Abstract: A tuning system for a television receiver includes a local oscillator which is controlled first by a phase lock loop arrangement and then by an AFT discriminator arrangement for tuning the receiver to non-standard as well as standard frequency carriers. The phase lock loop arrangement includes a programmable divider for dividing the local oscillator frequency by a programmable factor corresponding to the presently selected channel. When the local oscillator is being controlled by the AFT discriminator arrangement, the count accumulated by the programmable divider during a reference interval determines how far the local oscillator frequency has drifted from its nominal value. If a predetermined frequency offset has been exceeded, control is returned to phase lock loop control and the programmable factor is incrementally changed.

Abstract: Television tuning apparatus includes a first phase locked loop configuration for tuning a local oscillator to a nominal frequency appropriate for converting a standard radio frequency carrier allocated to a selected channel to a predetermined intermediate frequency (e.g., 45.75 MHz) and a second phase locked loop configuration for tuning the local oscillator to minimize any deviation between the actual frequency of the I.F. picture carrier and its nominal frequency which may occur, for example, because the receiver is coupled to a distribution system utilizing frequency conversion apparatus which provides nonstandard radio frequency carriers arbitrarily near respective standard frequency carriers. The two phase locked loop configurations include common elements and control apparatus to selectively initiate the operation of one loop while inhibiting the operation of the other in accordance with a predetermined tuning algorithm.

Abstract: A tuning system for a television receiver includes a first phase locked loop configuration for controlling the frequency of the receiver's local oscillator signal in accordance with the number of the channel presently being tuned and a second phase locked loop configuration for controlling the frequency of the local oscillator signal to reduce any frequency deviation between the receiver's IF picture carrier and 45.75 MHz corresponding to a frequency offset between the associated RF carrier and the standard RF carrier frequency for the channel being presently tuned due to the frequency translation provided by a television distribution system. The tuning system includes control units for automatically changing the channel number and selectively enabling the operation of the first and second phase locked loop configuration in accordance with a tuning algorithm so that active channels may be automatically located and tuned while preventing the receiver from being erroneously tuned to undesirable signals.

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.

Abstract: A phase locked loop type of television tuning apparatus includes an apparatus for dividing the frequency of a local oscillator signal by a number equal to the frequency of the local oscillator signal, in MHz, corresponding to the presently selected channel. The divider forms an output signal including first and second portions having durations respectively equal to first and second predetermined numbers of periods of the local oscillator signal. The first number is related to the number of the selected channel. The second number is related to the frequency band in which the selected channel resides. To determine the frequency band of the selected channels, band traversed signals are generated whenever the number of periods of the local oscillator signal generated since beginning of the first portion corresponds to the first channel in a band. When a new band traversed signal is generated, the previous band traversed signal is terminated.