<h2><SPAN name="CHAPTER_X" id="CHAPTER_X">CHAPTER X</SPAN><br/> <span class="subhead"><span class="smcap">Talking in the Sky</span></span></h2>
<p class="drop-cap3"><span class="smcap1">In</span> one field of war invention the United States
held almost a monopoly and the progress
Americans achieved was epoch-making.</p>
<p>Before the war, an aviator when on the wing
was both deaf and dumb. He could communicate
with other airplanes or with the ground
only by signal or, for short distances, by radiotelegraphy,
but he could not even carry on
conversation with a fellow passenger in the
machine without a speaking-tube fitted to mouth
and ears so as to cut out the terrific roar of
his own engine. Now the range of his voice
has been so extended that he can chat with fellow
aviators miles away. This remarkable
achievement and many others in the field of
radio-communication hinge upon a delicate electrical
device invented by Deforest in 1906 and
known as the "audion." For years this instrument
was used by radiotelegraphers without<span class="pagenum"><SPAN name="Page_185" id="Page_185">185</SPAN></span>
a real appreciation of its marvelous possibilities,
and, as a matter of fact, in its earlier
crude form it was not capable of performing the
wonders it has achieved since it was taken over
and developed by the engineers of the Bell Telephone
System.</p>
<h3>THE AUDION</h3>
<p>Although the audion is familiar to all amateur
radio-operators, we shall have to give a
brief outline of its construction and operation
for the benefit of those who have not had the
opportunity to dabble in wireless telegraphy.</p>
<p>The audion is a small glass bulb from which
the air is exhausted to a high degree of vacuum.
The bulb contains three elements. One is a
tiny filament which is heated to incandescence
by a battery, so that it emits negatively charged
electrons. The filament is at one side of the
bulb and at the opposite side there is a metal
plate. When the plate and the filament are
connected with opposite poles of a battery, there
is a flow of current between them, but because
only negative electrons are emitted by the
filament, the current will flow only in one direction—that
is, from the plate to the filament.<span class="pagenum"><SPAN name="Page_186" id="Page_186">186</SPAN></span>
If the audion be placed in the circuit of an alternating-current
generator, it will let through
only the current running in one direction.
Thus it will "rectify" the current or convert
alternating current into direct current.</p>
<p>But the most important part of the audion, the
part for which Deforest is responsible, is the
third element, which is a grid or flat coil of
platinum wire placed between the filament and
the plate. This grid furnishes a very delicate
control of the strength of the electric current
between plate and filament. The slightest
change in electric power in the grid will produce
large changes of power in the current
flowing through the audion. This makes it
possible to magnify or amplify very feeble electric
waves, and the extent to which the amplifying
can be carried is virtually limitless, because
a series of audions can be used, the current
passing through the first being connected
with the grid of the next, and so on.</p>
<h3>TALKING FROM NEW YORK TO SAN FRANCISCO</h3>
<p>There is a limit to which telephone conversations
can be carried on over a wire, unless there
is some way of adding fresh energy along the<span class="pagenum"><SPAN name="Page_187" id="Page_187">187</SPAN></span>
line. For years all sorts of experiments were
tried with mechanical devices which would receive
a telephone message and send it on with
a fresh relay of current. But these devices distorted
the message so that it was unintelligible.
