Armstrong_prototype_FM_transmitter_1935.jpg
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Summary
| Description |
English:
The first prototype FM (
frequency modulation
) transmitter, invented and built by
Edwin Armstrong
at the
Empire State Building
. Licensed as experimental station W2XDG, beginning June 2, 1934 Armstrong used it for a series of extensive secret tests of his new frequency modulation broadcasting system which he had been developing since 1928. The tests were successful, and in summer 1935 he announced his new system. The device transmitted on 41 MHz with an output power of 50 W, later increased to 2 kilowatts. It consisted of a low frequency
crystal oscillator
which was
phase modulated
by a
balanced modulator
, then was multiplied by a number of
frequency doubler
stages to the output frequency, which was applied to an ordinary transmitter RF amplifier. It had a frequency deviation of about 75 kHz. The 2 kW FM transmitter produced much better reception at a distance of 75 miles than a 50 kW AM transmitter broadcasting the same material. Information from
Kruse, Robert S., "The Armstrong System of Modulation" in
Radio
magazine, No. 204, January 1936, p. 62-67
. It took a number of years for FM broadcasting to catch on with listeners, but by 1970 most music broadcasting migrated to FM due to its superior audio quality.
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| Date | |
| Source | Retrieved October 26, 2015 from "New Radio System Eliminates Static" in Popular Science magazine, Popular Science Publishing Co., New York, Vol. 127, No. 1, July 1935, p. 16 on Google Books |
| Author | Unknown author |
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Permission
( Reusing this file ) |
This 1935 issue of Popular Science magazine would have the copyright renewed in 1963. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here . Search of the Renewals for Periodicals for 1962, 1963, and 1964 show no renewal entries for Popular Science . Therefore the copyright was not renewed and it is in the public domain. |
Licensing
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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.
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