Resetting the channels

So, as I previously mentioned, I got an OTA antenna so I can get HD channels for free, the ones that my cable provider doesn't provide. Well, I set it up and I now get those two channels I was missing. The problem is that apparently there is some sort of "shifting" during the day that affects my reception. Every once in a while, the signal goes a little funny and weak. The antenna has to be moved a little bit. This isn't a huge deal, but it is a little annoying.