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Title: Lessons in Wireless Telegraphy

Creator: Alfred Powell Morgan

Release date: September 29, 2020 [eBook #63345]

Language: English

Credits: Produced by James Simmons


*** START OF THE PROJECT GUTENBERG EBOOK LESSONS IN WIRELESS TELEGRAPHY ***




Produced by James Simmons.

This file was produced from page images at the Internet Archive.




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.




                                LESSONS

                                   IN

                          WIRELESS TELEGRAPHY


                 A SYSTEMATIC ELEMENTARY COURSE IN THE

                   PRINCIPLES OF WIRELESS TELEGRAPHY

                        AND THE ELECTRICAL LAWS

                         UPON WHICH IT DEPENDS


                                   BY

                             *A. P. Morgan*


                 _THIRD EDITION, Revised and Enlarged_




                              PUBLISHED BY

                             COLE & MORGAN

               Publishers of The Arts and Sciences Series

                      P. O. Box 1473 NEW YORK CITY

                           Printed in U.S. A.




                          COPYRIGHT 1912. 1917

                                   BY

                             COLE & MORGAN




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.

[Illustration: 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.

[Illustration: 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_.

[Illustration: 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_.

[Illustration: 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_.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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_.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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_.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: FIG. 19. Diagram of Dynamo Field Windings.]

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

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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 OF SPECIFIC INDUCTIVE CAPACITIES.

                    ────────────────────────────────
                    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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: FIG. 33. High Potential Closed Core Transformer.]

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: FIG. 37. A Damped Oscillation.]

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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."

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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_.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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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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)




                  Build Your Own Wireless Instruments

             Complete Up-to-the-Minute Authentic Practical

              WIRELESS TELEGRAPH CONSTRUCTION FOR AMATEURS


                        By ALFRED POWELL MORGAN


                               3d EDITION

                      220 Pages 163 Illustrations

                       *Price*, $1.50, *Postpaid*

                    *Handsomely Bound in Silk Cloth*

Thoroughly up to date and unusually complete. Gives in minute detail,
full directions for constructing wireless apparatus and various outfits
capable of receiving from 100 to 1,500 miles and transmitting 3 to 100
miles. Also clearly explains the purpose and action of each instrument.
Directions for Operating and Adjusting, etc.


                *A SPLENDID TREATISE OF WIRELESS ALONG*

                          *CONSTRUCTIVE LINES*


                       _Price_, $1.50, _Postpaid_


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.


       ENDORSED BY WIRELESS CLUBS THROUGHOUT THE COUNTRY AS BEING

             THE MOST PRACTICAL BOOK PUBLISHED ON WIRELESS.

          IF YOU ARE INTERESTED IN WIRELESS YOU NEED THIS BOOK




                        *Model Flying Machines*

                      *HOW TO BUILD AND FLY THEM*

                  Will prove interesting and valuable.


              Have you ever built and flown a Model Racer?


                   If not, you have missed something.


                       Price, 25 Cents, Postpaid.

Model Aeroplaning is one of the most fascinating and instructive of
sports.

Thousands of young men and boys have formed Model Aero Clubs and
organized Flying Contests throughout the country.

"MODEL FLYING MACHINES" of the _Arts and Sciences_ series is the only
book giving reliable data and instructions for the construction of
practical Model Aeroplanes.

IF YOU ARE A BEGINNER, this is the book that you ought to have. It will
start you right. It tells how to build seven different types of
machines, starting with the simplest Monoplane and finishing with
several Long Distance Racing Models.

IF YOU ARE INTERESTED IN MODEL AEROPLANING, this book will prove the one
you have been looking for. Gives valuable "Kinks". Tells how to carve
propellers, make winders, adjust and fly machines, etc. Fully
illustrated with large size, detailed working drawings, showing the
exact size of each part. Twelve full-page plates.

Printed on first-class paper. Heavy cover in three colors.

         Sent postpaid by return mail upon receipt of 25 cents.


               *EVERY MODEL AVIATOR OUGHT TO HAVE A COPY*




                  *Experimental Wireless Construction*

             *EIGHTY-SIX PAGES NINETY-THREE ILLUSTRATIONS*


                       *Only 25 Cents, Postpaid*

Here at last is the book which every young experimenter interested in
constructing his own wireless apparatus has been looking for.

A book which tells how to build apparatus which anyone would be proud to
own. It is a more advanced book than "Wireless Construction and
Installation for Beginners," and describes apparatus which is much more
elaborate and sensitive. The instruments have all been the subject of
considerable experimental work and study. All the apparatus has been put
to practical test and carefully improved by clever experts. By
purchasing this book you get the benefit of vast knowledge and
experience and are enabled to build far better instruments than by
following your own designs and haphazard methods.


THE TREMENDOUS POPULARITY OF THIS VALUABLE LITTLE BOOK IS ONLY AN
INDICATION OF ITS GREAT WORTH.


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.


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


The information is all intensely practical. Complete directions and
dimensions are given. Nothing is left to be guessed at. The book must
really be seen to be appreciated.


                           *Partial Contents*


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.




                      *The New Amateur’s Wireless*

                              *Handy Book*


                             FOURTH EDITION


                    Completely Revised and Enlarged


                        You Cannot Afford To Be

                           Without This Book


                        Price 25 Cents, Postpaid


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.


                        *BUT, THAT IS NOT ALL.*


THE CODES, BOTH MORSE AND CONTINENTAL, are shown in the form of two
large full-page charts printed in heavy black type so that they can be
read from a distance.

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.


                        *AND LAST BUT NOT LEAST*


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.


                 *SENT ANYWHERE POSTPAID FOR 25 CENTS*


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




         *Wireless Construction and Installation for Beginners*


             SEVENTY-THREE PAGES SIXTY-SEVEN ILLUSTRATIONS.


                           (Second Edition.)


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


                          *Only 25c. Prepaid*

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.


                       *EVERY BOY IS ADVISED TO*

                           *SEND FOR A COPY*


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.

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


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.


          *THE MOST THOROUGH AND COMPLETE ELEMENTARY WIRELESS*

                     *CONSTRUCTION BOOK PUBLISHED*


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.


                           *PARTIAL CONTENTS*


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.




            *The Operation of Wireless Telegraph Apparatus*

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.*

                       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.




                     *Three New Books on Home Made*

                         *Electrical Apparatus*


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.

                            *COLE & MORGAN*


               Publishers of the Arts and Sciences Series


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




*** END OF THE PROJECT GUTENBERG EBOOK LESSONS IN WIRELESS TELEGRAPHY ***


    

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