Abstract: A gain-controlled amplifier (24) in a sonic flow meter accepts an output signal from each transducer of a plurality of pairs of transducers (1a, 1b; 2a, 2b; 3a, 3b; and 4a, 4b) in sequence. A ramp generator (62) generates a time-varying-gain output, which increases between the transmission of a pulse by one transducer and the reception thereof by another. This time-varying-gain signal is one component of the amplifier's gain-control signal, which includes as another component an AGC value fetched from a memory (50) and rendered into analog form by a digital-to-analog converter (42). The value in the memory (50) is the difference between the time-varying-gain value and the value that other circuitry (30, 36) has determined to be necessary by monitoring the amplifier output produced during a previous operation of the same transducer pair.

Abstract: A hydrophone (16) having a short-baseline array of transducers (12A, 12B, and 12C) as well as a long-baseline array of transducers (14A, 14B, and 14C) includes switches 30A, 30B, and 30C) for selectively connecting the outputs of the arrays to a cable (18) that carries the signals to processing circuitry (20) aboard an ocean-going vessel (24). The switches (30A, 30B and 30C) change state in accordance with the output of a narrow-band filter (42), which indicates whether the received signal is of a predetermined frequency and thus is likely to have been produced by an intended source. Due to the delay inherent in the narrow-band filter 42, the processing circuitry (20) thus processes the response of the long-baseline array to the first part of a beacon pulse and the response of the short-baseline array to the second part of the beacon pulse.