| 摘要 |
PURPOSE:To detect interference precisely by using a receiving signal from which level fluctuation due to fading is removed and also using level fluctuation at the time of no modulation. CONSTITUTION:A receiving signal (in) is applied to an amplifying circuit 1 whose gain is automatically controlled, so that level fluctuation due to fading is removed. The outpt of the amplifying circuit 1 is applied to an amplitude detecting circuit 2 and a beat waveform is extracted. The beat waveform is applied to a level measuring circuit 3, the measured result is compared with a reference value Vc by a comparator 4 and carrier level fluctuation due to an interference wave is detected and applied to a gate circuit 7. On the other hand, the output of the amplifying circuit 1 is modulated by PM (or FM) demodulator 5. The demodulated output is applied to a call detecting circuit 6 and whether the signal is modulated or not is detected. During calling, a call detection signal is applied to the gate circuit 7 to close the gate 7. Thus the level fluctuation due to fading or at calling is prevented from being wrongly detected as the level fluctuation due to an interference wave, so that a precise detection output (out) can be obtained. |
