| 摘要 |
PURPOSE:To attain a small-sized device by detecting a signal of an auxiliary communication job channel directly from an FM stereo scopic composite signal so as to reduce the fine adjustment of the entire detector. CONSTITUTION:A local oscillation circuit 100 using a PLL circuit and a frequency divider circuit so as to output signals fa2, fb2 whose frequencies are coincident respectively with the frequencies fa, fb to be selected by a digital frequency modulation (FSK) carrier and a 1st detection circuit 300 detecting the presence and absence of a DC term in a beat component being a difference of frequency obtained through the multiplication between the fa2 signal and the FM stereo scopic composite signal so as to detect the presence and absence of the fa component in the FSK carrier are provided. Moreover, the 2nd detection circuit 400 detecting the presence and absence of a DC term in the beat component being the frequency difference through the multiplication of the fb2 signal and the FM stereo scopic composite signal to detect the presence and absence of the fb component of the FSK carrier is provided. Thus, the fine adjustment of the detector is decreased and the small-sized device is attained. |
