| 摘要 |
PURPOSE:To improve side tone characteristic and singing margin by detecting speaking current value and selecting plural balancing network circuits provided in a two-wire four wire converting circuit. CONSTITUTION:Current level of a main wire 3 is detected by a balancing network selecting circuit 7 that forms the loop circuit of a telephone exchange and exciting and non-exciting of a relay is controlled through a balancing network circuit selecting relay winding 10. A balancing network 15 or 16 corresponding to the amount of attenuation for the change of impedance depending on line distance is selected through a relay contact 14 of a two-wire four wire converting circuit 13. Consequently, side tone characteristic and singing margin in the telephone exchange can be improved.
|
