| 摘要 |
PURPOSE:To secure sufficiently secrecy by preventing a unit from getting out of synchronism due to a turnaround, by attaining synchronization by extracting synchronous information from an input secret signal. CONSTITUTION:The input period of a sound signal to be sent out is detected by sound detection circuit 8; only during the sound input period, analog switch 9a is turned ON to send out a secret sound signal with an additional synchronizing signal and in this transmission period, analog switch 9b is turned ON to stop the reception of the secret sound signal. In a period except the sound input period, switch 9a is OFF with switch 9b ON so as to receive the secret sound signal from other stations without sending the secret sound signal of its own out. Consequently, no turnaround of its own signal occurs in the reception of the secret sound signal and the excellent secret sound signal with its period stabilized can be restored. |
