Self aligning band-pass filtering system

Details Self aligning band-pass filtering system Self aligning band-pass filtering system

1980-06-16

1983-02-01

Chin, Tommy P.

Telecommunications

Receiver or analog modulated signal frequency converter

Frequency or phase modulation

455122, 455125, 331 16, 332 30V, H04B 118

Patent

active

043719805

ABSTRACT:
An FM receiver includes a varactor tuned RF filter to which is applied a bias voltage and a 20 Hz sinusoidal signal for varying the varactor capacitance and the resonant frequency of the filter. As a result, an FM broadcast signal in the pass-band of the filter is phase-modulated by the filter. The second harmonic of the phase modulation is recovered and coupled to a synchronous detector driven at a 40 Hz rate to provide an error voltage. The bias voltage is related to the integral of the error voltage. A difference between the frequency about which the tuned circuit periodically varies and the carrier frequency of the FM signal cause the bias voltage to vary so as to reduce the magnitude of the difference, thereby fine-tuning the receiver.

REFERENCES:
patent: 2474354 (1949-06-01), Guanella
patent: 3165697 (1965-01-01), Reich
patent: 3255414 (1966-06-01), Kawalek
patent: 3329900 (1967-07-01), Graves
patent: 4089495 (1978-05-01), Knight
patent: 4158182 (1979-06-01), Washburn

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