Radio Shack

A Two-wire Aerial.–An aerial with two wires will give better results
than a single wire and three wires are better than two, but you must
keep them well apart. To put up a two-wire aerial get (1) enough _No.
16_, or preferably _No. 14_, solid or stranded copper or aluminum
wire, (2) four porcelain insulators, see B in Fig. 5, and (3) two
sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the
_spreaders_, and bore 1/8-inch hole through each end of each one. Now
twist the ends of the wires to the insulators and then cut off four
pieces of wire about 6 feet long and run them through the holes in the
wood spreaders. Finally twist the ends of each pair of short wires to
the free ends of the insulators and then twist the free ends of the
wires together.
For the leading-in wire that goes to the lightning switch take two
lengths of wire and twist one end of each one around the aerial wires
and solder them there. Twist the short wire around the long wire and
solder this joint also when the aerial will look like Fig. 7. Bring
the free end of the leading-in wire down to the middle post of the
lightning switch and fasten it there and connect up the receiver to it
and the ground as described under the caption of _A Single Wire
Aerial_.
[Illustration: Fig. 7.–Two Wire Aerial.]
Connecting in the Ground.–If there is a gas or water system or a
steam-heating plant in your house you can make your ground connection
by clamping a ground clamp to the nearest pipe as has been previously
described. Connect a length of bare or insulated copper wire with it
and bring this up to the table on which you have your receiving set.
If there are no grounded pipes available then you will have to make a
good ground which we shall describe presently and lead the ground wire
from your receiving set out of the window and down to it.
How to Put Up a Good Aerial.–While you can use the cheap aerial
already described for a small spark-coil sending set you should have a
better insulated one for a 1/2 or a 1 kilowatt transformer set. The
cost for the materials for a good aerial is small and when properly
made and well insulated it will give results that are all out of
proportion to the cost of it.
An Inexpensive Good Aerial.–A far better aerial, because it is more
highly insulated, can be made by using _midget insulators_ instead of
the porcelain insulators described under the caption of _A Single Wire
Aerial_ and using a small _electrose leading-in insulator_ instead of
the porcelain bushing. This makes a good sending aerial for small sets
as well as a good receiving aerial.
The Best Aerial that Can Be Made.–To make this aerial get the
following material together: (1) enough _stranded or braided wire_ for
three or four lengths of parallel wires, according to the number you
want to use (2) six or eight _electrose ball insulators_, see B, Fig.
8; (3) two 5-inch or 10-inch _electrose strain insulators_, see C; (4)
six or eight _S-hooks_, see D; one large _withe_ with one eye for
middle of end spreader, see E; (6) two smaller _withes_ with one eye
each for end spreader, see E; (7) two still smaller _withes_, with two
eyes each for the ends of the end spreaders, see E (8) two _thimbles_,
see F, for 1/4-inch wire cable; (9) six or eight _hard rubber tubes_
or _bushings_ as shown at G; and (10) two _end spreaders_, see H; one
_middle spreader_, see I; and one _leading-in spreader_, see J.
[Illustration: (A) Fig. 8–Part of a Good Aerial.]
[Illustration: (B) Fig. 8.–The Spreaders.]
For this aerial any one of a number of kinds of wire can be used and
among these are (a) _stranded copper wire;_ (b) _braided copper wire;_
(c) _stranded silicon bronze wire,_ and (d) _stranded phosphor bronze
wire_. Stranded and braided copper wire is very flexible as it is
formed of seven strands of fine wire twisted or braided together and
it is very good for short and light aerials. Silicon bronze wire is
stronger State Alaska K11qt than copper wire and should be used where aerials are more
than 100 feet long, while phosphor bronze wire is the strongest aerial
wire made and is used for high grade aerials by the commercial
companies and the Government for their high-power stations.

