 

.. figure:: images/Image153.jpg
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   :alt: Fig. 153. Quenched Gap. 
   
   Fig. 153. Quenched Gap. 
   
.. figure:: images/Image154.jpg
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   :alt: Fig. 154. Quenched Gap. 
   
   Fig. 154. Quenched Gap. 
   
Fig. 154 shows an efficient form of quenched gap for use 
in stations up to 1 K.W. in power. 

The disks are shown in detail in Fig. 155. They are 
cast out of copper and then turned perfectly true and 
smooth in a lathe. After surfacing, the discharge surface 
should be heavily silver plated and buffed smooth. 

.. figure:: images/Image155.jpg
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   :alt: Fig. 155. Details of Disk and Ring. 
   
   Fig. 155. Details of Disk and Ring. 
   
The disks are piled on a marble base with a mica ring 
between each. They are clamped down by a strong set 
screw mounted on a heavy brass yoke. Enough pressure 
should be brought to bear to force the plates tightly 
together and make them air tight. 

.. figure:: images/Image156.jpg
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   :alt: Fig. 156. Explanatory Drawing of Quenched Gap. 
   
   Fig. 156. Explanatory Drawing of Quenched Gap. 
   
The number of disks required is governed by the voltage 
of the charging condenser. Generally speaking it is one 
section of .01-inch gap for each thousand volts delivered 
by the secondary of the transformer. It is very 
important to secure just the proper number of disks. If properly 
adjusted, the quenched gap will give one discharge for each 
alternation of the current and produce a musical tone. 

The quenched gap is placed in the same position in the 
transmitting circuit as any other form of gap. 

**ROTARY GAPS.**

Rotary gaps are divided into two general classes, the 
synchronous gap and the non-synchronous gap. 

The former usually consists of one or more stationary 
electrodes and a rotating member made like a star wheel 
with projecting spokes. This rotary member is attached 
directly to the shaft of the alternator or motor generator 
and arranged so that a spoke always comes opposite a 
stationary member at the exact moment that the 
maximum of potential is obtained in the condenser. Such an 
arrangement permits one discharge for each alternation of 
the current and produces a pure musical note easily 
distinguished in the telephone receivers at a distant station. 

In the non-synchronous rotary gap the wheel is driven at 
a high rate of speed without any regard to synchronism 
with the alternations of the current. 

The rotary gap shown in Fig. 157 is of the 
non-synchronous type. 

.. figure:: images/Image157.jpg
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   :alt: Fig. 157. Amco Rotary Gap.
   
   Fig. 157. Amco Rotary Gap.
   
The rotating member is cast from an alloy of equal 
parts of zinc and aluminum. It is necessary to first make 
a wooden pattern from which the casting may be made. 
The details of the wheel are shown in Fig. 158. The 
casting must be placed in a lathe chuck and turned true. It is 
mounted on a hard rubber disk 2 7/8 inches in diameter and 
1/4 of an inch thick. The disk serves to insulate the revolving 
electrodes from the motor shaft. The "rotor" is mounted 
upon the shaft by means of a small brass bushing which 
passes through the center of the disk. 

.. figure:: images/Image158.jpg
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   :alt: Fig. 158. Details of Revolving Parts of Rotary Gap. 
   
   Fig. 158. Details of Revolving Parts of Rotary Gap. 
   
The motor must be well built and capable of running at 
high speed. A "Juno" motor will be found very 
satisfactory. When running free its speed is about 4500 r.p.m. 
With the rotor in place the speed is about 3600 r.p.m. 

The motor should be mounted on a heavy marble base 
capable of absorbing any little vibration that the gap may 
be subject to when running at high speed. 

The stationary electrodes are made in the same manner 
as those for an ordinary gap and consists of two flanged 
zinc electrodes mounted upon threaded brass rods 
supported by two hexagonal standards. The axis of the 
electrodes should be the same height above the base as 
that of the motor shaft. 

The rotor should be carefully balanced so that it is 
practically free from vibration by boring small holes in the 
back face so as to make the weight on opposite sides equal. 

.. figure:: images/Image159.jpg
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   :alt: Fig. 159. Details of Rotary Gap. 
   
   Fig. 159. Details of Rotary Gap. 
   
The motor may be driven by a battery or from the same 
source that supplies the transformer, in series with two or 
three suitable lamps. A motor wound to run directly 
from the 110-volt line or a higher potential must have its 
fields wound with very fine wire and is apt to give trouble 
through "burn-outs," due to "kick back." When the 
motor is operated on batteries or is wound for running in 
series with a lamp the danger is lessened. 

A rotary gap is placed in the transmitting circuit in the 
same position as any other gap. Its use will result in a 
wonderful increase in the transmitting range of almost any 
station, for not only will the amount of energy passing 
through the aerial be raised, but the clear musical tone 
given off is more plainly distinguishable at a greater 
distance in the receiving station than a spark of the ordinary 
sort. 

