| 摘要 |
PURPOSE:To decrease adjacent interference, cross modulation interference or the like by shifting a tuning frequency of an antenna input circuit in the direction where a interfering signal is decreased. CONSTITUTION:If the interfering signal exists in a frequency higher than an intermediate frequency signal fi, an output of a BPF7 is detected at a detector 9 and applied to a negative polarity input terminal of a comparator 11. An output signal of the comparator 11 goes to negative and applied to a varactor diode 1a of an antenna input circuit 1. Thus, the tuning circuit of interference. If the interfering signal exists in a frequency lower than the signal fi, the output of a BPF8 is detected by a detector 10, applied to a positive polarity input terminal of the comparator 11, the output signal goes to positive and applied to the diode 1a. Thus, the tuning circuit of the circuit 1 is shifted to a higher frequency. As a result, a signal decreasing the interfering signal is outputted from the output of the mixing circuit 4, the signal fi, allowing to attain excellent receiving. |
