Demodulators – Amplitude modulation demodulator – Having specific distortion – noise or other interference...
Patent
1979-01-22
1981-10-06
Grimm, Siegfried H.
Demodulators
Amplitude modulation demodulator
Having specific distortion, noise or other interference...
329122, 455208, 455263, H03D 318
Patent
active
042938180
ABSTRACT:
In a frequency modulation detection system, the voltage controlled local oscillator is controlled by two feedback loops. One feedback loop, containing a phase detector and a resonant circuit, responds sensitively to slight lack of alignment between the phase of the intermediate frequency signal and the phase of the driven oscillations in the resonant circuit, to correct the local oscillator over an automatic frequency control circuit having a low pass characteristic. The other feedback circuit is a frequency compression loop which uses a linear discriminator circuit to demodulate the modulated intermediate frequency. The audio frequency output of this discriminator is used to cause the local oscillator to rapidly track, at intermediate frequency-offset the radio frequency input. By use of two feedback loops it is possible to use a narrow band intermediate frequency filter, thereby reducing noise, without having drift of the circuits internally create noise products.
REFERENCES:
patent: 2075503 (1937-03-01), Chaffee
patent: 2272401 (1942-02-01), Chaffee
patent: 3231822 (1966-01-01), Tillotson
patent: 3371281 (1968-02-01), Powell
patent: 3742361 (1973-06-01), Wason
patent: 4087756 (1978-05-01), Rogers, Jr.
patent: 4101837 (1978-07-01), Clayton, Jr. et al.
Grimm Siegfried H.
International Telephone and Telegraph Corporation
Morris Jeffrey P.
O'Halloran John T.
Westin Edward P.
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