SIGNAL SYNCHRONIZING CIRCUIT OF PRIVACY TELEPHONE TRANSMISSION SYSTEM

PURPOSE:To prevent the malfunction of synchronization at the mixing of noises and to remove the deterioration of reproduced sound quality due to a synchronous miss by superposing a synchronizing signal controlled by the output of a control circuit to a transmission signal. CONSTITUTION:The output of a synchronizing signal generating circuit 8 is gate controlled by the output of a control circuit 7 counting up clocks corresponding to the prescribed delay stages of a variable delay circuit 5 and superposed to a transmission signal and transmitted. On the receiving side, the transmission signal is separated from the synchronizing signal by a filter circuit 14, a pulse string is generated in accordance with the synchronizing signal and a trigger signal is generated synchronously with the pulse string. A control circuit in a clock selecting circuit 15 is preset in response to the trigger signal to synchronize the switching time of clock pulses of a transmitter/receiver and a switching time synchronizing signal for clock pulses is selected from the trigger signal by using the output signal of the control circuit in the circuit 15.