The range of wire telephony was greatly increased
by the use of certain coils invented by
Pupin, which were placed in the line at intervals;
but still there was a limit to which conversation
could be carried on by wire and it
looked as if it would never be possible to telephone
from one end of this big country of ours
to the other. But the audion supplied a
wonderfully efficient relay and one day we
awoke to hear San Francisco calling, "Hello,"
to New York.</p>
<p>Used as a relay, the improved audion made it
possible to pick up very faint wireless-telegraph
messages and in that way increased the
range of radio outfits. Messages could be received
from great distances without any extensive
or elaborate aërials, and the audion could
be used at the sending-station to magnify the
signals transmitted and send them forth with
far greater power.</p>
<p>Having improved the audion and used it successfully<span class="pagenum"><SPAN name="Page_188" id="Page_188">188</SPAN></span>
for long-distance telephone conversation
over wires, the telephone company began
to experiment with wireless telephony. They
believed that it might be possible to use radiotelephony
in places where wires could not be
laid. For instance, it might be possible to talk
across the Atlantic.</p>
<p>But before we go farther, just a word of explanation
concerning radiotelegraphy and radiotelephony
for the benefit of those who have
not even an elementary knowledge of the
subject.</p>
<h3>SIMPLE EXPLANATION OF RADIOTELEGRAPHY</h3>
<p>Suppose we should set up two stakes in a pond
of water, at some distance from each other, and
around each we set a ring-shaped cork float. If
we should move one of these floats up and down
on its stake, it would produce ripples in the
water which would spread out in all directions
and finally would reach the opposite stake and
cause the float there to bob up and down in
exactly the same way as did the float moved
by hand. In wireless telegraphy the two stakes
are represented by antennæ or aërials and the
cork floats are electric charges which are sent<span class="pagenum"><SPAN name="Page_189" id="Page_189">189</SPAN></span>
oscillating up and down the antennæ. The oscillations
produced at one aërial will set up
electro-magnetic waves which will spread out
in all directions in the ether until they reach a
receiving-aërial, and there they will produce
electric oscillations similar to the ones at the
transmitting-antenna.</p>
<p>Telegraph signals are sent by the breaking
up of the oscillations at the transmitting-station
into long and short trains of oscillations corresponding
to the dots and dashes of ordinary
wire telegraphy. In other words, while the
sending-key is held down for a dash, there will
be a long series of oscillations in the antenna,
and for the dot a short series, and these short
and long trains of waves will spread out to the
receiving-aërial where they will reproduce the
same series of oscillations. But only a small
part of the energy will act on the receiving-aërial
because the waves like those on the pond
spread in all directions and grow rapidly
weaker. Hence the advantage of an extremely
delicate instrument like the audion to amplify
the signals received.</p>
<p>The oscillations used in wireless telegraphy
these days are very rapid, usually entirely too<span class="pagenum"><SPAN name="Page_190" id="Page_190">190</SPAN></span>
rapid, to affect an ordinary telephone receiver,
and if they did they would produce a note of
such high pitch that it could not be heard. So
it is customary to interrupt the oscillations,
breaking them up into short trains of waves,
and these successive trains produce a note of
low enough pitch to be heard in the telephone
receiver. Of course the interruptions are of
such high frequency that in the sending of a dot-and-dash
message each dot is made up of a great
many of the short trains of waves.</p>
<p>Now in radiotelephony it is not necessary to
break up the oscillations, but they are allowed to
run continuously at very high speed and act as
carriers for other waves produced by speaking
into the transmitter; that is, a single speech-wave
would be made up of a large number
of smaller waves. To make wireless telephony
a success it was necessary to find some
way of making perfectly uniform carrier-waves,
and then of loading on them waves of speech.
Of course, the latter are not sound-waves, because
they are not waves of air, but they are
electro-magnetic waves corresponding exactly
to the sound-waves of air and at the receiving-end
they affect the telephone receiver in the<span class="pagenum"><SPAN name="Page_191" id="Page_191">191</SPAN></span>
same way that it is affected by the electric
waves which are sent over telephone wires. The
telephone engineers found that the audion
could be used to regulate the carrier-waves and
also to superpose the speech-waves upon them,
and at the receiving-station the audion was used
to pick up these waves, no matter how feeble
they might be, and amplify them so that they
could be heard in a telephone receiver.</p>
<h3>TALKING WITHOUT WIRES</h3>
<p>Attempts at long-distance talking without
wires were made from Montauk Point, on the
tip of Long Island, to Wilmington, Delaware,
and they were successful. This was in 1915.