**"KICK BACK."**

The oscillations taking place in the closed circuit and 
aerial system of a wireless transmitter continue to surge 
after the current in the condenser has dropped below a 
certain value, and react upon the primary winding of the 
coil or transformer by induction and produce high voltage, 
high frequency currents termed "kick back," in wireless 
telegraph parlance. 

"Kick back," wherever it exists to an appreciable 
extent, is liable to damage insulation and cause possible 
"burn-outs." The "kick-back" preventers illustrated 
in the accompanying diagrams will be found an efficient 
method of avoiding this danger. 

.. figure:: images/Image160.jpg
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   :alt: Fig. 160. Methods of Preventing "Kick Back." 
   
   Fig. 160. Methods of Preventing "Kick Back." 
   
The first method shows an ordinary pressed telephone 
condenser of about two microfarads capacity connected 
directly across the A. C. mains near the transformer 
terminals, in series with two 6-ampere fuses. The 
condenser is shunted by a small spark gap made of needle 
points with a very small space, about .005 of an inch, 
between them. 

The second method is an elaboration of the first and 
shows two sets of condensers in series with fuses and 
bridged by spark gaps with a "ground" through a third 
condenser connected between. This second method is the 
best and is often used to prevent delicate instruments, 
such as a voltmeter, from the effects of "kick back." 

A proper "kick-back" preventer is part of the Fire 
Insurance Underwriters requirements for a wireless 
telegraph station. 

