| 摘要 |
PURPOSE:To attain reception with high sensitivity and to prevent cross modulation even at a weak electric field, by providing an electric field detecting wire to a car body to suppress an input voltage to a high-frequency active circuit when the detected electric field exceeds a specific level. CONSTITUTION:When a broadcast station is located at a remote location and the electric field is weak, the power induced in the wire 19 is small, a transistor (TR)24 is turned off and a switch 26 is opened. Thus, the electromotive force received and induced in an antenna 11 is amplified at the high-frequency active circuit 12 and transmitted to a receiver via a tramsmission cable 16. Thus, a voltage drop is produced across a resistor 20 even under a strong electric field, this voltage drop is detected and amplified by a TR21, and a storage potential of a capacitor 23 is increased. Thus, when the TR24 is turned on, the switch 26 is closed, and the electromotive force of the antenna 11 is grounded via a resistor 27, then the input potential to the high-frequency active circuit 12 is decreased even under a strong electric field and no intermodulation takes place. |
