| 摘要 |
PURPOSE:To make it possible to decide difference of control by double detecting m- ans accurately even if the control signal is subjected to cross modulation distortion, by incorporating a malfunction preventing circuit into the switching signal generating circuit. CONSTITUTION:The control channel signal is input to BPF13, and the output is input to waveform shaping circuit 14 and AM detector 18. The 55.1kHz subcarrier signal is shaped into a square wave by circuit 14 and is input to NAND gate 20. The control signal obtained by subjecting the 55.1kHz subcarrier wave to AM modulation is output in detector 18 and is input to waveform shaping circuit 19. Gate 20 has switching controlled by the pulse whdth of control signals 922.5Hz and 982.5Hz which had waveforms shaped. When gate 20 is opened, pulses of 55.1kHz are supplied to counter circuit 15, and circuit 15 starts counting. When circuit 15 counts a prescribed value, the discrimination information signal is supplied to switching signal generating circuit 16. This signal indicates that the control signal of 922.5Hz has come, and it is detected double by malfunction preventing circuit 17 incorporated in circuit 16. |
