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NOISE REJECTION CIRCUITRY

  • US 3,828,337 A
  • Filed: 08/20/1973
  • Issued: 08/06/1974
  • Est. Priority Date: 08/20/1973
  • Status: Expired due to Term
First Claim
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1. For use in an electronic security system which includes means for providing in a surveillance zone an electromagnetic field of a frequency which is swept within a predetermined range, and means for detecting the presence of a resonant tag circuit having a frequency within said range, circuitry for discriminating between the presence of a valid tag circuit in said surveillance zone and spurious signals, said circuitry comprising:

  • means for receiving a train of pulses derived from detection of a tag circuit within said surveillance zone;

    means operative upon receipt of a predetermined number of pulses of predetermined periodicity to provide an alarm indication; and

    means for resetting said circuitry immediately upon detection of at least one missed pulse in the expected train of pulses.

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