| 摘要 |
PURPOSE:To improve the quality of transmission by providing a switching circuit detecting the disuse of both telephone sets of a talking section for transmission/ reception and switching the transmission level of a data signal from both transmission systems according to the detecting signal to the output side of both transmission systems. CONSTITUTION:The transmission system 3 consists of a transmission circuit 1 and a modulation circuit 2 and the reception system 6 consists of a demodulation circuit 4 and a reception circuit 5. Then a switching circuit 19 is provided between the modulation circuit 2 and a hybrid transformer 7. Then the 1st control signal is outputted to the switching circuit 19 from a control terminal 22 of a telephone circuit 10 through the changeover of the hook switch 21 of a telephone set 9 to the talking side and a transmission data signal comprising a data including an item for level changeover in each item of the data is transmitted from the transmission circuit 1 by the 1st control signal. The 2nd control signal is outputted respectively to the changeover circuit 19 from the control terminal 23 of the data reception circuit 5 receiving the data signal. Multiplex communication is attained via a device 17 and a communication line 15 similarly. |
