| 摘要 |
PURPOSE:To automatically set a transmission signal on a telephone line by performing control on the passing band of a reception filter, checking the level of the transmission signal on the telephone line and varying the gain of a transmission amplifier. CONSTITUTION:A modulation/demodulation circuit 12 informs the entry of a mode to check the level of the transmission signal to an amplifier 15 and a clock generator 13 by using a control signal. Then, the amplifier 15 stops output. In other words, the input signal of an adder 2 is limited only to the transmission and a reception signals from the telephone line 1. Also, the generator 13 varies a clock frequency to be supplied to the reception filter 4, and varies it to a band area where the carrier of the transmission signal passes. The output of the adder 2 is inputted to the reception filter 4, and goes to only the component of the transmission signal, and after that, it is supplied to the modulation/demodulation circuit 12 via a reception amplifier 5. The modulation/demodulation circuit 12 checks the level of the transmission signal, and varies the gain of the transmission amplifier 14, then, sets the optimum gain. |
