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Lessons in Wireless Telegraphy
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.. meta::
        :PG.Title: Lessons in Wireless Telegraphy
        :PG.Id: 63345
        :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: Lessons in Wireless Telegraphy
        :DC.Language: en
        :DC.Created: 1917
        :PG.Released: 2020-09-29
        :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. I have included the ads for other books
    found in the back pages of these scans.

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       LESSONS 

       IN 

       WIRELESS TELEGRAPHY 
       
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       A SYSTEMATIC ELEMENTARY COURSE IN THE 

       PRINCIPLES OF WIRELESS TELEGRAPHY 

       AND THE ELECTRICAL LAWS 

       UPON WHICH IT DEPENDS 
       
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       BY 
 
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       **A. P. Morgan**

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       *THIRD EDITION, Revised and Enlarged*

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       PUBLISHED BY 

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       COLE & MORGAN 

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       Publishers of The Arts and Sciences Series 
       
       \P. O. Box 1473 NEW YORK CITY 

       Printed in U.S. A. 

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      COPYRIGHT 1912. 1917
      
      BY 

      COLE & MORGAN 

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LESSONS IN WIRELESS TELEGRAPHY 
------------------------------

INTRODUCTION 
````````````

This little book has been brought forward in order 
to supply the demand for a systematic elementary 
course in the principles of wireless telegraph apparatus 
and the electrical laws upon which it depends. 

Many operators, both amateur and professional, 
although perfectly well able to send and receive messages, 
do not thoroughly understand the rudimentary theory 
of the instruments. 

It is readily realizable that it is quite impossible to 
enter into all the engineering details in a book of this size, 
but at the same time it has been possible to present a 
very comprehensive treatise of the subject and embody 
sufficient material to give a thorough grounding in the 
subject. 

In order to avoid repetition and confusion and to make 
each instrument or principle which has been discussed 
stand distinctly by itself, the text has been divided into 
separate lessons following in their arrangement, as far as 
has been possible, the logical sequence. 

For the same reason, and also because of lack of 
space all details pertaining to the actual maintenance 
and adjustment of the instruments has been embodied in 
another book called "The Operation of Wireless 
Telegraph Apparatus." 

LESSON ONE. MAGNETISM.
``````````````````````

**Natural Magnets. Artificial Magnets. Magnetic Field 
of Force.**

It was known to the ancients that certain hard, black 
stones, an iron ore consisting of iron and oxygen 
found notably at Magnesia in Asia Minor, possessed the 
power of attracting small pieces of iron or steel. This 
almost magic attribute of the stone was early turned to 
account in navigation and secured for it the name of 
Lodestone (leading-stone) because of its remarkable 
property of pointing north and south when suspended by 
a thread. The name of magnet (magnes lapis) was 
also given to these stones. 

*Magnetism* is the peculiar property occassionally 
possessed by certain bodies (more especially by iron and 
steel) whereby they attract or repel one another. 

If a piece of hard iron or steel be rubbed with a 
lodestone it will be found to have also acquired the properties 
of the stone. If hung up by a thread it will point north 
and south, will attract light bits of iron and if dipped into 
iron filings will cause the latter to cling in two small 
tufts near the ends with few, if any, near the middle. 

.. figure:: images/Image1.jpg
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   :alt: FIG. 1. Lodestone which has been Dipped in Filings to show Poles 
   
   FIG. 1. Lodestone which has been Dipped in Filings to show Poles 

This indicates that the attractive power of the magnet 
is concentrated in two opposite parts. These parts are 
called the *Poles*. The line joining the poles is the 
*Magnetic Axis*. 

*Artificial Magnets* are those made from steel by the 
aid of a lodestone or some other magnetising force. The 
principal forms of artificial magnets are the *Bar* and 
*Horseshoe*, so called from their shape. 

.. figure:: images/Image2.jpg
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   :alt: FIG. 2. Bar and Horseshoe Magnet. 
   
   FIG. 2. Bar and Horseshoe Magnet. 

If a magnet (either artificial or natural) is suspended 
by a thread so that it may swing freely, and a second 
magnet held in the hand is presented successively to the 
two poles of the first, it will be observed that one pole is 
*attracted* and swings toward the magnet held in the hand, 
but that the other is *repelled* and *swings away*. 

.. figure:: images/Image3.jpg
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   :alt: FIG. 3. Lodestone suspended from thread so as to point North and South. 
   
   FIG. 3. Lodestone suspended from thread so as to point North and South. 

Furthermore, if the poles of the suspended magnet 
are marked so as to easily be identified it will be found 
that it is always the same pole that swings towards the 
north. There would therefore appear to be two kinds 
of magnetism or at least two kinds of magnetic poles. 
The end swinging toward the north is termed the "north 
seeking pole" and the opposite end called the "south 
seeking pole." In common parlance they are simply 
termed the North and South poles. It is usual to mark 
the North Pole with the letter N. 

There is no known insulator of magnetism: it passes 
through everything. A *magnetic substance* is one which 
offers little resistance to the field of force. 

Magnetism flows along certain lines called *Lines of 
Magnetic Force*. These lines always form closed paths 
or circuits. The region in the neighborhood of a magnet 
through which these lines pass is called the *Field of Force* 
and the path through which they flow is called the *Magnetic Circuit*. 

.. figure:: images/Image4.jpg
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   :alt: FIG. 4. Lines of Force around a Bar Magnet. 
   
   FIG. 4. Lines of Force around a Bar Magnet. 

The paths of the lines of force can be demonstrated 
by placing a piece of paper over a bar magnet and then 
sprinkling iron filings over the paper which should be 
jarred slightly in order that the filings may be drawn 
into the magnetic paths. The filings arrange themselves 
in curved lines, diverging from one pole of the magnet 
and meeting again at the opposite end. The lines of force 
are considered as extending outward from the North pole 
of the magnet, curving around through the air to the 
South pole and completing the circuit back through the 
magnet. 

The phenomena of magnetism and its laws form a very 
important branch of the study of electricity, for they 
play a part in the construction and operation of almost 
all electrical apparatus. 

LESSON TWO. MAGNETIC INDUCTION.
```````````````````````````````

In 1831 Michael Faraday, the great physicist, made the 
valuable discovery that electric currents are 
induced in a closed circuit by moving a magnet near it or 
vice versa, by moving the circuit across the field of force, 
If a coil of insulated wire be connected in circuit with 
a sufficiently delicate galvanometer (a galvanometer is 
an instrument for detecting feeble electric currents) and 
a bar magnet suddenly plunged into the hollow of the 
coil as shown in the illustration, a momentary current 
will be indicated as flowing through the galvanometer 
while the magnet is being moved in the coil. If the 
magnet is then rapidly pulled out of the coil another 
momentary current will be observed to flow in the *opposite 
direction from the former*. 

.. figure:: images/Image5.jpg
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   :alt: FIG. 5. Magnetic Induction. 
   
   FIG. 5. Magnetic Induction. 

So long as the magnet lies motionless in the coil it 
induces no currents. The field of force in the 
neighborhood of a magnet grows weaker as the distance from 
the magnet increases. When the magnet is plunged into 
the coil, the strength of the magnetic field in the vicinity 
of the coil grows stronger due to the approach of the 
magnet, and when it is withdrawn the field becomes 
weaker. 

Currents are only induced in the coil when the magnet 
is moving, or in other words when the strength of the 
magnetic field is changing, either increasing or decreasing. 

The currents generated in the coil are called *induced 
currents*. The action of the magnetic field in producing 
induced currents is termed *Induction*. 


LESSON THREE. PRIMARY CELLS. SECONDARY CELLS.
`````````````````````````````````````````````

If a piece of zinc is dipped in dilute sulphuric acid, the 
zinc will be attacked by the acid and replace hydrogen 
in it, the hydrogen appearing as bubbles on the zinc and 
passing off as a gas. 

.. figure:: images/Image6.jpg
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   :alt: FIG. 6. Simple Voltaic Cell 
   
   FIG. 6. Simple Voltaic Cell 

If the zinc is connected by means of a wire, W, with 
a strip of copper, C, dipping in the same solution, the 
zinc will still to continue to dissolve but the hydrogen 
bubbles will now form on the surface of the copper 
strip as well as on the zinc. It will be found that the 
wire W becomes heated. If the copper and zinc are 
connected to a galvanometer it will show the presence of an 
electric current passing through the circuit. The cell 
may be considered as a sort of chemical furnace in which 
fuel is burned to drive the current. The zinc is the 
fuel. The copper is merely present to "pick up" the 
current and takes no part chemically. 

If a number of such simple cells are properly united, 
the zinc of one being joined to the copper of the next 
and so on, a *battery* is formed. The current flows from 
the copper, called the *positive* pole, through the wires 
(when they are joined) to the zinc or negative pole and 
back to the copper through the solution. 

The electricity generated by the cells exerts a certain 
pressure or tendency to pass through the wires. This 
tendency is called the *potential*. The potential is 
measured in volts. The potential (also called the 
electromotive force) in the case of the Voltaic Cell just 
described is 1.07 volts. If the copper strip is replaced with 
one of graphite or carbon, the voltage will rise to 1.73 
volts. 

After a cell has been in action for a short time, the 
positive plate (copper or carbon, as the case may be) 
becomes covered with a film of hydrogen. The cell is 
then said to be *polarized*. The film of gas bubbles 
partially shields the plate from contact with the liquid. 
When the plate becomes in this condition, the current is 
much feebler than when it is clear. 

The most effective way of removing the hydrogen is 
to add some chemical to the sulphuric acid solution which 
will combine chemically with the hydrogen as soon as it 
appears. The usual substance is *bichromate of potash*. 
The voltage of the battery will rise to 2.2 volts and the 
polarization be stopped when bichromate of potash is 
added. The bichromate of potash enters into chemical 
action with the sulphuric acid and forms chromic acid. 
Such cells are usually termed chromic acid cells. 

One of the principal disadvantages of a cell such as that 
just described lies in the fact that the zinc is continuously 
consumed whether the cell is in action or not and in order 
to prevent its rapid waste must be lifted out of the 
solution and washed each time after using. 

Various methods have been devised for overcoming 
this objection, the most prominent of the resulting cells 
being known as the Fuller, Gordon and Edison-Lalande 
Cells. 

.. figure:: images/Image7.jpg
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   :alt: FIG. 7. Edison Cell. 
   
   FIG. 7. Edison Cell. 

The liquid excitant of the Gordon and Edison-Lalande 
cells is a strong solution of sodium hydroxide. The 
positive pole of these cells is a block of compressed copper 
oxide and the negative a pair of zinc plates. In the 
Gordon cell the positive is enclosed in a porous chamber. 

.. figure:: images/Image8.jpg
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   :alt: FIG. 8. Dry Cell. 
   
   FIG. 8. Dry Cell. 

One of the best known forms of cell is the dry cell. 
It consists of an outer shell of zinc forming the negative 
electrode and a central rod of carbon as the positive. 
The active agent of the cell is a paste composed 
principally of sal ammoniac lining the interior of the zinc 
shell. The depolarizing agent of the cell is manganese 
dioxide mixed with crushed carbon and packed tightly 
around the carbon rod. The cell is not as its name 
implies perfectly dry inside, but the chemicals are in paste 
form. The cell is sealed at the top by a bituminous 
compound making the cell air tight and portable. Dry 
cells are only successful for intermittent work, that is, 
where they are not required to deliver a heavy current 
continuously. They deteriorate after long standing 
because the moisture evaporates. Dry cells, however, are 
a very convenient source of current where the demand 
is not too great and portability is desired. 

The cells so far described are all of the type known as 
primary cells. 

**SECONDARY CELLS.**

The storage cell or secondary cell is made up of
plates of lead, or an alloy of lead, cast in the form 
of a grid or framework of bars. The spaces formed in 
the plate by the little bars are filled with a paste of lead 
oxide. The paste for the positive plates are made of 
red lead while litharge is used for the negatives. 

.. figure:: images/Image9.jpg
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   :alt: FIG. 9. A Storage Battery Grid. 
   
   FIG. 9. A Storage Battery Grid. 

The positive and negative plates are placed alternately 
in a bundle with a wooden or rubber separator between, 
there always being one more negative plate than positive. 
The negative plates are all connected in parallel at one 
end of the cell by means of lead connecting strips. The 
positive plates are connected at the other end. The plates 
are placed in a jar, usually glass or hard rubber, and 
covered with a dilute sulphuric acid solution. 

The storage cell is then connected to a dynamo, the 
positive pole of the cell being connected to the positive 
pole of the dynamo and the current allowed to flow 
through until the plates are *formed*, that is to say, until 
the paste in the positive changes to *peroxide of lead* and 
that in the negative to *spongy* lead. When the cell is 
disconnected it will give out a current of its own lasting 
until it becomes discharged. The charging and 
discharging must be repeated several times before the cell 
really becomes efficient. 

.. figure:: images/Image10.jpg
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   :alt: FIG. 10. Storage Cells. 
   
   FIG. 10. Storage Cells. 

