| 摘要 |
PURPOSE:To stop the automatic sweep accurately in a high speed, by making the sweep speed low to perform the counting operation when a station signal indicating whether a broadcasting signal is present or absent. CONSTITUTION:A band muting signal generating circuit 15 is used as a station detecting circuit which detects whether the broadcasting signal is present or not, and a band muting signal M of its output is used as the station signal indicating whether the broadcasting signal is present or not. When the signal M does not exist and is in the level L, the counting operation is not performed, and the high-speed sweep is performed. When the signal M becomes the level H, the sweep speed is switched from the high speed to the low speed to perform the counting operation, and the automatic sweep is stopped if the counted value does not reach a prescribed value within a certain time. Consequently, the malfunction due to erroneous counting in the high-speed sweep is prevented, and the sweep time is shortened. |
