| 摘要 |
PURPOSE:To decrease amount of detour to a prescribed value even if any subscriber line is connected to a 2/4-wire converting circuit by changing the value of a balancing circuit to correspond to the impedance of a subscriber line. CONSTITUTION:In the 2/4-wire converting circuit having a balancing circuit network 2' connected with a circuit connecting resistors R21-R2n and capacitors C1-Cn in parallel are connected in series with resistors R11-R1n, the resistors and the capacitors are formed into plural resistor and capacitor groups having selectable and different values. A subscriber device has an oscillator 8 having a frequency within a signal frequency band and a prescribed output level and an oscillator 9 having a frequency where the impedance of the capacitors is taken to a sufficiently small value and a prescribed output level. Further, the output of the oscillators 8, 9 is transmitted until the subscriber starts communication, and the resistors and capacitors matching with the subscriber impedance are selected by a selection control circuit 15 from a measuring value of a loop resistance measuring circuit 10 and level detectors 13, 14 of the detectors 11, 12 so as to reduce the amount of detour for a value satisfying a prescribed value. |