What is effected in the storage cell is really the storage 
of chemical energy and not the storage of electricity, for, 
properly speaking, the energy is put into the form of 
chemical *affinity* and there is in reality no more 
electricity actually *in the cell* at the end of a charge than there 
is when the cell is discharged. 

The storage battery is the most convenient means of 
absorbing electrical energy at one time or place and using 
it at another time or place. 

Storage cells are very often employed in wireless 
stations for emergency purposes so that in case the dynamo 
supplying current fails the station will not be thrown out 
of operation. 

The voltage of a storage cell is about two volts. 


LESSON FOUR. ELECTRIC CURRENTS.
```````````````````````````````

**The Units of Measurement. Direct and Alternating 
Currents. Ohm’s Law.**

Electric Currents may be divided into two 
classes known as *direct* and *alternating* current. 
Either one may be measured or qualified by two electrical 
units called the *Ampere* and the *Volt*. The volt may be 
explained by likening it to the "unit of pressure" of the 
current, while the ampere measures the unit rate of 
current flow. For example, in the case of water the voltage 
corresponds to the pressure in pounds while the 
amperage would indicate the rate of water flowing. 

.. figure:: images/Image11.jpg
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   :alt: FIG. 11. Hydraulic Analogy between Voltage and Amperage. 
   
   FIG. 11. Hydraulic Analogy between Voltage and Amperage. 

The accompanying sketches show graphically the 
analogy between the voltage and amperage of an electric 
current and the pressure and volume of a stream of water. 
In the first illustration a tank is shown at a high elevation 
from which a small pipe leads. The voltage or pressure 
in such a pipe would be high in comparison with that in 
a pipe leading from a lower tank. 

In the second illustration the pipe leading from the 
tank is much larger than that from the first and 
consequently the amperage or volume flowing is greater in 
comparison. From this it may be readily seen that every 
circuit through which a current is flowing must exhibit 
both quantities. 

The unit of electrical work or energy is the *Watt*. 
Seven hundred and forty-six watts constitute an 
electrical horse-power. The number of watts is indicated by 
the voltage times the amperage. Thus the amount of 
energy in a circuit in which 50 amperes at 100 volts 
pressure are passing is 50 x 100 or 5,000 watts. 

The *Couloumb* represents the quantity of electricity 
flowing in a circuit-where the rate of flow is one 
ampere per second. 

In order to properly indicate comparative amounts 
of energy the element of time must also be taken into 
consideration. One watt passing for one hour is a 
*watt-hour*. Seven hundred and forty-six watts passing for 
one hour or one watt passing for seven hundred and 
forty-six hours is a *horse-power hour*. 

The instruments used for measuring the amperage and 
voltage of a circuit are called respectively the *ammeter* 
and the *voltmeter*. That used for registering watt-hours 
is called the *integrating watt-meter*.

.. figure:: images/Image12.jpg
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   :alt: FIG. 12. Diagram Showing Alternating and Direct Current. 
   
   FIG. 12. Diagram Showing Alternating and Direct Current. 

Direct current is current that passes or flows in one 
direction only. The current of all primary and secondary 
cells and of certain forms of dynamos is direct. 

Alternating current is current that repeatedly reverses 
its direction of flow. A direct current may be 
represented by a straight line. An alternating current is shown 
by a wavy line crossing and recrossing a straight line. 
The current gradually rises from zero to a maximum 
and then dies away. It does not stop at this point 
however, but starts to rise again, this time flowing in a 
reverse direction. After reaching a maximum it dies away 
again and the cycle is repeated. From *a* to *c* represents 
a *cycle* and from *a* to *b* an *alternation*. Alternating 
currents usually have a frequency of 30, 60 or 120 cycles 
per second. Sixty is the most common frequency. Many 
wireless telegraph stations now employ currents having 
a frequency of 500 cycles. 

**Ohm’s Law.**

Mention has been made above of certain electrical 
magnitudes, namely, voltage or electromotive 
force and amperage or strength of current. These bear 
an important relation in determining a property of an 
electric circuit called *resistance*. 

No conducting body possesses perfect electrical 
conductivity, but presents a certain amount of obstruction or 
resistance to the passage of electricity. The practical 
unit of resistance is the Ohm. It is represented by the 
resistance offered to an unvarying electric current by 
a column of mercury at the temperature of melting ice, 
\14.4521 grams in mass, of a constant cross sectional area 
and of the length of 106.3 centimetres. 

The resistance of a conductor is proportional to its 
length, that is, provided two conductors are made of the 
same material and of the same diameter and one is twice 
as long as the other, the resistance of the longer will 
be twice that of the shorter conductor. The resistance is 
inversely proportional to the cross sectional area, which 
is to say that a conductor of smaller cross section has a 
greater resistance than one of larger section. 

The laws of resistance are conveniently expressed by 
the following formula called Ohm’s Law. 

|       C = E/R

| where E=electromotive force in volts. 
|       C=current in amperes. 
|       R=resistance in ohms. 

If two factors are known, the third can be found by 
substitution. 


LESSON FIVE. ELECTROMAGNETISM.
``````````````````````````````

**The Electromagnet. The Solenoid.**

If a current of electricity is passed through a copper 
wire, the wire will attract to itself iron filings, etc., 
as long as the current continues to flow. There is then a 
magnetic field around the wire. As soon as the current 
is shut off the filings drop away because the field 
immediately disappears with the cessation of the current. 

.. figure:: images/Image13.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 13. Magnetic Phantom about a Wire Carrying Current. 
   
   FIG. 13. Magnetic Phantom about a Wire Carrying Current. 

The lines of force flow around the wire in a circle. 
The circular lines of the field of force surrounding a 
straight wire may be shown by passing a wire vertically 
through a hole in the centre of a horizontal card. Iron 
filings are sifted over the card and a strong current passed 
through the wire. On tapping the card gently, the filings 
near the wire set themselves in concentric circles round it. 

The creation of a magnetic field by a conductor in its 
own neighborhood when carrying a current of electricity 
is one of the most important phenomena of electrical 
science. 

Electrical energy must be expended in producing a 
magnetic field. When a current of electricity is turned 
on in a wire the magnetic field grows around the wire, 
some of the energy of the current being used for the 
building process. 

This reactive effect of the surrounding magnetic field 
is one reason why electric currents do not instantly rise 
to their full value. 

.. figure:: images/Image14.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 14. Diagram showing how Lines of Force Form about a Loop of Wire.
   
   FIG. 14. Diagram showing how Lines of Force Form about a Loop of Wire.

If a wire is connected to a battery or some other source 
of electric current and a portion of the circuit twisted so 
as to form a loop, the entire space enclosed by the loop 
will be a magnetic field and possess magnetic properties. 

By forming a wire into a spiral coil the combined 
effect of each individual turn is concentrated in a small 
space and a powerful field of force is produced. If the 
coil is provided with an iron core, the lines of force can 
be concentrated and will exercise a very powerful 
attractive effect upon any neighboring masses of iron or 
steel. Such a coil is called an *electromagnet*. A hollow 
coil without any core is called a *solenoid*. 

.. figure:: images/Image15.jpg
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   :scale: 85 %
   :alt: FIG. 15. Magnetic Phantom about a Coil of Wire. 
   
   FIG. 15. Magnetic Phantom about a Coil of Wire. 

Solenoids and electromagnets play a very important 
part in the construction of most electrical instruments. 

The strength of an electromagnetic coil is proportional 
to its *ampere turns*. The ampere turns of a coil are 
obtained by multiplying the number of amperes flowing 
through the coil by the number of turns of wire 
composing it. 


LESSON SIX. DYNAMO ELECTRIC MACHINERY.
``````````````````````````````````````

**The Dynamo. The Alternator. The Motor.**

The discovery of the induction of currents in wires 
by moving them across a magnetic field led to the 
construction of electrical machines, called dynamos, to 
generate current in place of batteries. 

The dynamo is perhaps the most important piece of 
electrical apparatus there is for it is the source of 
ninety-nine percent of all the electricity now in use. It is 
practically necessary in any case where a considerable 
quantity of electricity is used to have a dynamo on the spot 
or else bring the currents over a wire from some supply 
station where dynamos are kept running. 

The operation of a dynamo is dependent upon current 
induction. It contains a system of closed conductors 
revolving in a magnetic field in such a way as to 
continuously vary the number of lines of force threading among 
them. 

.. figure:: images/Image16.jpg
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   :alt: FIG. 16. Diagram showing the principle of the Dynamo. 
   
   FIG. 16. Diagram showing the principle of the Dynamo. 

The illustration show's the ideal simple dynamo, which 
consists of a loop of wire arranged to revolve between 
the poles of a permanent magnet in the direction of the 
arrow and around a horizontal line as an axis. The lines 
of magnetic force (represented by the fine straight lines) 
pass across from N to S as indicated. When in the 
position shown, the coil of wire encloses the largest 
possible number of lines of magnetic force. When it 
has revolved ninety degrees or a quarter of a turn as 
shown by the dotted lines, the lines of force will be 
parallel to the plane of the coil and none will pass 
through. During this quarter of the turn the number of 
lines of force has been decreasing. During the next 
quarter of a turn the lines will increase again, but will 
this time pass through from the opposite side of the loop. 
This decrease and increase of the number of lines of 
force passing through the loop generates therein a current 
of electricity. The same process is repeated during the 
next half of a revolution. However, since the lines of 
force flow through from opposite sides of the coil every 
half revolution, the current reverses twice during the 
same period. 

In the illustration the loop is represented as forming a 
complete closed circuit in itself. In order to draw any 
current for external use some method of establishing 
connection to the terminals of the coil must be had. This 
is furnished by two circular rings called *collector rings*. 
The little strips of metal or carbon employed to form 
contact with the rings are called brushes. 

.. figure:: images/Image17.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 17. Simple Alternator. 
   
   FIG. 17. Simple Alternator. 

Such a machine, so equipped will deliver alternating 
currents and illustrates the principle of the alternating 
current dynamo or *alternator*. 

With the aid of a device called a *commutator* and 
consisting of a ring split in sections as shown in the 
illustration, all the successive current impulses may be turned 
in the same direction and the current made direct. 

In practice many coils of wire wound around an iron 
core called the *armature*, the purpose of which is to 
concentrate the magnetic lines of force, are made to revolve 
in a powerful *field* between the poles of adjacent 
electromagnets. Electromagnets are used because they are 
capable of producing a stronger magnetic field than 
magnetized bars of steel. The electromagnets used for this 
purpose are called *field magnets*. The central iron portion 
upon which the revolving coils are wound, called the 
*armature*, is usually built up of a number of thin sheets 
of soft steel called armature disks or laminations. 

.. figure:: images/Image18.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 18. Simple Dynamo showing Commutator. 
   
   FIG. 18. Simple Dynamo showing Commutator. 

The modern armature is very complex. A simple coil 
such as those shown in Figs. 17 and 18 will not yield a 
steady current for twice in each revolution the 
electromotive force dies away to zero. The coils of large dynamos 
are grouped so that some of them are always active. 

There are three general methods of supplying current 
to the held magnets of a dynamo, known as the *series*, 
*shunt* and *compound* windings. 

The series dynamo is arranged so that the coils of the 
held magnets are in series with those of the armature. 

In the shunt dynamo, the coils of the held magnet 
form a shunt to the main circuit and being made of many 
turns of thin wire, draw off only a small fraction of the 
whole current. 

.. figure:: images/Image19.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 19. Diagram of Dynamo Field Windings.
   
   FIG. 19. Diagram of Dynamo Field Windings.

The compound dynamo is partly excited by shunt coils 
and partly by series coils. 

.. figure:: images/Image20.jpg
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   :scale: 85 %
   :alt: FIG. 20. Motor Generator.
   
   FIG. 20. Motor Generator.

Each variety of dynamo winding has a certain 
advantage depending upon the condition of use. 

In the case of alternating current dynamos, the field 
magnets are sometimes supplied from a separate dynamo 
called an "exciter." In other cases the dynamo is 
provided with two sets of windings, one connected to a 
commutator producing a direct current which excites 
the field coils and the other connected to a set of rings 
and supplying the alternating current. 

In case a supply of either direct or alternating 
current is available and it is desirable to change the supply 
from direct to alternating or vice versa, it may be 
accomplished by employing a Motor-Generator. A 
motor-generator consists of an electric motor operating from 
the source of current supply on hand and driving a 
dynamo which supplies current of the kind desired. 

A motor is exactly the reverse of a dynamo. If a 
current of electricity is passed into a dynamo, the armature 
will be dragged around by the mutual action of the 
currents flowing in the copper conductors and the magnetic 
field in which they lie. Such a device constitutes a motor 
and may be employed to do useful work. 

Motors are classified as alternating and direct current 
machines accordingly as they are built to operate on either 
kind of current. 

LESSON SEVEN. THE INDUCTION COIL.
`````````````````````````````````

The Induction Coil is an apparatus for producing 
currents of a very high electromotive force. It 
consists of a helix of large, insulated wire surrounding an 
iron core, and this again surrounded by a second coil 
consisting of many thousand turns of very fine wire 
carefully insulated. The inner or primary coil is 
connected in series with a battery, the circuit also including 
a device called an *interrupter*. The object of the 
interrupter is to make and break the primary circuit in rapid 
succession. Every time the current is turned on in the 
primary circuit, the primary coil creates a magnetic field 
which induces a current in the secondary in accordance 
with the laws of induction. 

