First_vacuum_tube_AM_radio_transmitter.jpg (448 × 360 pixels, file size: 90 KB, MIME type: image/jpeg)
Summary
DescriptionFirst vacuum tube AM radio transmitter.jpg |
English: Apparently the first commercial AM Audion vacuum tube radio transmitter, built in 1914 by Lee De Forest who invented the Audion (triode) in 1906, from a short announcement in Electrical World magazine. It was not the first AM (sound) transmitter; short-lived technologies like the Poulsen arc and Alexanderson alternator| had been transmitting sound since 1906. But the vacuum tube feedback oscillator, invented in 1912 by Edwin Armstrong, replaced them, and has remained the key technology used in radio transmitters to the present day.
The device used a tickler-feedback Armstrong oscillator circuit. The Audion is mounted outside, on the side of the enclosure, so the operator can check if the filament is glowing and adjust the filament voltage visually. Audions were always mounted hanging upside down, so the fragile filament in the tube wouldn't sag and touch the grid. The telephone-type carbon microphone was connected directly in the transmitter's antenna wire, and its varying resistance modulated the current going to the antenna. The low power of the early Audion gave it a limited range of 1 to 3 miles. The text of the article that accompanied the photo: |
Date | |
Source | Downloaded 25 September 2013 from "High-Frequency Oscillating Transmitter for Wireless Telephony", Wireless World, Vol. 66, 18 July 1914, p. 144 on Thomas H. White's Early United States Radio History website |
Author | Lee De Forest |
Licensing
Public domainPublic domainfalsefalse |
This media file is in the public domain in the United States. This applies to U.S. works where the copyright has expired, often because its first publication occurred prior to January 1, 1929, and if not then due to lack of notice or renewal. See this page for further explanation.
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This image might not be in the public domain outside of the United States; this especially applies in the countries and areas that do not apply the rule of the shorter term for US works, such as Canada, Mainland China (not Hong Kong or Macao), Germany, Mexico, and Switzerland. The creator and year of publication are essential information and must be provided. See Wikipedia:Public domain and Wikipedia:Copyrights for more details.
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Items portrayed in this file
depicts
inception
18 April 1914Gregorian
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image/jpeg
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 15:13, 2 May 2021 | 448 × 360 (90 KB) | Materialscientist | FFT | |
19:13, 25 September 2013 | 448 × 360 (45 KB) | Chetvorno | User created page with UploadWizard |
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