Radio Shack

Kinds of Wireless Systems.–There are two distinct kinds of wireless
systems and these are: the _wireless telegraph_ system, and the
_wireless telephone_ system. The difference between the wireless
telegraph and the wireless telephone is that the former transmits
messages by means of a _telegraph key_, and the latter transmits
conversation and music by means of a _microphone transmitter_. In
other words, the same difference exists Central Ny News, Inc. Wwti between them in this respect
as between the Morse telegraph and the Bell telephone.
Parts of a Wireless System.–Every complete wireless station, whether
telegraph or telephone, consists of three chief separate and distinct
parts and these are: (a) the _aerial wire system_, or _antenna_ as it
is often called, (b) the _transmitter_, or _sender_, and (c) the
_receiver_, or, more properly, the _receptor_. The aerial wire is
precisely the same for either wireless telegraphy or wireless
telephony. The transmitter of a wireless telegraph set generally uses
a _spark gap_ for setting up the electric oscillations, while usually
for wireless telephony a _vacuum tube_ is employed for this purpose.
The receptor for wireless telegraphy and telephony is the same and may
include either a _crystal detector_ or a _vacuum tube detector_, as
will be explained presently.
The Easiest Way to Start.–First of all you must obtain a government
license to operate a sending set, but you do not need a license to put
up and use a receiving set, though you are required by law to keep
secret any messages which you may overhear. Since no license is needed
for a receiving set the easiest way to break into the wireless game is
to put up an aerial and hook up a receiving set to it; you can then
listen-in and hear what is going on in the all-pervading ether around
you, and you will soon find enough to make things highly entertaining.
Nearly all the big wireless companies have great stations fitted with
powerful telephone transmitters and at given hours of the day and
night they send out songs by popular singers, dance music by jazz
orchestras, fashion talks by and for the ladies, agricultural reports,
government weather forecasts and other interesting features. Then by
simply shifting the slide on your tuning coil you can often tune-in
someone who is sending _Morse_, that is, messages in the dot and dash
code, or, perhaps a friend who has a wireless telephone transmitter
and is talking. Of course, if you want to _talk back_ you must have a
wireless transmitter, either telegraphic or telephonic, and this is a
much more expensive part of the apparatus than the receptor, both in
its initial cost and in its operation. A wireless telegraph
transmitter is less costly than a wireless telephone transmitter and
it is a very good scheme for you to learn to send and receive
telegraphic messages.
At the present time, however, there are fifteen amateur receiving
stations in the United States to every sending station, so you can see
that the majority of wireless folks care more for listening in to the
broadcasting of news and music than to sending out messages on their
own account. The easiest way to begin wireless, then, is to put up an
aerial and hook up a receiving set to it.
About Aerial Wire Systems.–To the beginner who wants to install a
wireless station the aerial wire system usually looms up as the
biggest obstacle of all, and especially is this true if his house is
without a flag pole, or other elevation from which the aerial wire can
be conveniently suspended.
If you live in the congested part of a big city where there are no
yards and, particularly, if you live in a flat building or an
apartment house, you will have to string your aerial wire on the roof,
and to do this you should get the owners, or agents, permission.
This is usually an easy thing to do where you only intend to receive
messages, for one or two thin wires supported at either end of the
building are all that are needed. If for any reason you cannot put
your aerial on the roof then run a wire along the building outside of
your apartment, and, finally, if this is not feasible, connect your
receiver to a wire strung up in your room, or even to an iron or a
brass bed, and you can still get the near-by stations.
An important part of the aerial wire system is the _ground_, that is,
your receiving set must not only be connected with the aerial wire,
but with a wire that leads to and makes good contact with the moist
earth of the ground. Where a house or a building is piped for gas,
water or steam, it is easy to make a ground connection, for all you
have to do is to fasten the wire to one of the pipes with a clamp.
[Footnote: Pipes are often insulated from the ground, which makes them
useless for this purpose.] Where the house is isolated then a lot of
wires or a sheet of copper or of zinc must be buried in the ground at
a sufficient depth to insure their being kept moist.

About Mechanical Tuning.–A tuning fork is better than a spring or a
straight steel bar for setting up mechanical vibrations. As a matter
of fact a tuning fork is simply a steel bar bent in the middle so that
the two ends are parallel. A handle is attached to middle point of the
fork so that it can be held easily and which also allows it to vibrate
freely, when the ends of the prongs alternately approach and recede
from one another. When the prongs vibrate the handle vibrates up and
down in unison with it, and imparts its motion to the _sounding box_,
or _resonance case_ as it is sometimes called, where one is used.