CHAPTER VI
HOW THE TRANSMITTING AND RECEIVING SETS WORK
The easiest way to get a clear conception of how a wireless
transmitter sends out electric waves and how a wireless receptor
receives them is to take each one separately and follow: (1) in the
case of the transmitter, the transformation of the low voltage direct,
or alternating current into high potential alternating currents; then
find out how these charge the condenser, how this is discharged by the
spark gap and sets up high-frequency currents in the oscillation
circuits; then (2) in the case of the receptor, to follow the high
frequency currents that are set up in the aerial wire and learn how
they are transformed into oscillations of lower potential when they
have a larger current strength, how these are converted into
intermittent direct currents by the detector and which then flow into
and operate the telephone receiver.
How Transmitting Set No. 1 Works. The Battery and Spark Coil
Circuit.–When you press down on the knob of the key the silver points
of it make contact and this closes the circuit; the low voltage direct
current from the battery now flows through the primary coil of the
spark coil and this magnetizes the soft iron core. The instant it
becomes magnetic it pulls the spring of the vibrator over to it and
this breaks the circuit; when this takes place the current stops
flowing through the primary coil; this causes the core to lose its
magnetism when the vibrator spring flies back and again makes contact
with the adjusting screw; then the cycle of operations is repeated.
A condenser is connected across the contact points of the vibrator
since this gives a much higher voltage at the ends of the secondary
coil than where the coil is used without it; this is because: (1) the
self-induction of the primary coil makes the pressure of the current
rise and when the contact points close the circuit again it discharges
through the primary coil, and (2) when the break takes place the
current flows into the condenser instead of arcing across the contact
points.
Changing the Primary Spark Coil Current Into Secondary Currents.–Now
every time the vibrator contact points close the primary circuit the
electric current in the primary coil is changed into closed magnetic
lines of force and as these cut through the secondary coil they set up
in it a _momentary current_ in one direction. Then the instant the
vibrator points break apart the primary circuit is opened and the
closed magnetic lines of force contract and as they do so they cut the
turns of wire in the secondary coil in the opposite direction and this
sets up another momentary current in the secondary coil in the other
direction. The result is that the low voltage direct current of the
battery is changed into alternating currents whose frequency is
precisely that of the spring vibrator, but while the frequency of the
currents is low their potential, or voltage, is enormously increased.
What Ratio of Transformation Means.–To make a spark coil step up the
low voltage direct current into high potential alternating current the
primary coil is wound with a couple of layers of thick insulated
copper wire and the secondary is wound with a thousand, more or less,
number of turns with very fine insulated copper wire. If the primary
and secondary coils were wound with the same number of turns of wire
then the pressure, or voltage, of the secondary coil at its terminals
would be the same as that of the current which flowed through the
primary coil. Under these conditions the _ratio of transformation_, as
it is called, would be unity.
The ratio of transformation is directly proportional to the number of
turns of wire on the primary and secondary coils and, since this is
the case, if you wind 10 turns of wire on the primary coil and 1,000
turns of wire on the secondary coil then you will get 100 times as
high a pressure, or voltage, at the terminals of the secondary as that
which you caused to flow through the primary coil, but, naturally, the
current strength, or amperage, will be proportionately decreased.
The Secondary Spark Coil Circuit.–This includes the secondary coil
and the spark gap which are connected together. When the alternating,
but high potential, currents which are developed by the secondary
coil, reach the balls, or _electrodes_, of the spark Kpet 690 Khz In Lamesa gap the latter
are alternately charged positively and negatively.
Now take a given instant when one electrode is charged positively and
the other one is charged negatively, then when they are charged to a
high enough potential the electric strain breaks down the air gap
between them and the two charges rush together as described in the
chapter before this one in connection with the discharge of a
condenser. When the charges rush together they form a current which
burns out the air in the gap and this gives rise to the spark, and as
the heated gap between the two electrodes is a very good conductor the
electric current surges forth and back with high frequency, perhaps a
dozen times, before the air replaces that which has burned out. It is
the inrushing air to fill the vacuum of the gap that makes the
crackling noise which accompanies the discharge of the electric spark.

Though the vacuum tube detector requires two batteries to operate it
and the receiving circuits are somewhat more complicated than where a
crystal detector is used still the former does not have to be
constantly adjusted as does the latter and this is another very great
advantage. Taken all in all the vacuum tube detector is the most
sensitive and the most satisfactory of the detectors that are in use
at the present time.