Receiving Apparatus.
````````````````````

**THE VARIOMETER.**

A variometer is a tuning device in which two coils of 
wire are placed in series and connected so that the turns 
can be made to oppose one another. One coil is movable 
and by turning it the currents flowing through the 
adjacent coils oppose each other and decrease the 
self-induction of the whole and consequently the period of the 
circuit. 

.. figure:: images/Image161.jpg
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   :alt: Fig. 161. Variometer. 
   
   Fig. 161. Variometer. 
   
The accompanying illustration shows the constructive 
details of an efficient form of variometer. 

The coils are wound around two cardboard cylinders. 
One cylinder is 6 inches in diameter and the other 5 inches. 
Both are 2 inches long. The large cylinder is wound with 
twenty-five turns of No. 22 B. S. gauge single silk covered 
wire wound in two sections so as to leave a space 3/8 inch 
wide in the center. The small cylinder is wound in the 
same manner with the same size of wire but contains 
thirty turns so as to make the length of wire in each of 
the coils practically equal. 

The space in the center of each of the coils allows a 
supporting rod to pass through without interfering with 
the wire. The shaft is a piece of 5/16 *brass* rod about 7 1/2 
inches long. The upper end is provided with a knob and 
a pointer. The large coil is mounted on the under side of 
a wooden cover made to fit a containing case of the proper 
size to receive the variometer and of a style similar to that 
ordinarily used to enclose a variable condenser. 

The shaft passes through the larger coil, at two points 
diametrically opposite, but should not fit tightly. It also 
passes through the smaller coil but is fastened to the 
latter by means of a cross bar so that when the knob is 
turned the coil will revolve also. The coils are connected 
by means of a piece of braided wire or flexible conductor, 
long enough so as not to interfere with the movement of 
the inner coil. 

The outside terminals of the coils terminate in binding 
posts mounted on the top of the case. When making a 
variometer be careful not to employ any iron or steel in its 
construction, not even iron screws. 

The variometer is placed in the receiving circuit by 
connecting it in series with the aerial before it reaches the 
tuning coil or loose coupler. 

**NEW CRYSTAL DETECTORS.**

**Silicon Detector.**—The silicon detector is always 
interesting because it was one of the first mineral rectifiers 
to come into extended use. The photograph shown 
below illustrates one of the latest forms of the silicon 
detector. 

.. figure:: images/Image162.jpg
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   :alt: Fig. 162. Silicon Detector.
   
   Fig. 162. Silicon Detector.
   
The large cup supported by the left-hand standard 
contacts several pieces of fused silicon embedded in fusible 
alloy. The right-hand standard supports a movable 
"offset" cup the same as that used on the Perikon type of 
Detector. A small piece of *arsenic* is mounted in this cup 
and may be brought to bear against any portion of any 
of the silicon crystals. 

**Pyron Detector.**—The Pyron detector is not new, but 
the photograph shows a very simple and efficient form in 
which a fine wire is brought to bear against a crystal of 
iron pyrites mounted in a small cup. 

.. figure:: images/Image163.jpg
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   :alt: Fig. 163. Pyron Detector. 
   
   Fig. 163. Pyron Detector.  

**Galena Detector.**—Although *galena* is named in the 
list of sensitive minerals on page 132 it has come into such 
extensive use as a detector since the first edition of this 
book to be worthy of special attention. Galena detectors 
are often spoken of as "cat-whisker" detectors because 
of the long fine wire used to secure a delicate contact with 
the mineral. 

The mineral is usually placed in a cup and held in 
position by imbedding in fusible alloy or clamped with a 
set screw. The best surface of the mineral should be 
selected by testing previous to imbedding it in the cup. 
Contact is made with the surface of the mineral by means 
of a piece of No. 30 phosphor bronze wire mounted on 
the end of a short brass rod fitted with an adjusting screw 
so that by turning or twisting the surface of the mineral 
may be "searched" and the tension varied. 

.. figure:: images/Image164.jpg
   :align: center
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   :alt: Fig. 164. Galena Detector. 
   
   Fig. 164. Galena Detector. 

Such an arrangement is illustrated in Fig. 164. The 
base is a hard rubber block 3 3/4 x 1 3/4 x 1/2. The binding 
posts are of the type commonly used on electrical 
instruments. One of the posts is pivoted by placing a spring 
washer under the head of the screw which holds the post 
to the base. A short piece of brass rod fitted with a hard 
rubber knob passes through the wire hole in the post. A 
piece of No. 30 phosphor bronze wire is soldered to the 
end of the rod. By twisting the post and sliding the rod 
any portion of the mineral surface may be selected. 
Twisting the rod varies the tension of the contact. 

The galena detector is connected in the receiving 
circuit in the same manner as other detectors of the mineral 
type. 

**THE AUDION.**

**The Audion**—is finding favor in many amateur wireless 
stations, because of its almost entire lack of adjustment 
and of the loud clear signals which it gives even when used 
for long distance work. 

The illustration shows the latest form of audion, the 
plate and the grid both being on the same side of the 
filament. 

The filament of an audion is usually lighted by means of 
a six-volt storage battery. A small battery rheostat placed 
in series with the battery serves to regulate the amount of 
current flowing through the filament. Only one filament 
is used at a time, the other being saved as a reserve in case 
the first burns out. 

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   :alt: Fig. 165. Audion.
   
   Fig. 165. Audion.

The higher voltage necessary to operate an audion is 
supplied by a battery consisting of fifteen flashlight 
batteries, each flashlight battery being composed of three 
separate cells. The batteries are connected to an 
