Signal-seeking radio receivers

Claim 1

For use in a signal-seeking radio receiver which includes an antenna, a receiver mixer and local oscillator means for generating a plurality of different frequency local oscillator signals automatically in seqence, thereby automatically and sequentially to tune said receiver to receive a predetermined spectrum of radio frequency signals, means for holding said receiver tuned to those signals in response to reception thereof, and means for reproducing the intelligence therein, a tuning circuit comprising: a. first control signal generating means coupled to said local oscillator means to receive said different frequency local oscillator signals for generatiNg a plurality of first control signals, there being one of said control signals generated in response to each of said local oscillator signals, said first control signal generating means including therein a resonant circuit having a predetermined impedance vs. frequency characteristic, the magnitude of each said control signal being proportional to the impedance of said resonant circuit at each of the respective frequencies of said local oscilator, said resonant circuit including means for selectively altering said characteristic thereby to selectively alter the relative magnitudes of said first control signals; b. second control signal generating means coupled to said first control signal generating means to receive said first control signals for adding thereto a signal of predetermined magnitude to produce a plurality of second control signals corresponding to said first control signals but altered in magnitude by said predetermined signal; and c. a radio frequency amplifier coupled between said antenna and said reproducing means, said amplifier including at least one tuned radio frequency circuit, said tuned circuit having a voltage-variable reactance device therein which determines the pass-band thereof coupled to said second control signal generating means to receive said second control signals, the reactance of said device corresponding to the magnitude of the signal applied thereto, whereby, the pass-band of said tuned circuit is automatically and sequentially tuned to pass a band of frequencies about each of said predetermined radio frequencies in synchronism with the tuning of said receiver thereto; said first control signals being alternating current signals, the second control signal generating means including means for rectifying said first control signals, said predetermined signal and said second control signals being direct current signals, said first control signal generating means including a first amplifier circuit having a load circuit, said resonant circuit being in said load circuit.