.. figure:: images/Image21.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 21. Diagram of Induction Coil. 
   
   FIG. 21. Diagram of Induction Coil. 

Likewise at every "break" in the circuit caused by the 
interrupter, the lines of force disappear and a second 
current impulse is induced in the *secondary* coil. As the 
number of lines of magnetic force created and destroyed 
at each make and break is the same, the two electromotive 
impulses in the secondary are equal. By adding a 
*condenser*, however, the current at "make" is caused to 
take a considerable fraction of time to grow, while at 
"break" the cessation is instantaneous in comparison. 
The rate of "cutting" of the lines of force is very much 
more rapid at "break" than at "make" therefore. The 
currents at "break" manifest themselves as a brilliant 
torrent of sparks between the ends of the secondary 
wires when they are brought near enough together. 

The central iron core around which the coils are wound 
is for the purpose of increasing or concentrating the 
number of lines of force that pass through the coils. 
Magnetic lines flow more easily through iron than 
through air and so prefer that path. It is made up of a 
bundle of fine iron wires in order to avoid induced 
currents which would be set up in the iron were it a solid 
mass and so retard its rapidity of magnetization or 
demagnetization as to hamper the efficiency of the coil. 

LESSON EIGHT. THE PRINCIPLE OF THE TRANSFORMER.
```````````````````````````````````````````````

The transformer is a device for raising or lowering 
A the electromotive force of an alternating current. 
In principle it consists of two insulated coils of wire 
called the *primary* and the *secondary* wound around an 
iron ring as shown in the illustration. 

.. figure:: images/Image22.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 22. Diagram showing the principle of a Transformer. 
   
   FIG. 22. Diagram showing the principle of a Transformer. 

If the primary coil is connected to a source of 
alternating current it will rapidly magnetize and demagnetize 
the iron ring. The magnetic lines thus created will pass 
through the secondary coils setting up induced currents. 

The ratio of the electro-motive force of the induced 
current to that of the primary current is in direct 
proportion to the ratio of the number of turns in the two 
coils. For example, if the secondary contains twice as 
many turns as the primary, its electro-motive force will 
be twice as great. 

.. figure:: images/Image23.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 23. Open and Closed Core Transformers. 
   
   FIG. 23. Open and Closed Core Transformers. 

Transformers are of two general types, the "open" 
core and the "closed" core. Closed core transformers 
are the most efficient. The open core transformer is 
similar in construction to an induction coil, the core 
being a straight bar, while that of the closed core machine 
is usually in the form of a hollow square or rectangle. 

In practice, the cores of transformers are built up of 
*laminations*, usually of thin, soft sheet iron strips piled 
together and shaped so as to constitute a closed 
magnetic circuit of rectangular shape in order to avoid 
constructional difficulties incurred in making a ring. 

LESSON NINE. THE LEYDEN JAR AND CONDENSER.
``````````````````````````````````````````

The Leyden Jar, called after the city of Leyden, 
Holland, where it was invented, is a form of condenser 
consisting of a glass jar coated up to a certain height 
inside and out with tinfoil. 

.. figure:: images/Image24.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 24. Leyden Jar. 
   
   FIG. 24. Leyden Jar. 

A Leyden jar may be charged by holding the rod to 
the prime conductor of an electric machine, the outer 
coating being held in the hand. If a piece of wire 
connected to the outer coating is then brought near the rod 
a brilliant snapping spark will pass across the space. 

Any two conductors, separated by an insulating 
medium termed the dielectric, constitute a condenser and 
possesses the property of receiving and retaining an 
electric charge. 

If a charged condenser or Leyden jar is discharged 
slowly by allowing the electricity to pass through a high 
resistance conductor the flow of current increases in 
strength at first and then gradually dies away. 

If, however, the condenser is discharged through a 
coil of wire of one or more turns, the discharge consists 
of a number of excessively rapid oscillations or surgings. 
The first rush of current serves to more than empty the 
condenser and charges it the opposite way, then follows 
a reverse discharge, which also oversteps itself and 
charges the condenser the same way as the first and so 
on, each successive oscillation being weaker than the one 
before until the discharge dies away as in Fig. 36. 
The discharge of a condenser under such conditions 
consists of a number of successive sparks in reverse 
directions. 

The ability of a condenser to receive and retain an 
electrical charge is termed the *capacity* and is measured 
by a unit called the *farad*. The farad is so large a 
quantity, however, that it is never met in practise and 
for convenience the *micro-farad* which is one millionth 
of a farad has been adopted. 

A condenser of one farad capacity is such as would be 
raised to a potential of one volt by a charge of one 
coulomb of electricity. 

The capacity of the condenser is dependent upon the 
thickness and nature of the insulating medium or 
*dielectric*. The quality of a dielectric which decides the 
capacity of a condenser in which it may be a part is 
called its *specific inductive capacity*. The following table 
shows the relative specific inductive capacity of several 
materials, air being the standard: 

.. table:: TABLE OF SPECIFIC INDUCTIVE CAPACITIES.
   :hrules: table
   :align: center
   :width: 50%
   :float: none

   ============== ===================
   Substance.     Constant.  
   ============== ===================
   Air            1.00 
   Paraffin       1.68—2.47 
   Petroleum      2.02—2.19 
   Gutta Percha   3.00 
   Hard Rubber    2.28 
   Mica           6.64 
   Glass          6.72—7.38 
   ============== ===================

LESSON TEN. THE ETHER AND THE ELECTROMAGNETIC THEORY OF LIGHT.
``````````````````````````````````````````````````````````````

All space is filled with a weightless, invisible medium 
called Ether. It is the substance with which the 
universe is filled, it reaches to the stars and through the 
very earth itself. 

It has been known for some time that light consists 
of vibrations or motions in the ether. In 1867, Clerk 
Maxwell offered the theory that these light waves are 
not merely mechanical motions of the ether, but are 
electrical undulations. According to this theory, the 
phenomena of electro-magnetism and the phenomena of 
light are all due to certain modes of motion in the ether. 

Twenty years later, Heinrich Hertz discovered 
convincing proofs of Maxwell’s theory and succeeded in 
producing electro-magnetic waves in such a manner that they 
possessed the same properties, traveled at the same speed, 
and were capable of being reflected, refracted, 
polarized, etc. 

.. figure:: images/Image25.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 25. Hertzian Oscillator and Resonator. 
   
   FIG. 25. Hertzian Oscillator and Resonator. 

Hertz employed an apparatus consisting of two metallic 
balls connected by metal rods to two metal sheets. The 
two balls were also connected to the secondary terminals 
of an induction coil. This apparatus comprised the 
oscillator and served to create the electro-magnetic waves. 

In order to detect the waves, he employed a resonator 
consisting of a circle of wire having in it a minute spark 
gap capable of fine adjustment. 

As soon as the coil is set in operation a spark snaps 
across the gap and sets up a temporary conducting path 
for the surgings that follow. Each spark sent by the 
coil across the gap consists of a dozen or so *oscillations*, 
each lasting less than a millionth of a second. 

Then if the resonator is placed a few feet away from 
the oscillator and turned broadside on to the oscillator, 
it will be found that small sparks jump across the gap. 
Hertz employed various arrangements for reflecting and 
polarizing the waves and definitely proved that their 
nature is the same as that of light. 

LESSON ELEVEN. ELECTRIC WAVES.
``````````````````````````````

When a Leyden jar discharges under the conditions 
set forth in one of the previous lessons, portions 
of the energy of the current or discharge are thrown off 
from the conductor and do not return to it, but go 
traveling on in space. 

If a current is sent through a circuit, as the current 
increases, the magnetic field also increases, the magnetic 
lines enlarging and spreading outward from the conductor 
like the ripples on a pond. If the current is decreased, 
the magnetic lines all return back and close up upon 
the conductor, the energy all being re-absorbed into the 
circuit. 

If electrical oscillations of extreme rapidity such as 
those generated by a condenser discharge are substituted 
for a current slowly rising and falling, part of the energy 
radiates off into the ether as *electromagnetic* waves and 
only a part returns back. 

The discharge of a Leyden jar or condenser only 
oscillates when the circuit contains a certain amount of 
*capacity* and *inductance* in proportion to the resistance 
of the circuit. 

Inductance is the property of a circuit by virtue of 
which lines of force are developed around it. Circuits 
containing a certain amount of inductance, capacity and 
resistance tend to oscillate electrically at a certain 
frequency. 

.. figure:: images/Image26.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 26. Electric Waves. 
   
   FIG. 26. Electric Waves. 

The electromagnetic waves thrown off by the aerial 
system follow the contour of the earth and so may cross 
mountains or travel anywhere. The waves emitted by 
the ordinary wireless station, making use of an aerial 
and a ground are *half* waves terminating in the earth 
as shown in the illustration. In passing over the earth 
they are accompanied by ground currents which waste 
a certain amount of their energy in overcoming ohmic 
resistance and so reduce the intensity of the waves. For 
this reason propagation is always the best over water or 
moist earth whose resistance is low. 

A further peculiar weakening of the waves due to the 
absorbtion taking place in the air during sunlight. The 
difference between the signals in the day and their 
strength at night is very marked, being much stronger 
in the later case. 

LESSON TWELVE. PRINCIPLES OF WAVE TELEGRAPHY.
`````````````````````````````````````````````

Wireless Telegraphy as practiced to-day is merely 
a method of setting up electromagnetic waves in 
the ether and then detecting their existence at a distant 
point. It may be divided into four distinct and individual 
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. 

We have already learned how electrical oscillations 
may be generated by the discharge of a Leyden jar or a 
condenser. In order to perform the first two operations 
named above, it is therefore merely necessary to arrange 
a condenser in such a way that it is most effective. 

The induction coil or transformer is employed to 
charge the condenser because the currents of these 
instruments are much more powerful than those of a static 
electric machine. The induction coil is connected to a 
set of batteries and a key so that the periods during 
which the current is on and off may be controlled at 
will by the pressure of the fingers. 

.. figure:: images/Image27.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 27. Diagram of Wireless Transmitter. 
   
   FIG. 27. Diagram of Wireless Transmitter. 

The secondary of the coil is connected to a battery of 
Leyden jars or a condenser. The fact was mentioned 
above that a certain amount of inductance in the circuit 
is necessary for the production of electrical oscillations 
This is furnished, or at least the greater part, by a 
device called a helix which consists of a coil of heavy wire 
wound around a suitable framework. 

The spark discharge takes place across a device called 
a spark gap. 

When the key is pressed, the high potential currents 
of the induction coil charge the Leyden jar or condenser 
and cause it to discharge through the helix and across the 
spark gap. High frequency oscillations are immediately 
created in this part of the circuit. The spark gap, 
condenser and that part of the helix included, constitute the 
closed circuit. The electromagnetic waves thrown off 
by such an oscillatory system would not be very far 
reaching in their effects because the disturbances would 
be confined to the immediate neighborhood of the 
apparatus, so recourse is had to the aerial and ground. The 
aerial consists of a network of wires elevated high in the 
air. The ground or earth connection is simply a large 
metal plate buried in moist earth or thrown into the sea. 
By connecting the aerial and ground to the helix in the 
manner shown in Fig. 27, the high frequency 
currents are caused to surge up and down the aerial system 
into the ground and create very powerful electromagnetic 
waves which possess the power of exciting electrical 
oscillations in another aerial even though it may be 
located many miles away. 

The existence of these oscillations is made known to 
the receiving operator by a device known as a detector, 
described fully in one of the following lessons. 

LESSON THIRTEEN. THE AERIAL.
````````````````````````````

The aerial system or antenna might be termed the 
mouth and ear of the wireless station, for it is 
this huge network of wires stretching high into the air 
that emits or intercepts the electromagnetic waves upon 
which such systems of communication depend. 

.. figure:: images/Image28.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 28. General Types of Aerials 
   
   FIG. 28. General Types of Aerials 

The value of an aerial is dependent upon its height 
above the surface of the earth. The greater its height the 
wider will be the field of force or strain set up in its 
neighborhood and consequently more powerful electric 
waves will be developed. Proximity to all large 
conductors, such as smokestacks, telephone lines, etc., is 
always avoided because these obstacles would absorb 
appreciable amounts of the energy sent out from the station 
and also shield it somewhat from the incoming waves. 
Aerials are usually constructed of conductors made up 
of a number of wires stranded together. High frequency 
currents only travel near the surface of conductors and 
stranded wires consequently offer less resistance because 
they possess more surface than a solid conductor of equal 
cross section. 

