PURPOSE: To reduce the power consumption of a communications satellite by incorporating a signal current transmitting circuit which is controlled by the start and stop pulses and transmitting signals only when necessary.

CONSTITUTION: The earth information is supplied to a control circuit 3 at the transmission side, and a start pulse which is turned on only for a fixed period of time is transmitted to a switch circuit 2 through a transmission start pulse generating circuit 4. Thus a signal current is supplied to a talking circuit L from a signal frequency oscillator 1 only in the period of the start pulse. The signal frequency is detected by a detecting circuit 9 at the reception side. Then it is decided that the start is applied when the signal frequency is received longer than the period set by a timer. Then the circuit 2 is controlled by the pulse given from a reception start pulse generating circuit 6 and via a reception control circuit 8. Thus the earth information is continuously delivered through an SR terminal.