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Signal classifier

  • US 4,227,255 A
  • Filed: 04/11/1979
  • Issued: 10/07/1980
  • Est. Priority Date: 04/11/1979
  • Status: Expired due to Term
First Claim
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1. A system for classifying high frequency communications signals according to the nature of modulation appearing on the signals, said system being arranged to process an intermediate frequency (IF) signal which has been translated in frequency at a receiver, said system comprising:

  • means for controlling the level of said IF signal to maintain it within a predetermined range of levels;

    means for controlling the frequency of said IF signal to maintain it within a predetermined frequency range;

    amplitude demodulator means for detecting the envelope of the level and frequency controlled IF signal;

    activity factor circuit means for providing a first indication of the percentage of time that the detected envelope is at a level above a predetermined threshold level;

    AM variation circuit means responsive to said detected envelope for providing a second indication of amplitude variations in said IF signal;

    AM zero crossing circuit means for providing a third indication of the frequency at which zero level crossings occur in said detected envelope;

    FM demodulator means for detecting frequency modulation appearing on said IF signal;

    FM variation circuit means for providing further indications when the detected frequency modulation subsists in a first relatively low frequency band and a second relatively high frequency band; and

    logic means responsive to the indications provided by said activity factor, AM variation, AM zero crossing and FM variation circuit means for determining the nature of modulation appearing on said IF signal.

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