| 摘要 |
PURPOSE:To keep excellent receiving state at all times, by using a synchronizing detection output of a receiving signal for the purpose of automatic control so as to prevent the generation of abnormal sound at leading of modulation and sudden change in sound volume. CONSTITUTION:An output signal of an intermediate frequency amplifier circuit 4 is processed respectively at a PLL circuit 6, multipliers 5, 9 and LPFs 7, 10 and an output of the LPFs 7, 10 is processed at a matrix circuit 13. An output of the LPF7 or LPF10 is provided with an LPF25 comprising a resistor 23 and a capacitor 24, the LPF25 extracts a DC component included in an output of the LPF7, and the DC component is applied to an automatic gain control circuit 17. Then, the DC component is brought into correspondence with the carrier component and the difference between no modulation and modulation is eliminated, the DC component controls automatically the gain of a high frequency amplifier circuit 1 and an amplifier circuit 4 so as to prevent the generation of abnormal sound and to keep the excellent receiving state at all times. |
