| 摘要 |
PURPOSE:To control a front end in accordance with the level of disturbance due to an approximate disturbance wave, by extracting a low frequency signal by giving an wave detection to an envelope signal and at the same time superposing the low frequency signal on an AGC control signal after amplifying and detecting the low frequency signal component. CONSTITUTION:A part of a high frequency signal delivered from a front end 1 is supplied to an AGC amplifier 4 to receive the amplification and wave detection. Then the DC component corresponding to the field intensity is fed back to the front end 1 via a superposing circuit 5 and in the form of an AGC control signal. On the other hand, a low frequency signal produced from the amplifier 4 through amplification and wave detection is supplied to an AC amplifier 6 to receive again the amplification and wave detection, supplied to the circuit 5 to be superposed on the AGC control signal delivered from the amplifier 4 and then fed back to the front end 1. Thus the cross modulation, the disturbance of RF mutual modulation, etc. caused at the front end 1 by an approximate disturbance wave can be eliminated. |
