A foxhole radio is a makeshift radio that was used by soldiers in World War II. The foxhole radio differed from the crystal radio. A razor blade and pencil were used as a diode in a foxhole radio while a piece of crystal is used as a diode in a crystal radio.
The foxhole radio is like a crystal set, in that it does not require an external power source. The radio is powered by the radio signal it receives. This made the foxhole radio ideal for prisoners of war (POW). Prisoners of war made these radios to keep up with current events. Generally, this radio named after foxholes—small man-made earthen shelters along defensive lines during the war. So, any radio built during the war could be considered a foxhole radio, ideally so if it doesn't use semiconductors or a power supply.
During World War II, Toivo Kujanpaa, stationed at Anzio Beachhead, used a Foxhole radio to receive German propaganda programs. The propaganda programs were directed towards American military from an Axis station in Rome. American G.I.'s in Italy would put several radios together. The G.I.s would listen at night near the front lines to phonograph records played on a radio station in Rome. You could usually hear a radio station on a foxhole radio if you lived twenty five or thirty miles away.
Foxhole radios were built using numerous designs. Most used a double edge razor blade with a wire running from each edge between the headphone terminals and antenna, and a pencil lead sitting on the blade. Most of these wartime sets did not have a slider-tuner arm. Without a tuner, they could only tune to one frequency. Richard Lucas, a POW in Vietnam, constructed a radio in camp and built his own earphones. Richard built his earphones by binding four nails together with cloth then winding wire and dripping wax over the turns. After about ten layers of wire he placed it in a piece of bamboo. A tin can lid was placed over the coil of wire. The listener connected the improvised earphone to the foxhole radio and received three radio stations. The best listening was at night, according to Lucas.
These radio receivers are only crudely tuned to a frequency by the aerial and coil. The radio frequency signal, received by the aerial, causes an electrical current to oscillate back and forth in the coil. To receive an AM (amplitude modulation) radio transmission the signal must be rectified to recover the audio modulation of the signal. The safety razor and graphite point of the pencil form a crude single-diode rectifier, the oxide layer on the razor blade and the point contact of the pencil lead only allowing the current to flow in one direction. After rectification by this improvised diode, the audio signal drives the headphones.
- Gould Jack, 1958 "How to build a foxhole radio." All about Radio and Television. Random House. Pages 58-72.
- R G Wells: The need for a radio., Oral History Research Unit at Bournemouth University, retrieved 2011-10-19
- Make a crystal radio, wikihow.com, retrieved 2011-10-21
- foxehole, bizarrelabs.com, retrieved 2011-10-19