Is this the system you are trying to monitor?
Jacksonville City - First Coast Radio Trunking System Profile
www.radioreference.com
Looking at your county,
Duval, it appears that most of the public safety agencies, including Jackson Fire & Rescue, are in that system, though I do see a number of conventional (non-trunked) frequencies listed for EMS, mostly for communications with specific hospitals.
For the trunked system I
linked, the primary site is Simulcast. Simulcast can be a major hinderance for every scanner except Uniden's SDS series.
More on Simulcast is in the Wiki.
Simulcast digital distortion - The RadioReference Wiki
The Simulcast site has a number of transmit towers (sub-sites), which all transmit the exact same radio traffic, on the same frequency, from all of them.Those signals, at various distances from you, arrive at your location out of sync, so your 436HP cannot readily decode the transmissions. Click on the
Simulcast site line to see the tower locations for that site. Comments on the system's page indicate that 7 more sites will be added,, bringing it from the current eight towers to fifteen.
As already mentioned, your 436HP cannot reliably receive & decode transmissions from a simulcast site. The SDS100 can handle that.
I would also note that for Jacksonville Fore & Rescue, the Dispatch talkgroups for Fire & EMS, as well as foreground talkgroups, are available via the Calls platform.
View attachment 143587
If you click on one of the talkgroups highlighted in blue, you can listen to that TGID without using a scanner.