The apparatus was still further improved and
then the experiment was tried of talking from
the big Arlington station near Washington to
Darien, on the Isthmus of Panama. This was
a distance of twenty-one hundred miles, and
speech was actually transmitted through space
over that great distance. That having proved
successful, the next attempt was to talk from
Arlington to Mare Island and San Diego, on the
Pacific Coast, a distance of over twenty-five
hundred miles. This proved a success, too, and<span class="pagenum"><SPAN name="Page_192" id="Page_192">192</SPAN></span>
it was found possible even to talk as far as
Honolulu.</p>
<div class="center"><div class="container">
<div id="ip_192" class="figleft" style="width: 247px;">
<ANTIMG src="images/i_192.jpg" width-obs="247" height-obs="272" alt="" /><br/>
<div class="captionl">(C) G. V. Buck</div>
<div class="caption0">Radio Head-gear of an Airman</div>
</div>
<div id="ip_192b" class="figright" style="width: 348px;">
<ANTIMG src="images/i_192b.jpg" width-obs="348" height-obs="274" alt="" /><br/>
<div class="captionl">(C) G. V. Buck</div>
<div class="caption0">Carrying on Conversation by Radio with an Aviator
Miles Away</div>
</div></div>
</div>
<p>The engineers now felt confident that they
could talk across the Atlantic to Europe, and
so in October of 1915 arrangements were made
to conduct experiments between Arlington and
the Eiffel Tower in Paris. Although the war
was at its height, and the French were straining
every effort to hold back the Germans at
that time, and although there were constant demands
for the use of radiotelegraphy, the
French showed such an appreciation of science
that they were willing to lend their aid to these
experiments. The Eiffel Tower could be used
only for short periods of time, and there was
much interference from other high-powered
stations. Nevertheless, the experiment proved
perfectly successful, and conversation was carried
on between our capital and that of France,
a distance of thirty-six hundred miles. At the
same time, an operator in Honolulu, forty-five
hundred miles away, heard the messages, and
so the voice at Arlington carried virtually one
third of the way around the globe. After that
achievement, there was a lull in the wireless-telephone
experiments because of the war.</p>
<p><span class="pagenum"><SPAN name="Page_193" id="Page_193">193</SPAN></span>
But there soon came an opportunity to make
very practical use of all the experimental work.
As soon as there seemed to be a possibility that
we might be drawn into the war, the Secretary
of the Navy asked for the design of apparatus
that would make it possible for ships to converse
with one another and with shore stations. Of
course all vessels are equipped with wireless-telegraph
apparatus, but there is a decided advantage
in having the captain of one ship talk
directly with the captain of another ship, or
take his orders from headquarters, with an
ordinary telephone receiver and transmitter.
A special equipment was designed for battle-ships
and on test it was found that ships could
easily converse with one another over a distance
of thirty-five miles and to shore stations from
a distance of a hundred and seventy-five miles.
The apparatus was so improved that nine conversations
could be carried on at the same time
without any interference of one by the others.</p>
<div id="ip_193" class="figcenter" style="width: 600px;">
<ANTIMG src="images/i_193.jpg" width-obs="600" height-obs="383" alt="" /><br/>
<div class="captionl">(C) American Institute of Electrical Engineers</div>
<div class="caption0">Long Distance Radio Apparatus at the Arlington (Va.) Station, with enlarged view of the
Type of Vacuum Tube used</div>
</div>
<p>When it became certain that we should have
to enter the war, there came a call for radiotelephone
apparatus for submarine-chasers, and
work was started on small, compact outfits for
these little vessels.</p>
<p><span class="pagenum"><SPAN name="Page_194" id="Page_194">194</SPAN></span></p>
<h3>RADIOTELEPHONES FOR AIRPLANES</h3>
<p>Then there was a demand for radiotelephone
apparatus to be used on airplanes. This was a
much more complicated matter and called for a
great deal of study. The way in which problem
after problem arose and was solved makes an
exceedingly interesting narrative. It seemed
almost absurd to think that a delicate radiotelegraph
apparatus could be made to work in
the terrific noise and jarring of an airplane.
The first task was to make the apparatus noise-proof.
A special sound-proof room was constructed
in which a noise was produced exactly
imitating that of the engine exhaust of an airplane
engine. In this room, various helmets
were tried in order to see whether they would
be proof against the noise, and finally a very
suitable helmet was designed, in which the telephone
receiver and transmitter were installed.</p>
<p>By summer-time the work had proceeded so
far that an airplane equipped with transmitting-apparatus
could send spoken messages to an
operator on the ground from a distance of two
miles. The antenna of the airplane consisted
of a wire with a weight on the lower end, which<span class="pagenum"><SPAN name="Page_195" id="Page_195">195</SPAN></span>
hung down about one hundred yards from the
body of the machine. But a trailing antenna
was a nuisance in airplane manœuvers, and it
was also found that the helmet which was so
satisfactory in the laboratory was not just the
thing for actual service in an airplane. It had
to fit very tightly around the ears and the
mouth, and as the airplane went to high altitudes
where the air-pressure was much lower
than at the ground level, painful pressures were
produced in the ears which were most annoying.
