I'd check the cable your using to make the connection as well as the input on your television. I have an antenna amplifier if that's what you mean by a line amp. It does a great job of improving reception for our rural off air reception. It could be that the tuner in your set is not very good. I'm guessing you are running through a vcr and its tuner when you say you are using the video input. My toshiba vcr tuner seems somewhat better than my toshiba tv tuner.

Mark