| 摘要 |
PURPOSE:To reduce an S/N in both a stereo demodulation mode and a monaural action mode by detecting that the stereo demodulator has a stereo demodulating action or that the stereo demodulation mode is switched to the monaural action mode in response to the reduction of the field intensity. CONSTITUTION:A voltage control resistor 33 which obtains the resistance value from the noise level of a reception signal in the stereo demodulation mode of an FM demodulator 26 is set in a transmission route for noise signals. At the same time, the resistance value is set at a low level in the demodulation mode. Then the noise of the wave detection output is detected at a low threshold level. In a weak field intensity mode the resistance value is set at a high level in response to the monaural action of the demodulator 26. Then the noise of the wave detection output is detected at a high threshold level. Thus it is possible to reduce the S/N in response to deletion of noises of high or low levels when the stereo demodulation is possible at the high field intensity and when the stereo demodulation is impossible at the low field intensity. |
