| 摘要 |
PURPOSE:To suppress a echo during conversation by accurately inferring subscriber impedance regardless of fluctuation of a central office power supply voltage so as to optimumly set a balance network based upon the inferred result. CONSTITUTION:A balance network 11 for improving a separation characteristic between a transmission signal and a reception signal at a two-wire/four-wire converting part 13 and a SEL circuit part 12 for setting an impedance of the balance network 11 are provided. Further, a voltage detecting circuit 1 for detecting a line voltage of a subscriber line, a current detecting circuit 2 for detecting a loop current which flows in the subscriber line and an arithmetic processing part 3 which calculates a DC line resistance of a subscriber based upon the outputs from the voltage detecting circuit 1 and the current detecting circuit 2 are provided. From the operating result at this arithmetic processing part 3, an optimum impedance for the balance network 11 is selected, and a selected command is transmitted to the SEL circuit part 12 by a balance network controlling part 4. |
