A foxhole radio is a makeshift radio that was first used by soldiers in World War II, specifically at Anzio, spreading later across the European and Pacific theaters. There were different versions of the foxhole radio; all used a safety razor blade as a radio wave detector. The "classic" foxhole radio was configured like a crystal radio, with the blade acting as the crystal and a wire, safety pin, or, later, a pencil serving as the cat's whisker. Other versions were similar to the microphone detector of David Edward Hughes, rediscovered by Harry Shoemaker and Walter Wentworth Massie, popular among amateurs in the early days of radio. They were named, likely by the press, for the foxhole, a defensive fighting position developed before and during the war.
Soldiers were not allowed to have ordinary vacuum tube radios because the regenerative and superheterodyne receivers of the time radiated radio waves which could give away their position to the enemy. The foxhole radio was a crude crystal radio which was powered by the radio waves of the station being received, so it did not radiate a signal, and also did not require batteries to run, making it ideal for troops on the move.
The maker of the first foxhole radio is unknown, but it was almost certainly invented by a soldier stationed at the Anzio beachhead during the stalemate of February – May 1944. One of the first newspaper articles about a foxhole radio ran in the New York Times April 29, 1944. That radio was built by Private Eldon Phelps of Enid, Oklahoma, who later claimed to have invented the design. It was fairly crude, a razor blade stuck into a piece of wood acted as the crystal, and the end of the antenna wire served as a cat whisker. He managed to pick up broadcasts from Rome and Naples.
The idea spread across the beachhead and beyond. Toivo Kujanpaa built a receiver at Anzio and was able to receive German propaganda programs. The propaganda programs were directed towards Allied military from an Axis station in Rome. Many veterans of Anzio refer to the female announcer they heard as "Axis Sally", the nickname usually used when referring to propagandist Mildred Gillars, however Gillars broadcast from Berlin, and the men at Anzio were more likely hearing Rita Zucca, who broadcast from Rome. Though Gillars is more often associated with the "Sally" moniker, it was Zucca who actually referred to herself as "Sally" during broadcasts.
There were also allied broadcasts available, from the 5th Army Mobile Radio Station and the BBC.
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. In 1942, Lieutenant Colonel R. G. Wells—a prisoner of war in Japan—built a foxhole radio to get news about the international situation. "The whole POW camp craved news", according to Wells.
Designs and principles of operation
Foxhole radios were built using numerous designs. All of them receive AM (amplitude modulation) radio transmission without the need for a power source. They use an antenna or wire aerial, a coil serving as inductor, head phones, and some sort of improvised diode to rectify the signal. A diode can be built from an oxidized razor blade (rusty or flamed) with a pencil lead sitting on the blade. The oxide layer on the razor blade and the point contact of the pencil lead form a Schottky diode and only allow current to flow in one direction.
The antenna is connected to the grounded inductor, which is connected to the head phones, which is connected to the diode, which is connected to the antenna, completing the circuit.
The coil has an internal parasitic capacitance and therefore acts like an LC resonator with a specific resonant frequency. By varying the inductivity with a slider-tuner arm, the radio can be tuned to receive different frequencies. Most of these wartime sets did not have a slider-tuner arm and 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.
- Gould Jack, 1958 "How to build a foxhole radio." All about Radio and Television. Random House. Pages 58-72.
- "G.I. Uses Razor as Radio". New York Times. 29 April 1944.
- Make a crystal radio, wikihow.com, retrieved 2011-10-21
- R G Wells: The need for a radio., Oral History Research Unit at Bournemouth University, retrieved 2011-10-19
- foxehole, bizarrelabs.com, retrieved 2011-10-19