eight-point switch so that throwing the switch on the first point 
will connect five sets of batteries. The second point 
places five more in circuit and each additional point one 
set only. It is also a good plan to connect a four-point 
switch and three separate cells of battery in series with 
the eight-point switch so that they may be added to the 
circuit one at a time and the potential varied more closely than 
the steps on the eight-point switch permit. The 
maximum voltage of such a battery is approximately 56 volts. 

The diagram in Fig. 166 shows exactly how an audion 
is connected. The wires *A* and *B* are the terminals 
leading to the tuning coil or loose coupler. It is not 
necessary that the telephone receivers used with an audion be 
wound to a high resistance in order to secure good results. 

.. figure:: images/Image166.jpg
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   :alt: Fig. 166. Audion Circuit. 
   
   Fig. 166. Audion Circuit. 

The audion is placed in operation by turning the rheostat 
until the filament lights brightly. Then adjust the 
voltage of the high potential battery until the signals are 
clearest. If the voltage is too high the audion will become 
filled with a bluish light and the voltage should be 
immediately reduced. The signals will be loudest when the 
filament is brilliantly lighted. No more current should be 
passed through the filament than is necessary to render 
the signals plain, for if "forced" its life will be limited to 
only a few hours. 

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   :alt: Fig. 167. Rotary Variable Condenser. 
   
   Fig. 167. Rotary Variable Condenser. 

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   **APPENDIX.**
   
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   [PUBLIC No. 264.] 
   
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   [S. 6412.]

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   An Act to Regulate Radio Communication. 

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*Be it enacted by the Senate and House of Representatives of 
the United States of America in Congress assembled.* That a 
person, company, or corporation within the jurisdiction of 
the United States shall not use or operate any apparatus 
for radio communication as a means of commercial 
intercourse among the several States, or with foreign nations, 
or upon any vessel of the United States engaged in 
interstate or foreign commerce, or for the transmission of 
radiograms or signals the effect of which extends beyond the 
jurisdiction of the State or Territory in which the same are 
made, or where interference would be caused thereby with 
the receipt of messages or signals from beyond the 
jurisdiction of the said State or Territory, except under and 
in accordance with a license, revocable for cause, in that 
behalf granted by the Secretary of Commerce and Labor 
upon application therefor; but nothing in this Act shall 
be construed to apply to the transmission and exchange of 
radiograms or signals between points situated in the same 
State: *Provided*, That the effect thereof shall not extend 
beyond the jurisdiction of the said State or interfere with 
the reception of radiograms or signals from beyond said 
jurisdiction; and a license shall not be required for the 
transmission or exchange of radiograms or signals by or on 
behalf of the Government of the United States, but every 
Government station on land or sea shall have special call 
letters designated and published in the list of radio stations 
of the United States by the Department of Commerce and 
Labor. Any person, company, or corporation that shall 
use or operate any apparatus for radio communication in 
violation of this section, or knowingly aid or abet another 
person, company, or corporation in so doing, shall be 
deemed guilty of a misdemeanor, and on conviction thereof 
shall be punished by a fine not exceeding five hundred 
dollars, and the apparatus or device so unlawfully used and 
operated may be adjudged forfeited to the United States. 

SEC. 2. That every such license shall be in such form as 
the Secretary of Commerce and Labor shall determine and 
shall contain the restrictions, pursuant to this Act, on and 
subject to which the license is granted; that every such 
license shall be issued only to citizens of the United States 
or Porto Rico or to a company incorporated under the laws 
of some State or Territory or of the United States or Porto 
Rico, and shall specify the ownership and location of the 
station in which said apparatus shall be used and other 
particulars for its identification and to enable its range to 
be estimated; shall state the purpose of the station, and, 
in case of a station in actual operation at the date of passage 
of this Act, shall contain the statement that satisfactory 
proof has been furnished that it was actually operating on 
the above-mentioned date; shall state the wave length or 
the wave lengths authorized for use by the station for the 
prevention of interference and the hours for which the 
station is licensed for work; and shall not be construed to 
authorize the use of any apparatus for radio 
communication in any other station than that specified. Every such 
license shall be subject to the regulations contained herein, 
and such regulations as may be established from time to 
time by authority of this Act or subsequent Acts and 
treaties of the United States. Every such license shall 
provide that the President of the United States in time of 
war or public peril or disaster may cause the closing of any 
station for radio communication and the removal therefrom 
of all radio apparatus, or may authorize the use or control 
of any such station or apparatus by any department of the 
Government, upon just compensation to the owners. 

SEC. 3. That every such apparatus shall at all times 
while in use and operation as aforesaid be in charge or 
under the supervision of a person or persons licensed for 
that purpose by the Secretary of Commerce and Labor. 
Every person so licensed who in the operation of any radio 
apparatus shall fail to observe and obey regulations 
contained in or made pursuant to this Act or subsequent Acts 
or treaties of the United States, or any one of them, or who 
