PURPOSE: To reduce the influence of underwater noise by sending out an ultrasonic signal obtained by applying a sound signal with analog modulation, into the water, and providing a level deciding means for a received demodulating signal and a timer for deciding the detection of a signal and its end.
CONSTITUTION: An underwater communication is executed by sending out an ultrasonic signal which is applied with analog modulation by a sound signal, into the water, in a transmitting part, and demodulating said signal in a receiving part. In such a case, when the level of an input signal becomes higher than a prescribed level, a demodulating circuit inputs a carrier detecting signal (b), starts a first timer 21, and when the signal (b) is continued longer than a time time T1, a comparing circuit 22 decides it to be signal detection, and by turning on a power amplifier control signal (c), the output of voice is started. After the voice output is started, when the level of the input signal becomes lower than the prescribed level, the signal (b) is turned off, a second timer 24 is started, and when the signal (b) is turned off longer than a timer time T2, a comparing circuit 25 decides it to be a signal disconnection and stops the output of the voice. In such a way, the influence of underwater noise can be reduced.
SUZUKI MASAMITSU
KADOKAWA YUICHI