If, now, you will mount the fork on a sounding box which is tuned so
that it will be in resonance with the vibrations of the fork there
will be a direct reinforcement of the vibrations when the note emitted
by it will be Jw Broadcasting, Llc Kmiz augmented in strength and quality. This is called
_simple resonance_. Further, if you mount a pair of forks, each on a
separate sounding box, and have the forks of the same size, tone and
pitch, and the boxes synchronized, that is, tuned to the same
frequency of vibration, then set the two boxes a foot or so apart, as
shown at A in Fig. 36, when you strike one of the forks with a rubber
hammer it will vibrate with a definite frequency and, hence, send out
sound waves of a given length. When the latter strike the second fork
the impact of the molecules of air of which the sound waves are formed
will set its prongs to vibrating and it will, in turn, emit sound
waves of the same length and this is called _sympathetic resonance_,
or as we would say in wireless the forks are _in tune_.
[Illustration: Fig. 36.–Sound Wave and Electric Wave Tuned Senders
and Receptors. A - variable tuning forks for showing sound wave
tuning. B - variable oscillation circuits for showing electric wave
tuning.]
Tuning forks are made with adjustable weights on their prongs and by
fixing these to different parts of them the frequency with which the
forks vibrate can be changed since the frequency varies inversely with
the square of the length and directly with the thickness [Footnote:
This law is for forks having a rectangular cross-section. Those having
a round cross-section vary as the radius.] of the prongs. Now by
adjusting one of the forks so that it vibrates at a frequency of, say,
16 per second and adjusting the other fork so that it vibrates at a
frequency of, say, 18 or 20 per second, then the forks will not be in
tune with each other and, hence, if you strike one of them the other
will not respond. But if you make the forks vibrate at the same
frequency, say 16, 20 or 24 per second, when you strike one of them
the other will vibrate in unison with it.

It is not advisable to use an induction coil for the modulator for
this set, but use, instead, either a telephone transformer, or better,
a magnetic modulator of the second size which has an output of from
1-1/2 to 3-1/2 amperes. The magnetic modulator is described and
pictured in this chapter.
A 50 to 100 Mile Wireless Telephone Transmitting Set–With 110 Volt
Alternating Current.–If you have a 110 volt [Footnote: Alternating
current for lighting purposes ranges from 102.5 volts to 115 volts, so
we take the median and call it 110 volts.] alternating current
available Wcsj 1550 Khz In Morris you can use it for the initial source of energy for your
wireless telephone transmitter. The chief difference between a
wireless telephone transmitting set that uses an alternating current
and one that uses a direct current is that: (1) a _power transformer_
is used for stepping up the voltage instead of a motor-generator, and
(2) a _vacuum tube rectifier_ must be used to convert the alternating
current into direct current.
The Apparatus You Need.–For this telephone transmitting set you need:
(1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone
modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry
battery_ or a 6 volt storage battery; (6) one _microphone
transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9)
one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11)
one _blocking condenser_; (12) one _oscillation choke coil_; (13) two
_filter condensers_; (14) one _filter reactance coil_; (15) an
_alternating current power transformer_, and (16) two _20 watt
rectifier vacuum tubes_.
All of the above pieces of apparatus are the same as those described
for the _100 Mile C. W. Telegraph Transmitter_ in Chapter XVII,
except: (a) the _microphone modulator_; (b) the _microphone
transmitter_ and (c) the _dry_ or _storage battery_, all of which are
described in this chapter; and the new parts which are: (d) the
_rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the
_filter reactance coil_; further and finally, the power transformer
has a _third_ secondary coil on it and it is this that feeds the
alternating current to the rectifier tubes, which in turn converts it
into a pulsating direct current.
The Vacuum Tube Rectifier.–This rectifier has two electrodes, that
is, it has a filament and a plate like the original vacuum tube
detector, The smallest size rectifier tube requires a plate potential
of 550 volts which is developed by one of the secondary coils of the
power transformer. The filament terminal takes a current of 7.5 volts
and this is supplied by another secondary coil of the transformer.
This rectifier tube delivers a direct current of 20 watts at 350
volts. It looks exactly like the 5 watt oscillator tube which is
pictured at E in Fig. 77. The price is $7.50.
The Filter Condensers.–These condensers are used in connection with
the reactance coil to smooth out the pulsating direct current after it
has passed through the rectifier tube. They have a capacitance of 1
mfd. and will stand 750 volts. These condensers cost about $2.00 each.
