Yesterday, talking about Seattle traffic control. Lots of licenses for this frequency, but I couldn't find one with P25 voice... and why the oddball NAC on an interop channel?

Yes, but City of Seattle somehow has a license for digital DATA.

But which Seattle agency would have VHF P25 radios? SDOT? Marine units? I know WSP and DNR do.

Not supposed to be using digital on interop channels anyways. But you can never get these rouge agencies to listen.

Not exactly true...from some seminar I took, if you must P25 on VTAC, you must use a NAC of $293 and you put DG on the end of the channel name; its advisable to be in mixed mode.

And if anything throws off that data stream and it’s not aligned or in order, what comes out at the other end is either garbled — you get parts of things, but it’s unintelligible, or, and this is totally different from our old system, you’ll get complete dead silence,” he said.

Not to further muddy the waters here, . . .
EXAMPLE: in WA State H-S Region 9 ( greater Spokane area ) the TX PL is 203.5.

Thats the problem- Everyone has different information and spread it as gospel. I know of no reason that anyone "must (use) P25 on VTAC" other than their people forgot or decided against putting these frequencies into their equipment set as analog.

You have to look at it from the department (who has no digital radios) perspective. If someone comes into a major incident that can't use digital mods then it can cause major issues. And visa versa- An agency sending people over that have no clue they need to switch to analog will never hear the traffic until they locate someone in the know.. if they ever do. Mixed mode only works if the people using the radios understand whats going on. One talks analog which gets received fine. But the operator of the mixed mode radio then tries to respond on digital. Cops and fire personnel dont want to understand their radios for the most part. They just want to push to talk and usually go to interop channels kicking and screaming. Don't need this kind of confusion right after the 9.0 earthquake that everyone talks about.

Well, for the situation you describe, analog for that kind of mutual aid is the smartest idea; the seminar I took was for those situations where you have an COM-L writing a ICS-205 and taking in account of what agencies are coming from where and knowing their capabilities. I've rarely seen VTAC used in P25, but I know USFS around here has them programmed in. And I also, it was recommended to leave VCALL in analog, make a contact with whoever you need on there, advise to switch to VTACX and its digital, then swtich.

""advise to switch to VTACX and its digital, then swtich.""
Why? Just so Motorola can sell more $4000.00 radios? You have more of a chance of missing words in a weak signal area with digital(especially in the rough country in this state) than with 12.5kc analog when people learn how to correctly speak into the mic. ((This is probably why I don't get invited back to Motorola training classes. :) :) ))

My design book=

1. no digital on interop channels. Ever! Its all about muscle memory. If you want digital then apply for some other frequencies.

2. If you use other digital modulations on your primaries then you need to recognize that those around you might not be able to keep up soon if ever. Your guys may be on their own until dispatch can make some phone calls for help.

Guess the Motorola top brass will never take me out to those big expensive lunches eh?

Leifer said eschewing digital and P25 in general would cause public safety to lose features such as directed unit-to-unit call, call check and call alert and others. “These features, which would be useful in a multiagency interoperability environment, would not be available using analog FM,” Leifer said.