File:Foxhole radio from WW2.jpg

Summary

A "foxhole radio" receiver from World War 2. Not allowed powered radio receivers, which could give away their position to the enemy by the signal radiated by their <a href="https://en.wikipedia.org/wiki/local_oscillator" class="extiw" title="w:local oscillator">local oscillator</a>, American soldiers in World War 2 constructed their own homemade <a href="https://en.wikipedia.org/wiki/crystal_radio" class="extiw" title="w:crystal radio">"crystal" radios</a> so they could listen to news and music. The tuning coil (cylinder) was attached to a long wire antenna and ground. For a detector, this used a graphite pencil lead attached to the point of a safety pin, pressing against a "blue" steel <a href="https://en.wikipedia.org/wiki/razor_blade" class="extiw" title="w:razor blade">razor blade</a>. The graphite point touching the <a href="https://en.wikipedia.org/wiki/semiconductor" class="extiw" title="w:semiconductor">semiconducting</a> oxide coating of the razor blade formed a crude point contact <a href="https://en.wikipedia.org/wiki/semiconductor_diode" class="extiw" title="w:semiconductor diode">semiconductor diode</a> which <a href="https://en.wikipedia.org/wiki/rectification" class="extiw" title="w:rectification">rectified</a> the radio signal from the coil, extracting the audio signal from the radio frequency <a href="https://en.wikipedia.org/wiki/carrier_wave" class="extiw" title="w:carrier wave">carrier wave</a>, which was listened to with the earphones. The operator dragged the pencil lead across on the razor blade's surface until a sensitive spot was found and the station was heard, which required a lot of patience. The source says this foxhole radio belonged to Leutenant M. L. Rupert and was used on the Italian front.

Licensing

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