Not only is the vacuum tube a detector of electric wave signals and
speech and music but it can also be used to _amplify_ them, that is,
to make them stronger and, hence, louder in the telephone receiver and
further its powers of amplification are so great that it will
reproduce them by means of a _loud speaker_, just as a horn amplifies
the sounds of a phonograph reproducer, until they can be heard by a
room or an auditorium full of people. There are two general types of
loud speakers, though both use the principle of the telephone
receiver. The construction of these loud speakers will be fully
described in a later chapter.
Assembled Vacuum Tube Receiving Sets.–You can buy a receiving set
with a vacuum tube detector from the very simplest type, which is
described in this chapter, to those that are provided with
_regenerative circuits_ and _amplifying_ tubes or both, which we shall
describe in later chapters, from dealers in electrical apparatus
generally. While one of these sets costs more than you can assemble a
set for yourself, still, especially in the beginning, it is a good
plan to buy an assembled one for it is fitted with a _panel_ on which
the adjusting knobs of the rheostat, tuning coil and condenser are
mounted and this makes it possible to operate it as soon Wevo Mhz Concord as you get it
home and without the slightest trouble on your part.
You can, however, buy all the various parts separately and mount them
yourself. If you want the receptor simply for receiving then it is a
good scheme to have all of the parts mounted in a box or enclosed
case, but if you want it for experimental purposes then the parts
should be mounted on a base or a panel so that all of the connections
are in sight and accessible.
A Simple Vacuum Tube Receiving Set.–For this set you should use: (1)
a _loose coupled tuning coil,_ (2) a _variable condenser,_ (3) a
_vacuum tube detector,_ (4) an A or _storage battery_ giving 6 volts,
(5) a B or _dry cell battery_ giving 22-1/2 volts, (6) a _rheostat_
for varying the storage battery current, and (7) a pair of 2,000-ohm
_head telephone receivers_. The loose coupled tuning coil, the
variable condenser and the telephone receivers are the same as those
described in Chapter III.
The Vacuum Tube Detector. With Two Electrodes.–A vacuum tube in its
simplest form consists of a glass bulb like an incandescent lamp in
which a _wire filament_ and a _metal plate_ are sealed as shown in
Fig. 37, The air is then pumped out of the tube and a vacuum left or
after it is exhausted it is filled with nitrogen, which cannot burn.
[Illustration: Fig. 37.–Two Electrode Vacuum Tube Detectors.]
When the vacuum tube is used as a detector, the wire filament is
heated red-hot and the metal plate is charged with positive
electricity though it remains cold. The wire filament is formed into a
loop like that of an incandescent lamp and its outside ends are
connected with a 6-volt storage battery, which is called the A
battery; then the + or _positive_ terminal of a 22-1/2 volt dry cell
battery, called the B battery, is connected to the metal plate while
the - or _negative_ terminal of the battery is connected to one of the
terminals of the wire filament. The diagram, Fig. 37, simply shows how
the two electrode vacuum tube, the A or dry battery, and the B or
storage battery are connected up.
Three Electrode Vacuum Tube Detector.–The three electrode vacuum tube
detector shown at A in Fig. 38, is much more sensitive than the two
electrode tube and has, in consequence, all but supplanted it. In this
more recent type of vacuum tube the third electrode, or _grid_, as it
is called, is placed between the wire filament and the metal plate and
this allows the current to be increased or decreased at will to a very
considerable extent.
[Illustration: Fig. 38.–Three Electrode Vacuum Tube Detector and
Battery Connections.]

Now connect one of the posts of the rheostat to one terminal of the
filament Wffc Mhz Ferrum and the other terminal of the filament to the - or _negative_
terminal of the A or storage battery and the + or _positive_ terminal
of the A or storage battery to the other post of the rheostat. Finally
connect the + or positive terminal of the A or storage battery with
the wire that runs from the head phones to the variable condenser, all
of which is shown in the wiring diagram at B in Fig. 41.
