I think NH has more or less standardized on a NAC of 117.
As to coordination, it's pretty much ad hoc. Back in the mid 1970s when BAPERN and other regional systems were coming on line, the systems dictated what the PL would be. BAPERN was 131.8, NEMLEC 146.2, Plymouth County 203.5, and Bristol County 203.5. Frequencies were coordinated so that Bristol and Plymouth didn't overlap, so they could use the same PL on a few shared channels. NEMLEC used the same frequency range, but with a different PL.
One of the reasons for that was the technical limitations of the radios available back then. Nothing was computer based, it was all analog components. Adding multiple PL on a Micor radio meant adding a "Systems 90" component box. Adding scan meant another box, and so on. It was even tougher with portable radios. A MX portable could only have so many features or options added. That band width available was also why some agencies on UHF had to move to UHF-T, the radios just weren't that broad band.
Synthesized radios started to change that and now radios are wider banded, have way more options, can use any PL or DPL combination, etc. Individual components are needed, it's all done with firmware and programming.
Oh, as to the UHF-T band, public safety will have to move off of it in a few years. That spectrum is being refarmed so everyone on it will have to go somewhere else. That's one of the reasons that New York City got a waiver so they didn't have to narrowband their UHF-T.
Probably more than you wanted to know.
Originally Posted by mainetrunk
Well, thats a shocker. People just saying what their P.L will be..Someone decided that the Maine pl's for the most part is 192.8... N.H decided to be 136.5. Mass most used is 146.2 and 131.8.... O.K Same said for "nac"s ??