The aerial is always carefully insulated by means of 
special high tension insulators, made of insulating 
composition molded into a corrugated bar having iron rings 
embedded in each end to which the wires may be fastened. 

Aerials take many different forms, but may be classified 
into two general groups called the vertical aerials and 
flat top aerials. 

Vertical aerials compose the *grid*, *fan*, *cage* and *umbrella* forms. 

Flat top aerials are known as the *T*, *inverted U*, *L* and 
*V* types, according to their shape. 

The Pyramid Aerial is only employed in ultra-powerful 
stations and is becoming an obsolete form. 

The Fan Aerial is a good type of especial value in 
crowded quarters. 

The Grid Aerial is probably the best form of vertical 
aerial, but is gradually giving way to those of the flat 
top class. 

The Cage Aerial is rarely used nowadays and may be 
considered obsolete. 

The Umbrella Aerial is a very good type now being 
employed in many high power stations. A metallic pole 
or mast insulated at the base used to support the wires, 
so that it is part of the aerial itself. 

The "T" Aerial is the most nearly perfect and gives 
the best "all around" results. 

The "L" or Horizontal type of aerial is used 
wherever it is desirable for any reason to send the 
most powerful waves in one direction. 

The "V" type is used where the highest point must be 
near the station. 

The wire leading into the station, from the aerial is 
called the "rat-tail" or "lead-in." It is always very 
carefully insulated and usually enters the station through 
a hole in the window or wall by means of a "window 
pane bushing" or "leading-in insulator." 

Certain aerials possess a directive action, that is they 
radiate and receive messages in some directions better 
than others. Flat top aerials possess this peculiarity more 
noticeably than the vertical types. Flat top aerials receive 
and radiate waves coming from 
and going towards a direction opposite 
to that in which the free end points. 

.. figure:: images/Image29.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 29. Spiral Aerial.
   
   FIG. 29. Spiral Aerial.

The free end is the opposite end to 
that to which the "rat-tail" is connected. 

There are two free ends on a "T" 
aerial and so this form radiates and 
receives its waves equally well in two directions. 

The inverted "L" and "V" types possess a 
very decided directive action. 

Certain aerial forms may be classed as 
loop and straightaway accordingly as 
they are connected and led into the station. 
In the straightaway form of antenna, 
the wires are connected together 
as a whole and one rat-tail led into the 
station. In the loop form the wires are 
all connected together and divided into 
two sections. Two wires are led into the 
station. 

The loop form gives slightly better results in a short 
aerial, but in most cases the straight away is decidedly 
the most efficient. 

LESSON FOURTEEN. THE WIRELESS COIL.
```````````````````````````````````

The induction coil used for wireless telegraph 
purposes differs from the ordinary coil commonly 
employed in the laboratory in that it is usually built in a 
more substantial manner and gives a heavier, 
more powerful discharge from the secondary. 

Induction coils of this type are usually enclosed in a 
strong wooden case filled with insulating compound and 
are sometimes termed box coils. They are fitted with an 
interrupter arranged to give a very long period of "make" 
and a short "break." 

Coils giving sparks greater than six inches in length are 
usually provided with an independent interrupter which 
may be one of several types. 

.. figure:: images/Image30.jpg
   :align: center
   :scale: 85 %
   :alt: Fig. 30. Wireless Spark Coil.
   
   Fig. 30. Wireless Spark Coil.

The ordinary independent interrupter consists of the 
usual form of interrupter, but is operated by the 
magnetism of a separate electromagnet in place of that of the 
coil primary itself. An independent interrupter of this 
type is usually provided with screws for adjusting the 
speed, and the duration of make and break. 

.. figure:: images/Image31.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 31. Independent Interrupter. 
   
   FIG. 31. Independent Interrupter. 

The Mercury Turbine form of interrupter is a very 
unsuccessful type in which 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 into a mercury reservoir so that when 
the spiral is revolved, the mercury rises in the tube by 
centrifugal action and is thrown out from the upper end 
in the form of a jet. 

When the revolving jet strikes one of the metal teeth 
the circuit is made and when it passes between it is broken. 
Raising and lowering the saw teeth so that the mercury 
strikes either the lower or upper part varies the ratio 
of time of the make and break. 

.. figure:: images/Image32.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 32. Electrolytic Interrupter. 
   
   FIG. 32. Electrolytic Interrupter. 

The electrolytic interrupter consists of a cathode or 
negative electrode of sheet lead immersed in diluted 
sulphuric acid and an anode composed of 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 portion of the wire is exposed to contact with the 
liquid. When a strong electric current is passed through 
the acid electrolyte, the current is very rapidly interrupted 
by the formation of gases on the small platinum electrode. 
The number of breaks per second possible with an electrolytic 
interrupter is extremely high. A potential of at 
least 40 volts is required to operate such an interrupter, 
however. 

LESSON FIFTEEN. THE HIGH POTENTIAL TRANSFORMER.
``````````````````````````````````````````````` 

The transformer, like the induction coil, steps up the 
voltage of the current to a value where it is sufficient 
to charge the condenser. 

The transformer for wireless work should have a 
potential of from 15,000 to 40,000 volts. Several 
manufacturers claim advantage for low voltages and build 
machines having a potential of only about 8,000 volts, 
but experiments have shown that under most ordinary 
conditions higher voltages permit greater range of transmission. 

Both open and closed core machines may be used with 
good results. Probably, however, neither one is the 
best. 

The core of a wireless transformer is built up of sheet 
iron "laminations" to reduce core losses and eddy currents. 

.. figure:: images/Image33.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 33. High Potential Closed Core Transformer. 
   
   FIG. 33. High Potential Closed Core Transformer. 

.. figure:: images/Image34.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 34. Method of Protection against "Kick-Back"
   
   FIG. 34. Method of Protection against "Kick-Back"

The secondary windings are very carefully insulated 
with empire cloth or paper and may or may not be immersed 
in oil accordingly as they are designed. 

A transformer, more especially than an induction coil, 
produces a "kick-back" on the line. "Kick-back" is a 
high potential current caused by the counter action of 
currents in the condenser and aerial system, due to the 
fact that they continue to surge after the current has 
dropped to zero or so low that it is unable of its own 
accord to produce secondary currents which will jump 
the spark gap. 

"Kick-back" destroys insulation and is liable to cause 
burnouts of other electrical instruments supplied from the 
same system. It may be guarded against by providing 
the line with a protective device which consists of a 
condenser having a capacity of one or two micro-farads 
placed directly across the terminals of the transformer 
in series with two five-ampere fuses. A small spark gap 
open about 1/64 of an inch wide is connected across the 
terminals of the condenser. 

In case special protection is desired for some instrument 
in the circuit, such as a meter, a protective device 
should be connected directly across its terminals. 


LESSON SIXTEEN. THE OSCILLATION CONDENSER.
``````````````````````````````````````````

The Oscillation Condenser might almost be termed the 
most important part of a wireless station. 

Transmitting Condensers usually take the form of a 
battery of Leyden jars arranged in a suitable case or 
container. Very often they are placed in a tank of oil 
to eliminate *brush* discharges or leakage which takes place 
from the edges of the tinfoil. 

.. figure:: images/Image35.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 35. Plate Condenser. 
   
   FIG. 35. Plate Condenser. 

Leyden jars are usually covered with very heavy tinfoil or 
thin sheet copper to prevent blistering. The best 
method, however, is to deposit a metallic covering 
electrolytically. 

The principle objection to Leyden jars is their bulk. 

Glass plate condensers are not so bulky or expensive 
and do not blister. 

Plate condensers are sometimes merely placed in racks, 
but more often in a tank of oil to eliminate all brush discharges. 

Condensers are always made so as to be adjustable in 
order that the capacity of the circuit may be carefully 
regulated. 

Only the finest selected glass of the greatest dielectric 
strength is used in making condensers, in order to avoid 
all losses and possibility of breakdown. 

Whenever condensers must withstand a very heavy 
voltage, they may be connected in series so that the 
voltage is divided between them and the strain is not so 
great. This method reduces the capacity just one-half, 
however, and when used requires four times as many 
plates or jars, as the case may be, than if they were 
connected in one multiple set. 

LESSON SEVENTEEN. THE HELIX. 
````````````````````````````

The Helix supplies the greater part of the inductance 
to the closed circuit of the transmitter. It also 
acts as a transformer, serving to raise the voltage of the 
currents surging through the closed circuit and impress 
them upon the aerial system. The turns of the helix included 
in the closed circuit constitute the primary of the 
transformer, while those in the open circuit form the 
secondary. 

A helix consists of a heavy conductor, either brass or 
copper, wrapped around a suitable frame of wood or hard 
rubber. Some forms consist of a spiral of copper ribbon 
clamped between two cross-shaped frames. 

.. figure:: images/Image36.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 36. Helix.
   
   FIG. 36. Helix.

Helixes are of two kinds, known as "close" or direct 
coupled and "loose" or inductively coupled. In an 
inductively coupled transmitter the primary and secondary 
are wound upon separate frames and are not connected 
together. 

The U. S. Government Radio regulations place a limit 
on the amount of *damping* permissable in a transmitter. 

It has already been explained in one of the previous 
lessons how the oscillations or surgings of the spark 
discharge rapidly die away. A spark which thus rapidly 
dies away is said to be *rapidly damped*. The damping 
of a loose coupled transmitting set is never as great as 
that of a close coupled set. 

.. figure:: images/Image37.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 37. A Damped Oscillation. 
   
   FIG. 37. A Damped Oscillation. 

.. figure:: images/Image38.jpg
   :align: center
   :scale: 85 %
   :alt: Close-Coupled Transmitter vs. Loose-Coupled Transmitter
   
   Close-Coupled Transmitter vs. Loose-Coupled Transmitter

For this reason the old style helixes are now practically 
obsolete and the loose or inductively coupled helix is 
the one most commonly used. Loose coupled helixes are 
also often termed oscillation transformers. 

.. figure:: images/Image38a.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 38. An Inductively Coupled Helix. 
   
   FIG. 38. An Inductively Coupled Helix. 

An ordinary transmitter tends to emit two sets of 
waves of different length. By carefully adjusting the 
coupling, pure trains of waves are formed by attracting 
the apices of the two sets of waves into one. 

LESSON EIGHTEEN. SPARK GAPS. 
````````````````````````````

A Spark Gap is the medium across which the 
oscillatory discharge takes place. It usually consists 
of two electrodes of zinc alloy, nickel steel or brass, 
suitably mounted on an insulating base and standards. 

.. figure:: images/Image39.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 39. Spark Gap. 
   
   FIG. 39. Spark Gap. 

The electrodes are usually provided with flanges or 
radiators which tend to dissipate the heat and keep them 
cool. If the electrodes should become very hot the spark 
would arc, that is, pass across the gap without generating 
any electrical oscillations. Spark gap electrodes are 
usually flat or else hollow on the sparking surface. 

The proper adjustment of the gap, i.e., the distance 
between the electrodes is a matter of the utmost 
importance for there is a point just where the maximum amount 
of energy will be radiated. 

.. figure:: images/Image40.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 40. Quenched Spark Gap. 
   
   FIG. 40. Quenched Spark Gap. 

The Quenched Gap, consists of a number of brass or 
copper disks placed in a pile, each disk being separated 
from the other by a thin mica ring. The distance between 
two adjacent disks is usually only about .01 inch. The 
effect of the quenched gap is to considerably reduce the 
damping of the system and make it possible to send 
signals very great distances with the consumption of only 
comparatively small amounts of energy. 

.. figure:: images/Image41.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 41. Rotary Spark Gap. 
   
   FIG. 41. Rotary Spark Gap. 

The Rotary Gap consists of a number of electrodes 
mounted on a motor shaft and arranged to revolve rapidly. 
The spark discharge takes place between the revolving 
electrodes and one or two fixed contacts. The effect of 
a rotary gap is to considerably increase the efficiency of 
the transmitter by allowing the condenser to become 
highly charged before it discharges and also reducing the 
possibility of arcing by keeping the electrodes cool and 
moving. 

Rotary gaps are of two types, *synchronous* and 
*non-synchronous*. Synchronous rotary gaps are mounted directly 
on the shaft of the generator supplying current to 
the transmitter and arranged so that the electrodes are 
opposite each other once during each alternation of the 
current. 

The rotary gap, commonly used by amateur experimenters 
and consisting of a toothed disk mounted on 
the shaft of a small motor is of the non-synchronous 
type.

Rotary gaps are sometimes enclosed in an air tight 
case and the electrodes arranged so that the results 
obtained are characteristic of both the quenched and 
rotary gaps. This type of gap is known as the rotary 
quenched. 

LESSON NINETEEN. THE KEY. 
`````````````````````````

Some means of controlling the currents flowing 
through the transmitter in order to divide them into 
periods corresponding to the dots and dashes of the 
Morse Code is necessary. 

This is supplied by a hand operated switch, called a 
key. A key used for wireless purposes must be much 
larger and heavier than an ordinary key employed for 
line work in order to carry the more powerful currents. 

In spite of the size and weight of a wireless key, if it 
is properly balanced, it may be handled with perfect 
control and ease. 