Adjusting the Vacuum Tube Detector Receiving Set.–A vacuum tube
detector is tuned exactly in the same way as the _Crystal Detector Set
No. 2_ described in Chapter III, in-so-far as the tuning coil and
variable condenser are concerned. The sensitivity of the vacuum tube
detector receiving set and, hence, the distance over which signals and
other sounds can be heard depends very largely on the sensitivity of
the vacuum tube itself and this in turn depends on: (1) the right
amount of heat developed by the filament, or _filament brilliancy_ as
it is called, (2) the right amount of voltage applied to the plate,
and (3) the extent to which the tube is exhausted where this kind of a
tube is used.
To vary the current flowing from the A or storage battery
through the filament so that it will be heated to the right degree you
adjust the rheostat while you are listening in to the signals or other
sounds. By carefully adjusting the rheostat you can easily find the
point at which it makes the tube the most sensitive. A rheostat is
also useful in that it keeps the filament from burning out when the
current from the battery first flows through it. You can very often
increase the sensitiveness of a vacuum tube after you have used it for
a while by recharging the A or storage battery.
The degree to which a vacuum tube has been exhausted has a very
pronounced effect on its sensitivity. The longer the tube is used the
lower its vacuum gets and generally the less sensitive it becomes.
When this takes place (and you can only guess at it) you can very
often make it more sensitive by warming it over the flame of a candle.
Vacuum tubes having a gas content (in which case they are, of course,
no longer vacuum tubes in the strict sense) make better detectors than
tubes from which the air has been exhausted and which are sealed off
in this evacuated condition because their sensitiveness is not
dependent on the degree of vacuum as in the latter tubes. Moreover, a
tube that is completely exhausted costs more than one that is filled
with gas.

The Grid and Blocking Condensers.–Each of these is a fixed condenser
of .002 mfd. capacitance and is rated to stand 3,000 volts. It is
made like the aerial condenser but has only two terminals. It costs
$2.00.
The Key Circuit Apparatus.–This consists of: (1) the _grid leak_; (2)
the _chopper_; (3) the _choke coil_, and (4) the _key_. The grid leak
is connected in the lead from the grid to the aerial to keep the
voltage on the grid at the right potential. It has a resistance of
5000 ohms with a mid-tap at 2500 ohms as shown at C. It costs $2.00.
The chopper is simply a rotary interrupter driven by a small motor. It
comprises a wheel of insulating material in which 30 or more metal
segments are set in an insulating disk as shown at D. A metal contact
called a brush is fixed on either side of the wheel. It costs about
$7.00 and the motor to drive it is extra. The choke coil is wound up
of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered
magnet wire on a spool which has a diameter of 2 inches and a length
of 3-1/4 inches.
The 5 Watt Oscillator Vacuum Tube.–This tube is made like the
amplifier tube described for use with the preceding experimental
transmitter, but it is larger, has a more perfect vacuum, and will
stand a plate potential of 350 volts while the plate current is .045
ampere. The filament takes a current of a little more than 2 amperes
at 7.5 volts. A standard 4-tap base is used with it. The tube costs
$8.00 and the porcelain base is $1.00 extra. It is shown at E.
The Storage Battery and Rheostat.–This must be a 5-cell battery so
that it will develop 10 volts. A storage battery of any capacity can
be used but the lowest priced one costs about $22.00. The rheostat for
regulating the battery current is the same as that used in the
preceding experimental transmitter.
The Filament Voltmeter.–To get the best results it is necessary that
the voltage of the current which heats the filament be kept at the
same value all of the time. For this transmitter a direct current
voltmeter reading from 0 to 15 volts is used. It is shown at F and
costs $7.50. The Oscillation Choke Coil.–This is made exactly like
the one described in connection with the experimental transmitter.
The Motor-Generator Set.–Where you have only a 110 or a 220 volt
direct current available as a source of power you need a
_motor-generator_ to change it to 350 volts, and this is an expensive
piece of apparatus. It consists of a single armature core with a motor
winding and a generator winding on it and each of these has its own
commutator. Where the low voltage current flows into one of the
windings it drives its as a motor and this in Mineral Television District #1 K06nq turn generates the
higher voltage current in the other winding. Get a 100 watt 350 volt
motor-generator; it is shown at F and costs about $75.00.
