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Two hardy youths strolling along the deck, who hadnt been touched by
the epidemic of seasickness, stopped to peer in at the porthole. They
had mischief in their eyes, and as they caught sight of Slims
humorously pathetic countenance, one of them muttered in a low but
distinct voice: “Howd you like to have some fried sausage, and some
plum pudding, and some—-”
“Shut up!” bawled out Jerry with what strength he had left.
With a loud laugh the two withdrew their heads and disappeared.
At that moment the ships physician, accompanied by Lieutenant
Mackinson, arrived to give what further comfort he could to the seasick
lads.
“It is clearing,” the lieutenant told them, while the doctor measured
out a powder for each boy. “The wind has died down and the sea is
becoming calm.”
“Oh, yes,” the physician added, “in an hour or so you will be feeling
better than you did before. Seasickness has a tonic effect, but its
rather a bitter dose.”
“Sure is,” said Slim weakly.
Nevertheless, it was just about an hour later that Jerry, feeling his
nausea leave him almost as suddenly as it had appeared, raised himself
on one elbow and looked across at his companion in misery.
“How do you feel, Slim?” he inquired.
“Almost human again,” the stout lad replied.
“Going to get up?”
“Guess I can in a few minutes.”
“Im going to try it now,” said Jerry. “Seems as if the pilot of this
ferry had learned to steer her a whole lot better than he did earlier in
the day.”
“Yep,” agreed Slim, sliding from his bunk. “Certainly was tough, wasnt
it?”
“I feel sort of weak in the legs yet,” said Jerry, by way of answer.
“Lets go up on deck and get some fresh air.”
“Stomach feels as empty as a vacant Wlpt 88.3 Mhz In Jesup house; hows yours?” Slim inquired.
“Nothing in it but the lining, and I guess most of thats pried loose.
Weve got to wait more than two hours for mess, too.”
“How about some fried sausage, and some plum pudding, and some—-”
Jerry laughed for the first time that day. “That fellow certainly did
make me mad,” he admitted.
“Yeh, he made you mad,” said Slim in a remorseful tone, “but he made me
sick.”
On deck a hundred or more vigorous young men were exercising their
muscles in various forms of athletic sport. Here a group crowded around
a contest in broad jumping, eagerly echoing the distances made, and
there the men of another throng loudly applauded their favorites in a
stiff boxing bout, while on another part of the deck a pair of
one-hundred-and-eighty-pound huskies were struggling in a friendly
wrestling match.
A bright sun shone upon a sparkling sea, and the air was just crisp
enough to be invigorating. At that moment Joe came up to inquire how his
two chums felt.
“Fine,” declared Jerry.
“Like a two-year-old,” added Slim. “That doctor was telling the truth. I
believe I never felt better in my life,” and he began flapping his arms
up and down like a rooster flails the air with its wings.
“A fat mans race three times around the ship!” a youth yelled, spying
Slims activities.
“Hurrah!” cried the crowd. “Get them started.”

There are four different ways employed at the present time to break up
the continuous waves of a wireless telegraph transmitter into groups
and these are: (_a_) the _heterodyne_, or _beat_, method, in which
waves of different lengths are impressed on the received waves and so
produces beats; (_b_) the _tikker_, or _chopper_ method, in which the
high frequency currents are rapidly broken up; (_c_) the variable
condenser method, in which the movable plates are made to rapidly
rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is
often called, and which is really a modified form of and an
improvement on the tikker. The heterodyne method will be described in
this chapter.
What the Heterodyne or Beat Method Is.–The word _heterodyne_ was
coined from the Greek words _heteros_ which means _other_, or
_different_, and _dyne_ which means _power_; in other words it means
when used in connection with a wireless receptor that another and
different high frequency current is used besides the one that is
received from the sending station. In music a _beat_ means a regularly
recurrent swelling caused by the reinforcement of a sound and this is
set up by Iditarod Area School District K02je the interference of sound waves which have slightly
different periods of vibration as, for instance, when two tones take
place that are not quite in tune with each other. This, then, is the
principle of the heterodyne, or beat, receptor.
In the heterodyne, or beat method, separate sustained oscillations,
that are just about as strong as those of the incoming waves, are set
up in the receiving circuits and their frequency is just a little
higher or a little lower than those that are set up by the waves
received from the distant transmitter. The result is that these
oscillations of different frequencies interfere and reinforce each
other when _beats_ are produced, the period of which is slow enough to
be heard in the headphones, hence the incoming signals can be heard
only when waves from the sending station are being received. A fuller
explanation of how this is done will be found in Chapter XV.
