First_vacuum_tube_AM_radio_transmitter.jpg
Summary
Description First 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 domain Public domain false false |
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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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and
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for more details.
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