The Panel Cut-Out.–This switch and fuse block is the same as that
used in the experimental set.
The Protective Condenser.–This is a fixed condenser having a
capacitance of 1 mfd. and will stand 750 volts. It costs $2.00.
Connecting Up the Transmitting Apparatus.–From all that has gone
before you have seen that each piece of apparatus is fitted with
terminal, wires, taps or binding posts. To connect up the parts of
this transmitter it is only necessary to make the connections as shown
in the wiring diagram Fig. 78.
[Illustration: Fig. 78.–5 to 50 Watt C. W. Telegraph Transmitter.
(With Single Oscillation Tube.)]
A 200 Mile C. W. Telegraph Transmitter.–To make a continuous wave
telegraph transmitter that will cover distances up to 200 miles all
you have to do is to use two 5 watt vacuum tubes in _parallel_, all of
the rest of the apparatus being exactly the same. Connecting the
oscillator tubes up in parallel means that the two filaments are
connected across the leads of the storage battery, the two grids on
the same lead that goes to the aerial and the two plates on the same
lead that goes to the positive pole of the generator. Where two or
more oscillator tubes are used only one storage battery is needed, but
each filament must have its own rheostat. The wiring diagram Fig. 79
shows how the two tubes are connected up in parallel.
[Illustration: Fig. 79.–200 Mile C.W. Telegraph Transmitter (With Two
Tubes in Parallel.)]
A 500 Mile C. W. Telegraph Transmitter.–For sending to distances of
over 200 miles and up to 500 miles you can use either: (1) three or
four 5 watt oscillator tubes in parallel as described above, or (2)
one 50 watt oscillator tube. Much of the apparatus for a 50 watt tube
set is exactly the same as that used for the 5 watt sets. Some of the
parts, however, must be proportionately larger though the design all
the way through remains the same.

Damped and Sustained Electric Oscillations.–The vibrating steel
spring described above is a very good analogue of the way that damped
electric oscillations which surge in a circuit set up and send out
periodic electric waves in the ether while the electric driven tuning
fork just described is likewise a good analogue of how sustained
oscillations surge in a circuit and set up and send out continuous
electric waves in the ether as the following shows.
Now the inductance and resistance of a circuit such as is shown at A
in Fig. 35, slows down, and finally damps out entirely, the electric
oscillations of the high frequency currents, see B, where these are
set up by the periodic discharge of a condenser, precisely as the
vibrations of the spring are damped out by the friction of the air and
other resistances that act upon it. As the electric oscillations surge
to and fro in the circuit it is opposed by the action of the ether
which surrounds it and electric waves are set up in and sent out
Gerald Locklear Wpem-lp through it and this transformation soon uses up the energy of the
current that flows in the circuit.
[Illustration: Fig. 35.–Damped and Sustained Electric Oscillations.]
To send out _continuous waves_ in the ether such as are needed for
wireless telephony instead of _damped waves_ which are, at the present
writing, generally used for wireless telegraphy, an _electric
oscillation arc_ or a _vacuum tube oscillator_ must be used, see C,
instead of a spark gap. Where a spark gap is used the condenser in the
circuit is charged periodically and with considerable lapses of time
between each of the charging processes, when, of course, the condenser
discharges periodically and with the same time element between them.
Where an oscillation arc or a vacuum tube is used the condenser is
charged as rapidly as it is discharged and the result is the
oscillations are sustained as shown at D.

Where this type of interrupter is employed the condenser that is
usually shunted around the break is not necessary as the interrupter
itself has a certain inherent capacitance, due to electrolytic action,
and which is called its _electrolytic capacitance_, and this is large
enough to balance the self-induction of the circuit since the greater
the number of breaks per minute the smaller the capacitance required.
