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Armstrong's "feed back" circuit drawing, from Radio Broadcast vol. 1 no. 1 1922. Armstrong began working on his first major invention while still an undergraduate at Columbia. In late 1906, Lee de Forest had invented the three-element (triode) "grid Audion" vacuum-tube. How vacuum tubes worked was not understood at the time.
Several of the French A-1 artillery receiving set were sent to the American radio laboratory in the summer of 1917 and copied with minor modifications. It was first released as the AR-4 in limited numbers for field tests, supervised by Captain Edwin Armstrong. [1] Several changes were made based on his suggestions.
Homebuilt Armstrong one-tube regenerative shortwave radio with construction characteristic of the 1930s - 40s. The controls are (left) regeneration, (lower center) filament rheostat, (right) tuning capacitor. Rear view of the above radio, showing the simplicity of the regenerative design.
The Armstrong 521 was a stereo hi-fi amplifier from the Armstrong Audio company and was marketed as 2 x 25W amplifier.. It employed germanium AL102 transistors in its output stages and these had a reputation for failure and are now unobtainable although it is possible, with modification to replace these with newer, silicon transistors.
In 1914 Edwin Armstrong described the audion receiver. [1] In 1915 he described some regenerative audion receivers. [2] Fig.3 shows the audion, Fig. 8 the tickler coil regenerative audion and Fig. 9 the Miller effect regenerative audion. All circuits use one tube for RF amplification, RF demodulation and audio amplification.
The result is a narrow-band radio-frequency filter and amplifier. The non-linear characteristic of the transistor or tube also demodulated the RF signal to produce the audio signal. The circuit diagram shown is a modern implementation, using a field-effect transistor as the amplifying element. Armstrong's original design used a triode vacuum tube.
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Armstrong charged that this reassignment had the covert goal of disrupting FM radio development, [10] however RCA's proposal prevailed, and on June 27, 1945 the FCC announced the reassignment of the FM band to 80 channels from 88–106 MHz (which was soon expanded to 100 channels from 88–108 MHz), while allocating the former FM band ...