Theft alarm for vehicle carried radio equipment

摘要

A theft alarm is provided for use in conjunction with vehicular mounted radio equipment, such as the popular but too frequently stolen citizens' band transceivers, which is responsive to either physical separation of the equipment being protected from the common electrical ground provided by the chassis of the vehicle or disconnection from such equipment of the cable by which it is normally coupled with an antenna mounted on the same vehicle. In order to permit locating and/or coupling the alarm circuit components with the equipment at points remote from the latter, so that the alarm portion of the system may be in a protected location or its presence not revealed by "extra" wires leading directly to the equipment or both, and in order that the alarm may function reliably and immediately in response to an attempted theft without adversely affecting the transmission of radio frequency signals between the equipment and the antenna and without possible impairment of the functioning of the alarm due to spurious electrical paths, the cable for connecting the equipment to the antenna is electrically separated into two sections at a zone intermediate its length, at which zone each conductor of one section is capacitatively coupled with the corresponding conductor of the other section, and the alarm controlling circuit is then coupled between the common ground and one of the conductors of the section of the antenna cable electrically adjacent to the equipment to be protected.