The Filter Reactance Coil.–This reactor which is shown in Fig. 92,
has about the same appearance as the power transformer but it is
somewhat smaller. It consists of a coil of wire wound on a soft iron
core and has a large inductance, hence the capacitance of the filter
condensers are proportionately smaller than where a small inductance
is used which has been the general practice. The size you require for
this set has an output of 160 milliamperes and it will supply current
for one to four 5 watt oscillator tubes. This size of reactor costs
$11.50.
[Illustration: Fig. 92.–Filter Reactor for Smoothing out Rectified
Currents.]
Connecting Up the Apparatus.–The wiring diagram in Fig. 93 shows how
the various pieces of apparatus for this telephone transmitter are
connected up. You will observe: (1) that the terminals of the power
transformer secondary coil which develops 10 volts are connected to
the filaments of the oscillator tubes; (2) that the terminals of the
other secondary coil which develops 10 volts are connected with the
filaments of the rectifier tubes; (3) that the terminals of the third
secondary coil which develops 550 volts are connected with the plates
of the rectifier tubes; (4) that the pair of filter condensers are
connected in parallel and these are connected to the mid-taps of the
two filament secondary coils; (5) that the reactance coil and the
third filter condenser are connected together in series and these are
shunted across the filter condensers, which are in parallel; and,
finally, (6) a lead connects the mid-tap of the 550-volt secondary
coil of the power transformer with the connection between the reactor
and the third filter condenser.
[Illustration: Fig 93.–100 to 200 Mile Wireless Telephone
Transmitter.]

Electricity at Rest and in Motion.–Any wire or a conductor of any
kind can be charged with electricity, but a Leyden jar, or other
condenser, is generally used to hold an electric charge because it has
a much larger _capacitance_, as its capacity is called, than a wire.
As a simple analogue of a condenser, suppose you have a tank of water
raised above a second tank and that these are connected together by
means of a pipe with a valve in it, as shown at A in Fig. 28.
[Illustration: Fig. 28.–Water Analogue for Electric Pressure.]
[Illustration: original © Underwood and Underwood. First Wireless
College in the World, at Tufts College, Mass.]
Now if you fill the upper tank with water and the valve is turned off,
no water can flow into the lower tank but there is a difference of
pressure between them, and the moment you turn the valve on a current
of water will flow through the pipe. In very much the same way when
you have a condenser charged with electricity the latter will be under
_pressure,_ that is, a _difference of potential_ will be set up, for
one of the sheets of metal will be charged positively and the other
one, which is insulated from it, will be charged negatively, as shown
at B. On closing the switch the opposite charges rush together and
form a current which flows to and fro between the metal plates.
[Footnote: Strictly speaking it is the difference of potential that
sets up the electromotive force.]
The Electric Current and Its Circuit.–Just as water flowing through a
pipe has _quantity_ and _pressure_ back of it and the pipe offers
friction to it which tends to hold back the water, so, likewise, does
electricity flowing in a circuit have: (1) _quantity_, or _current
strength_, or just _current_, as it is called for short, or
_amperage_, and (2) _pressure_, or _potential difference_, or
Wmte-fm 101.5 Mhz In Manistee _electromotive force_, or _voltage_, as it is variously called, and
the wire, or circuit, in which the current is flowing has (3)
_resistance_ which tends to hold back the current.
A definite relation exists between the current and its electromotive
force and also between the current, electromotive force and the
resistance of the circuit; and if you will get this relationship
clearly in your mind you will have a very good insight into how direct
and alternating currents act. To keep a quantity of water flowing in a
loop of pipe, which we will call the circuit, pressure must be applied
to it and this may be done by a rotary pump as shown at A in Fig. 29;
in the same way, to keep a quantity of electricity flowing in a loop
of wire, or circuit, a battery, or other means for generating electric
pressure must be used, as shown at B.
[Illustration: Fig. 29.–Water Analogues for Direct and Alternating
Currents.]
If you have a closed pipe connected with a piston pump, as at C, as
the piston moves to and fro the water in the pipe will move first one
way and then the other. So also when an alternating current generator
is connected to a wire circuit, as at D, the current will flow first
in one direction and then in the other, and this is what is called an
_alternating current_.
Current and the Ampere.–The amount of water flowing in a closed pipe
is the same at all parts of it and this is also true of an electric
current, in that there is exactly the same quantity of electricity at
one point of the circuit as there is at any other.
