Yep in addition to making sure the the antenna has a good ground, it has to be trimmed. (I think it something called standing raido waves, a residgual buildup of raido waves in the antenna.)

It has been my experaince that antenna boosters are a waste of money. If you try one, before you buy it, you might want to ask if it comes with a money back garuntee. If they say no, you might want to pass on it.