A multi site simulcast trunk system is a fairly complex operation but it invisible to the user. A bit similar to a cell phone where you can drive to the grocery store and go from tower to tower. With most phones, you cannot use it in another country without the system manager (cell company) allowing you to roam.
For a talkgroup to be heard on a simulcast zone, there has to be a radio affiliated on that group/site or the group allowed to broadcast regardless of affiliation (to allow fire pagers that can't talk to the system to work for example). The talkgroup must be allowed on that site.
So a K trooper that is going to transport a prisoner from York CC to Hartford will leave Troop K and be on Troop K Disp 1. They drive into E's area but since the K Disp 1 TG is allowed on E, they do not have to do anything. They drive along 95 and into F's area and still no problem as K is heard there as well. However, when they get to the area where F's signal is weak and the radio goes looking for a stronger signal, they hit H's simulcast. Radio registers, good, allowed on the system, radio tries to affiliate to K Disp 1, uh-oh, K Disp 1 not allowed on H simulcast. Radio goes back to scanning control channels. and after a brief time, will alert the user that the TG is out of range. The trooper switches to H Disp 1 and all is happy again.
The goal is to not load the simulcast cell with conversations no one is listening to.
During the Boston Marathon bombing suspect search, many sites on the MA trunked system were overloaded as users outside the Boston area turned their radios to the active TGs for the incident. Those conversations plus normal local traffic overloaded the zones that normally could carry 4 or 5 simultaneous transmissions because there were too many.
For example, Groton fireground activity, while perhaps something that is worth monitoring at times, is not allowed to be broadcast across the state.
