Television tuning system with provisions for receiving RF carrie

Details Television tuning system with provisions for receiving RF carrie Television tuning system with provisions for receiving RF carrie

1976-05-21

1977-06-21

Richardson, Robert L.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

325419, 325423, 325470, 358195, H04N 550, H04B 126

Patent

active

040315495

ABSTRACT:
A tuning system for a television receiver includes a phase locked loop for tuning a local oscillator to the nominal local oscillator frequencies required to tune the receiver to RF carriers at standard broadcast frequencies allocated to the various channels a viewer may select. The tuning system also includes an automatic fine tuning (AFT) frequency discriminator for tuning the local oscillator to minimize any deviation between the frequency of an actual picture carrier and the nominal picture carrier frequency. If the receiver is coupled to a television distribution system which provides RF carriers having nonstandard frequencies arbitrarily near respective ones of the standard broadcast frequencies, when the phase locked loop has achieved lock at a nominal frequency, a mode control unit selectively couples the discriminator and a frequency drift control circuit to the local oscillator. If the frequency of the local oscillator drifts more than a predetermined offset from the frequency synthesized under phase locked loop control because no carrier has been detected by the discriminator, discriminator and drift control are terminated so that the receiver will not be tuned to an undesired carrier such as, for example, the lower adjacent channel sound carrier, and phase locked loop control is reinitiated to synthesize a local oscillator signal having a frequency different from the frequency of the originally synthesized local oscillator signal by a predetermined amount. After the phase locked loop is locked at the new frequency, discriminator control is again initiated.

REFERENCES:
patent: 3411103 (1968-11-01), Deman et al.
patent: 3949158 (1976-04-01), Rzeszewski et al.

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