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In the Armstrong method, the audio signal and the radio frequency carrier signal are applied to the balanced modulator to generate a double sideband suppressed carrier signal. The phase of this output signal is then shifted 90 degrees with respect to the original carrier. The balanced modulator output can either lead or lag the carrier's phase.
Edwin Howard Armstrong (December 18, 1890 [2] – February 1, 1954 [3]) was an American electrical engineer and inventor who developed FM (frequency modulation) radio and the superheterodyne receiver system.
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.
An intermediate frequency was first used in the superheterodyne radio receiver, invented by American scientist Major Edwin Armstrong in 1918, during World War I. [ 7 ] [ 8 ] A member of the Signal Corps , Armstrong was building radio direction finding equipment to track German military signals at the then-very high frequencies of 500 to 3500 kHz.
The type 36 screen-grid tube (obsolete since the mid-1930s) had a non-regenerative detection gain (audio frequency plate voltage divided by radio frequency input voltage) of only 9.2 at 7.2 MHz, but in a regenerative detector, had detection gain as high as 7,900 at critical regeneration (non-oscillating) and as high as 15,800 with regeneration ...
Modifications requested by the Signal Corps were performed by Hallicrafters' engineers working with U.S. Army technicians at Fort Monmouth. They made a new version of the HT-4, which was known as the BC-610 transmitter, a part of the SCR-299 mobile communications unit, and production began in 1942.
A 5-tube superheterodyne receiver manufactured by Toshiba circa 1955 Superheterodyne transistor radio circuit circa 1975. A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency.
The pentagrid converter is a type of radio receiving valve (vacuum tube) with five grids used as the frequency mixer stage of a superheterodyne radio receiver. The pentagrid was part of a line of development of valves that were able to take an incoming RF signal and change its frequency to a fixed intermediate frequency , which was then ...