shall fail to enforce obedience thereto by an unlicensed 
person while serving under his supervision, in addition to 
the punishments and penalties herein prescribed, may suffer 
the suspension of the said license for a period to be fixed 
by the Secretary of Commerce and Labor not exceeding 
one year. It shall be unlawful to employ any unlicensed 
person or for any unlicensed person to serve in charge or in 
supervision of the use and operation of such apparatus, and 
any person violating this provision shall be guilty of a 
misdemeanor, and on conviction thereof shall be punished by 
a fine of not more than one hundred dollars or 
imprisonment for not more than two months, or both, in the 
discretion of the court, for each and every such offense: 
*Provided*, That in case of emergency the Secretary of 
Commerce and Labor may authorize a collector of customs 
to issue a temporary permit, in lieu of a license, to the 
operator on a vessel subject to the radio ship Act of June 
twenty-fourth, nineteen hundred and ten. 

SEC. 4. That for the purpose of preventing or 
minimizing interference with communication between stations in 
which such apparatus is operated, to facilitate radio 
communication, and to further the prompt receipt of distress 
signals, said private and commercial stations shall be subject 
to the regulations of this section. These regulations shall 
be enforced by the Secretary of Commerce and Labor 
through the collectors of customs and other officers of the 
Government as other regulations herein provided for. 

The Secretary of Commerce and Labor may, in his 
discretion, waive the provisions of any or all of these 
regulations when no interference of the character above mentioned 
can ensue. 

The Secretary of Commerce and Labor may grant special 
temporary licenses to stations actually engaged in 
conducting experiments for the development of the science of 
radio communication, or the apparatus pertaining thereto, 
to carry on special tests, using any amount of power or any 
wave lengths, at such hours and under such conditions as 
will insure the least interference with the sending or receipt 
of commercial or Government radiograms, of distress signals 
and radiograms, or with the work of other stations. 

In these regulations the naval and military stations shall 
be understood to be stations on land. 

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   REGULATIONS. 

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   NORMAL WAVE LENGTH. 

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First. Every station shall be required to designate 
certain definite wave length as the normal sending and 
receiving wave length of the station. This wave length 
shall not exceed six hundred meters or it shall exceed one 
thousand six hundred meters. Every coastal station open 
to general public service shall at all times be ready to 
receive messages of such wave lengths as are required by 
the Berlin convention. Every ship station, except as 
hereinafter provided, and every coast station open to general 
public service shall be prepared to use two sending wave 
lengths, one of three hundred meters and one of six hundred 
meters, as required by the international convention in force: 
*Provided*, That the Secretary of Commerce and Labor may, 
in his discretion, change the limit of wave length reservation 
made by regulations first and second to accord with any 
international agreement to which the United States is a 
party. 

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   OTHER WAVE LENGTHS. 
   
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Second. In addition to the normal sending wave 
length all stations, except as provided hereinafter in these 
regulations, may use other sending wave lengths: 
*Provided*, That they do not exceed six hundred meters or 
that they do exceed one thousand six hundred meters: 
*Provided further*, That the character of the waves emitted 
conforms to the requirements of regulations third and 
fourth following. 

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   USE OF A "PURE WAVE"
   
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Third. At all stations if the sending apparatus, to be 
referred to hereinafter as the "transmitter," is of such a 
character that the energy is radiated in two or more wave 
lengths, more or less sharply defined, as indicated by a 
sensitive wave meter, the energy in no one of the lesser 
waves shall exceed ten per centum of that in the greatest. 

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   USE OF A "SHARP WAVE."
   
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Fourth. At all stations the logarithmic decrement per 
complete oscillation in the wave trains emitted by the 
transmitter shall not exceed two-tenths, except when 
sending distress signals or signals and messages relating thereto. 

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   USE OF "STANDARD DISTRESS WAVE." 
   
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Fifth. Every station on shipboard shall be prepared to 
send distress calls on the normal wave length designated by 
the international convention in force, except on vessels of 
small tonnage unable to have plants insuring that wave 
length. 

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   SIGNAL OF DISTRESS. 
   
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Sixth. The distress call used shall be the international 
signal of distress: dot dot dot, dash dash dash, dot dot dot. 

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   USE OF "BROAD INTERFERING WAVE" FOR DISTRESS SIGNALS. 
   
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Seventh. When sending distress signals, the transmitter 
of a station on shipboard may be tuned in such a manner 
as to create a maximum of interference with a maximum 
of radiation. 

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   DISTANCE REQUIREMENT FOR DISTRESS SIGNALS. 
   
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Eighth. Every station on shipboard, wherever 
practicable, shall be prepared to send distress signals of the 
character specified in regulations fifth and sixth with 
sufficient power to enable them to be received by day over sea 