The contact points of a wireless key are necessarily 
large and heavy. Special alloys found to be the most 
suitable for the purpose are usually employed. A large 
condenser having a mica dielectric is very often connected 
across the contacts to reduce the sparkling. 

.. figure:: images/Image42.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 42. Wireless Key.
   
   FIG. 42. Wireless Key.

In very large stations where extremely heavy currents 
must be handled, the key controls a large switch operating 
in oil. Every time the key is pressed the switch closes 
and when the key is released, opens. The currents of the 
transmitter are "made" and broken by the switch without 
passing through the key. 

LESSON TWENTY. AERIAL SWITCHES. 
```````````````````````````````

Since the same aerial is used both for transmitting 
and receiving, some method of quickly connecting 
it to either the transmitter or receiving apparatus must 
be provided. This is accomplished by means of an aerial 
switch. 

The best and most efficient switch adopted generally 
by the commercial stations is the "T" type, consisting of 
a double pole, double throw switch having very long 
blades. One set of contacts is mounted on the switch 
base and the second are carried on a "T"-shaped support 
from which the switch derives its name. The aerial 
and ground are connected to the blades of the switch. 

The lower contacts lead to the transmitting apparatus 
and the upper ones to the receiving instruments. By 
simply moving the switch up or down the aerial and 
ground may be connected to either the transmitter or the 
receptor at will. 

.. figure:: images/Image43.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 43. Aerial Switch. 
   
   FIG. 43. Aerial Switch. 

A third blade, much shorter than the other two is 
usually provided and connected by means of an insulating 
bar to the other blades so that when they are moved 
it also moves. It connects with a contact arranged so 
that when the switch is thrown into position for 
transmitting the two come together. This blade and contact 
are made a part of the circuit supplying current to the 
primary of the coil or transformer so that in case the 
key should be accidentally touched while receiving the 
powerful discharge of the transmitter would not destroy 
the adjustment of the detector. 

LESSON TWENTY-ONE. ANCHOR GAPS. 
```````````````````````````````

Certain types of aerial switches require the use of 
what is known as an *anchor gap*. 

An anchor gap consists of a small insulating ring, 
usually hard rubber, having two and sometimes three 
electrodes set in the periphery and almost touching each 
other at the sparking points. 

Anchor gaps having two electrodes are used in the 
aerial circuit of most Break-in-Systems to prevent the 
receiving currents from flowing directly into the ground 
through the transmitter without passing through the detector. 

.. figure:: images/Image44.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 44. Anchor Gaps.
   
   FIG. 44. Anchor Gaps.

A Break-in System enables the operator to hear the 
signals of any other station which may be transmitting 
at the same time when he is operating his own key. 

The three-electrode anchor gap is commonly used on 
loop aerial systems. Two of the points are connected to 
the aerial, one to each half and the other to the lead 
from the helix. The high potential currents from the 
helix easily leap across the little gap and divide between 
the two halves of the aerial. 

LESSON TWENTY-TWO. DETECTORS. 
`````````````````````````````

The little bobbins of the telephone receivers exert a 
very powerful choking action upon the currents of 
high frequency which effectually blocks their passage and 
prevents them from having any action upon the receiver. 

The purpose of the detector is to change these currents 
into such as will flow readily through the magnets of the 
telephone receiver and manifest themselves as sounds 
recognizable from their duration and periodicity as 
signals of the telegraph code. 

.. figure:: images/Image45.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 45. Electrolytic Detector. 
   
   FIG. 45. Electrolytic Detector. 

Probably the most well known form is the electrolytic 
detector which consists of an exceedingly fine platinum 
wire dipping into a cup of dilute nitric acid far enough 
to just touch the surface of the liquid. The telephone 
receivers are connected to the detector, in series with a 
battery. The current from the detector causes bubbles 
to continuously form on the end of the wire and insulate 
it from the liquid so that the current cannot flow. When 
the aerial is struck by a wave, the feeble alternating 
currents break down the bubbles and permit the currents 
to flow, causing a sound in the telephone receivers. 

The detectors in most common use to-day are of the 
crystal or rectifying type. There are a great many different 
forms of this type of detector, each one of which 
possesses certain features making it peculiarly adaptable 
under certain circumstances. 

.. figure:: images/Image46.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 46. Silicon Detector. 
   
   FIG. 46. Silicon Detector. 

The silicon detector consists of a flat surface of highly 
polished silicon upon which rests a brass point. 

The Pyron detector is composed of a crystal of iron 
pyrites embedded in a cup of fusible metal. A small 
wire spring bears against the surface of the crystal. The 
Pyron detector is somewhat harder to adjust than other 
forms of crystal detector, but remains in a sensitive 
condition much longer. 

.. figure:: images/Image47.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 47. Perikon Detector. 
   
   FIG. 47. Perikon Detector. 

The Perikon detector consists of a cup of fusible alloy 
in which are imbedded several pieces of a mineral called 
zincite. Another cup containing a fragment of 
chalcopyrites or bornite is held in a cup carried on the end of a 
rotating rod. The chalcopyrites is brought into contact 
with one of the crystals of zincite and the pressure adjusted 
by means of a spring. The Perikon detector will 
operate without a battery, but that latter is necessary in 
order to obtain the best results when receiving faint or 
far away signals. 

.. figure:: images/Image48.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 48. Galena Detector. 
   
   FIG. 48. Galena Detector.

The Perikon Electra detector is a very sensitive form 
of the regular Perikon detector fitted with a micrometer 
adjustment. 

The Galena detector consists of a crystal of that material to which 
contact is made by means of a fine wire 
spring exerting very light pressure. 

.. figure:: images/Image49.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 49. Audion Detector. 
   
   FIG. 49. Audion Detector. 

Crystal detectors act as rectifiers and change the 
alternating currents Into direct currents, which will pass 
through the telephone receivers. Minerals used for this 
purpose are said to possess *unilateral conductivity*, that 
is, they conduct currents better in one direction than the 
other and act much the same as a valve which allows 
water to flow in one direction, but not in the other. 

Another well known detector of the "valve" type is that 
known as the *Audion*, consisting of a small incandescent 
lamp containing a small grid and plate of nickel. When 
the lamp is lighted by connecting a battery to the filament, 
a flow of ions passing from the hot filament through 
the grid to the plate is set up. The grid and plate form 
part of the receiving circuit containing the telephones. 
The flow of ions carries the oscillatory currents from the 
grid to the plate, but does not allow them to pass back 
again. In this manner, the alternating oscillatory currents 
are converted into direct currents, which will pass 
through the telephone receivers. 

.. figure:: images/Image50.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 50. Carborundum Detector. 
   
   FIG. 50. Carborundum Detector. 

The Carborundum detector, as its name implies, is a 
device making use of the *unilateral conductivity* of 
carborundum. This form of detector is very sensitive and 
has been employed for a number of years in all the 
installations of the United Wireless Telegraph Co. 

It consists of a small crystal of carborundum clamped 
tightly between two carbon electrodes. It may be used 
with or without a battery. The battery is preferred. 

The Magnetic detector is a very sensitive device utilizing 
the changes in the magnetic state of iron, which are 
caused by rapidly oscillating currents. If a core of 
iron wires be placed in a varying magnetic field, the 
magnetization of the iron will lag behind the magnetizing 
force on account of *hysteresis* or "magnetic friction." 

.. figure:: images/Image51.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 51. Marconi Magnetic Detector 
   
   FIG. 51. Marconi Magnetic Detector 

But if a rapidly oscillating current is passed through a 
coil surrounding the iron, a sudden change in magnetization 
occurs, sufficient to induce an E. M. F. in a second 
coil surrounding the core and thus operate a telephone 
receiver in series with this coil. 

The usual form of magnetic detector consists of a 
belt of fine iron wires passing over two pulleys which are 
driven by clockwork. A pair of permanent magnets supply the 
field which induces a continuously varying magnetization 
in the moving core. The core passes through 
the centre of a double coil, one part of which is connected 
to the telephone receivers and the others to the aerial 
and ground. 

LESSON TWENTY-THREE. TUNING COILS. 
``````````````````````````````````

The tuning coil is a device consisting of a large number of turns of 
wire wound in the form of a cylinder and provided with 
one or more sliding contacts which 
can be brought into touch with any one of the turns at 
will in order to increase or decrease the electrical length 
or period of the circuit to suit the incoming waves. 

.. figure:: images/Image52.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 52. Double Slide Tuning Coil. 
   
   FIG. 52. Double Slide Tuning Coil. 

A circuit containing a certain amount of inductance, 
capacity and resistance tends to oscillate at a certain 
frequency. Therefore, the oscillations in every transmitting 
set have a certain frequency depending upon these 
factors. It is necessary to adjust the receiving apparatus 
so that it possesses the same frequency as the transmitter. 
The electro magnetic waves from the transmitting station 
will strike the aerial of the receiving station at a certain 
frequency and induce currence in it. If the receiving 
station is *tuned* to the same *period* as the transmitter 
each wave will give a slight impulse to the readily excited 
oscillations, which will grow in intensity just as 
small impulses given to a pendulum at the right times 
will make it swing violently. 

The purpose of the tuning coil is to adjust the receiving 
circuit to the same period as that of the transmitter. 

Tuning coils are wound of bare copper wire over a 
core composed of a specially treated cardboard tube. 
The wires are spaced apart so that they do not touch 
one another. Either one, two or three variable contacts 
or sliders are provided. The coils are consequently 
known as "single," "double" or "three" slide tuners. 

A loading coil is a supplementary coil sometimes 
placed in series with the regular tuning coil to give a 
greater inductance to the circuit so that it may be given 
a much lower frequency in order to receive waves of 
greater length. 

LESSON TWENTY-FOUR. LOOSE COUPLERS. 
```````````````````````````````````

A Loose Coupler or Receiving Transformer is a tuning 
coil in which the *coupling*, as well as the inductance, 
is variable. We have already explained that an ordinary 
transmitting set throws off two sets of wave trains of 
slightly different length, one being somewhat weaker than 
the other. 

.. figure:: images/Image53.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 53. Loose Coupler. 
   
   FIG. 53. Loose Coupler. 

The purpose of the loose coupler is not only to adjust 
the receiving set to the period of the transmitter in the 
manner of the tuning coil, but by varying the coupling to 
attract the apices of the weaker trains of waves to the 
same apex as the stronger waves and so really create 
a *pure* wave out of the other two. 

This may be more easily understood from the accompanying 
illustration which represents diagrammatically a 
double train of waves and a pure train. 

In construction, the loose coupler consists of a primary 
winding much the same as an ordinary tuning coil provided 
with a single slider. 

A second winding called the secondary, divided into 
a number of sections and adjustable by means of a 
multi-pointed switch mounted on one end, slides in and 
out of the primary. 

LESSON TWENTY-FIVE. FIXED CONDENSERS. 
`````````````````````````````````````

A fixed condenser usually implies the condenser used 
in the receiving circuit to furnish part of the necessary 
*capacity* and to shunt the telephone receivers, or as 
in cases where a battery is used in connection with the 
detector to force the current to choose a path through 
the comparatively low resistance turns of the tuning coil. 

.. figure:: images/Image54.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 54. Fixed Condenser. 
   
   FIG. 54. Fixed Condenser. 

A fixed condenser, as its name implies, has a fixed 
value or capacity. It is usually constructed of sheets of 
tinfoil interposed between sheets of thin paraffined paper 
or mica. The capacity of a fixed condenser usually varies 
from .002 to .005 microfarads. 

An alternating current passes readily through a condenser 
but a direct current is effectually blocked. 

When a direct current is led into a condenser as shown 
in the diagram, the half of the condenser represented by 
A becomes positively charged. When A receives a positive 
charge it repels the positive charge from B and 
attracts the negative thus making B negative. There is 
no change in the direction of the current after the first 
connection and the charge remains fixed and no currents 
pass. 

.. figure:: images/Image55.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 55. 
   
   FIG. 55. 

If an alternating current is applied to the condenser 
when A receives a positive charge, B becomes negative. 
When A reverses and becomes negative B becomes positive. 
This process goes on, the two halves constantly 
changing their charge with the result that the current 
continues to flow. 

A fixed condenser may occupy one of two places in a 
receiving circuit, either in series with the tuning coil and 
detector or directly across the telephone receivers. In the 
illustration A shows a detector requiring a battery with 
a fixed condenser in series with it and the coil. The 
oscillations set up in the circuit by the incoming waves 
can readily pass through the condenser and effect the 
detector because they are *alternating*. If it were not for 
the condenser the *direct* battery current would pass 
through the tuning coil instead of the detector because 
of the comparatively low resistance of the former. 

Crystal detectors do not require a battery and may 
be connected to a tuning coil with a condenser in series 
and the telephone receivers either across the terminals 
of the detector or across the terminals of the condenser. 
When in the latter position, the proper capacity for the 
fixed condenser will depend upon the resistance of the 
telephone receivers, the higher the resistance the less the 
capacity that will be required and vice versa. 

