Identifying Talkgroups Limited to Specific P25 Sites

[mikewren]

Potentially dumb question about radio reference’s website re: P25 systems:

Is there a way to identify if certain talkgroups are only available on specific sites/cells of a P25 system?

Apologies if this has been asked/answered before, I couldn’t find it via search.

 

[RaleighGuy]

No, there is no way to tell without having inside information or spending a lot of time monitoring the system itself. Some systems have standard procedures for TG assignment others allow roaming, this will vary by system and determined by system admin.

 

[jtwalker]

I set up all the sites that are potentially within range of my house and log activity with ProScan, then review logs.

 

[Spitfire8520]

Yes, you can go down the rabbit hole of trunked system logging and use the affiliation data collected to figure out if a talkgroup is restricted to specific sites. It is different from listening to the system as your listen to the control channel and collect the data being transmitted.

How it works is that every radio on a trunked radio system needs to affiliate to a talkgroup on the site it is trying to use before it can transmit or receive. When a radio tries to do this with a site, the site will let the radio know if it is successful or if it has been denied. Being denied affiliation is a sign that the specific talkgroup that the radio is trying to use is not allowed on that specific site and the radio is then forced to try to affiliate to a different site.

For P25 systems, I personally prefer Pro96Com if you have a supported scanner as it has the most intuitive UI out of the different programs out there. There are a bunch of others programs out there that are listed on the Trunked Radio Decoders page, many of which work best if you use a software defined radio (SDR).

There is an entire Voice/Control Channel Decoding Software forum dedicated to monitoring radio systems this way.

 

[marksmith]

The Unitrunker software application used with a cheap $25 USB dongle allows you to tune a sight via its control channel and automatically log all activity by TGID and even Unit ID on a given system.

 

[MTS2000des]

Then there is ISSI and the temporary talk groups created by authorized foreign groups on a given system. Without actually knowing how talk groups are provisioned in the core by the system owners, gleaming stuff off the air is a crap shoot. We make changes frequently on our system as do most owners. Radio systems, especially large, multi-zone P25 networks, are ever evolving environments. The fun of scanning is trying to figure it all out.

 

[natedawg1604]

The Unitrunker software application used with a cheap $25 USB dongle allows you to tune a sight via its control channel and automatically log all activity by TGID and even Unit ID on a given system.

The current "Beta" Unitrunker 2.0 is very comprehensive, it's lets you glean a wealth of information about how a particular site operates. It certainly helps to log as many sites as you can. For those who are a bit crazy, you could even get a small laptop setup with a RTL dongle in the car, to help you log sites while traveling.