Laboratory tests with active hydroacoustic echo reduction

An active sonar detects an object by its echo. If the object transmits a copy of its echo but with 180 degrees phase shift this will cancel the echo at the sonar. This concept works only in monostatic cases. In this report the design and construction of a simple echo canceller is described and the measurements performed in a tank are analyzed and presented. The results show that better than -20 dB cancelling is possible against pings with slowly varying amplitudes and/or frequencies.