What would be the logic behind having two separate systems at each airport that are either co-located or located in very close proximity to each other as this system is?
Also, I'm not very familiar with the networked DMR systems. Would this have the potential for someone to bring a radio with an ORD TG programmed in it to DEN and be able to talk to ORD through the DEN site?
Craig, are you asking about multiple sites at DIA or multiple systems as in DMR and the older Moto trunk?
As far as the multiple sites part is concerned, it's most likely a simulcast system. DIA has some challenges for radio penetration into the buildings and the shadowed areas close to the concourses. The multiple sites cover those areas pretty well (or did the last time I worked there.) The city system was a simulcast while I was there, with a site at the towers on the west boundary and another on Concourse A.
If you're asking about the other thing, I'll leave that to someone more knowledgeable, but there's probably an overlap as they switch from one to the other.
DMR has proven VOIP capability so I would be more surprised if the United systems weren't linked, at least with their home office. And yes, if the talkgroups are programmed the same at each location, a radio would potentially work anywhere on the system. Or they could simply program a zone or two from each and put all of them on each radio, also possible.