Once again, interoperability ain't rocket science, and the interoperability goals do seem to be grossly misunderstood here. Generically speaking, interoperability is not aimed at having interoperability on your main operating channels, it's aimed at having common channels and formats of interoperability that the comm centers and all units can take advantage of. You can have any freq and any kind of system you want for your day-to-day ops. It's when you switch over to the channels you have designated as your interops channels that you are required to meet interops parameters. If they are of differing frequency, technology, and format, then somewhere along the line, there has to be an interface that converts your format to the APCO 25 interoperability standard, and there are predetermined standards for doing that, too.
The local, state, and federal band plans already have certain agreed-upon channels designated as common channels for interoperability in your respective jurisdictions and services. If you have a 450 mHz LTR system and another jurisdiction has 150 mHz and the state has the 800 mHz system, then all you have to do is link the COMMON INTEROPERABILITY channels together through an interface that enters each respective system at the controller level. Most likely, that's where the state sites will come into play. The state sites will be the ones to have the interops interfaces, and it's there that the controller level interfaces will take place. The simple thing to do would be for the counties involved to buy the interface equipment and have it installed at the state sites. The state has already provided the ACU1000 interface units to be installed at some of their sites, and some are in place and operating, although they're not tied to the microwave system as yet. And yes, the one for Troop D at Cane Mtn in Alamance County is in place and does function, but again, it is not tied to anything yet. Once it's tied, there's your connection to the state's APCO 25 channels.
More important, the ACU1000 has the capability to provide interconnection through radios on each respective frequency like a cross-band repeater of sorts (bad, very bad), or through a port connection to the respective system controllers (good, very good). If the controllers happen to be co-located with the state equipment, that's a no brainer, but a simple full duplex microwave or other RF link (good) or wireline link (not as good) can make the connections if they are at separate locations. This has been done for decades in utility grid systems, etc., and covers both SCADA and voice.
