| 摘要 |
PURPOSE:To switch and control the band width of an IF stage even though numbers of high band components are contained in the desired receiving signal and to prevent a malfunction, by performing the switch control to the band width of the IF stage in response to the audio output excluding the beat components of signals of the desired receiving station and the adjacent station. CONSTITUTION:The signal of the adjacent station is amplified by a variable gain amplifier 9 which uses the output of a filter 3 as an input and in response to the gain controlling voltage and rectified by a rectifying circuit 10 to be applied to a comparator 11. At the same time, the audio output of a notch filter 6 is applied to a high-pass filter 7. The beat component is eliminated through the filter 7 for the desired receiving signal and the adjacent station signal. These signals are rectified by the rectifying circuit 8, and this rectified voltage is supplied in the form of the gain controlling voltage. The rectified voltage of the output of the amplifier 9 is compared with the prescribed voltage level through circuit 11. If the rectified voltage is higher than the prescribed level, the band switch signal is supplid to an IF filter 2 through a switch command signal generating circuit 12. Furthermore the output of the signal is discontinued when the voltage is less than the 2nd level. |
