H - Electricity – 04 – B
Patent
H - Electricity
04
B
365/5
H04B 1/16 (2006.01) H03J 5/02 (2006.01) H03J 7/06 (2006.01) H04B 1/26 (2006.01)
Patent
CA 1108322
RCA 70,849 TELEVISION TUNING SYSTEM WITH PROVISIONS FOR RECEIVING RF CARRIER AT NONSTANDARD FREQUENCY Abstract of Disclosure 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 fox 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 freq- uencies arbitrarily near respective ones of the standard broadcast frequencies, when the phase locked loop has achi- eved 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 off- set from the frequency synthesized under phase locked loop control because no carrier has been detected by the discrim- inator, 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 carr- ier, and phase locked loop control is reinitiated to synthe- size a local oscillator signal having a frequency incremented from the frequency of the originally synthesized local oscillator signal by a predetermined amount. After the phase locked loop is locked at an incremented frequency, discriminator control is again initiated. If, during this cycle of discriminator control, the local oscillator again drifts more than the predetermined offset from the --1-- RCA 70,849 incremented local oscillator frequency because no carrier is detected by the discriminator, phase locked loop control is again reinitiated to synthesize a local oscillator signal having a frequency decremented from the frequency of the originally synthesized local oscillator signal by the pre- determined amount. If during any discriminator control cycle the local oscillator has not drifted further than the predetermined offset because the discriminator has tuned the local oscillator to a carrier within the predetermined offset, phase locked loop control is not reinitiated and the tuning sequence is complete. -1a-
277947
Henderson John G. N.
Rast Robert M.
Wine Charles M.
Morneau Roland L.
Rca Corporation
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