The Autodyne or Self-Heterodyne Long-Wave Receiving Set.–This is the
simplest type of heterodyne receptor and it will receive periodic
waves from spark telegraph transmitters or continuous waves from an
arc or vacuum tube telegraph transmitter. In this type of receptor the
detector tube itself is made to set up the _heterodyne oscillations_
which interfere with those that are produced by the incoming waves
that are a little out of tune with it.

For a full moment Captain Hallowell was silent. “There is only one way,”
he said finally, “and that is a dangerous way. Blast them out.”
“Blast them out?” repeated the colonel, but apparently without surprise.
“How?”
“It would take too long to dig them out,” Captain Hallowell answered.
“And, besides, that could hardly be done without some sort of light, and
that would Wogk Mhz Ocala attract enemy fire. There is but one chance, and that is to
blast them out with one of our big guns!”
“Can you do it?” the colonel demanded again, in his blunt, insistent
way.
“I will do my utmost to save them, sir,” Captain Hallowell replied.
“Very well, then,” answered his superior officer. “If you feel certain
that is the only way, go ahead. Personally, knowing the place as I do, I
see no other method myself. Have you the range?”
“I did have, sir,” said Captain Hallowell, “but in such a delicate
matter as this it would be necessary to be absolutely accurate. We have
been firing practically all day, and the position of the guns changes
slightly, of course. I would want to find a new and exact range.”
He had noticed Franks limp arm, and he turned to Joe.
“Take this flashlight,” he ordered. “It is more powerful than yours. Get
back there as quickly as you can, and follow to the letter these
directions: Keep between us and that hill until you get to it. Stay on
this side of the hill and crawl around toward the entrance until you get
to a point where you can place this light, facing us, two feet above the
ground and one foot in from the outer surface extremity. Leave it there
until you see three quick successive rockets go straight up in the air
from here. After that I will give you three minutes in which to get back
to a place of safety. Ill put that flashlight out of business, and I
think I can liberate your friends.”
“Is your injury a serious one?” the colonel demanded of Frank.
“Very slight, sir. Only a flesh wound,” Frank responded eagerly.
“Then take this light,” the colonel ordered, “and follow him at a
distance of a hundred yards. If anything should happen to your friend,
you follow the directions you have just heard.”
“Yes, sir,” the lads responded in unison, and, with a hasty salute, were
off.
Three times did Joe drop to the ground, as a shadow seemed to move
somewhere out in the distance before him. But each time he was up and
off again almost upon the instant, thinking of his own safety only as
that of his three friends depended upon it.
And what of those inside?
Even the courageous Lieutenant Mackinson was beginning to show the
anxiety he felt, while Jerry and Slim, despite their bravest efforts,
gave way to occasional expressions of the horror of the thing.
They had pounded upon the walls until they had been overcome with
despair, and then they had set to work digging with the only instruments
at hand–the bayonets on the German rifles.

Poor Slim! He showed his disappointment in every look and every action.
“What kind of a book did you see it in?” asked Jerry, in a tone almost
as sad as Slims.
“In the manual,” Slim groaned. “Herb Wallace showed it to me.”
“That settles it,” exclaimed Joe. “If Herb Wallace had a hand in it
anywhere theres something wrong. Ill tell you what well do, fellows.
Well go and ask the headmaster.”
Now the headmaster of Brighton had once been a boy himself. He could be
stern, even cruelly severe, when occasion demanded, but he was kind of
heart and broad of understanding.
Before him the three lads laid their case, as before the final tribunal.
“Hm,” said he, when all the details had been related and the
all-important information asked. “You say Herbert Wallace showed you
this in a manual?”
Slim solemnly affirmed that that was the case.
The headmaster pushed a button on the side of his desk and in a few
seconds his secretary, a big, bluff fellow, appeared.
“Bring Herbert Wallace here at once,” said the headmaster. And in five
more minutes, while the headmaster was shrewdly questioning the three
lads as to the seriousness of their determination to enlist, the
secretary returned, accompanied by young Wallace, flushed and
shamefaced.
“Well, Wallace,” said the principal of Brighton, “I hear youve been
studying up on military subjects. Intending to get into the fight?”
Herbert Wallace hung his head and muttered an unintelligible reply.
“Now look here, Wallace,” spoke the headmaster sternly, “where did you
get the military manual from which you gave Goodwin the information that
he could not pass the examination for the army?”