a distance of one hundred nautical miles by a shipboard 
station equipped with apparatus for both sending and 
receiving equal in all essential particulars to that of the 
station first mentioned. 

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   FOR DISTRESS SIGNALS. 
   
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Ninth. All stations are required to give absolute priority 
to signals and radiograms relating to ships in distress; to 
cease all sending on hearing a distress signal; and, except 
when engaged in answering or aiding the ship in distress, 
to refrain from sending until all signals and radiograms 
relating thereto are completed. 

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   REDUCED POWER FOR SHIPS NEAR A GOVERNMENT STATION. 
   
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Tenth. No station on shipboard, when within fifteen 
nautical miles of a naval or military station, shall use a 
transformer input exceeding one kilowatt, nor, when within 
five nautical miles of such a station, a transformer input 
exceeding one-half kilowatt, except for sending signals of 
distress, or signals or radiograms relating thereto. 

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   INTERCOMMUNICATION. 
   
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Eleventh. Each shore station open to general public 
service between the cost and vessels at sea shall be bound 
to exchange radiograms with any similar shore station and 
with any ship station without distinction of the radio 
systems adopted by such stations, respectively, and each 
station on shipboard shall be bound to exchange 
radiograms with any other station on shipboard without 
distinction of the radio systems adopted by each station 
respectively. 

It shall be the duty of each such shore station, during the 
hours it is in operation, to listen in at intervals of not less 
than fifteen minutes and for a period not less than two 
minutes, with the receiver tuned to receive messages of 
three hundred meter wave lengths. 

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   DIVISION OF TIME. 
   
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Twelfth. At important seaports and at all other places 
where naval or military and private or commercial shore 
stations operate in such close proximity that interference 
with the work of naval and military stations can not be 
avoided by the enforcement of the regulations contained 
in the foregoing regulations concerning wave lengths and 
character of signals emitted, such private or commercial 
shore stations as do interfere with the reception of signals 
by the naval and military stations concerned shall not use 
their transmitters during the first fifteen minutes of each 
hour, local standard time. The Secretary of Commerce 
and Labor may, on the recommendation of the department 
concerned, designate the station or stations which may be 
required to observe this division of time. 

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   GOVERNMENT STATIONS TO OBSERVE DIVISION OF TIME. 
   
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Thirteenth. The naval or military stations for which 
the above mentioned division of time may be established 
shall transmit signals or radiograms only during the first 
fifteen minutes of each hour, local standard time, except 
in case of signals or radiograms relating to vessels in distress, 
as hereinbefore provided. 

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   USE OF UNNECESSARY POWER. 
   
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Fourteenth. In all circumstances, except in case of 
signals or radiograms relating to vessels in distress, all 
stations shall use the minimum amount of energy necessary 
to carry out any communication desired. 

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   GENERAL RESTRICTIONS ON PRIVATE STATIONS. 
   
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Fifteenth. No private or commercial station not engaged 
in the transaction of bona fide commercial business by radio 
communication or in experimentation in connection with 
the development and manufacture of radio apparatus for 
commercial purposes shall use a transmitting wave length 
exceeding two hundred meters, or a transformer input 
exceeding one kilowatt, except by special authority of the 
Secretary of Commerce and Labor contained in the license 
of the station: *Provided*, That the owner or operator of a 
station of the character mentioned in this regulation shall 
not be liable for a violation of the requirements of the third 
or fourth regulations to the penalties of one hundred dollars 
or twenty-five dollars, respectively, provided in this section 
unless the person maintaining or operating such station 
shall have been notified in writing that the said transmitter 
has been found, upon tests conducted by the Government, 
to be so adjusted as to violate the said third and fourth 
regulations, and opportunity has been given to said owner 
or operator to adjust said transmitter in conformity with 
said regulations. 

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   SPECIAL RESTRICTIONS IN THE VICINITIES OF GOVERNMENT STATIONS. 
   
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Sixteenth. No station of the character mentioned in 
regulation fifteenth situated within five nautical miles of 
a naval or military station shall use a transmitting wave 
length exceeding two hundred meters or a transformer input 
exceeding one-half kilowatt. 

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   SHIP STATIONS TO COMMUNICATE WITH NEAREST SHORE STATIONS. 
   
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Seventeenth. In general, the shipboard stations shall 
transmit their radiograms to the nearest shore station. A 
sender on board a vessel shall, however, have the right to 
designate the shore station through which he desires to 
have his radiograms transmitted. If this can not be done, 
the wishes of the sender are to be complied with only if the 
transmission can be effected without interfering with the 
service of other stations. 

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   LIMITATIONS FOR FUTURE INSTALLATIONS IN VICINITIES OF GOVERNMENT STATIONS. 
   