The Rotary Spark Gap.–In this type of spark gap the two fixed
electrodes are connected with the terminals of the secondary coil of
the power transformer and also with the condenser and primary of the
oscillation transformer. Now whenever any pair of electrodes on the
rotating disk are in a line with the pair of fixed electrodes a spark
will take place, hence the pitch of the note depends on the speed of
the motor driving the disk. This kind of a rotary spark-gap is called
_non-synchronous_ and it is generally used where a 60 cycle
alternating current is available but it will work with other higher
frequencies.
The Quenched Spark Gap.–If you strike a piano string a single quick
blow it will continue to vibrate according to its natural period. This
is very much the way in which a quenched spark gap sets up
oscillations in a coupled closed and open circuit. The oscillations
set up in the primary circuit by a quenched spark make only three or
four sharp swings and in so doing transfer all of their energy over to
the secondary circuit, where it will oscillate some fifty times or
more before it is damped out, because the high frequency currents are
not forced, but simply oscillate to the natural frequency of the
circuit. For this reason the radiated waves approach somewhat the
condition of continuous waves, and so sharper tuning is possible.
The Oscillation Transformer.–In this set the condenser in the closed
circuit is charged and discharged and sets up oscillations that surge
through the closed circuit as in _Set No. 1_. In this set, however, an
oscillation transformer is used and as the primary coil of it is
included in the closed circuit the oscillations set up in it produce
strong oscillating magnetic lines of force. The magnetic field thus
produced sets up in turn electric oscillations in the secondary coil
of the oscillation transformer and these surge Millard County K36fy through the aerial wire
system where their energy is radiated in the form of electric waves.
The great advantage of using an oscillation transformer instead of a
simple inductance coil is that the capacitance of the closed circuit
can be very much larger than that of the aerial wire system. This
permits more energy to be stored up by the condenser and this is
impressed on the aerial when it is radiated as electric waves.
How Receiving Set No. I Works.–When the electric waves from a distant
sending station impinge on the wire of a receiving aerial their energy
is changed into electric oscillations that are of exactly the same
frequency (assuming the receptor is tuned to the transmitter) but
whose current strength (amperage) and potential (voltage) are very
small. These electric waves surge through the closed circuit but when
they reach the crystal detector the contact of the metal point on the
crystal permits more current to flow through it in one direction than
it will allow to pass in the other direction. For this reason a
crystal detector is sometimes called a _rectifier_, which it really
is.

But soon they realized that this, too, was as hopeless as the pounding,
for it further exhausted the energy which the foul air was rapidly
sapping, without making any apparent opening in the thick earthen wall
that surrounded them.
“Well,” said Slim at last, gulping back his nausea, and smiling almost
in his old time way, “Im as anxious as anybody to keep up hope to the
last. But if this is to be our end, I guess we can face it as Americans
should.”
“Bravo!” exclaimed Lieutenant Mackinson, “I always knew that each one of
you fellows had the right sort of stuff in you.”
And Jerry, too, slapped him affectionately on the back.
“Slim,” he said, smiling over at his chum, and ready for his pun, even
under such circumstances, “my head is feeling a trifle heavy, but Im
game to stand up to the last.”
Thus they sat down to wait–for just what, they did not know–while at
that very moment, four feet away from them on the other side of the
wall, faithful Joe was setting up the flashlight exactly according to
directions.
For a few seconds he waited, and then, three times in quick succession,
a rocket went into the air from just behind the American lines.
Over there Captain Hallowell himself found the range, submitted it to
his most expert gunner, who verified it, and then they waited for the
three minutes to elapse, during which Joe was to seek a place of safety.
It was in that interval, too, that Fate intervened for those within the
cave, for they were sitting with their backs to the very point against
which the shell was to be directed.
“We need all our strength,” Lieutenant Mackinson was saying. “So long as
possible we want to remain in full possession of our senses. The air is
purer near the floor. I think it would be better to lie down.”
And following his suggestion and example, the other two stretched
themselves out in the middle of the cavern.
