| 摘要 |
PURPOSE:To realize the muting system for the mobile FM radio receiver to secure the easy-to-hear voice, by muting the low-frequency signal hard at the detuning time and soft at the time of the weak field intensity respectively. CONSTITUTION:The IF level signal of IF amplifier circuit 2 obtained through level detecting circuit 5 and band pass filter 6 plus the detection output level signal of FM detector 3 obtained through level comparator 7 are applied to AND circuit 8. And circuit 8 applies the output signal shown in (a) to OR circuit 9 at the tuning operation time. At the tuning operation time, circuit 9 gives the control to attenuator 4 by the signal shown in (a) to carry out the hard muting. And in case the field intensity is reduced at the tuning time, the control is given to attenuator 4 by the signal shown in (b) which is supplied from circuit 5 to carry out the soft muting. |