LESSON TWENTY-SIX. VARIABLE CONDENSERS. 
```````````````````````````````````````

The point of sharpest resonance does not always 
happen to come on a turn of the tuner where it can be 
reached by the slider. The variable condenser makes it 
possible to adjust the circuit to the exact point of resonance. 

.. figure:: images/Image56.jpg
   :align: center
   :scale: 85 %
   :alt: FIG 56. Rotary Variable Condenser. 
   
   FIG 56. Rotary Variable Condenser. 

Variable condensers are of two general types, the 
Sliding Plate and the Rotary Variable. The rotary 
variable is the most convenient and easy to manipulate. It 
consists of a number of fixed semi-circular metal plates 
between which swings a set of smaller movable semicircular 
plates. The fixed plates form one half of the 
condenser and the movable plates the other. In this way 
the capacity of the condenser is very closely adjustable. 
The movable plates are provided with a pointer moving 
over a graduated scale so that the comparative amount 
of capacity in the circuit is indicated. 

The sliding plate type of condenser consists of a number 
of rectangular fixed plates between which slide a set 
of movable plates. 

The dielectric between the plates of a variable condenser 
is air. There are no losses of energy due to 
hysteresis in a condenser having an air dielectric. 
Rotary condensers employing silk or some such material are not to 
be recommended. 

LESSON TWENTY-SEVEN. TELEPHONE RECEIVERS. 
`````````````````````````````````````````

Telephone receivers employed for wireless 
telegraphy are the same in principle as the ordinary 
telephone receiver but differ in construction and detail 
slightly. 

They are always of the watch case type, this style being 
small and light, and consist of a ring or horseshoe 
shaped permanent magnet upon the poles of which are 
mounted two small bobbins containing many turns of 
fine insulated wire. Over the magnets, very close to but 
not quite touching, is placed a circular diaphram of thin 
sheet iron. The lines of force created by the permanent 
magnet pass through the cores of the little bobbin and 
exert a constant pull on the diaphram. 

The little bobbins of wire or electromagnets are connected 
in series. If a current of electricity is sent 
through them they will create a little field of force of 
their own which will strengthen or decrease that of the 
permanent magnets according in which direction the 
current flows. Each change in the pull exerted on the 
diaphragm causes it to move and send out little sound 
waves which may be heard when the receiver is held close. 

We have already learned that the 
strength of a magnet depends upon 
the *ampere* turns. Suppose that a 
current of one ampere passed 
through a coil containing 100 
*turns* x 1 *amp.* = 100 *ampere turns*. 
If only one-tenth of an ampere 
was available and we wished to retain the same magnetic strength in 
the coil, the number of turns would 
have to be increased to one thousand in order for the ampere turns 
to remain equal; 1/10 *amp.* x 1.000 *turns* = 100 *ampere 
turns*. 

.. figure:: images/Image57.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 57. Types of Telephone Head Sets. 
   
   FIG. 57. Types of Telephone Head Sets. 

The currents passing through the receiver from the 
detector are exceedingly weak, and so in order to 
produce the maximum effect on the diaphragm, the 
electromagnets must be wound with a large number of turns 
of very fine wire. The resistance of fine wire is very 
great and for this reason wireless telephone receivers 
are usually termed *high resistance receivers*. 

Winding a receiver with many turns of fine wire does 
not make it more sensitive in the true sense of the word 
or from the standpoint of efficiency, but makes it better 
suited to the minute fluctuations of a weak current. 

The classification of receivers, according to their 
resistance is a method of indicating the comparative 
number of turns and the finess of the wire used in winding 
the electromagnets. Receivers should be wound with 
copper wire only. 

Wireless receivers come in pairs provided with a 
head-band so that they may be securely clamped on the ears. 

The receiver cases are made of rubber, composition, 
brass and aluminum depending upon the design and 
manufacture. It is immaterial which. 

LESSON TWENTY-EIGHT. THE HOT WIRE AMMETER.
``````````````````````````````````````````

The hot-wire ammeter is a device for indicating when 
the transmitting circuits are properly adjusted and 
arranged to emit the maximum amount of energy. 
It is placed in series in the aerial circuit so that the high 
frequency currents surging in the latter must pass 
through the meter and indicate their strength by moving 
the pointer a certain distance over a graduated scale. 

When a current of electricity flows through a wire 
it develops a certain amount of heat therein. If the 
wire is of high resistance the heat will be great enough to 
cause the wire to expand. Advantage has been taken of 
this fact in the construction of the hot-wire ammeter. 
This device consists of a piece of platinum wire or a 
platinum alloy stretched taut between two posts. The 
wire is included in the aerial circuit. The platinum wire 
is connected to a spindle carrying a pointer in such a 
manner that when the heat causes the wire to expand 
the expansion is conveyed to the spindle and the pointer 
moves over the scale magnifying the motion. The 
greater the current flowing through the wire the greater 
will be the deflection of the pointer. The scale is 
calibrated by comparison with a standard meter to read in 
amperes. 

.. figure:: images/Image58.jpg
   :align: center
   :scale: 85 %
   :alt: FIG 58. Diagram showing the Constructive Principle of a Hot Wire Ammeter. 
   
   FIG 58. Diagram showing the Constructive Principle of a Hot Wire Ammeter. 

When a hot-wire ammeter is placed in circuit the latter 
is tuned by moving the position of the helix clips on the 
helix, altering the length of the spark gap and the condenser 
capacity until the maximum deflection is indicated. 
It is then removed from the circuit. 

LESSON TWENTY-NINE. POTENTIOMETER
`````````````````````````````````

The potentiometer is an instrument for carefully 
regulating the voltage of the battery supplying a 
detector of the electrolytic or carborundum types with 
current. 

It is necessary to bring the potential of the battery 
to a certain critical point where it is just insufficient to 
"break down" the detector, that is, overcome the 
resistance which it offers to the oscillatory currents. 
In construction, the potentiometer usually consists of 
a small rod wound with German silver wire and provided 
with an adjustable contact. Graphite resistance 
rods are merely a cheap method of making a potentiometer 
and are to be avoided as entirely unsatisfactory 
for the purpose. 

.. figure:: images/Image59.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 59. Potentiometer. 
   
   FIG. 59. Potentiometer. 

LESSON THIRTY. DEAD END LOSSES AND "NO DEAD END" SWITCHES.
`````````````````````````````````````````````````````````` 

Practically every radio circuit includes an adjustable 
inductance of some sort, usually consisting 
of a layer of wire wound over a tube and arranged so that 
the amount of wire in the circuit can be varied by means 
of a switch, a plug or a slider. These methods of 
variation are familiar in the ordinary tuning coil, loose coupler, 
loading coil, etc. 

.. figure:: images/Image60.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 60. Diagram representing the effect of Distributed Capacity. 
   
   FIG. 60. Diagram representing the effect of Distributed Capacity. 

If the plug, switch or sliding contact, depending upon 
the method of variation employed, is at E as in Fig. 
60 so that only the portion of the coil A E B is in the 
circuit, then the portion E F together with A E may 
form an oscillator which, in order for the reader to obtain 
a better conception, may be likened to a sort of 
secondary winding, with A E considered as the primary. 
The oscillations of this part of the system may produce 
some very undesirable disturbances, especially so when 
the frequency of the currents in the circuit A E bear a 
certain relation to the natural frequency of the oscillator 
or E F. The losses due to the disturbance of these 
undesirable oscillations and also those resulting from eddy 
currents induced in the free portion or oscillator E F by 
the magnetic flux of A E are known as "dead-end effects." 

These losses are very much more noticeable in receiving 
circuits than in transmitters on account of the very 
weak currents in the former and the importance of 
preserving all the energy when it is already very small. 

Dead end losses take place principally in receiving 
transformers, loading coils and tuning coils. The losses 
are much more marked on short waves than long waves. 

The presence of these highly objectionable losses, and 
they are large enough to not only seriously decrease the 
strength of signals but also to make selective tuning 
impossible, may be avoided by only using coils which are 
just the right size so that they can be entirely included 
in the circuit. 

This is a very easy matter when only one wave length 
or at the most, two or three wave lengths are to be received, 
because it is then easily possible to quickly connect the coil 
of the proper size in the circuit. It is desirable however 
in most stations, and especially so in 
amateur stations that the apparatus be universal so as to 
be quickly and easily tunable to any wave length within 
its range. 

Many amateurs build large loose couplers having a very 
wide wave length range under the impression that they 
have an ideal instrument. The truth of the matter is 
however that such an arrangement is decidedly inefficient 
especially on the shorter waves when only a portion of 
the windings are in circuit and there is a large dead end 
portion. 

The better types of receiving transformers are now 
provided with "no dead end loss switches" which 
automatically break the windings up into a number of groups 
so that only that portion which is actually required to 
tune the circuit to a certain wave length is in circuit and 
the remainder of the coil is entirely disconnected. 

These switches are located at certain definite points 
as previously determined by measurements of the coil 
with the aid of a wave meter. 

.. figure:: images/Image61.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 61. Diagram explaining how "end losses" are eliminated 
   
   FIG. 61. Diagram explaining how "end losses" are eliminated 

The diagram in Fig. 61 illustrates the principle of 
such an arrangement. The points marked 1, 2 and 3 
are the places in the coil where the switches are located 
so as to divide the winding up into separate parts. Suppose 
that it is necessary to move the slider or switch to 
such a point on the coil as represented by its position in 
the illustration marked E. The switch located at 1 would 
then automatically close as the slider or switch moved 
past 2 and 3 would however still remain open because 
that part of the winding which they connect would not be 
required. If it became necessary to include more of the 
winding in the circuit, 2 and 3 would automatically close 
as the slider or switch was moved along the coil and 
open again as it was moved back. 

The automatic arrangement of the switches is easily 
accomplished in a number of different manners by means 
of levers, cams, trips, or some other mechanical means. 

LESSON THIRTY-ONE. DISTRIBUTED CAPACITY AND CAPACITY LOSSES. 
````````````````````````````````````````````````````````````

Every coil of wire possesses the property, not only of 
carrying a current of electricity but of *holding a 
charge* of electricity as well. This property is called 
capacity. The *capacity* of a condenser is its property for 
holding a charge of electricity. The capacity of a coil is 
termed its "distributed capacity" in order to distinguish it 
from the capacity of a condenser. The distributed capacity 
of a coil is due to the condenser effect which exists 
between the adjacent turns of the wire. The effect of this 
distributed condenser is exactly the same as if a small 
condenser was connected across the ends of the coil as 
shown in the accompanying illustration. 

Distributed capacity is very objectionable in most receiving 
circuits because a radio detector depends upon 
voltage for its operation and when a circuit contains an 
appreciable amount of distributed capacity the voltage 
is considerably lower than it would be otherwise. 

The usual method of reducing the distributed capacity 
of a coil is to use wire having comparatively thick 
insulation so that the wires are spaced farther apart. Certain 
shellacs and varnishes used in impregnated windings 
increase the specific dielectric capacity of the space between 
the turns and increase the distributed capacity of the 
winding. 

The same objection to distributed capacity also holds 
good in the case of what might be termed capacity losses 
which are due to improperly arranged connections, contact 
points, etc. Every pair of leads or taps from a 
coil possesses capacity. They really form a miniature 
condenser, the wires corresponding to the tinfoil or metal 
sheets of the condenser and the air between being the 
dielectric. 

For that reason the leads should always be as far 
apart from one another as possible and contact points 
should be as small as possible. It is unwise to use 
"double conductor" having two parallel conductors 
bound together for leading out connections or connecting 
radio apparatus. 

If capacity losses and distributed capacity are reduced 
to a minimum in a circuit, it is possible to employ more 
inductance than would be otherwise in order to tune the 
circuit to a certain frequency and the voltage is thereby 
preserved and full benefit derived therefrom by the 
changes which it produces in the detector. 

