| 摘要 |
PURPOSE:To ensure an accurate control for switching between the monaural and stereo modes, by installing the means that is controlled under a stereo state after triggering during existence of the difference signal and reset when the level of the received signal drops or no sum signal exists. CONSTITUTION:In case the field intensity is large enough with existence of the audio signal, a difference signal is delivered from the FM wave detector 2 in a stereo broadcast mode. The output of the rectifying circuit 6 has a high level to trigger the memory circuit 7, and the stereo/monaural change-over switch 3 is controlled to a stereo mode. With a reduction of the field intensity, the output of the comparator 10 to which the output of the rectifying circuit 9 is applied has a low level. Thus the circuit 7 is reset, and the switch 3 is controlled to a monaural state. When the audio signal is discontinued, the output of the rectifying circuit 8 to which the sum signal is applied from the AM wave detector 1 has a low level to reset the circuit 7. Thus a monaural state is held. |
