The performance of two automatic gain control circuits is compared in an underwater acoustic receiver: a low-power hardware gain control and a software-controlled gain control that disables the gain change for a predetermined time interval after a valid signal level. Binary digits “0” and “1” are transmitted using bursts of the frequencies 33kHz and 43kHz, respectively, in two modes of operation. In the first mode, each digit is sent as one frequency burst followed by a pause. In the second mode, a frequency burst is transmitted at the beginning of a clock interval. Experiments are conducted in shallow waters. The results show that the hardware gain control circuit is suitable to equal time intervals between the transmitted bursts. The software gain control circuit allows arbitrary time intervals between the transmitted bursts. Increased power consumption of the device is detected as a disadvantage of the software gain control circuit.
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