LESSON THIRTY-TWO. THE POULSEN ARC OR GENERATOR. 
````````````````````````````````````````````````

**Method of Producing Undamped Oscillations for 
Radio Telegraphy and Telephony.**

A radio transmitter whose waves are generated by 
undamped oscillations has many advantages over 
the ordinary spark transmitter, the oscillations of which 
are necessarily damped. 

The efficiency of an undamped wave transmitter is far 
greater in almost every respect. The selectivity at 
a receiving station listening to undamped wave signals is 
very marked in comparison to that when spark signals 
are received. 

The problem of producing undamped oscillations by 
means of an arc was first solved by Poulsen and is known 
as the Poulsen arc or generator. This type of generator 
is used for radio work in this country, by the Federal 
Telegraph Co., in the stations at Sayville and Tuckerton, 
in many U. S. Naval stations and on board all the U. S. 
first line battleships. 

.. figure:: images/Image62.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 62. The Poulsen Arc for generating Undamped Oscillations. 
   
   FIG. 62. The Poulsen Arc for generating Undamped Oscillations. 

An arrangement by which such oscillatory currents 
may be produced is shown in its simplest form in 
Fig. 62. It consists of an arc, around which is shunted a 
condenser in series with an inductance. The arc is 
connected to a source of direct current, preferably having 
an E. M. F. of 500 volts or more. 

The positive electrode of the arc is copper, kept cool 
by circulating water through a hollow interior or a water 
jacket. The gap in itself is enclosed in a chamber filled 
with hydrogen gas or a gas containing hydrogen. The 
arcs in practical use for generating undamped oscillations 
are arranged so that they operate in a strong magnetic 
field. The carbon electrode is constructed so that it is 
slowly revolved by a small electric motor. 

The hydrogen gas atmosphere in which the arc is enclosed is 
produced by a small feed cup, similar to the 
ordinary lubricating oil cup, located over the case and 
filled with alcohol which continuously drips into the 
flame chamber, where it is vaporized by the heat. 

Arc transmitters of large capacity are not as expensive 
or as bulky as spark transmitters of equal power. The 
difficulties of handling and controlling a large amount of 
power in connection with a transmitter of this sort are 
also not as great as in the case of a spark transmitter. 
The condenser used with an arc is not nearly so large as 
that required for a spark transmitter of equal capacity 
and the voltage of the current is much lower. Condenser 
breakdown, leakage and insulation problems are therefore 
not as great. 

For telegraphing with damped transmitters, a key 
which alternately makes and breaks the primary circuit 
is sufficient. This is not possible, however, with an arc. 
The distance between the arc electrodes is usually greater 
than the gap length which the dynamo voltage would 
jump and form an arc whenever the key should be 
closed. It is therefore usual to arrange a key or relay 
so that it short circuits a portion of the aerial inductance 
or helix when closed. This short circuit is sufficient to 
throw the circuit out of tune so that it cannot be heard 
at the receiving station without readjusting the instruments. 

The Poulsen arc may be used for radio telephony. A 
telephone receiver is arranged so as to vary the currents 
and impress the vibrations of the voice upon the oscillations set up by the arc. 

LESSON THIRTY-THREE. RECEIVING UNDAMPED WAVES. THE TICKER. 
``````````````````````````````````````````````````````````

A decided difference is encountered between 
damped and undamped oscillations when receiving 
signals. The ordinary detector cannot be used for 
receiving undamped oscillations without first being properly 
modified. 

When telegraphing the dots and dashes of the code 
by undamped oscillations the change taking place in the 
detector circuit would merely move the telephone receiver 
diaphragm from its normal position at the beginning of 
each dot or dash, causing a click to be heard and nothing
more. The telephone receiver diaphragm would remain 
in a fixed position just as long as the waves from the 
transmitter kept coming in during each signal. Both dots 
and dashes would be heard simply as clicks and not appear 
distinguishable from one another. 

The most common and perhaps also the best method is 
to employ a device called a "ticker" in place of 
the detector for receiving undamped oscillations. 

This arrangement is illustrated in Fig. 63. The left 
hand part of the illustration is the circuit diagram. A 
detail of the "ticker" wheel is shown at the right. 

The condenser F C is of comparatively large capacity 
and is fixed. The condenser C is also fixed but is of 
much smaller capacity. F C is usually a condenser 
having a capacity of several tenths of a microfarad while C 
has only a few thousands of a microfarad capacity. 

.. figure:: images/Image63.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 63. The Poulsen Ticker for receiving undamped Waves. 
   
   FIG. 63. The Poulsen Ticker for receiving undamped Waves. 

T is the ticker wheel and consists of a small brass wheel 
having a groove in the periphery like a pulley. This 
wheel is mounted on the shaft of a small motor so that 
it can be revolved at high speed. 

A fine wire is arranged to rub against the groove in 
the wheel and make contact with the latter. 

When the wheel is revolving at high speed, the wire 
does not make perfect contact at all points but tends 
to vibrate and to act as the equivalent of a very high 
speed interrupter by rapidly opening and closing the 
circuit. 

The basic idea in employing a device and a circuit of 
this sort in receiving undamped waves is as follows: 

When the contact is broken at the ticker wheel and 
the condenser F C is disconnected from the oscillating 
circuit formed by the condenser C and the secondary of 
the receiving transformer, the condenser C accumulates 
a relatively large amount of energy. 

Then when the ticker connects the condenser F C in 
parallel with C, F C takes the major part of the stored 
energy and discharges it through the telephones P, causing 
a click to be heard in the latter. 

The interruptions of the "ticker" are very rapid, a 
great many taking place during the duration of a dot or 
a dash, so that the resultant clicks occur very close 
together and the dots and dashes sound very similar to the 
spark signals of a transmitter sending forth damped 
waves. 

The sensitiveness of the ticker arrangement is very 
great, in fact much greater than that of any detector. 


LESSON THIRTY-FOUR. THE AUDION AMPLIFIER.
`````````````````````````````````````````

The audion amplifier is an arrangement whereby an 
A audion bulb such as that which has already been 
described in the Lesson on Detectors is so connected that 
it acts as a relay and also amplifies minute pulsating 
electric impulses. An ordinary audion detector bulb will 
serve as an amplifier bulb but it is usual to modify it 
somewhat and provide a grid and a wing on both sides of 
the filament as this arrangement gives the best results. 

The audion amplifier is of especial advantage in amplifying 
weak wireless signals from a detector which would 
otherwise be unreadable. It is not necessary that the 
audion amplifier be used in connection with another 
audion serving as a detector. It will amplify the signals 
of any other form of detector such as an electrolytic, 
crystal, magnetic, etc. 

.. figure:: images/Image64.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 64. The Audion Amplifier Circuit. 
   
   FIG. 64. The Audion Amplifier Circuit. 

Figure 64 shows an audion amplifier connected to an 
audion amplifier connected to an audion detector so that 
the signals from the latter will be greatly increased in 
strength. 

L C is a loose coupler connected to the aerial and 
ground in the ordinary manner. P and S are respectively 
the primary and secondary of the loose coupler. B is 
the "wing" battery of the detector circuit and B¹ is the 
"wing" battery of the amplifier circuit. T is the telephone 
receiver headset in which the amplified signals are 
heard. 

P¹ and S¹ are the primary and secondary of a small 
open core transformer called the "Amplifier Coil." The 
windings contain a great many turns of very fine wire. 
The primary of the transformer is connected so as to 
be included in the wing circuit of the detector. It should 
be noticed that only one terminal of the secondary is 
connected to the amplifier circuit, this one terminal being 
connected to the grid of the amplifier bulb. 

An arrangement of this sort, where one amplifier bulb 
is used is called a "one step amplifier." Amplifiers 
having two and three bulbs, respectively known as "two 
step" and "three step" amplifiers give much greater 
amplification than a one step amplifier and are often used. 


LESSON THIRTY-FIVE. "HOOK-UPS." 
```````````````````````````````

**Or Methods of Connecting the Instruments.** 

"Hook-ups" or circuit diagrams showing the manner of 
connecting various instruments are well 
worth considerable study if one is desirous of securing 
the greatest selectivity and distance from his apparatus. 

There are almost an endless number of ways and combinations 
of ways of connecting apparatus, and strange 
to say, different people seem to be able to secure the 
best results with widely different methods. In spite of 
the fact that circuits of this kind are very numerous 
they can all be reduced to a few fundamental forms and 
an understanding of these forms will enable a person 
to devise his own "hook-ups" at will. 

Transmitting circuits are fundamentally almost the 
same. The only real difference in arrangement is made 
by interchanging the condenser and spark gap. Either 
one may be placed across the terminals of the induction 
coil or transformer. There is no difference in the results. 

.. figure:: images/Image65.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 65. 
   
   FIG. 65. 

Consider the circuit shown in the accompanying illustration. 
The action of the transformer is to charge 
the condenser to such a point that the voltage is sufficient 
to leap the spark gap and cause a discharge. The 
rush of current which is oscillatory takes place through 
the condenser, spark gap and *primary* turns of the helix, 
or in other words through the *closed* circuits. The *secondary* 
turns of the helix, which are those forming part 
of the aerial circuit, are larger in number than those of 
the primary, and because of this ratio cause currents 
of higher voltage than those of the condenser to be 
impressed upon the aerial system. The currents in the 
aerial system surge up and down the aerial through the 
helix into the ground. 

.. figure:: images/Image66.jpg
   :align: center
   :scale: 85 %
   :alt: FIG. 66. Receiving Circuits. 
   
   FIG. 66. Receiving Circuits. 

A shows a simple receiving circuit wherein a single 
slide tuning coil is connected to a detector. The high 
frequency currents generated in the aerial surge up and 
down the system and pass through the detector on their 
way to the ground. By moving the slider back and forth 
the electrical length of the circuit may be varied to suit 
the length of the incoming waves. Oscillations may be 
*forced* upon such a circuit, that is, if the waves are very 
powerful they will pass through the system and effect 
the detector no matter whether the slider is adjusted to 
suit them or not. This would cause interference and 
confusion in case more than one station were operating 
at a time. 

By adding a second slider and a condenser as shown 
in B, this may be avoided to a considerable extent, for 
slider No. 1 may be adjusted to the desired signals and 
slider No. 2 placed in a position such as will give the 
branch of the circuit from the aerial, through the coil 
and into the ground of which it is a part, a period suited 
to the objectionable wave and so *carry off* the latter into 
the ground without effecting the detector. The desired 
signals will pass into the ground through the other 
branch of the circuit and operate the detector which lies 
in their path. The selectivity of the outfit may be further 
increased by the addition of a variable condenser. 

A variable condenser may be placed in one or more 
of a great many positions. The accompanying illustrations 
show several. The effect of a condenser placed in 
series with the ground or aerial is just the opposite of 
that of a loading coil. It decreases the period and 
shortens the wave length to which it is adapted. 

The Amateur’s Wireless Handy Book shows over one 
hundred wiring diagrams starting from the simplest and 
going to the most complicated in a natural sequence. 

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   COLE & MORGAN 

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   Publishers of the Arts and Sciences Series 

   \P. O. Box 1473 New York, N. Y. 

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   **The Boy Electrician**

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   Practical Plans for Electrical Toys and Apparatus, with an Explanation 

   of the Principles of Everyday Electricity. 

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   **By ALFRED P. MORGAN.**

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   Telegraphy and Telephony," etc. 

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   **With full-page Illustrations and 324 Working Drawings and Diagrams**
   
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This is the age of electricity. The most fascinating of all 
books for a boy must therefore be one dealing with the 
mystery of this ancient force and modern wonder, even a 
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upon which these depend for operation, and how the 
same thing is done in the every-day world be well 
presented and so attractive is this really great book that it will 
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illustrations, clearness of expression and the large number 
of subjects that are covered. It is beyond doubt the best 
book in this line that has ever been written or published. 
It is a book that will delight every boy who has a leaning 
towards electrical experiments. The author writes in a clear 
and chatty style and while he has a thorough 
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in treating it in a simple manner 
so that it is readily intelligible to his young readers. 

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   **Among the Chapter Headings and Contents are:**

Magnets and Magnetism—Static Electricity—Static Electric Machines—Cells and Batteries—Electro-Magnetism and Magnetic Induction—Electrical Units—Electrical Appurtenances—Electrical Measuring Instruments—Bells, Alarms and Annunciators—Electric Telegraphs—Microphones and Telephones—Induction Coils—Transformers—Wireless Telegraphy—Wireless Telephony—Electric Motors—Dynamos—An Electric Railway—Miniature Lighting—Miscellaneous Electrical Apparatus. 

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   **READ WHAT HAS BEEN SAID OF IT.**

"Even a casual glance through the many pages of the book does not fail to 
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"Well presented and attractive this book will be a source of great benefit and delight 
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   **Wireless Telegraphy and Telephony Simply Explained**

   By ALFRED P. MORGAN. 

   **A NEW BOOK by the author of "Wireless Telegraph Construction for Amateurs."**

.. figure:: images/Image68.jpg
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   :alt: Book Cover Wireless Telegraphy and Telephony Simply Explained

This is undoubtedly one of the most complete and comprehensive 
treatises on the subject ever published, and a close 
study of its pages will enable one to master all the details 
of the wireless transmission of messages. The author has 
filled a long-felt want and has succeeded in furnishing a 
lucid, comprehensible explanation in simple language of the 
theory and practice of wireless telegraphy and telephony. 
The book treats the subject from an entirely new standpoint. 
Several very novel and original ideas have been carried out 
in its making. It is well illustrated by over one hundred 
and fifty interesting photographs and drawings. All diagrams 
have been made in perspective showing the instruments as 
they actually appear in practice. The drawings are carefully 
keyed and labeled. Many of the photographs are accompanied 
by phantom drawings which reveal the name and purpose of 
each part. 

It is a book which the wireless experimenter cannot afford to 
be without. It will prove even more valuable to the layman. 