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Eighteenth. No station on shore not in actual operation 
at the date of the passage of this Act shall be licensed for 
the transaction of commercial business by radio 
communication within fifteen nautical miles of the following naval 
or military stations, to wit: Arlington, Virginia; Key West, 
Florida; San Juan, Porto Rico; North Head and Tatoosh 
Island, Washington; San Diego, California; and those 
established or which may be established in Alaska and in 
the Canal Zone; and the head of the department having 
control of such Government stations shall, so far as is 
consistent with the transaction of governmental business, 
arrange for the transmission and receipt of commercial 
radiograms under the provisions of the Berlin convention 
of nineteen hundred and six and future international 
conventions or treaties to which the United States may be a 
party, at each of the stations above referred to, and shall 
fix the rates therefor, subject to control of such rates by 
Congress. At such stations and wherever and whenever 
shore stations open for general public business between the 
coast and vessels at sea under the provisions of the Berlin 
convention of nineteen hundred and six and future 
international conventions and treaties to which the United 
States may be a party shall not be so established as to insure 
a constant service day and night without interruption, and 
in all localities wherever or whenever such service shall not 
be maintained by a commercial shore station within one 
hundred nautical miles of a naval radio station, the 
Secretary of the Navy shall, so far as is consistent with the 
transaction of governmental business, open naval radio stations 
to the general public business described above, and shall 
fix rates for such service, subject to control of such rates by 
Congress. The receipts from such radiograms shall be 
covered into the Treasury as miscellaneous receipts. 

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   SECRECY OF MESSAGES. 
   
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Nineteenth. No person or persons engaged in or having 
knowledge of the operation of any station or stations shall 
divulge or publish the contents of any messages transmitted 
or received by such station, except to the person or persons 
to whom the same may be directed, or their authorized 
agent, or to another station employed to forward such 
message to its destination, unless legally required so to do 
by the court of competent jurisdiction or other competent 
authority. Any person guilty of divulging or publishing 
any message, except as herein provided, shall, on conviction 
thereof, be punishable by a fine of not more than two 
hundred and fifty dollars or imprisonment for a period of 
not exceeding three months, or both fine and imprisonment, 
in the discretion of the court. 

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   PENALTIES. 
   
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For violation of any of these regulations, subject to which 
a license under sections one and two of this Act may be 
issued, the owner of the apparatus shall be liable to a 
penalty of one hundred dollars, which may be reduced or 
remitted by the Secretary of Commerce and Labor, and 
for repeated violations of any of such regulations, the 
license may be revoked. 

For violation of any of these regulations, except as 
provided in regulation nineteenth, subject to which a license 
under section three of this Act may be issued, the operator 
shall be subject to a penalty of twenty-five dollars, which 
may be reduced or remitted by the Secretary of Commerce 
and Labor, and for repeated violations of any such 
regulations, the license shall be suspended or revoked. 

SEC. 5. That every license granted under the provisions 
of this Act for the operation or use of apparatus for radio 
communication shall prescribe that the operator thereof 
shall not wilfully or maliciously interfere with any other 
radio communication. Such interference shall be deemed 
a misdemeanor, and upon conviction thereof the owner or 
operator, or both, shall be punishable by a fine of not to 
exceed five hundred dollars or imprisonment for not to 
exceed one year, or both. 

SEC. 6. That the expression "radio communication" as 
used in this Act means any system of electrical 
communication by telegraphy or telephony without the aid of any wire 
connecting the points from and at which the radiograms, 
signals, or other communications are sent or received. 

SEC. 7. That a person, company, or corporation within 
the jurisdiction of the United States shall not knowingly 
utter or transmit, or cause to be uttered or transmitted, any 
false or fraudulent distress signal or call or false or 
fraudulent signal, call, or other radiogram of any kind. The 
penalty for so uttering or transmitting a false or fraudulent 
distress signal or call shall be a fine of not more than two 
thousand five hundred dollars or imprisonment for not more 
than five years, or both, in the discretion of the court, for 
each and every such offense, and the penalty for so uttering 
or transmitting, or causing to be uttered or transmitted, 
any other false or fraudulent signal, call, or other radiogram 
shall be a fine of not more than one thousand dollars or 
imprisonment for not more than two years, or both, in the 
discretion of the court, for each and every such offense. 

SEC. 8. That a person, company, or corporation shall 
not use or operate any apparatus for radio communication 
on a foreign ship in territorial waters of the United States 
otherwise than in accordance with the provisions of sections 
four and seven of this Act and so much of section five as 
imposes a penalty for interference. Save as aforesaid, 
nothing in this Act shall apply to apparatus for radio 
communication on any foreign ship. 

SEC. 9. That the trial of any offense under this Act shall 
be in the district in which it is committed, or if the offense 
is committed upon the high seas or out of the jurisdiction 
of any particular State or district the trial shall be in the 
district where the offender may be found or into which he 
shall be first brought. 

SEC. 10. That this Act shall not apply to the Phillippine 
Islands. 

