Patent
1974-09-04
1976-07-27
Griffin, Robert L.
325459, 325470, H04B 116
Patent
active
039719910
ABSTRACT:
An all channel television varactor diode tuning system has a presettable counter for deriving the number of the receivable television channel by counting pulses indicative of the tuner local oscillator frequency, which is varied by a voltage ramp circuit under the control of a comparator. The derived channel number is supplied to one input of the comparator, and a channel number selector supplies an encoded desired channel number to the other comparator input and to a frequency band decoder. The band decoder supplies signals to establish appropriate preset counts for the counter in accordance with the frequency band. Malfunction detection circuitry for detecting an improper number of pulses for the presettable counter, when in the low VHF frequency bands, is coupled to the channel number selector and connected through the comparator to force the tuning voltage circuit to drive the varactor in a direction opposite to that indicated by the comparator. This is done by monitoring the tens digit in the counter for occurrence of an 8 or 9.
REFERENCES:
patent: 3611152 (1971-10-01), Sakai
patent: 3736513 (1973-05-01), Wilson
patent: 3818353 (1974-06-01), Sakamoto
patent: 3845394 (1974-10-01), Hamada
Camasto Nicholas A.
Downey Joseph T.
Griffin Robert L.
Ng Jin F.
Zenith Radio Corporation
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