Within the American lines, at that point where a regiment of heavy
artillery was stationed, Captain Hallowell raised his hand in signal to
his gunner. Out on the parapet of the front trench an anxious colonel
was standing, regardless of all danger, a pair of powerful glasses to
his eyes. His vision was focused upon a little light far out in No Mans
Land.
Two hundred feet away from that light Joe and Frank Hoskins lay prone
upon the ground, silent, impatient, fearful, hoping.
With a quick motion the artillery captain swung his outstretched arm
downward. There was a roar, a flash, and a great shell tore through the
air. Out in No Mans Land there was a second explosion as the shell hit,
and the target–a flashlight–was blown to atoms.
Over in the German trenches a sentinel chuckled at the thought of
another wasted American shell, but out of the hole that that shell had
torn three pale, haggard, and exhausted youths were crawling to safety
and Gods fresh air. And across No Mans Land dashed two pals to greet
them.
American determination and American marksmanship had Wokw 102.9 Mhz In Curwensville saved three
American lives. The German sentinel might have his laugh if he liked.
It was hours later before the three who had been imprisoned learned how
their rescue had been effected; but they got an inkling of it as they
came within four hundred yards of the American-French front.
“What are you doing?” Lieutenant Mackinson had asked, as Joe brought the
party to a stop.
“Just a moment and you will see,” Joe had responded.
And, first in wonder and then with a dawning understanding, the other
three read off his flashed message:
“Signal Corps men, and whole party safe.”
CHAPTER XV
THE SURPRISE ATTACK–PROMOTION
During the week that followed, the lads were confined almost entirely to
regular routine work, with nothing particularly exciting. Frank Hoskins
elbow wound healed quickly, without any serious results; and Tom Rawle,
who had been under treatment at the field hospital, was able to get
about the camp, although still pale and weak, and limping considerably
from his injury.

A Cheap Transmitting Set (No. 1).–For this set you will need: (1) a
_spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4)
a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation
transformer_. There are many different makes and styles of these parts
but in the last analysis all of them are built on the same underlying
bases and work on the same fundamental principles.
The Spark-Coil.–Spark coils for wireless work are made to give sparks
from 1/4 inch in length up to 6 inches in length, but as a spark coil
that gives less than a 1-inch spark has a very limited output it is
best to get a coil that gives at least a 1-inch spark, as this only
costs about $8.00, and if you can get a 2- or a 4-inch spark coil so
much the better. There are two general styles of spark coils used for
wireless and these are shown at A and B in Fig. 18.
[Illustration: (A) and (B) Fig. 18.–Types of Spark Coils for Set. No.
1.]
[Illustration: (C) Fig. 18.–Wiring Diagram of Spark Coil]
A spark coil of either style consists of (_a_) a soft _iron core_ on
which is wound (_b_) a couple of layers of heavy insulated Redwood Improvement Corporation W64ac wire and
this is called the _primary coil_, (_c_) while over this, but
insulated from it, is wound a large number of turns of very fine
insulated copper wire called the _secondary coil_; (d) an
_interrupter_, or _vibrator_, as it is commonly called, and, finally,
(e) a _condenser_. The core, primary and secondary coils form a unit
and these are set in a box or mounted on top of a hollow wooden base.
The condenser is placed in the bottom of the box, or on the base,
while the vibrator is mounted on one end of the box or on top of the
base, and it is the only part of the coil that needs adjusting.
The vibrator consists of a stiff, flat spring fixed at one end to the
box or base while it carries a piece of soft iron called an _armature_
on its free end and this sets close to one end of the soft iron core.
Insulated from this spring is a standard that carries an adjusting
screw on the small end of which is a platinum point and this makes
contact with a small platinum disk fixed to the spring. The condenser
is formed of alternate sheets of paper and tinfoil built up in the
same fashion as the receiving condenser described under the caption of
_Fixed and Variable Condensers_, in Chapter III.
