Automatic frequency control

Details Automatic frequency control Automatic frequency control

1988-05-23

1989-03-21

Groody, James J.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

455192, 455182, H04N 550

Patent

active

048148873

ABSTRACT:
An automatic frequency control tracks a television signal before and after a period of interruption. The automatic frequency control comprises a voltage controlled feedback loop including a voltage controlled local oscillator and a mixer for mixing the output of the oscillator with the TV signal. The output of the mixer is filtered to remove unwanted components of the mixed signal and to equalize sidebands of the television signal. The output of the filter is supplied to a detector which is tuned to a component of the television signal, and produces a voltage corresponding to the frequency of the component. The output of the detector is supplied to the voltage control input of the local oscillator to track the television signal component. Circuitry automatically senses the absence of the TV signal component from the mixer, and automatically applies a reference voltage to the voltage control input of the oscillator when the TV signal component is absent. The detector is operative to detect the television signal component following the application of reference voltage to the oscillator so that when the television signal returns, the detector is capable of tracking it.

REFERENCES:
patent: 3980951 (1976-09-01), Breeze et al.
patent: 4214274 (1980-07-01), Rzeszewski et al.
patent: 4263611 (1981-04-01), Gibson et al.
patent: 4263675 (1981-04-01), Hongu et al.
patent: 4392254 (1983-07-01), Ecklund
patent: 4556988 (1985-12-01), Yoshisato
patent: 4630118 (1986-12-01), Suzuki

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