“I–I got it from the library, sir.”
“Got it without permission, too, didnt you?” pursued the headmaster.
“Yes, sir,” said Wallace, in confusion.
“And didnt know that it was out of date, and that the requirements were
completely changed after the United States entered this war, eh?”
“No, sir,” answered Wallace, on the verge of a breakdown.
“Ill decide upon your punishment later,” announced Wisu Mhz Terre Haute the headmaster.
“See me here at four oclock. Meanwhile, Wallace, be careful where you
get information, and be careful how you dispense it.”
And Herbert Wallace, utterly humiliated, was glad to flee from the room.
“I dont think,” said the headmaster, “that any of you will have
difficulty passing the examinations. I dislike to see you go, but you
speak the truth when you say that your country does need you, and I pay
a great tribute of respect to you for the patriotism and courage with
which you step forth to shoulder your obligations. Others already have
gone from Brighton. Still others will go in the future. God bless all of
you, and may you return safe and sound to reap the full benefits of the
democracy for which you are going to fight.”
The suspicion of tears dimmed the kindly eyes of the headmaster, and
each boy choked up as he bade him good-by.
But, after all, this was no time for sadness. Young gladiators were
going forth to the fray. And so we will skip over the farewells the
following day, in which the parents of each lad, with many a heartache
but never a word of discouragement, bade the boys Godspeed in the
service of their country.

These three coils are mounted with panel plugs which latter fit into a
stand, or mounting, so that the middle coil is fixed, that is,
stationary, while the two outside coils can be swung to and fro like a
door; this scheme permits small variations of coupling to be had
between the coils and this can be done either by handles or by means
of knobs on a panel board. While I have suggested the use of the
smallest size coils, you can get and use those wound for any wave
length you want to receive and when those are connected with
variometers and variable condensers, and with a proper aerial, you
will have a highly efficient receptor that will work over all ranges
of wave lengths. The smallest size coils cost about $1.50 apiece and
the mounting costs about $6 or $7 each.
The A Battery Potentiometer.–This device is simply a resistance like
the rheostat described in connection with the preceding vacuum tube
receiving sets but it is wound to 200 or 300 ohms resistance as
against 1-1/2 to 6 ohms of the rheostat. It is, however, used as well
as the rheostat. With a vacuum tube detector, and especially with one
having a gas-content, a potentiometer is very necessary as it is only
by means of it that the potential of the plate of the detector can be
accurately regulated. The result of proper regulation is that when the
critical potential value is reached there is a marked increase in the
loudness of the sounds that are emitted by the head phones.
As you will see from A in Fig. 51 it has three taps. The two taps
which are connected with the ends of the resistance coil are shunted
around the A battery and the third tap, which is attached to the
movable contact arm, is connected with the B battery tap, see B, at
which this battery gives 18 volts. Since the A battery gives 6 volts
you can vary the potential of the plate from 18 to 24 volts. The
potentiometer must never be shunted around the B battery or the latter
will soon run down. A potentiometer costs a couple of dollars.
[Illustration: (A) Fig. 51.–The Use of the Potentiometer.]
The Parts and How to Connect Them Up.–For this regenerative set you
will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2)
two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025
mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube
detector_; (6) a _6 volt A battery_; (7) _a rheostat_; (8) a
_potentiometer_; (9) an _18_ or _20 volt B battery_; (10) a _fixed
condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000
ohm head phones_.
To wire up the parts connect the leading-in wire of the aerial with
the primary coil, which is the middle one of the tuner, and connect
the other terminal with the ground. Connect the ends of the secondary
coil, which is the middle one, with the posts of the variable
condenser and connect one of the posts of the latter with one post of
the fixed .00025 mfd. condenser and the other post of this with the
grid; then shunt the grid leak around it. Next connect the other post
of the variable condenser to the - or _negative_ electrode of the _A
battery_; the + or _positive_ electrode of this to one terminal of the
detector filament and the other end of the latter to the electrode of
the A battery.
Now connect one end of the tickler coil with the detector plate and
the other post to the fixed .001 mfd. condenser, then the other end of
this to the positive or carbon pole of the B battery.
This done shunt the potentiometer around the A battery and run a wire
from the movable contact of it (the potentiometer) over to the 18 volt
tap, (see B, Fig. 51), of the B battery.
Finally, shunt the head phones and the .001 mfd. fixed condenser and
you are ready to try out conclusions.
