| 摘要 |
A television receiver is disclosed including a varactor-type tuner selectively coupled to a synthesizer. Illustratively, the synthesizer includes a keyboard for selecting the desired channel within the UHF or VHF band, a channel memory for receiving and storing the selected channel and a programmable divider which divides selectively the output of the tuner's local oscillator in accordance with the selected channel to generate and apply its output to a phase comparator. The output of a reference oscillator also is applied to the phase comparator, whereby the output of the programmable divider is mixed therewith to obtain a tuning voltage to be applied to the tuner, which is associated with an automatic fine-tuning circuit (AFT); the AFT is adapted to be detuned selectively to increase the amplitude of the picture carrier signal and therefore, enhance the quality of the displayed images for weak signals, such as received from distant stations.
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