| 摘要 |
PURPOSE:To increase the dynamic range, by turning on and off the attenuator provided at the input terminal of the received signal in coupling to the AGC. CONSTITUTION:The AGC value is proportional to the gain of the amplifying circuit, and the gain is set to 100dB when the AGC value is 1,000. When the gain of the amplifying circuit reaches the upper limit value 80dB, the AGC value of 800 is detected by the attenuator on/off control circuit 13. Thus the attenuator 7 is turned off. In this case, the AGC value is corrected to the value with 300 reduced when the amount of attenuation of the attenuator 7 is 30dB. Then the AGC value increases as the signal is weakened. When the received signal becomes strong up to the limit of the dynamic range, the AGC value becomes to 400. In this instant, the circuit 13 turns on the attenuator 7, and at the same time the AGC value is corrected to the value with 300 increased. |
