What Kind of Filter Should I Get?

Ok so here is where I am at...I live about 20 miles Southeast of the Philadelphia area and am just out of range of a bunch of 800 MHz systems (Philadelphia P25, Montgomery County PA Smartzone, Cherry Hill NJ PD, Delaware State, etc). Last summer I invested in a small 800/900 terrawave yagi antenna I can mount onto a desktop (I really don't have access to an upper attic). I pointed it towards the Northwest and got some marginal improvement on my PSR 800 scanner. I then took a GRE Super Preamplifier, cranked it up all the way, and stuck it on top of the scanner and between the coax from the yagi, and I got very satisfying results. The only thing I discovered was slight overload from the NJSP tower about 3 miles to the NW (The direction I had to point the antenna). During the fall I noticed that overload got a bit worse once all the leaves came off the trees. Then one day I noticed everything was completely overloaded in the 700 and 800 band to the point it was unlistenable with this set up. If I took the preamp off, the desired 800 MHz signals were too weak. If I put the amp on and turned it on, it created a lot of overload static. If I turned it up all the way, and used the attenuator feature on my PSR 800 some of the signals were a bit better but most were for the most part uncopyable. I went to the site of that NjSP tower with an 800 antenna and the preamp and noticed that I could still get other 800mhz signals in over that signal. I also noticed driving around my vicinity with the amp on turned up and an 800 MHz antenna on my PSR 800 that I was getting lots of overload. But if I headed about 1/2 mile in any direction it would go away and I could hear signals again. I also noticed about a mile to my Northwest there was a new complete dead zone in the 700/800 MHz range due to what I believe is a cell tower. And I really think that is my problem. Now it's summer and the overload has backed off a bit with leaves on the trees but I still am trying to get more out my scanners and set up in the 800 band.

So all of this to say, is there a good filter that works specifically to block out signals in the cellular band that would help me in my situation? I can't take a lot of loss in the band I am trying to listen to, and I don't need a lot of loss in the cellular band, just enough to allow some of these other signals to overcome the stronger cell signal which appears to be coming from about a mile away. Any suggestions? Do you need anymore info?