Among the contents are: Introductory. Wireless Transmission and Reception. 
The Ether. Electrical Oscillations. Electromagnetic Waves. The Means for 
Radiating and Intercepting Electric Waves. Aerial Systems. Earth Connection. 
The Transmitting Apparatus. Current Supply. Spark Coils and Transformers. 
Condensers. Helixes. Spark Gaps. Anchor Gaps. Aerial Switches, Etc. The 
Receiving Apparatus. Detectors, Etc. Tuning Coils and Loose Couplers. Variable 
Condensers. Tuning and Coupling. Directive Wave Telegraphy. The Dignity of 
Wireless. Its Applications and Service. Wireless in the Army and Navy. Wireless 
on an Aeroplane. How a Message is Sent and Received. The Wireless Telephone. 
The Ear. How We Hear. Sound and Sound Waves. The Vocal Cords. 
The Structure of Speech. The Telephone Transmitter and Receiver. 
The Photophone. The Thermophone. The Selenium Cell. 

Handsomely Bound in Cloth with Embossed Cover. (Postpaid, $1.00) 

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   Build Your Own Wireless Instruments 

   Complete Up-to-the-Minute Authentic Practical 

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   WIRELESS TELEGRAPH CONSTRUCTION FOR AMATEURS 

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   By ALFRED POWELL MORGAN 

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   3d EDITION 

   220 Pages 163 Illustrations 

   **Price**, $1.50, **Postpaid** 

   **Handsomely Bound in Silk Cloth**

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Thoroughly up to date and unusually complete. Gives 
in minute detail, full directions for constructing wireless 
apparatus and various outfits capable of receiving from 
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The value of this book has been greatly increased by the addition of much new 
subject matter and many illustrations of recent interest. 

The new text explains fully how to build the most recent forms of Quenched Gaps. 
Rotary Gaps, Dough-Nut Tuners, Kick-back Preventers, Audion Detectors and numerous 
other instruments, accompanied by dimensioned working drawings. Several very 
interesting and instructive photographs have been included. 

\I.—Introduction. II.—The Apparatus. III.—Aerials and Earth Connections. IV.—Induction Coils. V.—Interrupters. VI.—Transformers. VII.—Oscillation Condensers and Leyden Jars. VIII.—Spark Gaps or Oscillators. IX.—Transmitting Helixes. X.—Keys. XI.—Aerial Switches and Anchor Gaps. XII.—Hot Wire Ammeter. XIII.—Oscillation Detectors. XIV.—Tuning Coils and Tuning Transformers. XV.—Receiving Condensers. XVI.—Telephone Receivers and Headbands. XVII.—Operation. XVIII.—The Amateur and the Wireless Law. How to Secure a License. Oscillation Helix. Quenched Spark Gap. Rotary Gaps. Kick-Back. The Variometer. New Crystal Detectors. The Audion.—Appendix. 

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   IF YOU ARE INTERESTED IN WIRELESS YOU NEED THIS BOOK 

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Model Aeroplaning is one of the most fascinating and 
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Here at last is the book which every young 
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A book which tells how to build apparatus 
which anyone would be proud to own. It is 
a more advanced book than "Wireless Construction 
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have all been the subject of considerable experimental 
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By purchasing this book you get the benefit of vast 
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THE TREMENDOUS POPULARITY OF
THIS VALUABLE LITTLE BOOK IS ONLY 
AN INDICATION OF ITS GREAT WORTH. 

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It has only been on the market a short time, 
yet the sales will undoubtedly soon reach a 
point which would indicate that experimenters unquestionably 
consider, that in proportion to its size, it is the best book on the 
market. 

It does not describe any old or obsolete forms of wireless apparatus but only the 
latest types of aerials, spark coils, keys, gaps, condensers, 
helixes, oscillation transformers, loose couplers, tuning coils, 
detectors, loading coils, variable condensers, 
aerial switches, etc. 

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IT IS ONE OF THE MOST DETAILED AND THOROUGH BOOKS EVER PUBLISHED. 

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.. container:: center large

   .. vspace:: 2

   **Partial Contents**

   .. vspace:: 2

Chapter I.—THE AERIAL. The Location of the Station. The Construction of 
an Operating Bench. The Aerial and Ground. The Supports or Masts. Types 
of Aerials. How to Erect an Aerial. Protection from Lightning, Etc. 

Chapter II.—SPARK COILS. The Construction of Spark Coils. A 1/4-inch Spark 
Coil. A 1/2-inch Spark Coil. A 1-inch Spark Coil. A 1 1/2-inch Coil. A 2-inch 
Coil. Sources of Current. Dry Cells. Storage Cells. Wireless Keys, Etc. 

Chapter III.—TRANSMITTING APPARATUS AND ITS CONSTRUCTION. 
Step-down Transformers. Spark Gaps. The Oscillation Condenser. Leyden Jars. 
Helixes. Oscillation Transformers, Etc. 

Chapter IV.—THE RECEIVING APPARATUS AND ITS CONSTRUCTION. A 
Silicon Detector. A Galena Detector. The Double Slide Tuning Coil. How to 
Make a Fixed Condenser. Building a Loose Coupler. The Loading Coil. How to 
Make a Variable Condenser, Etc. 

Chapter V.—ARRANGEMENT AND OPERATION OF THE APPARATUS. Aerial 
Switches. The Buzzer Test. Using More Than One Detector. 
Shunting the Detector. Complete Outfits. Portable Sets. The 
Operation of the Station, Etc. 

.. clearpage::

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   **The New Amateur’s Wireless**

   **Handy Book**

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   FOURTH EDITION 

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   Completely Revised and Enlarged 

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   You Cannot Afford To Be 

   Without This Book 

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   Price 25 Cents, Postpaid    

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If you want to be an expert and an 
authority you must surround yourself 
with all available aids and helps. You 
have one of the best in the AMATEUR’S WIRELESS HANDY 
BOOK. 

THERE HAVE BEEN MORE COPIES OF 
THIS GREAT BOOK SOLD THAN OF ANY 
OTHER WIRELESS BOOK. 

It contains nearly SIX THOUSAND calls of 
Wireless Stations, including all Land Stations, Ship Stations, U. S. Army and Navy 
Stations and all AMATEURS licensed to date 
of publication. 

Every registered station of the U. S. is included. They are all there. All the calls 
are classified alphabetically. The list is the 
most reliable and complete in existence. All 
obsolete stations have been abolished. All 
corrections and changes have been made from the official lists. 

.. container:: center large

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   **BUT, THAT IS NOT ALL.**

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THE CODES, BOTH MORSE AND CONTINENTAL, are shown in the form of two 
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A BEGINNER’S SPEED CHART of both Codes so arranged that the codes may 
be quickly learned or consulted is provided. 

ALL THIS ABBREVIATIONS used so constantly by the wireless operator to save 
time and labor are included. There are a couple of pages of them. 

.. container:: center large

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   **AND LAST BUT NOT LEAST**

   .. vspace:: 2

Nearly 100 large hook-ups of wiring diagrams fully illustrated in a concise and 
clear manner. Loop and straightaway aerials, grounds, helixes, spark gaps, anchor 
gaps, leyden jars, induction coils, transformers, keys, aerial switches, tuning coils, 
loading coils, loose couplers, variometers, fixed condensers, silicon, electrolytic, 
carborundum, perikon and audion detectors, telephones, potentiometers, etc., you can 
find them all and how to connect. A hook-up for any set accompanied by full explanation. 
None are missing. They are all there. There are no two alike. 

The most complete and reliable data ever collected. The result of thousands of 
experiments by some of the most famous wireless experts in the country. 

Read now before the supply is exhausted or you forget. You will be sorry if you 
don’t. 

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   **SENT ANYWHERE POSTPAID FOR 25 CENTS**

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Note: This book is always kept up-to-date by frequently issuing new editions. 
Send for the latest copy. 

.. clearpage::

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   **Wireless Construction and Installation for Beginners**

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   SEVENTY-THREE PAGES SIXTY-SEVEN ILLUSTRATIONS. 

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   (Second Edition.) 

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   A Practical Handbook giving detailed 
   instructions for the Construction and 
   Operation of a Boy’s Wireless Outfit. 

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   **Only 25c. Prepaid**

.. figure:: images/Image73.jpg
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   :alt: Book Cover

An indispensible book for the young wireless 
experimenter. It not alone shows how to build 
the various instruments but describes their 
actual workings and tells how to operate them. 

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   **EVERY BOY IS ADVISED TO**

   **SEND FOR A COPY**

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Written in a very clear and simple style, the 
book is invaluable to a beginner. He will be 
able with its aid to construct simple apparatus 
of the latest and approved type. The instruments 
described in the book have been the 
subject of considerable experimental work and special study. 
They are modeled along simple lines 
so that they will be easy and inexpensive to 
construct, but at the same time combine features 
which make them very sensitive and 
capable of receiving or transmitting messages 
greater distances than some more complicated 
apparatus. 

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   **THIS BOOK, CONSIDERING ITS WORTH, IS A GIFT AT 25c.**

   .. vspace:: 2

There are no old or obsolete forms of wireless apparatus discussed, but only the latest 
types of tuning coils, receiving transformers, fixed condensers, keys, spark coils, 
detectors, etc. The book is illustrated by numerous detailed working drawings giving all 
dimensions. Several full-page views of the apparatus enable the beginner to fully 
comprehend the text. 

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   **THE MOST THOROUGH AND COMPLETE ELEMENTARY WIRELESS**

   **CONSTRUCTION BOOK PUBLISHED**

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The pages on the construction and installation of aerials will be found to be of 
considerable help to the experimenter, for it is here that the most trouble is experienced 
by the beginner. The practical and helpful information on this subject is alone worth 
several times the cost of the book. 

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   **PARTIAL CONTENTS**

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Chapter I.—**WIRELESS TELEGRAPHY**. An intensely interesting subject; amateur 
wireless telegraphy; the purpose of the aerial and ground; the apparatus used to send 
messages; the apparatus used to receive messages. 

Chapter II.—**AERIALS AND GROUNDS**. Where to put up the aerial; types of 
aerials; the "T" aerial; the masts; the wire; insulators; leading in the wires; the 
ground. 

Chapter III.—**HOW TO BUILD AND OPERATE THE SIMPLEX DOUBLE SLIDE 
RECEIVING OUTFIT**. The tuning coil; the tube; the sliders; the fixed condenser; 
the detector parts; assembling the set; connecting the instruments; operation. 

Chapter IV.—**HOW TO BUILD THE SIMPLEX LOOSE COUPLER, DETECTOR 
AND CONDENSER**. The base; the primary; the secondary; the pillar; the switch; 
How to make the Simplex cat whisker detector; How to make the Simplex fixed condenser; How to connect the apparatus; How to tune with the loose coupler; How to adjust the detector. 

Chapter V.—**TELEPHONE RECEIVERS AND HEADBANDS.** 

Chapter VI.—**HOW TO BUILD THE SIMPLEX SPARK COIL.** The core; the secondary; the condenser; the coil heads; the base; the interrupter parts; the bridge. 

Chapter VII.—**HOW TO MAKE THE SIMPLEX KEY**. 

Chapter VIII.—**HOW TO CONNECT AND OPERATE THE APPARATUS**. How to connect and operate a complete wireless station; How to operate; the code, etc. 

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   **The Operation of Wireless Telegraph Apparatus**

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Do your Wireless friends come to you for advice on 
constructing and operating their apparatus or do you go 
to them for information? 

Here is a chance for YOU to become the authority. 

**This book is a necessity to every Progressive Experimenter.** 

**It shows how to obtain the very highest efficiency from 
any station, and how to comply with the law. How 
to tune, adjust your detector, spark gap, phones, etc.**

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   Price, 25 Cents, Postpaid. 

This book was written for the wireless experimenter who 
has passed the amateur stage, but explains how the beginner also can 
obtain the very best results from his 
station. It contains much useful information to this end 
and many "kinks". 

**IT SHOWS HOW** to receive or send on long or short 
wave lengths with highest efficiency, to tune for longest 
distance reception of messages, to use the buzzer test, 
how to test and connect condensers, receivers, etc., 
how to use receiving transformers, variometers, etc., 
all with highest efficiency in view. 

**IT ALSO DESCRIBES** the construction and use of a simple, inexpensive wave 
meter to tune the station to any desired wave length, and tells how to obtain a 
sharp wave and a pure wave. 

**EXTRACTS FROM THE LAW** are also given in such a manner that they are 
easily understood. 

If you want to get the best results from your station this is your opportunity.

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   **Three New Books on Home Made**
   
   **Electrical Apparatus**

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or rather, three parts of one book, each 25 cents per copy, 
are now in preparation and should be ready in June, 1917. 

They will cover every kind of electrical apparatus, including primary 
and storage batteries, dynamos and motors, induction coils, rectifiers, 
transformers, telegraphs and telephones, etc.—all of which 
have actually been built. 

The three parts will also be furnished as a single volume 
in cloth covers at $1.00 per copy, postpaid. 

If interested, simply send us a postal and when the books 
are ready we will send you full descriptions. 

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   **COLE & MORGAN**

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   Publishers of the Arts and Sciences Series 

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   \P. O. Box 1473 NEW YORK, N. Y. 

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