| 摘要 |
PURPOSE:To hold the noise level in a fixed value or less to prevent degradation of the transmission quality, by returning increment of the noise level in an idle-state auxiliary band as a detection signal to control the input signal. CONSTITUTION:The noise level is detected in noise level detecting circuit 14 by output line 13 of idle-state auxiliary band f2 from carrier frequency multiplex terminal station 11. When the detection level exceeds a set value, the line of the (n-1)th communication hannel #n-1 is used to transfer the detection signal to the carrier frequency multiplex terminal station 10 side by level discriminating circuit 15 and transfer circuit 16. In the terminal station 10 side, the returned detection signal is detected by discriminating circuit 17, and the control signal is supplied to level control circuit 18, and amplifier 19(n) is controlled by the output to rise the gain automatically, and simultaneously, the gain of amplifiers 19(1)-19(n-1) connected to inputs of other communication lines #1-#n-1 is lowered. |
