Bad DTV and HDTV reception in basement, please help


I'm in sioux falls sd and thus far have had fairly good luck on my first two dtv converter box setups. I had just received a nice TV that I've decided to put in my bedroom. I went out and got an RCA box, as well as a fairly expensive antenna. As you hopefully have assumed by the title of this thread, this final setup is in my basement bedroom. I did the initial scan and picked up 5 channels. A little shy of the 15 channels I get on my other two TVs. I checked the signal strength and did the tedious task of getting the highest possible reception. Re scanned and found a new station! Yay! I now have six. Here's the kicker and the main point... My max reception now is 38%! That's horrible! I'm fully aware that not all stations are broadcasting in full power. But I received better signal before the whole hdtv idea. I'm hoping this won't be a continued problem. If anyone out there has discovered a fix or has knowledge of what my problem is, please respond.