You mean connect it to an antenna? Any antenna better than the stock one will improve things...to a point. You may experience overload issues from several sources, FM broadcast, cell towers, etc. If you're talking mobile the Larsen NMO-150/450/800 works very well. It can also be used with a radial kit as a base antenna. A cheaper option for a base setup would be a discone, which if you get it up high should work well even though it has zero gain. For a cheaper mobile option the Spectrum Force has good reviews if you won't ever need to transmit on it. If your feedline is more than 15' or so get some good co-ax, RG-58 is going to experience a lot of loss on UHF/800. LMR-240 works well for a mobile setup, for a longer feed for a base such as 50' I'd use no less than LMR-400.
@evfd 1625: That's pretty common practice from what I've seen. Rural VFD's tend to have less of the higher end gear to access the TSYS so that traffic lingers on VHF. But if they're hitting a repeater, he should be hearing them. For the other (LE I presume) that only simulcasts Dispatch on the 800, he should be hearing all of it on the 800 side...unless they're doing something weird. Up to the P25 upgrade Vigo SD still simulcasted Dispatch traffic on their old VHF, but you could hear both of them on the Safe-T side.