A Regenerative Audio Frequency Amplifier Receiving Set.–The use of
amateur regenerative Wcpn 90.3 Mhz In Cleveland cascade audio frequency receiving sets is getting
to be quite common. To get the greatest amplification possible with
amplifying tubes you have to keep a negative potential on the grids.
You can, however, get very good results without any special charging
arrangement by simply connecting one post of the rheostat with the
negative terminal of the filament and connecting the _low potential_
end of the secondary of the tuning coil with the - or negative
electrode of the A battery. This scheme will give the grids a negative
bias of about 1 volt. You do not need to bother about these added
factors that make for high efficiency until after you have got your
receiving set in working order and understand all about it.

Operation of Autodyne and Heterodyne Receiving Sets.–On page 109
[Chapter VII] we discussed and at A in Fig. 36 is shown a picture of
two tuning forks mounted on sounding boxes to illustrate the principle
of electrical tuning. When a pair of these forks are made to vibrate
exactly the same number of times per second there will be a
condensation of the air between them and the sound waves that are sent
out will be augmented. But if you adjust one of the forks so that it
will vibrate 256 times a second and the other fork so that it will
vibrate 260 times a second then there will be a phase difference
between the two sets of waves and the latter will augment each other 4
times every second and you will hear these rising and falling sounds
as _beats_.
Now electric oscillations set up in two circuits that are coupled
together act in exactly the same way as sound waves produced by two
tuning forks that are close to each other. Since this is true if you
tune one of the closed circuits so that the oscillations in it will
have a frequency of a 1,000,000 and tune the other Weei 850 Khz Boston circuit so that the
oscillations in it have a frequency of 1,001,000 a second then the
oscillations will augment each other 1,000 times every second.
As these rising and falling currents act on the pulsating currents
from the B battery which flow through the detector tube and the
headphones you will hear them as beats. A graphic representation of
the oscillating currents set up by the incoming waves, those produced
by the heterodyne oscillator and the beats they form is shown in Fig.
73. To produce these beats a receptor can use: (1) a single vacuum
tube for setting up oscillations of both frequencies when it is called
an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum
tube for setting up the oscillations for the second circuit when it is
called a _heterodyne_ receptor.
[Illustration: Fig. 73.–How the Heterodyne Receptor Works.]
The Autodyne, or Self-Heterodyne Receiving Set.–Where only one vacuum
tube is used for producing both frequencies you need only a
regenerative, or feed-back receptor; then you can tune the aerial wire
system to the incoming waves and tune the closed circuit of the
secondary coil so that it will be out of step with the former by 1,000
oscillations per second, more or less, the exact number does not
matter in the least. From this you will see that any regenerative set
can be used for autodyne, or self-heterodyne, reception.

Connecting Up the Parts–Receiving Set No. 1.–For this set get (1) a
_crystal detector_, (2) a _two-slide tuning coil_, (3) a _fixed
condenser_, and (4) a pair of 2,000 ohm head phones. Mount the
detector on the right-hand side of a board and the tuning coil on the
left-hand side. Screw in two binding posts for the cord ends of the
telephone receivers at _a_ and _b_ as shown at A in Fig. 15. This done
connect one of the end binding posts of the tuning coil with the
ground wire and a post of one of the contact slides with the lightning
arrester or switch which leads to the aerial wire.
[Illustration: Fig. 15.–Top View of Apparatus Layout for Receiving
Set No. 1.]
[Illustration: (B) Fig. 15.–Wiring Diagram for Receiving Set No. 1.]
Now connect the post of the other contact slide to one of the posts of
the detector and the other post of the latter with the binding post
_a_, then connect the binding post _b_ to the ground wire and solder
the joint. Next connect the ends of the telephone receiver cord to the
posts _a_ and _b_ and connect a fixed condenser also with these posts,
all of which are shown in the wiring diagram at B, and you are ready
to adjust the set for receiving.
Receiving Set No. 2.–Use the same kind of a detector and pair of head
phones as for _Set No. 1_, but get (1) a _loose coupled tuning coil_,
and (2) a _variable condenser_. Mount the loose coupler at the back of
a board on the left-hand side and the variable condenser on the
right-hand side. Then mount the detector in front Whog-fm Mhz Ormond-by-the-sea of the variable
condenser and screw two binding posts, _a_ and _b_, in front of the
tuning coil as shown at A in Fig. 16.
[Illustration: Fig. 16.–Top view of Apparatus Layout for Receiving
Set No. 2.]
