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FM Receiver for reception of special announcements and general programs

  • US 4,450,589 A
  • Filed: 11/09/1981
  • Issued: 05/22/1984
  • Est. Priority Date: 05/27/1981
  • Status: Expired due to Fees
First Claim
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1. FM receiver havinga radio frequency and tuning stage and a demodulator connected thereto for frequency demodulation of received signals including a carrier signal and an auxiliary carrier signal of a predetermined auxiliary carrier frequency,said auxiliary carrier being amplitude-modulated by at least one frequency within a predetermined frequency band;

  • a detector means connected to the radio frequency and tuning stage for detecting the auxiliary carrier signal of the predetermined auxiliary carrier frequency;

    an amplitude demodulator connected to the detector and detecting the amplitude modulation of the auxiliary carrier;

    a switchable output stage;

    a switch connected to the amplitude demodulator adapted to be controlled by the amplitude modulation of the auxiliary carrier and connected to the switchable output stage;

    a frequency selection filter tuned to pass at least one predetermined frequency of a frequency band of amplitude modulation on the auxiliary carrier, connected to receive the detected modulation from the amplitude demodulator, and providing an output signal representative of the level of amplitude modulation of the auxiliary carrier by said at least one predetermined frequency;

    means for detecting amplitude modulation of the auxiliary carrier by at least said one predetermined frequency of the frequency band;

    the improvement comprisingmeans for detecting change in the lever of percent of amplitude modulation of the auxiliary subcarrier by an least said predetermined frequency of said frequency band;

    and level sensing means responsive to said level of percent of amplitude modulation detecting means for providing a switching control signal to said switch when the level of percent of modulation of said auxiliary carrier by at least said predetermined frequency of said frequency band changes by a significant value from a previously existing percent level of modulation.

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