Radio beam alarm system

摘要

The invention relates to alarm devices and can be used for detecting frontier crossers when surveying long distance borders (up to 600 m). The inventive radio beam alarm device comprises a transmitting unit and a receiving unit which contains a data processing and warning means. An electromagnetic fence is formed between said units with the aid of a high-frequency radiation. The crossing of said fence actuates the alarm. The receiving unit comprises two identical receiving channels having a receiver and a receiving antenna. The direction of the steering angle of the receiving antennas are equal and opposite with respect to the transmitting unit-receiving unit. The receiving unit also comprises a comparator circuit which is arranged between the receiving channels and the data processing means. The invention makes it possible to form a radio alarm zone along both sides of the electromagnetic fence and asymmetrically receive the signals from both sides thereof. The asymmetry of the received signals also makes it possible to determine the direction of the frontier crosser's approach to the electromagnetic fence. The comparator circuit compares the signal coming from the receiving channels on the inputs thereof and forms a corresponding signal on the output when two equal signals simultaneously appear on the inputs thereof. This effect can take place only when a moving object (the frontier crosser) reaches a cross-section of the zone of equal signals of both channels. Correspondingly, the alarm emits signals only when the frontier crosser reaches the cross-section of the electromagnetic fence. The invention increases the reliability of the radio-beam alarm system independently from the length of the electromagnetic fence formed thereby, and reduces the number of faulty actuations.