[Illustration: (B) Fig. 16.–Wiring Diagram for Receiving Set No. 2.]

A 50 to 100 Mile Wireless Telephone Transmitter–With Direct Current
Motor Generator.–As Knnz 940 Khz In Cedar City the initial source of current available is taken
to be a 110 or 220 volt direct current a motor-generator having an
output of 350 volts must be used as before. The only difference
between this transmitter and the preceding one is that: (1) two 5 watt
tubes are used, the first serving as an _oscillator_ and the second as
a _modulator_; (2) an _oscillation choke coil_ is used in the plate
circuit; (3) a _reactance coil_ or _reactor_, is used in the plate
circuit; and (4) a _reactor_ is used in the grid circuit.
The Oscillation Choke Coil.–You can make this choke coil by winding
about 275 turns of _No. 28 B. and S. gauge_ cotton covered magnet wire
on a spool 2 inches in diameter and 4 inches long. Give it a good
coat of shellac varnish and let it dry thoroughly.
The Plate and Grid Circuit Reactance Coils.–Where a single tube is
used as an oscillator and a second tube is employed as a modulator, a
_reactor_, which is a coil of wire wound on an iron core, is used in
the plate circuit to keep the high voltage direct current of the
motor-generator the same at all times. Likewise the grid circuit
reactor is used to keep the voltage of the grid at a constant value.
These reactors are made alike and a picture of one of them is shown in
Fig. 91 and each one will cost you $5.75.
[Illustration: Fig. 91.–Plate and Grid Circuit Reactor.]
Connecting up the Apparatus.–All of the different pieces of apparatus
are connected up as shown in Fig. 89. One of the ends of the secondary
of the induction coil, or the microphone transformer, or the magnetic
modulator is connected to the grid circuit and the other end to _clip
3_ of the tuning coil.
A 100 to 200 Mile Wireless Telephone Transmitter–With Direct Current
Motor Generator.–By using the same connections shown in the wiring
diagrams in Fig. 89 and a single 50 watt oscillator tube your
transmitter will then have a range of 100 miles or so, while if you
connect up the apparatus as shown in Fig. 90 and use two 50 watt tubes
you can work up to 200 miles. Much of the apparatus for a 50 watt
oscillator set where either one or two tubes are used is of the same
size and design as that just described for the 5 watt oscillator sets,
but, as in the C. W. telegraph sets, some of the parts must be
proportionately larger. The required parts are (1) the _50 watt tube_;
(2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the
_filament storage battery_; and (5) the _magnetic modulator_. All of
these parts, except the latter, are described in detail under the
heading of a _500 Mile C. W. Telegraph Transmitting Set_ in Chapter
XVI, and are also pictured in that chapter.

Realizing now that Lieutenant Mackinson must have lost consciousness,
and that moments might mean life or death to him, the captain worked
with feverish haste. He drove the heavy chisel into the crack between
the door and the jam, and then, standing off to get a wider swing with
the hammer, struck it sidewise.
A panel of the door cracked and loosened. Two more attempts and the
panel fell in strips to the floor. Thus given something for a grip-hold,
the captain, who was a massive man, took hold with both hands, put his
right foot against the wall, and, with one tremendous tug, into which
he threw the whole weight of his body, brought the entire door from its
hinges.
The captain went staggering backward from the force of his effort and
the weight of the door.
The unconscious form of Lieutenant Mackinson tumbled out upon the floor.
His face was almost blue from suffocation.
The captain sounded three short, sharp blasts upon a whistle which he
had taken from his pocket, and two oilers came running to the spot.
“Help us carry this man to fresh air immediately,” he ordered. “He has
been overcome.”
With one of the oilers carrying the lieutenant by the feet, and the
other man and Slim at either shoulder, the unconscious young officer was
carried up flight after flight of steps until, the captain leading the
way, they arrived at the promenade deck.
A seaman was dispatched for the ships surgeon, who arrived a few
minutes later to find the first-aid efforts of the four men just
bringing Lieutenant Mackinson back to consciousness.
As the physician forced some aromatic spirits of ammonia between his
lips the lieutenant opened his eyes and gazed about vaguely.
“Whats the matter?” he asked weakly; but before anyone could answer he
had relapsed again, and there was another wait of several minutes.
But this time the lieutenants mind was clearing.
“Somebody shoved me–in that closet,” he gasped, “and then–slammed
and–locked–the door.”
