March 1944 Radio-Craft
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
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Electronic counter-warfare (ECW)
has been around nearly as long as electronic warfare (EW)
itself. Controlling what a population hears on its radios is a fairly
simple process since overwhelming a commercial broadcast station
signal requires only a more powerful transmitter. It was commonplace
during wartime for an invading force to set up high power stations
in population centers to block signals meant to inform people of
aggressor activity, or even to play music
(a form of psychological warfare as well). Often, not only
was the possession of a personal radio verboten, but even getting
caught listening to one could spell real trouble. However, as with
Prohibition, the mere fact that something was outlawed did not
prevent a large percentage of the population from owning and/or
listening to broadcasts. This article by Hugo Gernsback proposes
a method for informing a local area of an impending invasion force
in order to forestall panic and irrational behavior - like rushing
out into the open and becoming easy fodder for enemy fighters. It
involves dropping by parachute many high power (500 watts or more),
expendable transmitters with pre-recorded messages playing. The
interesting aspect about his scheme is exploiting the short intended
lifetime by pushing electronic components well beyond their intended
parameters in order to save space, cost, and weight. His logic was
that it wouldn't matter if an output stage vacuum tube designed
for 10 watts and a 5 year lifespan was pushed to 100 watts and a
30 minute lifespan because the transmitters would never operate
for more than 15 minutes or so - depending on the altitude at which
they are deployed and the size of the parachute used.
Sky Radio Blankets Enemy
By Hugo Gernsback
is never more important than at the moment of invading occupied
country. Instructions to the populace and directives to guerrillas
or underground groups may be of great strategic importance at such
moments. This article suggests an effective method for communicating
with these friends and activating our potential allies.
The present war has brought forth many new techniques in warfare
and many other new and surprising ones will be originated before
the war is brought to a successful conclusion.
This war has also shown that during an invasion the population
is easily panicked, and very frequently this hampers the invasion
forces. During the invasion of France and the Low Countries, the
demoralized population, as a rule, tried to get out in the open
and started their trek away from the invasion forces. Much needless
hardship, casualties and senseless killing of non-combatants was
caused in this manner.
In the United Nations' future invasions, in Europe and in Japan
and elsewhere, it is often of great importance that the population
should be informed when the invasion has been started and that the
people be instructed what to do. At certain times military strategy
requires that the population stay where it is; in other instances
where a town is to be shelled it is necessary to inform the inhabitants
to evacuate immediately, if large casualties are not to result.
Naturally the enemy does not concern himself about such details,
particularly where occupied country is concerned and the ruling
military are not likely to give the occupied population much notice
or comfort. For that reason the Allied Nations must do so themselves.
Several means are open for them to do this. They can either use
existing broadcast facilities and warn the population over their
regular radio receivers, or otherwise shower the towns to be occupied
with leaflets from the air. These two methods leave much to be desired.
Frequently it is not possible to receive Allied broadcasts in occupied
territory because the enemy may "jam" the usual broadcast wave lengths,
making Allied transmissions almost impossible to be heard. If the
Allies use short-wave frequencies, they know in advance that this
will not be very effective because the population is under a death
penalty if they use short-wave receivers, or listen to short-wave
Leaflets are not very effective either because the people know
that this is coupled with large hazards; the occupation authority
is stern in this respect and will often execute those who pick up
Allied leaflets and hand them around.
A different method in spreading important information to the
populace of occupied territories is shown on our front cover, as
well as the accompanying illustrations on this page.
The means concerns itself with launching over the occupied territory
expendable radio means which can either be in the form of a floating
broadcast station, or by direct sound method.
Let us first consider the radio broadcast method. It has been
suggested at times that a fairly strong broadcast station be set
up in a bomber which can then broadcast to the population within
a radius of from 50 to 100 miles. This method is not too good because
an airplane during war conditions cannot circle too long over a
city without being shot down. Furthermore, too many airplanes will
be required to cover even a fair-sized territory.
method which I suggest is, as mentioned above, an expendable broadcast
station. This then would be a compact radio unit weighing not more
than 200 pounds. It is attached to a regulation parachute and is
discharged - preferably at night - over the towns and cities where
the best result can be expected. The cost of these units is not
too great and the units are constructed in such a manner that once
they have achieved their purpose, they are no longer needed and
can be destroyed by the enemy if necessary. Or, if desired, when
the unit touches the ground, it automatically is destroyed by fire
The modus operandi is as follows:
A large transport plane flying at night over a large city, for
instance, will discharge a dozen or more of these 500-watt broadcast
units. Before they leave the transport plane, the tuning dials are
set and locked in such a manner that the broadcasting will be done
on from three to six different wave lengths. These are the normal
broadcast wave lengths on which the particular population usually
tunes in on their regular broadcast frequencies, in order to listen
in lawfully to the various radio broadcasts of their territory.
