| 摘要 |
PURPOSE:To solve the failure of lowering the communication state with suppressed transmission again after the transmission signal has interruption for a given time, by holding the detection threshold value for transmission signal interruption state detection, obtained immediately before the transmission signal interrupting state. CONSTITUTION:The threshold value and the signal level are compared at the comparison circuit 8 when only the reception signal is fed, and if the signal level is greater, the switch 1 is open and the ratio of the output of the peak hold circuit 3 to the echo signal is obtained in the division circuit 2 at the same time to obtain the maximum value in a given time. The minimum value among the maximum values is multiplied with the reception signal at the multiplication circuit 6 and compared with the transmission signal input at the comparison circuit 7. When the transmission signal is fed with this state, the transmission signal input is greater in the comparison circuit 7 to detect the transmission signal, the switch 1 is closed with this, the echo line loss coefficient is greater, and the entrance to the transmission suppression area again is blocked. |
