| 摘要 |
PURPOSE:To improve the S/N at the weak field through the mode switching from stereo to monaural as well as the high-band cutting circuit. CONSTITUTION:When the field intensity lowers down, the IF detection output lowers accordingly. As a result, the control voltage is produced. This control voltage lowers the switching signal output of 38kHz, and accordingly the value is decreased for demodulated stereo signals L-R and R-L. Thus the degree of stereo separation is deteriorated, but has S/N is improved since the monaural hearing mode becomes approximate. For the monaural mode too, the control is given so that transistor 26 may conducts if the field intensity lowers down so much that the S/N is deteriorated. Thus the high-band cutting main channel signal is led out to the base of transistor 33 from stereo composite signal input terminal 18 via high-band cutting circuit 32. As a result, the mode transfers smoothly from stereo to monaural and then to the high-band cutting. |
