CG on 412.8625

[Wilrobnson]

These are all on the same freq, same NAC. I've not yet heard them used simultaneously.

As an aside, I've only heard different TGIDs being used with the same NAC on the same freq one other time, a Seattle-area Emergency Management agency programmed NIFOG information with their own talkgroup number (as opposed to default 1) and was stumped that no one was hearing them during an exercise.

They later changed the NACs and thought the problem was 'fixed'.

 

[trentbob]

These are all on the same freq, same NAC. I've not yet heard them used simultaneously.

As an aside, I've only heard different TGIDs being used with the same NAC on the same freq one other time, a Seattle-area Emergency Management agency programmed NIFOG information with their own talkgroup number (as opposed to default 1) and was stumped that no one was hearing them during an exercise.

They later changed the NACs and thought the problem was 'fixed'.

Interesting, I get the part about one conventional p25 frequency having a different NAC applied to each group so only that group can hear each other and the others on the conventional p25 frequency cannot. That was obvious.

What's Curious is how you describe talk group IDs yet everyone's on the same NAC on the same conventional frequency.. what generates a talk group ID if it's not a system but a single conventional p25 frequency all using the same NAC?

Could it be a system with IDs combined with a p25 conventional frequency.

That's something I'd like to know more about, talk group IDs on a p25 conventional frequency with only one NAC.

I'd like to know if it's being used in the New York Long Island and Philly area, if so, I want to monitor it. Maybe it's done with other agencies.

 

[ChrisP]

What's Curious is how you describe talk group IDs yet everyone's on the same NAC on the same conventional frequency.. what generates a talk group ID if it's not a system but a single conventional p25 frequency all using the same NAC?

Trentbob, on a conventional system, it's just another way of separating users on a common channel. You can have a single frequency, with a single NAC for all users, but assign different talk groups to different users on the frequency. If your frequency is not busy, it allows multiple users that won't hear each other. But you can set up an Announcement Talk Group (on P-25 that's TG 4095) that goes to all users on the frequency regardless of what talk group their radios are set to.

I have seen some talk groups other than 1 and the Announcement talk group used on some US Secret Service, the FBI and Federal Protective Service conventional channels.

There is a single frequency used by the VA medical center near me that does that. They have a single DMR frequency and about 10 or 12 different talk groups on that frequencies for different users. It's not trunked, and it's not that busy, so anyone getting bonked with a busy signal is pretty rare.

 

[trentbob]

Trentbob, on a conventional system, it's just another way of separating users on a common channel. You can have a single frequency, with a single NAC for all users, but assign different talk groups to different users on the frequency. If your frequency is not busy, it allows multiple users that won't hear each other. But you can set up an Announcement Talk Group (on P-25 that's TG 4095) that goes to all users on the frequency regardless of what talk group their radios are set to.

I have seen some talk groups other than 1 and the Announcement talk group used on some US Secret Service, the FBI and Federal Protective Service conventional channels.

There is a single frequency used by the VA medical center near me that does that. They have a single DMR frequency and about 10 or 12 different talk groups on that frequencies for different users. It's not trunked, and it's not that busy, so anyone getting bonked with a busy signal is pretty rare.

Okay thank you for the explanation, I had figured out the different NAC's the same way you would a non digital conventional frequency and pl tones.

I wasn't thinking about the p25 capabilities.

I was hoping you were going to get back to me as I had a feeling you were going to know.

I don't believe I've ever encountered a setup like that on my Coast Guard monitoring.

Much obliged.

 

[ecps92]

Yes, while 412.8625 and 413.0875 have not been confirmed as USCG previously, the UHF "NET" listings are still an ongoing mystery and looking to be confirmed. And the NAC of 293 and RID of 0 certainly makes me think Coast Guard.

I don't think any of the NETs are repeaters, it's certainly possible for the Sector comms operator to select multiple sites to key up simultaneously.

- Chris

I've only encountered the VHF as pairs and that was early (long dismantled) P25 NETs and likely an assumption of that being an Official VHF Net channel

 

[ecps92]

Very interesting, I did not know that, so there are different talk groups on the one p25 conventional frequency but with different NAC? Is that how they are separated?

If you wouldn't mind Chris can you just elaborate more, always want to learn something new.

There can be, most just used TG 1, but I've also seen a 4095 (as CP Pointed out) used as an All Call (not CG, but others) and some have been more elaborate as Wil points out

 

[trentbob]

There can be, most just used TG 1, but I've also seen a 4095 (as CP Pointed out) used as an All Call (not CG, but others) and some have been more elaborate as Wil points out

Thank you Bill, I actually may have seen this with surveillance using fixed Wing aircraft in Philly. I'm glad I'm getting more familiar with it.

Appreciated very much helping this old dog learn new tricks😄

 

[ecps92]

Thank you Bill, I actually may have seen this with surveillance using fixed Wing aircraft in Philly. I'm glad I'm getting more familiar with it.

Appreciated very much helping this old dog learn new tricks😄

We all continue to learn in this hobby

 

[Wilrobnson]

I once used a Moto XTS5K on a large military base in the West for this thing I was doing. Dinking around with it on a break led to the discovery of a simplex zone with 16 channels. Someone who was in a position to actually know told me it was the same freq (38X.xxxx) with the same NAC, but 16 different talkgroups. The intention behind this was that no two channels would likely be used in the same area simultaneously. I never got a chance to independently verify this since the contract ended