| 摘要 |
PURPOSE:To make it possible to hear sound of other main and sub-channels automatically by operating a change-over switch circuit to invalidate selection of the second sub-channel signal by a manual switch when the second sub- channel signal is not being received or nor more received. CONSTITUTION:The automatic change-over switch circuit 50 of a sound multiplex signal demodulating circuit, on receiving output of low pass filters 26 and 38, determines whether the operation is to be switched by a manual switch 52 or automatically according to receiving state signals from an fH pilot detector 16 and a 5 fH carrier discriminator 32. An automatic switching stereo multiplexer 54 is controlled by an automatic change-over switch circuit 50, and when a stereo signal is selected, performs ordinary stereo demodulation, and when an SAP (Secmd Audis program) signal is selected, executes corresponding processing. Further, in the case where broadcast is monaural when a stereo signal is selected, it operates to output L+R signal from a low pass filter 14 to the two channel output. |
