Ultrasonic sound signal device to scare away birds - has one frequency linearly and one non:linearly varying with time between two limits

摘要

Device is intended for driving away birds by generating noise. It consists in generating at least two ultrasonic sound signals, the frequency of one of which varies linearly with time between two limit values, whilst the other varies non-linearly with time between two valves. The upper and lower frequency limits of the different signals maybe identical. The non-linearly varying signal may vary following a trapezium shaped curve. The limits may be 18.5 and 26.5 kHz.