Image: Foxhole radio from WW2

Description: 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 local oscillator, American soldiers in World War 2 constructed their own homemade "crystal" radios 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 razor blade. The graphite point touching the semiconducting oxide coating of the razor blade formed a crude point contact semiconductor diode which rectified the radio signal from the coil, extracting the audio signal from the radio frequency carrier wave, 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.
Title: Foxhole radio from WW2
Credit: Retrieved February 10, 2010 from John W. Campbell Jr., "Radio detectors and how they work" in Popular Science magazine, Popular Science Publishing Co., New York, Vol. 145, No. 4, October 1944, p. 209 on Google Books
Author: John W. Campbell Jr.
Permission: This 1944 issue of Popular Science magazine would have the copyright renewed in 1972. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1971, 1972, and 1973 show no renewal entries for Popular Science. Therefore the copyright was not renewed and it is in the public domain.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No