SEC. 11. That this Act shall take effect and be in force 
on and after four months from its passage. 

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Approved, August 13, 1912. 

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   LIST OF WORKS 

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   ON 

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   ELECTRICAL SCIENCE 

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   PUBLISHED AND FOR SALE BY 

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   \D. VAN NOSTRAND COMPANY, 

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   **25 Park Place, New York.**

**ABBOTT, A. V. The Electrical Transmission of Energy.** 
   A Manual for the Design of Electrical Circuits. *Fifth Edition, enlarged and rewritten.*
   With many Diagrams, Engravings and Folding Plates. 8vo., cloth, 
   675 pp Net, $5.00 

**ARNOLD, E. Armature Windings of Direct-Current Dynamos.** 
   Extension and Application of a general Winding Rule. Translated from 
   the original German by Francis B. DeCress. Illustrated. 8vo. 
   cloth, 124 pp $2.00 

**ASHE, S. W. Electricity Experimentally and Practically Applied.** 
   *Second Edition.* 422 illustrations. 12mo., cloth, 375 pp. Net, $2.00 

**ASHE, S. W., and KEILEY, J. D. Electric Railways Theoretically and Practically Treated.** 
   Illustrated. 12mo., cloth. 

**Vol. I. Rolling Stock.** 
   *Second Edition.* 285 pp Net, $2.50 

**Vol. II. Substations and Distributing Systems.** 
   296 pp Net, $2. 50 

**ATKINSON, A. A. Electrical and Magnetic Calculations.** 
   For the use of Electrical Engineers and others interested in the Theory and 
   Application of Electricity and Magnetism. *Fourth Edition*, revised 
   Illustrated. 12mo, cloth, 310 pp Net, $1.50 

**ATKINSON, PHILIP. The Elements of Dynamic Electricity and Magnetism.** 
   *Fourth Edition.* Illustrated. 12mo., cloth, 405 pp. $2.00 

- **Elements of Electric Lighting,** including Electric Generation, Measurement, Storage, and Distribution. *Tenth Edition*, fully revised and new matter added. Illustrated. 12mo., cloth, 280 pp $1.50 

- **Power Transmitted by Electricity and Applied by the Electric Motor,** including Electric Railway Construction. Illustrated. *Fourth Edition*, fully revised and new matter added. 12mo., cloth, 241 pp. $2.00 

**AUSTIN, E. Single-Phase Electric Railways.** 
   346 illustrations 
   8 x 11, cloth, 308 pp Net, $5.00 

**AYRTON, HERTHA. The Electric Arc.** 
   Illustrated. 8vo., cloth, 479 pp Net, $5.00 

**BAKER, J. T. The Telegraphic Transmission of Photographs.** 
   63 illustrations. 12mo., cloth, 155 pp Net, $1.25 

**BARHAM, G. B. Development of the Incandescent Electric Lamp.** 
   25 illustrations, 2 plates, 5 x 8 cloth. 206 pp $2.00 

**BEDELL, FREDERICK. Direct and Alternating Current Manual.**
   With directions for testing and a discussion of the theory of 
   electrical apparatus. *Second Edition, greatly enlarged*. Assisted by C. A. 
   Pierce. Illustrated. 6 x 9, cloth, 373 pp Net, $2.00 

**BLAINE, ROBERT G. The Calculus and Its Applications.** 
   A practical treatise for beginners especially engineering students. 79 
   illustrations. 12mo., cloth, 330 pp Net, $1.50 

**BONNEY, G. E. The Electro-Plater's Hand Book.** 
   A Manual for Amateurs and Young Students of Electro-Metallurgy. *Fifth Edition, 
   enlarged.* 61 Illustrations. 12mo., cloth, 208 pp $1.20 

**BOTTONE, S. R. Magnetos For Automobilists; How Made and How Used** 
   A handbook of practical instruction on the manufacture and 
   adaptation of the magneto to the needs of the motorist. *Second Edition, 
   enlarged*. 52 illustrations. 12mo., cloth, 118 pp Net, $1.00 

**BROADFOOT, S. K. Motors, Secondary Batteries and Accessory Apparatus.** 
   16 illustrations. 16mo., cloth. 100pp. (Installation Manuals 
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**BROUGHTON, H. H. Electric Canes.** 
   Their design, construction and application. 600 illustrations and plates. 120 tables, 6 x 9, cloth, 
   848 pp Net, $9.00 

**CHILD, C. D. Electric Arcs.** 
   Experiments upon arcs between different 
   electrodes in various environments and their explanation. 58 
   illustrations. 5 x 7, cloth, 203 pp Net, $2.00 

**COLLIS, A. G. High and Low Tension Switchgear Design.** 
   94 illustrations and folding plates, 6 x 9, cloth, 233 pp Net, $3.50 

- **Switchgear and The Control of Electric Circuits.** 47 illustrations. 4 1/2 x 6 1/2, cloth, 85 pp. (Installation Manuals Series) Net, 0.50 

**COMSTOCK, D. F., and TROLAND, L. T. The Nature of Matter and Electricity.**
   An outline of modern views. Illustrated. 5 x 7, 
   cloth, 200 pp Net, $2.00 

**COOPER, W. R. Primary Batteries: their Theory, Construction, and Use** 
   *New Edition in Press*
 
**CRAIG, J. W., and WOODWARD, W. P. Questions and Answers About Electrical Apparatus.**
   Third edition revised and enlarged. Illustrated. 
   4 x 6 Leather, 256 pp Net, $1.50 

**CRAMP, W. Continuous Current Machine Design.** 
   137 illustration. 
   8vo., cloth, 240 pp Net, $2.50 

**CREED Y, F. Single-Phase Commutator Motors.** 
   98 illustrations, 6 x 9, 
   cloth, 120 pp Net, $2.00 

**CROCKER, F. B. Electric Lighting.** 
   A Practical Exposition of the Art 
   for the use of Electricians, Students, and others interested in the 
   Installation or Operation of Electric Lighting Plants. 

- **Vol. I. The Generating Plant**. *Seventh Edition, entirely revised*. Illustrated. 8vo., cloth, 482 pp $3.00 

- **Vol. II. Distributing System and Lamps.** *Sixth Edition*. Illustrated 8vo., cloth, 505 pp. 

**CROCKER, F. B., and ARENDT, M. Electric Motors: Their Action, Control, and Application.** 
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    In addition to publishing a very large 

    and varied number of SCIENTIFIC AND 

    ENGINEERING BOOKS, D. Van Nostrand 

    Company have on hand the largest 

    assortment in the United States of such 

    books issued by American and foreign 

    publishers. 

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    All inquiries are cheerfully and 

    carefully answered and complete catalogs 

    sent free on request. 

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    25 PARK PLACE - - NEW YORK 

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