He recognized the captain and the doctor. As his eyes closed again he
added, in an almost inaudible whisper: “I was getting too close on
somebodys trail.”
The captain looked at the ships doctor significantly and dismissed the
two oilers with instructions to return to their duties.
“Found him locked in a small compartment down near the auxiliary engine
room,” the commander said briefly. “Hotter than blazes, and no air
whatever where he was. He made his whereabouts known by tapping a
message on a steam-pipe.”
“Hm,” said the doctor, whose youthful appearance might not give a
stranger a proper measure of his long and varied experience. “Nearly
suffocated, too. He couldnt have lasted there much longer. His heart
action is pretty weak even yet. Better have him removed to his bed, and
kept there for the rest of the day, at least.”
At that moment Jerry came hurrying down the deck. He was visibly
excited, but, unlike Slim, he did not forget that not only must a
soldier never permit his feelings to run away with Kkrs 97.3 Mhz In Davenport him, but that he must
be equally mindful of respect for superiors.
And so, even as two men carried Lieutenant Mackinson away, he remained
standing at salute, waiting for the captain to recognize him with a
return of the salute.
“And now what?” asked the captain.
Jerry stepped forward, with difficulty repressing his excitement.
“I stepped out of the wireless room for only a few moments,” he said.
“When I returned I found this lying upon the table.”
He opened his left hand. In it lay a piece of light chain, both ends
broken.
“Beside it,” he continued, “was this note.”
From his pocket he extracted a piece of paper, the edges of which were
roughly torn. He handed it to the captain, who read aloud:
“Let this be a warning that no further interference will be of
avail.”

A Super Loud Speaker.–This loud speaker, which is known as the
_Magnavox Telemegafone_, was the instrument used by Lt. Herbert E.
Metcalf, 3,000 feet in the air, and which startled the City of
Washington on April 2, 1919, by repeating President Wilsons _Victory
Loan Message_ from an airplane in flight so that it was distinctly
heard by 20,000 people below.
This wonderful achievement was accomplished through the installation
of the _Magnavox_ and amplifiers in front of the Treasury Building.
Every word Lt. Metcalf spoke into his wireless telephone transmitter
was caught and swelled in volume by the _Telemegafones_ below and
persons blocks away could hear the message plainly. Two kinds of these
loud speakers are made and these are: (1) a small loud speaker for the
use of operators so that headphones need not be worn, and (2) a large
loud speaker for auditorium and out-door audiences.
[Illustration: original © Underwood and Underwood. Worlds Largest
Loud Speaker ever made. Installed in Lytle Park, Cincinnati, Ohio, to
permit President Hardings Address at Point Pleasant, Ohio, during the
Grant Centenary Celebration to be heard within a radius of one
square.]
Either kind may be used with a one- or two-step amplifier or with a
cascade of half a dozen amplifiers, according to the degree of
loudness desired. The _Telemegafone_ itself is not an amplifier in the
true sense inasmuch as it contains no elements which will locally
increase the incoming current. It does, however, transform the
variable electric currents of the wireless receiving set into sound
vibrations in a most wonderful manner.
A _telemegafone_ of either kind is formed of: (1) a telephone receiver
of large proportions, (2) a step-down induction coil, and (3) a 6 volt
storage battery that energizes a powerful electromagnet which works
the diaphragm. An electromagnet is used instead of a permanent magnet
and this is energized by a 6-volt storage battery as shown in the
wiring diagram at A in Fig. 68. One end of the core of this magnet is
fixed to the iron case of the speaker and together these form the
equivalent of a horseshoe magnet. A movable coil of wire is supported
from the center of the diaphragm the edge of which is rigidly held
between the case and the small end of the horn. This coil is placed
over the upper end of the magnet and its terminals are connected to
the secondary of the induction coil. Now when the coil is energized by
the current from the amplifiers it and the core act like a solenoid in
that the coil tends to suck the core into it; but since the core is
fixed and the coil is movable the core draws the coil down instead.
The result is that with every variation of the current that flows
through the coil it moves up and down and pulls and pushes the
diaphragm down and up with it. The large amplitude of the vibrations
of the latter set up powerful sound waves which can be heard Wkxi-fm 107.5 Mhz In Magee several
blocks away from the horn. In this way then are the faint incoming
signals, speech and music which are received by the amplifying
receiving set reproduced and magnified enormously. The _Telemegafone_
is shown complete at B.
[Illustration: Fig. 68.–Magnavox Loud Speaker.]