| 摘要 |
PURPOSE:To separate four audio signals completely while reducing the disturbance of an SCA broadcast signal by use of an SCA filter, by providing a phase correcting circuit to a detecting method for the 3rd subchannel signal in a four-channel stereophonic demodulator. CONSTITUTION:To input terminal 1, a four-channel stereophonic composite signal is applied which consists of the main channel signal, the 1st subchannel signal, the 2nd subchannel signal, the 3rd subchannel signal, and a 19kHz pilot signal. Since the frequency band of the 3rd subchannel signal overlaps with that of an SCA broadcast signal, only the main channel signal and the 1st and 2nd subchannel signals pass through SCA filter 3 and the 3rd subchannel signal passes through phase correcting circuit 4. For this purpose, phase correcting circuit 4 corrects the phase shift of the main signal, etc., from the 3rd subchannel signal generated when it passes through SCA filter 3, and consequently a phase shift among four channel signals never appears in detection, so that four audio signals can completely be separated. |
