P25 voice NAC on Smartzone system

[mam1081]

Anyone have any idea if the system ID relates at all to the NAC used for digital talkgroups on a mixed-mode 3600 smartzone system?

A local system is mainly analog, but there are a few (encrypted) digital talkgroups. The system ID is 092C and the NAC I decoded on the transmissions (TGID #327 or 12912 in dec) was 2C4 (converted to decimal, that's 708 if it matters). On 9600 P25 systems, the system ID seems to correspond with the NAC - any idea if that is true on Type II systems too? Is that something that the radio shop has to actually set on the user radios - or does the system just pick it based on something else?

Thanks in advance!

 

[N4DES]

I manage a SZ 3.0 that has a similiar configuration and the NAC setting in the channel assignment for a talk-group is greyed out with the default 293. The NAC setting only comes into play when programming a conventional digital channel in my radio.

Hope this answers your question.

 

[obijohn]

Anyone have any idea if the system ID relates at all to the NAC used for digital talkgroups on a mixed-mode 3600 smartzone system?

The only time the NAC should be a concern is in Conventional channel use, as KS4VT pointed out- and in 9600 CC P25 all digital systems. ie not used in mixed mode systems.

 

[mam1081]

The only time the NAC should be a concern is in Conventional channel use, as KS4VT pointed out- and in 9600 CC P25 all digital systems. ie not used in mixed mode systems.

I see what you're saying, but why would that NAC pop up as "decoded" when listening to the "trunked" P25 voice signal in conventional mode? I would have thought it would have been 293 also, as KS4VT stated. I know what NACs are for - I've just never tried decoding one on a trunked voice channel - I just got curious yesterday and tried it out - and it wasn't what I expected...


Thanks for the replies!

 

[RocketNJ]

on 4.1 the NAC is automatically determined by system ID and connect tone. It is not user programmable for trunking 4.1

 

[WayneH]

3600: For P25 trunked traffic channels the NAC consists of the last two digits of the system ID and the connect tone in the format [AAB] A is the sysid and B is the connect tone.

For 9600 it consists of a network ID but I can't recall the specific name for the value. It is not a combination of values like 3600. For example, the DoD 380MHz system sends out $140.

These NACs are good identifiers when searching with a GRE-500 as you have a better idea of who is using that channel if you are pretty familiar with trunked system in your area.

 

[SCPD]

On 9600 P25 systems, the system ID seems to correspond with the NAC - any idea if that is true on Type II systems too? Is that something that the radio shop has to actually set on the user radios - or does the system just pick it based on something else?

On a P25 trunked system ... the NAC is separately configurable. IIRC, it is configurable on a per-channel basis. In practice I've always seen the same NAC value used across all channels for a given site.

 

[Mr_Observer]

3600: For P25 trunked traffic channels the NAC consists of the last two digits of the system ID and the connect tone in the format [AAB] A is the sysid and B is the connect tone.

This aroused my curiosity. I decided to break out the service monitor and do some experimenting. I was able to decode the NAC off of my local system here. It was formatted like you postulated.

Well done. Consider this info confirmed.


MR_O

 

[MattSR]

Umm

This is shown in every copy of the CPS ever released for programming trunked radios. No big find.

Cheers
Matt

 

[Grog]

Umm

This is shown in every copy of the CPS ever released for programming trunked radios. No big find.

Cheers
Matt

And we all know that everyone on this site has the need to have trunking CPS :roll:

 

[MattSR]

Your lack of knowledge isn't my fault!

 

[Grog]

Your lack of knowledge isn't my fault!

That's the kind of dumbass thing we would expect from N_Jay, you should do better than that.


So tell me sweetcheeks, do you expect everyone on this forum to own CPS even though 99% of them have no use for it?

 

[MattSR]

No - Of course I don't.

I also don't expect people to worry about hoiw a NAC is determined either - the only people that have to worry about this kind of info are people that have easy access to CPS.

Try again stupid.

 

[WayneH]

Lets up the maturity just a bit please. Thanks.

With the release of NAC decoding scanners it helps those of us that search for new things and come across unknown P25 channels. Knowing how to understand the NAC, when trunked, is very helpful.

No doubt someone would come along thinking a trunked channel was being used conventionally because they decoded a NAC. That's very possible to see on here!

 

[MattSR]

Agreed 100% there wayne, a lot of people I know were over the moon (including myself) when Rick released the first version of the kNACk.

The time here in Sydney, our Omnilink System was running a few mixed mode channels in the same band as some other ASTRO simplex frequencies were being used. Running the kNACk quickly showed which ones belonged to the trunk system (sysID - 3A0D with 90hz connect tone = NAC of 0D3)

As you said, it is a very helpful thing to be able to do

Cheers,
Matt

 

[melvin1987]

If the System ID is 04B and the WACN is 00001, How would I find the NAC?

 

[WayneH]

With true P25 trunking you have what's called a Dynamic NAC. In many cases it's going to vary respective to the site number. So the WACN doesn't matter. It's generally the first two digits of the SysID and Site Number so 040+site #.

Just keep in mind sometimes the site number won't be applied (i.e., just 040). This is a system configuration choice.

 

[W6IFA]

Every P25 system is not made by Motorola

I probably shouldn't pour gasoline on the fire here but not everybody programming a NAC is programming a Motorola system. I have EFJ, Daniels, Harris and Tait gear in my lab and not a bit of Motorola to be found ; hence no Motorola CSS.

 

[WayneH]

I probably shouldn't pour gasoline on the fire here but not everybody programming a NAC is programming a Motorola system. I have EFJ, Daniels, Harris and Tait gear in my lab and not a bit of Motorola to be found ; hence no Motorola CSS.

You're right. I should have figured with the non-Moto WACN there was a chance it could be different. But still useful regardless.