AM Radio having an automatic fine tuning circuit
AssigneeGeneral Electric Company
InventorBert K. Erickson
Life of this patent
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Abstract
An AM superheterodyne radio receiver has an RF filter which includes a biased varactor for providing a trimming capacitance and provides an AGC signal when it is tuned to a broadcast AM signal. The AGC signal and a derived time derivative signal are used to provide binary signals which drive a logic circuit and the logic circuit controls a generator which biases the varactor. The biased varactor fine tunes the RF filter towards the carrier frequency of the broadcast AM signal.
Claims13
A circuit for automatically fine tuning a bandpass filter in a receiver which is tunable to an amplitude modulated carrier signal at a frequency within a given relatively wide frequency band and which provides an output signal related to the amplitude modulation superimposed thereon, comprising:
- (a) a band-pass filter coarsely tunable within said relatively wide band of frequencies for providing a filtered signal proportionally related to said received amplitude modulated carrier signal said band-pass filter including fine tuning means responsive to an automatic fine tuning signal for approximately centering the pass band of said filter about a selected frequency by adjusting said passband over a relatively narrow band of frequencies within said relatively wide band;
- (b) means responsive to the presence of said filtered signal for generating a signal related to said modulation superimposed on said received carrier signal and for generating a first control signal which is related to the magnitude of said filtered signal;
- (c) means for deriving a second control signal, the second control signal being related to the derivative with respect to time of the first control signal;
- and
- (d) digital circuit means responsive to the first and second control signals for supplying said band-pass filter fine tuning means with an automatic fine tuning signal.
Dependencies are inferred from the claim text.