Aside from that, in actual warfare airplanes
have to operate at extreme heights,
where the air is so rare that oxygen must be
supplied to the aviators, and it was difficult to
provide this supply of oxygen with the radio
helmet tightly strapped to the head of the operator.
But after considerable experiment, this
difficulty was overcome and also that of the
varying pressures on the ears.</p>
<p>Another great difficulty was to obtain a steady
supply of power on the airplane to operate the
transmitting-apparatus. It has been the practice
to supply current on airplanes for wireless-telegraph
apparatus by means of a small electric
generator which is revolved by a little propeller.<span class="pagenum"><SPAN name="Page_196" id="Page_196">196</SPAN></span>
The propeller in turn is revolved by
the rush of air as it is carried along by the plane.
But the speed of the airplane varies considerably.
At times, it may be traveling at only
forty miles per hour, and at other times as high
as one hundred and sixty miles per hour, so
that the little generator is subjected to great
variations of speed and consequent variations
of voltage. This made it impossible to produce
the steady oscillations that are required in wireless
telephony. After considerable experiment,
a generator was produced with two windings,
one of which operated through a vacuum tube,
somewhat like an audion, and to resist the increase
of voltage produced by the other winding.</p>
<p>Then another trouble developed. The sparks
produced by the magneto in the airplane motor
set up electro-magnetic waves which seriously
affected the receiving-instrument. There was
no way of getting rid of the magneto, but the
wires leading from it to the engine were incased
in metal tubes which were grounded at
frequent intervals, and in that way the trouble
was overcome to a large extent. The magnetos
themselves were also incased in such a way that<span class="pagenum"><SPAN name="Page_197" id="Page_197">197</SPAN></span>
electro-magnetic waves would not be radiated
from them.</p>
<p>Instead of using trailing wires which were
liable to become entangled in the propeller, the
antenna was extended from the upper plane to
the tail of the machine, and later it was found
that by using two short trailing antennæ one
from each tip of the wings, the very best results
could be obtained. Still another development
was to embed the antenna wires in the wings
of the plane.</p>
<p>It was considered necessary, if the apparatus
was to be practicable, to be able to use it over
a distance of two thousand yards, but in experiments
conducted in October, 1917, a couple of
airplanes were able to talk to each other when
twenty-three miles apart, and conversations
were carried on with the ground from a distance
of forty-five miles. The conditions under which
these distances were attained were unusual, and
a distance of three miles was accepted as a
standard for communication between airplanes.
The apparatus weighed only fifty-eight pounds
and it was connected with both the pilot and the
observer so that they could carry on conversations<span class="pagenum"><SPAN name="Page_198" id="Page_198">198</SPAN></span>
with each other and could both hear
the conversation with other airplanes or the
ground. As a matter of fact, airplanes with
standard apparatus are able to talk clearly to a
distance of five miles and even to a distance of
ten miles when conditions are favorable, and
they can receive messages from the ground over
almost any distance.</p>
<p>A similar apparatus was constructed for submarine-chasers
with a standard range of conversation
of over five miles. Apparatus was
manufactured in large quantities in this country
and all our submarine-chasers were equipped
with it, as well as a great many of our airplanes
and seaplanes, and we furnished radio-apparatus
sets to our allies which proved of immense
value in the war. This was particularly
so in the case of submarine detection, when it
was possible for a seaplane or a balloon to report
its findings at once to submarine-chasers
and destroyers, and to guide them in pursuit of
submarines.</p>
<p>The improved audion holds out a wonderful
future for radiotelephony. For receiving,
at least, no elaborate aërial will be needed, and
with a small loop of wire, an audion or two,<span class="pagenum"><SPAN name="Page_199" id="Page_199">199</SPAN></span>
and simple tuning-apparatus any one can hear
the radio gossip of the whole world.</p>
<h3>TELEGRAPHING TWELVE HUNDRED WORDS PER MINUTE</h3>
<p>Some remarkable advances were made in
telegraphy also. During the war and since,
messages have been sent direct from Washington
to all parts of the world. In the telegraph
room operators are connected by wire with the
different radio stations along the coast and they
can control the radio transmitters, sending their
messages without any repeating at the radio
stations. Long messages are copied off on a
machine something like a type-writer, which,
however, does not make type impressions, but
cuts perforations in a long sheet of paper. The
paper is then run through a transmitter at a
high speed and the message is sent out at a rate
of as much as twelve hundred words a minute.
