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File:US Army acoustic aircraft locator 1925.jpg

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English: An acoustic aircraft locator developed by the US Army in 1925 to locate incoming enemy aircraft by listening for the sound of their engines. Between World War 1 and 2, before the development of radar, many nations used passive acoustic locators like this for air defense. It consists of 4 exponential horns which concentrate the faint sound of the aircraft, which is channeled through rubber hoses to stethoscope-type earphones worn by two observers. The horns are mounted on an altazimuth mount and the stereo earphones of the observers allow them to pinpoint the location of the aircraft. The horns are used in pairs; the vertical pair are attached to the earphones of the righthand observer, who adjusts the elevation wheel; the horizontal pair are attached to the earphones no the lefthand observer, who controls the azimuth (horizontal direction) wheel. They adjust the device until it is pointing at the plane, then report the bearings by phone to an air defence center.
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Source Retrieved September 24, 2014 from Popular Radio magazine, published by Popular Radio, Inc., New York, Vol. 8, No. 3, September 1925, p. 261 on American Radio History website. The image is credited to "Ordnance Department U.S. Army"
Author Unknown authorUnknown author
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  • The credit indicates the photo was taken by a member of the U.S. Army as part of his official duties, and therefore is in the public domain.
  • Even if not, the magazine it appears in is in public domain. This 1925 issue of Popular Radio magazine would have the copyright renewed in 1953. 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 1952, 1953, and 1954 show no renewal entries for Popular Radio. Therefore the magazine's copyright was not renewed and it is in the public domain.

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Public domain
This file is a work of a U.S. Army soldier or employee, taken or made as part of that person's official duties. As a work of the U.S. federal government, it is in the public domain in the United States.

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Public domain
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.

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current02:00, 25 September 2014Thumbnail for version as of 02:00, 25 September 2014931 × 1,063 (386 KB)Chetvorno (talk | contribs)User created page with UploadWizard

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