| 摘要 |
PURPOSE:To draw in the sweep to the most suited tuning point, by retarding the sweep a little and correcting the overshoot, after the stop of automatic sweep. CONSTITUTION:An up-pulse is transmitted from an automatic sweep control circuit 2 to an up-down-counter 3 at a switch means 1, the counter 3 makes up-count, the digital output is applied to a varactor diode of a tuner 5 via a D/A converter 4 and the tuning frequency of the tuner 5 is swept to high frequency side. When the tuning frequency comes to the most suited tuning point, the sweep is stopped and the digital output of the counter 3 is shifted to higher frequency due to the delay in time of the D/A conversion and the response of an AFC voltage from the optimum tuning point. The correction is made by transmitting the down-pulse from a down-pulse application means 7 to the counter 3. Thus, the tuning frequency can be drawn into the optimum tuning point with an automatic frequency fine tuning circuit 5 to be succeedingly operated. |
