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Theft alarm for vehicle carried radio equipment

  • US 4,035,765 A
  • Filed: 06/14/1976
  • Issued: 07/12/1977
  • Est. Priority Date: 06/14/1976
  • Status: Expired due to Term
First Claim
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1. For use in combination with:

  • a vehicle having an electrically conductive chassis providing a local, electrical, ground reference;

    an electrical direct current power source carried by said vehicle and having a pair of power terminals of which one is electrically connected with said ground reference;

    electrically actuatable horn means carried by said vehicle and having a pair of energizing terminals of which one is electrically connected with said ground reference;

    radio equipment means normally carried by said vehicle and having a ground terminal normally electrically connected with said ground reference when said equipment means is being carried by said vehicle, and a pair of antenna terminals of which one is electrically connected with said ground terminal of said equipment means; and

    antenna means carried by said vehicle and having a pair of connection terminals of which one is electrically connected with said ground reference;

    apparatus for operatively coupling said antenna terminals of said equipment with said connection terminals of said antenna means and for providing a theft alarm to protect said equipment means against unauthorized removal from said vehicle by providing an alram indication whenever said ground terminal of said equipment means is electrically disconnected from said ground reference, said apparatus including;

    first cable means having a pair of electrical conductors respectively releasably electrically connected adjacent one end of said first cable means with said antenna terminals of said equipment means;

    second cable means having a pair of electrical conductors respectively electrically connected adjacent one end of said second cable means with said connection terminals of said antenna means;

    a relay having a coil provided with a pair of operating terminals of which one is electrically connected with the other of said power terminals and the other of which is electrically coupled with one of said conductors of said first cable means,said relay including a switch which is open when said coil is energized and closed when said coil is deenergized and having a pair of switch terminals of which one is electrically connected with said other power terminal and the other of which is electrically connected with the other of said energizing terminals of said horn means;

    first electrical coupling means adjacent the other ends of said first and second cable means for electrically coupling the other conductor of said first cable means with one conductor of said second cable means; and

    second electrical coupling means adjacent the other ends of said first and second cable means comprising a capacitor interconnected between said one conductor of said first cable means and the other conductor of said second cable means for electrically intercoupling said cables for radio frequency signals while maintaining direct current isolation between said other operating terminal of said coil and said other conductor of said second cable means,whereby said one conductor of said first cable means is employed both as a part of the radio frequency signal transmission line between said equipment means and said antenna means and as a part of the alarm controlling circuit without impairment of either function thereof by the other.

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