File:Foxhole radio circuits.png
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[edit]DescriptionFoxhole radio circuits.png |
English: Two diagrams of circuits of foxhole radios, DIY crystal radios built by American soldiers on the European Front during World War 2, from a 1944 article in a radio hobbyist magazine. The soldiers were forbidden to use ordinary powered radios, because the local oscillator radiated radio waves that could give their position away to the enemy. So they built crude crystal radios, which had no power source and so did not radiate. These used a safety razor blade touched by a battery carbon or pencil lead as a detector to rectify the radio current to extract the audio modulation which produced sound in the earphones. Blued steel razor blades had a semiconducting oxide coating that could conduct current in only one direction. The image shows two foxhole radio circuits. The righthand diagram has a detector consisting of a razor blade touched by two battery carbons, with a battery that applied a bias of a few volts across it to make it more sensitive. The lefthand diagram shows a safety pin with a pencil lead as a contact. In both circuits the capacitance of the wire antenna combined with the inductance of the coil to make a tuned circuit which allowed through the frequency of the desired station. Since usually only one local station could be heard, the radio was not tunable, the builder just adjusted the number of turns on the coil to pick up the station. |
Date | |
Source | Retrieved 2 September 2020 from Hugo Gernsback "Foxhole emergency radios" in Radio-Craft magazine, Radio-Craft Publications, Inc., Vol. 15, No. 12, September 1944, p.730, Exhibit 1 and 3 |
Author | Hugo Gernsback |
Permission (Reusing this file) |
This 1944 issue of Radio-Craft 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. [1] Search of the Renewals for Periodicals for 1971, 1972, and 1973 show no renewal entries for "Radio-Craft". Therefore the magazine's copyright was not renewed and it is in the public domain. |
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This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties. العربية ∙ Deutsch ∙ English ∙ español ∙ français ∙ galego ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ português ∙ português do Brasil ∙ русский ∙ sicilianu ∙ slovenščina ∙ українська ∙ 简体中文 ∙ 繁體中文 ∙ +/− |
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current | 20:17, 2 September 2020 | 926 × 455 (80 KB) | Chetvorno (talk | contribs) | Uploaded a work by Hugo Gernsback from Retrieved 2 September 2020 from [https://worldradiohistory.com/Archive-Radio-Craft/1940s/Radio-Craft-1944-09.pdf Hugo Gernsback "Foxhole emergency radios" in ''Radio-Craft'' magazine, Radio-Craft Publications, Inc., Vol. 15, No. 12, September 1944, p.730, Exhibit 1 and 3] with UploadWizard |
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File change date and time | 19:24, 2 September 2020 |