Automatic fine tuning circuit

Details Automatic fine tuning circuit Automatic fine tuning circuit

1976-12-27

1978-10-17

Griffin, Robert L.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

325335, 325423, H04N 550, H04B 126

Patent

active

041212541

ABSTRACT:
A relatively broad band automatic fine tuning circuit covering a frequency band at least approximately as broad as a television channel and including means to shift the frequency of the television tuner up or down, as necessary, to the proper frequency within the automatic tuning range. A first control signal is obtained by comparing the average value of the envelope detected signal from the video detector with a voltage equal to the pedestal level if the signal were a properly tuned video signal. If the actual average value of the envelope is between zero volts and the pedestal voltage, the tuner is either correctly tuned or tuned at a somewhat lower frequency than is correct. If the voltage average value has a greater magnitude than the pedestal voltage the tuning of the tuner is too high. A frequency discriminator receiving the video IF signal controls the automatic tuning operation close to the desired frequency. A noise detector in the audio circuit controls a muting circuit to disable AFT operation if the receiver is so far out of tune as to receive noise instead of an audio signal.

REFERENCES:
patent: 3867568 (1975-02-01), Merriweather
patent: 3869674 (1975-03-01), Borbely
patent: 3940554 (1976-02-01), Masuda
patent: 3946329 (1976-03-01), Caspari
patent: 3949158 (1976-04-01), Rzeszewski
patent: 3952143 (1976-04-01), Siwko

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