Diebstahlschutzvorrichtung für ein Kraftfahrzeug

摘要

An anti-theft device for a motor vehicle e.g. car has a transmitter (1), a receiving antenna, an evaluation unit (2), a control device (3) and a safety unit (4). The radio antenna (5) of the car radio (6), already available in the vehicle, is used as the receiving antenna. The intermediate frequency filter (10) and the demodulator (11) of the car radio (6) are used for the evaluation unit (2). A code signal is produced by the transmitter (1), modulated with a high-frequency carrier signal, and transmitted as an identification signal. The identification signal is received by the radio antenna (5). In a conversion device (16) the identification signal is converted in its frequency state, filtered in the intermediate frequency filter (10), demodulated in the demodulator (11), and passed to the control device (3). In the case of a positive comparison between the signal and a desired signal the safety unit (4) is controlled. Parts (7,8,9) of the radio (6) may be used as the conversion device (16).