Variable phase signal demodulator

Details Variable phase signal demodulator Variable phase signal demodulator

1984-07-26

1987-01-13

Grimm, Siegfried H.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

329101, 329122, 331 4, 331 17, 331 23, 331DIG2, 455245, 455260, 455265, H03D 104, H02L 712

Patent

active

046367365

ABSTRACT:
A dual conversion variable bandwidth telemetry receiver employs a phase locked loop which controls the second local oscillator to maintain lock on the carrier frequency; the phase locked loop employing a loop filter with a variable time constant integrator, the time constant of which can be varied as a function of receiver bandwidth and the integrator with its associated capacitor and resistor banks being employed in a sweep, i.e. search, oscillator circuit enabled when the carrier signal is lost. A coherent double-balanced mixer is employed to detect carrier lock and if lock is lost but the carrier is still detected, a rapid response anti-sideband circuit in the phase detector of the phase locked loop is employed to suppress the sidebands and greatly increase the probability of relocking on the carrier. A synchronous AM detector employs quadrature IF and reference signals at the same frequency to produce a dc signal when phase lock occurs; the signal falling rapidly upon loss of lock. The synchronous AM detector employs a variable time constant integrator for eliminating noise above a low frequency to accommodate carrier fading, said integrator being located in an AGC circuit of an amplifier feeding a balanced mixer to hold the IF at a constant level, thus permitting detection of carrier signals at a carrier to noise ratio as low as a -20 dB. The AM detector also produces a substantially exact reproduction of the AM signal for use elsewhere in the receiver.

REFERENCES:
patent: 3958186 (1976-05-01), Jesse et al.
patent: 4007429 (1977-02-01), Cadalora et al.
patent: 4077015 (1978-02-01), Carson et al.
patent: 4206420 (1980-06-01), Querry et al.

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