| 摘要 |
PURPOSE:To prevent data and voice signals from mutual influences when both the signals are transmitted bi-directionally through the same transmission line by connecting subtracting circuits between the input and output terminals respectively. CONSTITUTION:When a data signal Ds is inputted to a data input terminal 79b, the input signal is modulated into a burst signal Bs with a tone frequency (f) included in a voice frequency band by a code modulating circuit 59b and supplied to an I/O part A through a transformer 66b and a transmission line 64a. Said input signal is amplified by an amplifier 50a and, even if a voice signal Vs is inputted simultaneously, only a burst signal Bs is selected by a band-pass filter 58a and demodulated and decoded into a data signal Ds. Said burst signal is simultaneously supplied to a subtracting circuit 74b. When a voice signal is not sent from the I/O part A, no signal is outputted from an amplifier 75b, but if a voice signal arrives, a voice signal is outputted from the subtracting circuit 74b to the amplifier 75b. In the same manner, voice and data signals are transmitted bi-directionally through a transmission line 64b. |
