Alarm sensor and antenna arrangement

Communications: electrical – Land vehicle alarms or indicators – Of burglary or unauthorized use

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Details

3404255, 340541, 340552, 307 102, B60R 2510

Patent

active

059990902

ABSTRACT:
A microwave frequency Doppler vehicle intruder alarm comprises an oscillator 3, a mixer 2 and an amplification stage 4, 5 having its output applied to a low-pass filter 7, whose output is split into two branches. A first branch, comprising a rectifier diode and a comparator, provides a signal on its output when a significant level of non-carrier microwave signals is received. This branch is sensitive to signals having Doppler frequencies of 0-200 Hz, which includes the intruder indicative frequencies. A second branch, comprising an amplifier 8, a high pass filter 9, and a comparator 10, provides an output signal on the detection of a significant level of signals in the 40-200 Hz band, which frequencies are indicative of externally generated interference. A logic element 15 mutes the output of the alarm when the second branch indicates the presence of externally generated interference. An antenna arrangement (FIG. 3, not shown) generates a rectangular radiation field which provides optimum coverage of the interior of a vehicle by being mounted in the roof thereof. Steering of the radiation field to provide optimum illumination when the arrangement is mounted off-center on the roof is achieved by the use of a shunt capacitor to effect a phase difference in signals applied to respective ones of first and second antennae.

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