The amount of electricity, or current, flowing in a circuit in a
second is measured by a unit called the _ampere_, [Footnote: For
definition of _ampere_ see _Appendix._] and it is expressed by the
symbol I. [Footnote: This is because the letter C is used for the
symbol of _capacitance_] Just to give you an idea of the quantity of
current an _ampere_ is we will say that a dry cell when fresh gives a
current of about 20 amperes. To measure the current in amperes an
instrument called an _ammeter_ is used, as shown at A in Fig. 30, and
this is always connected in _series_ with the line, as shown at B.
[Illustration: Fig. 30.–How the Ammeter and Voltmeter are Used.]

There was a strained silence for a moment. Then–
“Get Lieutenant Mackinson and those boys,” the captain continued, and
the ships surgeon started down the stairway to find that Joe and Jerry
already were summoning Slim and the lieutenant.
“It looks as though wed caught the man,” the doctor whispered.
As the four reached the deck where the captured man stood between the
first assistant engineer and the captain, who had by this time taken out
his revolver, there was a gasp of astonishment from Joe, followed by a
louder “Holy smoke!” from Slim.
“Do you recognize this man?” the captain asked in a sharp tone.
“I should say I do, sir,” Joe responded. “_He is the man who was
planting ammunition in the waters near the navy yard that night before
we sailed_!”
“The very same one, sir!” Slim exclaimed, with equal positiveness.
The ships surgeon, who had followed the others upon deck, stepped
closer for a better inspection of this enemy. At the same instant the
prisoner, striking out with both hands, knocked the captains revolver
hand into the air, and thrust the engineer from him. Before anyone could
interfere he was dashing down the deck toward the Fox Television Stations, Inc. Wdca stern.
Just as he took a wild, headlong leap over the rail the captain fired.
While the captain, through a speaking tube, was instructing the man in
the pilot house to signal below “Reverse engines,” the others rushed to
the stern of the ship.
Far behind them in the foamy trail left on the moonlit water by the
vessel they saw what seemed to be the head of a man bobbing up and
down–and then it entirely disappeared. The ship was turned, and that
portion of the sea searched, but without avail.
“Gone,” said the captain in tones of very evident relief. “Well, it was
death for him, one way or another, and he took his choice.”
As the captain and surgeon moved away from the stern rail of the
_Everett_, the three lads and the lieutenant still stood there, gazing
far out to sea.
“The man who made me nearly freeze to death in the water,” spoke Joe, as
though thinking aloud.
“And pummeled my stomach until it was sore for three days,” echoed Slim,
in sad reminiscence.
“And made me run a mile in nothing, flat,” added Jerry.
“And fought me to a knockout finish later,” mused Joe.
“And nearly smothered me to death,” spoke the lieutenant.
“And was finally corralled by an Irish engineer!” said Slim.
“Gone,” concluded Jerry, “and no one here will mourn his departure.”
CHAPTER IX
THE PERISCOPE AT DAWN
That night the boys had ample evidence that they were inside the
submarine zone, where anything might happen at any minute. Not a light
was permitted on any of the ships, and they traveled along in the most
peculiar fashion and over the most irregular course, never going at more
than half speed and not more than a mile or so without a complete change
of direction.
For no apparent reason whatever the engines would slow down and entirely
stop, and in that position they would remain for ten, fifteen, twenty
minutes or even half an hour, and then start up again on another tack.
“I believe weve become separated from our convoy,” said Slim, who had
been upon deck, and now entered the wireless room where Joe and Jerry
were watching Lieutenant Mackinson make some readjustments of the
wireless mechanism. “The pilot doesnt seem to know the course. Say,
wouldnt it be great sport if we should be lost from the others? But I
wonder why the captain does not wireless them?”
“No need,” Lieutenant Mackinson assured him, “for we are not lost, nor
are we separated from them. Every vessel in this fleet is simply
carrying out a program secretly arranged long in advance, and which was
in the nature of a sealed order which the various captains did not open
until this morning.
“I dare say that our convoy is as near us now as at any time during the
voyage, and that it is maintaining the same position at all times, going
through the exact maneuvers that the _Everett_ is performing.”
“It is to fool the submarines?” asked Joe.
“Exactly,” the lieutenant replied. “Our government is taking every
precaution, and no unnecessary risks. You see, there is no way of
keeping absolutely secret the departure of our transports. Nor is there
any assurance that the information does not go directly to the German
authorities, and from them to the commanders of the submarines. Our
actions are designed to prevent them from estimating our course or
position.
“It was their knowledge of that fact, and their determination to learn
our whereabouts in another way, which doubtless led to that spy being
aboard this transport. I feel—-”