Patent
1974-07-12
1976-02-03
Libman, George H.
325437, 325470, H04B 132
Patent
active
039367533
ABSTRACT:
A digital automatic frequency control circuit for use with a scanning type superheterodyne receiver, such circuit having an input for receiving the output of a related discriminator, and an output for providing an incrementally variable tuning voltage to a related local oscillator. My novel circuit has a search mode and a lock mode, and during the search mode, when the receiver tuning is swept past a pulsed radio signal, the discriminator produces a sequence of voltage output pulses whose polarity for a desired signal will be different from that of the signal's image. My circuit recognizes the polarity relationships of such pulses, and makes use of such information in a highly advantageous manner in order to cause the receiver to enter the lock mode only when the received signal has the correct relationship with the local oscillator, with the image signal thus being ignored. While in the lock mode, this circuit will track the frequency of the incoming radio frequency energy on a pulse-to-pulse basis, automatically compensating for drifts in the frequency of either the incoming energy or the local oscillator. Although the lock mode will be maintained for a brief, preselected period in the event of momentary fades or the like, after such preselected period is over, the search mode is automatically recommenced.
REFERENCES:
patent: 2951150 (1960-08-01), Rennenkampf
patent: 3174105 (1965-03-01), Morgan, Jr.
patent: 3388331 (1968-06-01), Rawley
Chin, Esquire Gay
Libman George H.
Martin Marietta Corporation
Renfro, Esquire Julian C.
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