| 摘要 |
PURPOSE:To suppress the detuning of a radio receiver for a vehicle, the generation of a beam noise, and the generation of distortion by varying the length of a receiving antenna according to the intensity of a received radio wave. CONSTITUTION:When a radio wave has enough intensity to be covered by normal AGC, turning on the power source of a radio receiver permits a motor controlling circuit 20 to drive a motor 19, and the length of a receiving antenna 10 is maximized. When a vehicle runs into an area where the received radio wave is intense, e.g., right under a transmitting antenna, the reception input increases and the output of an AGC circuit 18 connected to the output side of a detecting circuit 15 also increases to decrease the gains of a high frequency amplifying circuit 11 and an intermediate frequency amplifying circuit, but when an AGC voltage rises above a reference value, the motor controlling circuit 20 drives the motor 19 to shorten the length of the receiving antenna 10. |
