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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.
Edwin Howard Armstrong (1890–1954) was an American electrical engineer who invented wideband frequency modulation (FM) radio. [12] He patented the regenerative circuit in 1914, the superheterodyne receiver in 1918 and the super-regenerative circuit in 1922. [ 13 ]
The Armstrong oscillator [1] (also known as the Meissner oscillator [2]) is an electronic oscillator circuit which uses an inductor and capacitor to generate an oscillation. The Meissner patent from 1913 describes a device for generating electrical vibrations, a radio transmitter used for on–off keying .
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.
A modulator is a device or circuit that performs modulation. A demodulator (sometimes detector ) is a circuit that performs demodulation , the inverse of modulation. A modem (from mod ulator– dem odulator), used in bidirectional communication, can perform both operations.
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.
Signals sent by radio (or over long wires or when stored on magnetic media) must be modulated with some method that prevents their signal from degrading before the signals can be received.