| 摘要 |
PURPOSE:To perform impedance matching over a wide reception frequency range, by canceling the inductance of an antenna through the change of a capacitor of a varactor diode, in correspondence with the inductance change conforming to the change in a recpetion frequency of a defrosting heat coil. CONSTITUTION:To provide a signal from an antenna 18 serving also as a defrosting heat coil installed on glass to a reception circuit, an impedance matching circuit 81 is provided. A voltage dependant varactor diode 86 is inserted between the antenna 18 and the reception circuit, and voltage is given to this diode 86 from a varactor diode controlling circuit 100. This circuit 100 gives a voltage decreased as the reception frequency increase, at a reception frequency region less than the reception frequency where the inductance of the antenna 18 is minimized. At a reception frequency region at a reception frequency or over where the inductance of the antenna is minimized, a voltage increased as the reception frequency increases is provided. |
