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Abstract

A siren detector for detecting siren sounds which precess at known yelp, wail and high-low warble rates within a selected frequency band. A transducer detects siren sounds and produces a corresponding electrical output signal. The output signal is filtered to reject signal frequencies outside the selected frequency band. The signal amplitude is monitored and varied as required to produce a constant amplitude output signal. The constant amplitude output signal is low pass filtered for detection of siren high-low sounds and is also low pass filtered for detection and output of precession signals which pass through a selected center frequency. Subsequent filters are provided for detecting signals which vary at the wail and yelp warble rates. Wail, high-low and yelp warble rate signals output by the various filters respectively trigger wail and yelp clock generators which in turn drive don't walk and red light output flip-flops respectively. Operation of the red light output flip-flop is controlled by a delay mechanism which provides a further filtration level to prevent false triggering.

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First Claim