At the receiving-station, the message is received
photographically on a strip of paper. The receiving-instrument
has a fine quartz thread in
it, which carries a tiny mirror. A beam of light
is reflected from the mirror upon the strip of
sensitized paper. The radio waves twist the<span class="pagenum"><SPAN name="Page_200" id="Page_200">200</SPAN></span>
quartz thread ever so slightly, which makes the
beam of light play back and forth, but of course
the motion is greatly magnified. In this way
a perfect record is made of the message in dots
and dashes, which are translated into the corresponding
letters of the alphabet.</p>
<h3>DETECTING RADIO SPIES</h3>
<p>There is another radio invention which we
contributed during the war, that proved of utmost
service in thwarting German spies and
which is going to prove equally valuable in time
of peace. Although a war invention, its peacetime
service will be to save lives. It is a very
simple matter to rig up a wireless-telegraph
system that will send messages to a considerable
distance, and simpler still to rig up a receiving-set.
European governments have always discouraged
amateur radiotelegraphy, but in this
country restrictions used to be so slight that
almost any one could set up and use a radio
set, both for receiving and for transmitting.
When we entered the war we were glad that
amateurs had been encouraged to play with
wireless, because we had hundreds of good radio<span class="pagenum"><SPAN name="Page_201" id="Page_201">201</SPAN></span>
operators ready to work the sets which the army
and the navy needed.</p>
<p>But this was a disadvantage, too. Many
operators were either Germans or pro-Germans
and were only too willing to use their radio experience
in the interest of our enemies. It was
a simple matter to obtain the necessary apparatus,
because there was plenty of it to be had
everywhere. They could send orders to fellow
workers and receive messages from them, or
they could listen to dispatches sent out by the
government and glean information of great military
and naval importance. The apparatus
could easily be concealed: a wire hung inside
a chimney, a water-pipe, even a brass bedstead
could be used for the receiving-aërial. It was
highly important that these concealed stations
be located, but how were they to be discovered?</p>
<h3>THE WIRELESS COMPASS</h3>
<p>This problem was solved very nicely. The
audion had made it possible to receive radio
signals on a very small aërial. In place of the
ordinary stationary aërial a frame five feet
square was set up so that it could be turned<span class="pagenum"><SPAN name="Page_202" id="Page_202">202</SPAN></span>
to any point of the compass. A few turns of
copper-bronze wire were wound round it. This
was called the "wireless compass." It was set
up on the roof of the radio station and concealed
within a cupola. The shaft on which it was
mounted extended down into the operating-room
and carried a wheel by which it could be
turned. On the shaft was a circular band of
aluminum engraved with the 360 degrees of the
circle, and a couple of fixed pointers indicated
true north and south. Now when a signal was
received by the aërial, if it struck the frame
edgewise the radio waves would reach one side
before they would the other. Taking a single
wave, as shown by the drawing, <SPAN href="#ip_204">Fig. 11</SPAN>, we
see that while the crest of the wave is sweeping
over one side of the frame, the trough of the
wave is passing the other side. Two currents
are set up in the radio compass, one in the
wires at the near side of the compass, and another
in the wires at the far side of the compass.
As these currents are of the same direction,
they oppose each other and tend to kill
each other off, but one of the currents is
stronger than the other because the crest of the
wave is sweeping over that side, while the<span class="pagenum"><SPAN name="Page_204" id="Page_204">204</SPAN></span>
trough of the wave is passing over the other.
