| 摘要 |
PURPOSE:To loop back the transmission level of line standards even if secular change occurs in the line characteristic, by setting an amplification gain value, which compensates the difference between the measured value of a reception signal level and a reference transmission level, to an amplifying circuit in a back loop. CONSTITUTION:When the looping command from a modulating and demodulating device 2 passes a communication line 4 and is demodulated by a demodulating circuit 6 and is outputted as reception data 21, a control circuit 11 reads an output 22 from a level measuring circuit 10 which measures the reception signal. The gain of the amplifier 9 is controlled by a control signal 23 so that the output level of an output signal 25 of the amplifier 9 is 0dBm, and a control signal 24 is outputted to switch circuits 12 and 13 so that they are in contact states to form a loop. Thus, a transmission signal is transmitted in the loop-back transmission level in circuit standards even if the line loss characteristic is varied by secular change. |
