| 摘要 |
PURPOSE:To prevent erroneous channel selection due to a spurious and a low- level signal by connecting a constant voltage source to an AGC voltage applying terminal of an electronic tuner through a switch and controlling the gain of the tuner to an intermediate gain during the channel selecting operation. CONSTITUTION:A receiving signal is inputted to an electronic tuner 2 of a receiver, and a signal detected by a detecting circuit 3 is applied to an automatic sweeping circuit 5 to detect a variance of the AFC voltage, and a tuning voltage is applied to the tuner 2 to perform the channel selecting operation. A constant voltage source 11 is connected to an AGC voltage applying terminal 9 of the tuner 2 through a switch 10. This switch 10 is closed by a control signal from a sweep control circuit 7 of the circuit 5 simultaneously with start of the sweep channel selecting operation. The gain of the tuner 2 is controlled forcibly to the intermediate gain reduced in a certain degree during the sweep channel selecting operation to prevent the erroneous channel selecting operation due to the spurious of the tuner 2 itself and a low-level unnecessary signal. |
