File:Jenkins spinning disk televisor.jpg

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Summary

DescriptionJenkins spinning disk televisor.jpg	English: An early mechanical-scan television display device, the Jenkins Radiovisor, from an advertisement in a radio magazine by Jenkins Television Corp., Passaic, New Jersey, in 1931. It was used in experimental television receivers during the 1930s. During the 1920s and 30s dozens of experimental stations broadcast television using this mechanical-scan technology. The radiovisor consists of a metal disk pierced with a spiral pattern of holes, called a Nipkow disk, turned by a synchronous motor. Behind the disk is a neon glow lamp. When the disk is spun by the motor, each hole passing in front of the neon lamp creates a scan line in the image. The radio signal from the television station is picked up by an antenna attached to a vacuum tube receiver unit, producing a video signal which is applied to the neon lamp. The varying signal causes varying light intensity from the lamp, representing the different brightness values of the image. The result is a dim fuzzy monochrome orange picture about 1 1/2 inches (3 cm) square. The viewer looks into the lens (left) which magnifies the image. The most common standard was a 60- line image at a frame rate of 20 frames per second. For this standard there were 60 holes around the disk, each one producing a scan line. The disk made one rotation for each video frame, so it turned at a rate of 1200 RPM. It was sold as a kit for $42.50 with the lens extra.
Date	April 1931
Source	Retrieved March 19, 2014 from Television News magazine, Popular Book Corp., New York, Vol. 1, No. 2, March-April 1931, p. 67 on AmericanRadioHistory.com website.
Author	Unknown authorUnknown author
Permission (Reusing this file)	This image is from an advertisement for Jenkins Television Corp. without a copyright notice published in a 1931 magazine. In the United States, advertisements published in collective works (magazines and newspapers) are not covered by the copyright notice for the entire collective work. (See U.S. Copyright Office Circular 3, "Copyright Notice", page 3, "Contributions to Collective Works".) Since the advertisement was published before 1978 without a copyright notice, it falls into the public domain.

Licensing

This work is in the public domain in the United States because it was published in the United States between 1929 and 1977, inclusive, without a copyright notice. For further explanation, see Commons:Hirtle chart as well as a detailed definition of "publication" for public art. 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 (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.

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