| 摘要 |
PURPOSE:To prevent malfunction and abnornal operation of tuning indication by forcing the tuning indication operation to stop when an input signal is below a constant level. CONSTITUTION:When a reception frequency is swept upward from the lower part of tuning frequency f0, detecting circuit 2 outputs a S-curve DC signal to DC amplifying circuit 3, which amplifies the input signal to control driving circuit 6. If an intermediate frequency lowers below a certain level, a DC voltage rectified by rectifying circuit 4 also drops, and consequently the output of switching circuit 5 is inverted. Through this inversion, the S-curve detecting amplification output of amplifying circuit 3 is cut off and no input arrives at driving circuit 6, stopping the operation of the indicator. Thus, the malfunction and abnormal operation of tuning indication can be prevented from occurring when the input is zero or very small. |
