These Uniden receivers need help in the preselection area. I got interested, so I dug out of my closet a Coleman Microwave Co. Filter that looks sort of like the one above. It has a ribbon in a window that displays the tuning filter. In my case it was a filter for the LO of a L band 990 to 1590 MHz receiver ~460 MHz IF, so the tape indicates that range while the filter actually tunes ~ 690 to 990 MHz . I made a nomograph using Excel and glued it on so I can tune it quickly. My system is centered on 857.225 MHz +/- 3 MHz, and the Coleman Filter dial reading ~1317 MHz. I dont recall the bandwidth of this filter but it seems to be sharp enough.
With this in line with my short whip antenna and a couple of mods to the simulcast optimization of my BCD536HP to manual and setting 6 (was auto and default 8), my radio sounds better than ever. Not sure If the addition of the filter was the major improvement but it seemed to help right away. I do get an occasional transmission from dispatch with high BER.
Beware that I found that the radio is not very well bottled up and will receive strong signals without an antenna. To reduce this I have installed ferrite donuts on the power and GPS cables. RF getting into the receiver by path other than the antenna is a potential problem.