The wiring diagram C shows how the spark coil is wired up. One of the
battery binding posts is connected with one end of the primary coil
while the other end of the latter which is wound on the soft iron core
connects with the spring of the vibrator. The other battery binding
post connects with the standard that supports the adjusting screw. The
condenser is shunted across the vibrator, that is, one end of the
condenser is connected with the spring and the other end of the
condenser is connected with the adjusting screw standard. The ends of
the secondary coil lead to two binding posts, which are usually placed
on top of the spark coil and it is to these that the spark gap is
connected.

The Condensers.–For the aerial series condenser get one that has a
capacitance of .002 mfd. and that will stand a potential of 3,000
volts. [Footnote: The U C-1014 _Faradon_ condenser made by the Radio
Corporation of America will serve the purpose.] It is shown at C. The
other three condensers, see D, are also of the fixed type and may have
a capacitance of .001 mfd.; [Footnote: List No. 266; fixed receiving
condenser, sold by the Manhattan Electrical Supply Co.] the blocking
condenser should preferably have a capacitance of 1/2 a mfd. In these
condensers the leaves of the sheet metal are embedded in composition.
The aerial condenser will cost you $2.00 and the others 75 cents each.
[Illustration: (A) Fig. 75.–Apparatus for Experimental C. W.
Telegraph Transmitter.]
[Illustration: Fig. 75.–Apparatus for Experimental C. W. Telegraph
Transmitter.]
Waym 88.7 Mhz In Columbia The Aerial Ammeter.–This instrument is also called a _hot-wire_
ammeter because the oscillating currents flowing through a piece of
wire heat it according to their current strength and as the wire
contracts and expands it moves a needle over a scale. The ammeter is
connected in the aerial wire system, either in the aerial side or the
ground side–the latter place is usually the most convenient. When you
tune the transmitter so that the ammeter shows the largest amount of
current surging in the aerial wire system you can consider that the
oscillation circuits are in tune. A hot-wire ammeter reading to 2.5
amperes will serve your needs, it costs $6.00 and is shown at E in
Fig. 75.
[Illustration: United States Naval High Power Station, Arlington Va.
General view of Power Room. At the left can be seen the Control
Switchboards, and overhead, the great 30 K.W. Arc Transmitter with
Accessories.]
The Buzzer and Dry Cell.–While a heterodyne, or beat, receptor can
receive continuous wave telegraph signals an ordinary crystal or
vacuum tube detector receiving set cannot receive them unless they are
broken up into trains either at the sending station or at the
receiving station, and it is considered the better practice to do this
at the former rather than at the latter station. For this small
transmitter you can use an ordinary buzzer as shown at F. A dry cell
or two must be used to energize the buzzer. You can get one for about
75 cents.
The Telegraph Key.–Any kind of a telegraph key will serve to break up
the trains of sustained oscillations into dots and dashes. The key
shown at G is mounted on a composition base and is the cheapest key
made, costing $1.50.
The Vacuum Tube Oscillator.–As explained before you can use any
amplifying tube that is made for a plate potential of 100 volts. The
current required for heating the filament is about 1 ampere at 6
volts. A porcelain socket should be used for this tube as it is the
best insulating material for the purpose. An amplifier tube of this
type is shown at H and costs $6.50.
The Storage Battery.–A storage battery is used to heat the filament
of the tube, just as it is with a detector tube, and it can be of any
make or capacity as long as it will develop 6 volts. The cheapest 6
volt storage battery on the market has a 20 to 40 ampere-hour capacity
and sells for $13.00.
The Battery Rheostat.–As with the receptors a rheostat is needed to
regulate the current that heats the filament. A rheostat of this kind
is shown at I and is listed at $1.25.
The Oscillation Choke Coil.–This coil is connected in between the
oscillation circuits and the source of current which feeds the
oscillator tube to keep the oscillations set up by the latter from
surging back into the service wires where they would break down the
insulation. You can make an oscillation choke coil by winding say 100
turns of No. 28 Brown and Sharpe gauge double cotton covered magnet
wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches
long.
Transmitter Connectors.–For connecting up the different pieces of
apparatus of the transmitter it is a good scheme to use _copper
braid_; this is made of braided copper wire in three sizes and sells
for 7,15 and 20 cents a foot respectively. A piece of it is pictured
at J.