| 摘要 |
PURPOSE:To always obtain the best receiving sensitivity, by using a digital means to control automatically the tracking of an RF tuning circuit. CONSTITUTION:A tuning volume 10 is coupled with a changing volume for local oscillating frequency (not shown in the diagram). Then the volume 10 is varied with interlocking to the selection of a certain broadcast signal. Thus the DC voltage value close to the approximate value of the broadcast signal frequency is supplied to a varactor within an RF amplifier 2 via a photodetecting element 21. Under such conditions, a flip-flop 14 is set. Then an oscillating circuit 16 and a clock pulse generating circuit 17 are actuated by a control circuit 15. An up-down counter 18 receives a clock pulse from the circuit 17 and then supplies the DC signals corresponding to the number of pulses to a light emitting element 20. As a result, the resistance value of the element 21 is reduced until a signal showing the best receiving point is obtained from a receiving peak detector 13. |
