| 摘要 |
Method for the gain control of an intermediate amplifier used in two-wire connections of a dial telephone network. The invention is also concerned with an intermediate amplifier used in such connections, the direction of the gain of the amplifier being controlled in accordance with the signal strength. The method comprises measuring the amplitudes of signals coming from different transmission directions, comparing the measured amplitudes of signals coming from different directions with each other, and controlling the gain of controllable amplifiers (12, 22) on the basis of the difference value of the amplitudes by applying a control voltage to the controllable amplifiers (12, 22) through reverse-phase control adapters (13, 23). According to the invention the gain is controlled continuously and steplessly by means of the control voltage, which is continuously adjustable within the linear range thereof, whereby means for controlling the gain of controllable amplifiers (12, 22) comprise a level measuring circuit (A, B) provided separately for both transmission directions, a common difference amplifier (18) connected to the outputs of the level measuring circuits (A, B), and a PI-controller (19) connected to the output of the difference amplifier (18), the output of said controller being connected to the control adapters (13, 23). |
