TIME VALID GAIN CONTROL SYSTEM CORRESPONDING DOUBLE PULSE

PURPOSE:To improve the reception accuracy of a time variation gain control system by processing a 2nd response signal corresponding to depth with the same gain as that at the time of the reception of a 1st response signal corresponding to a distance. CONSTITUTION:An interrogation signal S is inputted to a transmitting circuit 21, the latch terminal L of a latch circuit 26, and the reset terminal R of a counter 25 and also converted into an interrogation signal Sa, which is sent in the sea by a transmitter 22. When a transponder 30 receives the signal Sa, said transponder 30 sends back a 1st signal Sb1 corresponding to the distance and sends a 2nd signal with time delay corresponding to the depth. When a receiver 23 receives the signal Sb1, said receiver 23 outputs it to a terminal L and then the counter 25 holds its numeral and outputs a time variation gain control signal output S26 to a receiving circuit 24. The circuit 24 amplifies the signals Sb1 and Sb2 according to the gain and supplies the amplified signals to a signal processing circuit.