I am trying to hear 800mhz system that is approx 30 miles away

Maybe it's been discussed (I just tuned in) but have you considered a
vertical beam antenna, like a TV antenna on it's side with just a slight
tilt.
I suspect you are fighting a loosing battle. My son (a fire fighter) lives
on top of a hill (you can see for miles from his porch) has tried to monitor
the 800 system in the city that he works in ( aprox 30-35 miles as the crow
flies) and can't even get an occasional peep out of the system.

I've never used a preamp on the 800 freq's but have on other freq's (HF and
VHF) and they have all (some homebrew and some store bought kits) been very
disappointing, seem like they raise the noise level more than anything. RM~