In the January 14, 1946 issue of “Broadcasting” magazine, a short article was published “TINY RADIO SETS FOOLED NAZIS” as below:
“TINY radio receiving sets, carefully concealed from the Germans, brought 40000 inhabitants of the British Channel Island of Jersey the daily news from London through three years of Nazi occupation.
Radios were banned by the Germans in June 1942, and houses were searched regularly. Death was the penalty for having a set. And yet, reports the “London Daily Mail”, 90% of the homes had a crystal set made or designed by Arthur Roche, an electrician, that brought them BBC news every day.
One set was concealed in a clock. Another was hidden in a two-inch-long beef cubes tin in somebody’s larder. Scores of sets were built into match boxes. Smallest of all was one built inside a phonograph-needle box.
Mr. Roche, caught repairing sets, spent several months in jail. When he was released, he had to make houndreds of calls around the island to catch up on repairs”.
Articles describing how to make a detector receiver (or a crystal set in other words) yourself can be found in many pre-WW II popular magazines for radio amateurs. Here is one of them, with a diagram and description of a simple detector receiver, published in the July 1937 issue of “Radiocraft” magazine:
“ONCE AGAIN it’s the crysal set! Like a bobbing cork on a frothing, tumultuous sea, it persistently breaks through the turbulent waves of radio evolution to ride, mockingly, each crest. Multi-tube, complex radio receivers and the hundreds of modern new-fangled radio gadgets do not in the least detract from its popularity. In fact many ol’ timers revert to it occasionally for sheer relaxation from the present furious gait of radio.
Yet, for more than any other reason, the crystal set owes its survival to the fresh class of beginners which crops up each year. For them it is the starting point in radio – the first stepping stone. To them it demonstrates, in a simple, easily-understood manner the fundamental theory of radio.
The crystal set described here is novel in that is a modification of a simple, commercially-available unit – a “wavetrap”. Thr beginner, therefore, for his first set at least, need not be bothered with the construction of the actual components. Besides the wavetrap, the only other parts necessary are: a 0.006-mf. (or “0 point double-0 six microfarad“) fixed condenser, a galena crystal, and a crystal holder with attached “catwhisker”. (And so on…)”.
The simplest detector receiver contains only an input tunable oscillatory circuit for tuning to the frequency of the received radio station, an amplitude detector on a diode (in the old circuits it was designated as a вЂњcrystalвЂќ) and a capacitor that acts as a low-pass filter. High-frequency amplitude-modulated signals from an external wire antenna connected to the receiver are fed to the input oscillatory circuit, which extracts the signal of the desired station from them. This signal without amplification is then rectified by an amplitude detector and “smoothed” by a low-pass filter capacitor. The low-frequency envelope signal selected in this way activates the electromagnetic system of high-impedance headphones connected to the detector receiver. Even a schoolboy could make such a detector receiver with his own hands.
During the years of fascist occupation, the use of a detector receiver was perhaps the safest way to listen to the radio. The detector receiver does not need power supply, which means that you do not need to look for batteries for it. It is not difficult to make such a receiver, and at the same time it will be smaller in size than any of the vacuum tubes in the tube receivers, which allows it to be easily and quickly hidden in case of a sudden search. And, finally, the main thing is that the detector receiver was almost impossible to detect using a direction finder, which cannot be said about radio receivers made according to superheterodyne and especially regenerative circuits.
Here is how the English historian Paul Sanders wrote about this in his book “The British Channel Islands Under German Occupation 1940-1945”:
“Confiscating the sets was only half the problem, as – and this is a good guess – only half of the radio sets had been handed in. In no time radio listening parties were organised where groups of islanders would congregate to listen to the news. The Germans never tackled the problem of radio offences. They launched occasional campaigns against radio listeners (one is documented for November 1944), they gave wide publicity to the trials of prominent islanders caught with a radio to deter others, but islanders countered the threat by switching to the near undetectable crystal sets. After D-Day these became a standard feature, as the radio signals from liberated France could be picked with no problem”.
Copyright © Sergii Zadorozhnyi, 2007
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