I have a UHF/HD antenna I bought from Best Buy a while back and Have it hooked up to a Samsung SIRT 451. I'm about 30-40 miles from the TV stations. While I get a decent signal from the stations, I have to reposition the antenna in order to pick each one up. Even though the stations are coming from the same general direction. Is this common? Is it possible I need a different antenna? Thanks for any comments.