| 摘要 |
PURPOSE:To prevent the stopping of the searching action at the idle channel caused by the effect of the adjacent channels in the strong field for the channel selecting device containing the automatic station searching function of the TV picture receiver or the like. CONSTITUTION:Comparators 24a and 24b plus 25a and 25b are connected to control input 26 and 27 of control unit 12 which controls the station searching action with supply of the division signal to PLL synthesizer 1. Then the output of VIF carrier detection circuit 9, synchronous signal detection circuit and IFAGC voltage production circuit 28 are supplied to comparator 24a, 24b and 25b, and 25a respectively. While the reference voltage is supplied to the other input according to the sensitivity setting position. In case the adjacent broadcast channels feature the strong field, the effect is given to the adjacent idle channels. But the station searching action does not stop since IF signal R and synchronous signal RL are secured when the sensitivity detting is under beta. And the AGC voltage becomes higher than RA at point (a) when the setting is right to beta, and thus the searching does not stop either owing to the output of comparators 25a and 25b. |
