| 摘要 |
PURPOSE:To prevent a channel transmitting a non-modulated carrier from being selected as a communicating channel without the delay of scanning frequency by using both carrier detection and low frequency detection. CONSTITUTION:A receiving signal from an input terminal 1 is received by a channel tuning circuit 2 in an automatic channel scanning system and its output is branched and inputted to a signal demodulation circuit 3 and a carrier detector 6. A low frequency signal demodulated by the circuit is branched, one branched signal is inputted to a speaker 5 through a low frequency output circuit 4 to output a voice and the other is applied to a low frequency detector 7. A detecting signal detected by the detector 6 is applied to the low frequency detector 7 and a scan stopping circuit 8 and a non-detected signal from the detector 7 is applied to the circuit 8. If no low frequency signal is detected by the detector 7 within a fixed period, a non-detecting signal is outputted to stop a signal from the detector 6. Then, a channel scanning circuit 9 starts to scan again and all circuits are restored to normal state. |
