| 摘要 |
PURPOSE:To prevent spurious radiation of a radio receiver with simple constitution, by inserting a prallel resonance circuit to an antenna circuit. CONSTITUTION:A broadcast signal incoming from an antenna 1 is applied to an antenna input circuit 2 via the parallel resonance circuit 6 and further inputted to a high-frequency amplifier circuit 3. A frequency mixing circuit 4 mixes an output of the high-frequency amplifier circuit 3 and an output of a local oscillating circuit 5, generates an intermediate frequency signal of a prescribed frequency and outputs the signal to an intermediate frequency amplifier (not shown) at a post-stage. The parallel resonance circuit 6 connected to the antenna circuit consists of an inductance L3, a varactor diode D1, and a capacitor C1, is controlled simultaneously with the local oscillating circuit 5 and controlled to a resonance frequency coincident with the local oscillating frequency. Then, the resonance circuit 6 prevents a signal of the local oscillating circuit 5 from being irradiated spuriously from the antenna 1 via the amplifier 3 and the antenna circuit 2. |
