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Field disturbance type motion detection system

  • US 3,925,774 A
  • Filed: 03/24/1975
  • Issued: 12/09/1975
  • Est. Priority Date: 03/24/1975
  • Status: Expired due to Term
First Claim
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1. A field disturbance motion detection system generating an electromagnetic wave pattern which is radiated to a selected location and being responsive to a predetermined disturbance of said wave pattern thereat to activate an alarm device, comprising in combination:

  • a housing having a front portion adapted to pass electromagnetic waves therethrough without substantial attenuation;

    a printed circuit board in said housing adjacently behind said front portion;

    said printed circuit board including thereon a single transceiver antenna comprised of a pair of opposing quarter wave antenna elements including a spacing therebetween forming a half-wave dipole antenna, and tuning control means located in said spacing coupled between said opposing elements;

    an electromagnetic wave reflecting plate attached to said housing substantially one quarter wavelength behind said printed circuit board thereby providing a predetermined antenna gain and directional sensitivity;

    a transceiver oscillator/detector circuit located immediately adjacent and coupled to said pair of antenna elements on said printed circuit board and including a single transistor having an emitter, base and collector, and additionally including a direct circuit connection of said base to one of said pair of antenna elements, first circuit means coupling said base to a point of reference potential, second circuit means coupling said emitter to said point of reference potential, third circuit means coupling said collector to said one antenna element, fourth circuit means coupling said collector to the other of said pair of antenna elements, and fifth circuit means coupling said collector to a supply potential, whereby said circuit is energized to provide oscillations which are coupled to said antenna whereupon electromagnetic signals of a predetermined frequency are radiated to a localized area which when a field disturbance occurs a change in collector current of said transistor results providing a relatively low level output signal of another predetermined frequency across said fifth circuit means;

    bandpass filter-amplifier means coupled to said collector and being responsive to said output signal occurring across said fifth circuit means and being adapted to increase the amplitude of said output signal by a predetermined gain;

    comparator circuit means having first and second input means respectively coupled to the output of said bandpass filteramplifier means and A reference potential whereby a control signal is generated in response to a field disturbance for initiating an alarm when the amplitude of said output signal from said bandpass amplifier exceeds said reference potential.

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