By using a number of broadcast units, the entire city will be
completely blanketed so that anyone who listens will, without any
doubt, get the message that the Allies want the city to hear.
The units are discharged from the transport at a height of about
25,000 feet. The parachutes will require anywhere from 18 minutes
to 24 minutes to strike the ground, depending on the type of 'chute
used, as well as weather conditions. This gives sufficient time
for the broadcast, because the messages are usually short and no
long-winded propaganda is necessary for an invasion. For instance,
the message that the invasion has commenced, or that the population
should either remain in the city (or evacuate), and other military
information, is given in short crisp sentences. The message is recorded
on either the new cellophane tape or a magnetic wire recorder is
used. The message is repeated over and over until the broadcast
unit finally hits the ground.
The most important point to remember is that these units are powerful
and of a strength of about 500 watts. This gives the same effect
as if you had a 500-watt broadcast station right in your backyard!
Therefore the recorded voice will come in on the average radio set
like a thunderous voice of do doom, so loud that it will blanket
any other radio program that might be on the air at the time. It
will completely obliterate distant broadcast stations, and that
is the only purpose of the scheme. In the end the effort will be
worthwhile and the moderate cost of the few transmitters is cheap
for the purpose which they achieve. More important, the Allies will
not lose valuable lives because no one can get hurt, and it is doubtful
even that the transport which discharges the broadcast units will
be much molested at night and at a height of 25,000 feet.
It may be asked: "How can you put a 500-watt broadcast unit into
a weight of 200 pounds?"
The answer is that it must be remembered that this is an expendable
broadcast unit. Its total life is about 30 minutes. Consequently,
everything in the set is designed for this purpose; everything that
goes into it is naturally as light as it can be made. We have already
valuable experience in this line with meteorological Radio-Sonde
transmitters which weigh only a few pounds and are sent into the
stratosphere. In our 500-watt broadcast unit, we overload all the
tubes to three or four times their normal capacity. That means that
we get an enormous gain in output. We can in this fashion increase
the plate current in the output enormously simply because the unit
has such a short life. We also get the maximum power out of the
batteries which are to operate the unit.
Amateurs many years ago learned that a remarkable increase in
power and transmitting efficiency could be obtained by disregarding
manufacturers' tube ratings. So-called 5-watt tubes were loaded
to 50 watts. But the amateur never lived, who, to increase his transmitting
efficiency, loaded his tubes and other equipment to a 20-minute
life expectancy. Needless to say, fantastic increases of power may
be expected from such loading, and this is the secret of our great
power with equipment of such moderate size and weight.
The illustrations show how the broadcast waves are radiated.
Instead of using the ordinary 'chute guide lines, we substitute
stranded wire. This gives us the antenna. For the counterpoise,
we use a phosphor-bronze flexible wire, weighted at the end to steady
it. The broadcast frequency will not "wander" too much with this
arrangement and should therefore remain fairly fixed and steady.
Within the broadcast unit, we have the record with the message,
which weighs only a few pounds and is of not much consequence as
far as weight is concerned.
If we do not wish to use a radio broadcast unit for certain reasons,
we have the alternative of using a Power Sound Unit, as is also
illustrated. The working of this is parallel to the radio unit,
except that the broadcasting is done by direct sound waves, just
as any public address outfit would do. In this case, too, the power
sound unit is also "loaded" to full capacity. In other words, it
is forced far beyond its normal rating, because in this case also
its total life is only less than half an hour. For that reason,
the tubes and the output are forced to just below the burnout point.
The power sound unit, as well as the 500-watt broadcast unit,
both have timing mechanisms. Thus, in the case of the power sound
unit, it does not commence the blasting of the message until it
reaches a point about 3,000 or 4,000 feet up - then continues to
repeat it in a stentorian voice so loud that people indoors can
hear it clearly. As the unit descends further down, its voice becomes
still stronger by the second until finally everyone in the neighborhood
will have little trouble in hearing the intended message.
I have dwelt in this article only on the more obvious features
of the idea. There are a number of technical details in both methods
that must be worked out, and experience will teach exactly how to
obtain the maximum results from either outfit.
It goes without saying that each of the two methods must use
recordings in the language of the populace for whom the message
is intended. For the French occupied territory, the language would
be French; in China, it will be Chinese, etc.
Yes, some of the units will be shot down if there are enemy fighter
planes around. That is to be expected. During war one cannot expect
to get 100% results from any means and that holds true for this
scheme as well.
It should, however, prove a valuable adjunct for our forces.
Posted October 7, 2014