| 摘要 |
PURPOSE:To obtain the stop signal which gives discontinuation to the frequency sweep action of the automatic tuning system of the receiver at the optimum tuning point and by means of the intermediate frequency signal of the narrow band and obtained through the mixing conversion of the intermediate frequency of FM and the intermediate frequency of FM. CONSTITUTION:The signal of IF (10.7MHz) of FM is applied to mixer 7, and at the same time the signal of 11.150MHz sent from crystal oscillation circuit 6 is injected also to mixer 7 to receive the mixing conversion into the signal of IF450KHz of AM. And the output is supplied to the ceramic filter of the narrow band with the central frequency of 450KHz as well as to IF amplifier 8. The output of amplifier 8 is supplied to detection part 9 to give smoothing to the AC component into the DC component. With such signal, the switched signal is obtained. On the other hand, the detection output given from FM detection circuit 10 is supplied to comparator 11, and signal S11 is delivered when the detection level enters the range of the upper and lower limit set levels. When both signals S10 and S11 feature the high level each, stop signal S12 is obtained from logic circuit 12 to prevent stop signal S12 from being caused by the noise. |
