| 摘要 |
PURPOSE:To eliminate an impulsive noise effectively, by amplifying harmonics of an output of an HPF passing a noise component, turning on and off a switching circuit at a suitable time constant and controlling a noise sensitivity adjusting circuit. CONSTITUTION:The harmonics appearing at an output of the HPF5 passing the noise component are amplified at a transistor (TR) 25, this output is inverted at a TR18 to control a switching TR24 via an integration circuit comprising capacitors 20, 22 and resistors 21, 23. The time constant of the integration circuit is selected so as to conduct the TR24 at a repetitive frequency such as ignition noise and to nonconduct the TR24 at an intermodulation interference and multipath interference and the like. When the TR 24 is conductive, the noise sensitivity adjusting circuit 8 is grounded to bring the operation of a noise detecting circuit 6 to the optimum sensitivity, a gate circuit 3 is operative via a trigger circuit 7 and the noise is interrupted. Thus, the noise eliminating circuit is operated effectively with respect to an impulsive noise, inoperative with respect to a randam interference having a quick period such as intermodulation interference and the like, thereby improving the sound quality of a desired signal. |
