| 摘要 |
PURPOSE:To make the output level of a line monitor at the time of reception constant by stopping the operation of an AGC circuit at the generating a signal tone sent from its own equipment. CONSTITUTION:A signal generated from a transmission section 3 reaches the AGC circuit 5 through a switching circuit 2. In such a case, a command is inputted from the transmission section 3 to an AGC control circuit 6 via a control line 10 and the AGC control circuit 6 turns off the AGC circuit 5 thereby preventing the change of the level adjustment through the operation of the AGC circuit 5 by a signal generated from the transmission section 3. On the other hand, a signal through a line is inputted through an NCU 1 at the time of reception and inputted to the AGC circuit 5 and the reception section 4 by the switching circuit 2. In such a case, since no command from the transmission section 3 is inputted to the AGC control circuit 6 via the control line 10, the AGC circuit 5 is activated to apply automatic adjustment to the reception level, thereby monitoring the line signal.
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