I think I misspoke. My setup uses a Radioshack inline signal amplifier (powered) and a second inline amplifier that is passive but is behind the power injector. It's not really a filter, it's just a amplifier over a given frequency range which I wrote as a filter (which it is not).
Radioshack amp:
http://www.radioshack.com/product/index.jsp?productId=11113014There are several similar amplifiers like the one I purchased from ebay, but I don't see the exact model. The one I bought had no documentation and was an off brand, so I wonder if it's intended to be powered (even though it doesn't say so). Several of the ones available now indicate "Powered by your satellite receiver or LNB power injector". Thus, if I place it prior to the power injector, it might degrade the signal rather than enhancing it. I only added it because I had low signal in the office but acceptable signal in the basement so I was trying to increase signal strength half way through the run as well as at the antenna (via the RS amp).