| 摘要 |
PURPOSE:To attain accurate tuning to a center frequency by inverting a sweep direction when a discrimination output in an automatic sweep exceeds a center voltage. CONSTITUTION:With switch ASW, search control part 11 is placed in automatic sweep mode and then signal RE resets selecting circuit 3 and counter 6. Next, counter 6 starts count-up operation with signal CU. Tuner 10 starts tuning operation by the output of counter 10 and control part 11 supervises a tuning discrimination output from AFC circuit part 18. Control part 11, when the output reaches a certain value exceeding a center voltage, uses horizontal and vertical synchronizing signals Hs and Vs and flyback pulse FBP from synchronous separating circuit 20 to find that broadcast signals are received properly and then makes counter 6 count down at a low speed with signal CU. When the discrimination output is equalized again to the center voltage, the value of the counter is stored in memory part 5 and then used for repetitive time channel selection. |