The length of the wave may be anything, but
always one side will be stronger than the other,
and a current equal in strength to the difference
between the two currents goes down into the
operating-room and affects the receiver. Now
when the compass is set at right angles to the
oncoming wave, both sides are affected simultaneously
and with the same strength, so that
they kill each other off completely, and no
current goes down to the receiver. Thus the
strength of the signal received can be varied
from a maximum, when the compass is parallel
to the oncoming waves, to zero, when it is at
right angles to them.</p>
<div id="ip_204" class="figcenter" style="width: 316px;">
<ANTIMG src="images/i_203.jpg" width-obs="316" height-obs="397" alt="" /><br/>
<div class="captionl">Courtesy of the "Scientific American"</div>
<div class="caption0"><span class="smcap">Fig. 11.</span> The radio compass turned parallel to an oncoming
electro-magnetic wave</div>
</div>
<p>To find out where a sending-station is, the
compass is turned until the loudest sound is
heard in the receiver and then the compass
dial shows from what direction the signals are
coming. At the same time, another line on the
signals will be found by a second station with
another compass. These directions are traced
on a map; and where they meet, the sending-station
must be located.</p>
<p>With this apparatus it was possible to locate
the direction of the station within a degree.</p>
<p><span class="pagenum"><SPAN name="Page_205" id="Page_205">205</SPAN></span>
After the station had been located as closely
as possible in this way, a motor-truck was sent
out in which there was a concealed radio compass.
The truck would patrol the region
located by the fixed compasses, and with it the
position of the concealed station could be determined
with perfect accuracy. The building
would be raided and its occupants jailed and the
radio equipment confiscated.</p>
<p>Even receiving-sets were discovered with the
portable compass, but to find them was a far
more difficult task. For the receiving of messages
from distant points without a conspicuous
aërial an audion would have to be used and this
would set up feeble oscillations which could be
picked up under favorable conditions by the
portable compass.</p>
<h3>PILOTING SHIPS INTO PORT</h3>
<p>And now for the peace-time application of all
this. If the compass could be used to find those
who tried to hide, why could it not also be used
to find those who wished to be found?</p>
<p>Every now and then a ship runs upon the
rocks because it has lost its bearings in the fog.
But there will be no excuse for such accidents<span class="pagenum"><SPAN name="Page_206" id="Page_206">206</SPAN></span>
now. A number of radio-compass stations have
been located around the entrance and approach
to New York Harbor. Similar stations have
been, or soon will be, established at other ports.
As soon as a ship arrives within fifty or a
hundred miles of port she is required to call for
her bearings. The operator of the control station
instructs the ship to send her call letters
for thirty seconds, and at the same time notifies
each compass station to get a bearing on the
ship. This each does, reporting back to the control
station. The bearings are plotted on a
chart and inside of two minutes from the time
the ship gives her call letters, her bearing is
flashed to her by radio from the control station.</p>
<div id="ip_206" class="figcenter" style="width: 491px;"><SPAN href="images/i_207l.jpg">
<ANTIMG src="images/i_207.jpg" width-obs="491" height-obs="306" class="lborder" alt="" /></SPAN><br/>
<div class="captionl">Courtesy of the "Scientific American"</div>
<div class="captionh0"><span class="smcap">Fig. 12.</span> Approaches to New York Harbor showing location of three radio compass stations
and how position of a ship sending signals from A may be determined</div>
</div>
<p>The chart on which the plotting is done is
covered with a sheet of glass. Holes are
pierced through the glass at the location of each
compass station. See <SPAN href="#ip_206">Fig. 12.</SPAN> On the chart,
around each station, there is a dial marked off
in the 360 degrees of the circle. A thread
passes through the chart and the hole in the
glass at each station. These threads are attached
to weights under the chart. When a
compass station reports a bearing, the thread
of that station is pulled out and extended across<span class="pagenum"><SPAN name="Page_208" id="Page_208">208</SPAN></span>
the corresponding degree on the dial. The
same is done as each station reports and where
the threads cross, the ship must be located.</p>
<p>Not only can the direction-finder be used to
pilot a ship into a harbor, but it will also serve
to prevent collisions at sea, because a ship
equipped with a radio compass can tell whether
another ship is coming directly toward her.</p>
<p>And so as one of the happy outcomes of the
dreadful war, we have an apparatus that will
rob sea-fogs of their terrors to navigation.</p>
<hr />
<p><span class="pagenum"><SPAN name="Page_209" id="Page_209">209</SPAN></span></p>
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