| 摘要 |
PURPOSE:To make a gain control circuit of a multi-frequency common amplifier consisting of a variable attenuator and a main amplifier simple and economical. CONSTITUTION:The input rectified voltage (1) is obtained by extracting a signal proportional to the level of a multi-frequency input signal through a distributor 3 and then rectifying the extracted signal by a rectifier 6. Meanwhile the output rectified voltage (2) is obtained by extracting a signal proportional to the level of the output signal extracted from a coupler 4 and then rectifying the extracted signal by a rectifier 7. Then both voltage (1) and (2) are supplied to a control circuit 5. A control signal (3) is applied to a variable attenuator 2 so that the difference between both voltage (1) and (2) is set within a prescribed range. Thus the gain of an amplifier is controlled and also an alarm (4) is produced when the difference of both voltage (1) and (2) exceeds the prescribed range. |
