A talkgroup is a numeric identifier that groups radios together for the purposes of voice traffic. When a radio is affiliated to a talkgroup and presses PTT, every other radio affiliated to that same talkgroup hears the call.
Talkgroups are the basic unit of "who is talking to whom" on a trunked system. They take the place of a fixed frequency: a conventional channel is defined by a frequency, but a trunked channel is defined by its talkgroup, and the actual voice frequency is chosen on the fly by the control channel.
A talkgroup is a non-negative integer. The script itself doesn't impose an upper bound; the actual range a system will accept is set by SCN admin staff per system.
A talkgroup ID lives on a channel entry inside a codeplug:
{
"name": "Dispatch",
"talkgroupID": 1001,
"secure": false,
"conventional": false
}
| Stage | What happens |
|---|---|
| Channel selection | The user selects a zone channel. The radio reads the talkgroupID from that channel. |
| Affiliation | The radio sends an AFFILIATE to the control channel with that talkgroup ID. |
| PTT | The radio sends a channel-grant request for the same talkgroup. The control channel grants a voice frequency. |
| RX | Other radios affiliated to the same talkgroup are notified of the grant and tune to the voice frequency. |
| Release | When PTT releases, the talkgroup keeps its hold on the voice frequency for hangtime, so replies stay on the same channel. |
A radio may only be affiliated to one talkgroup at a time. Switching channels deaffiliates from the old talkgroup and re-affiliates to the new one.
A system may patch two or more talkgroups together. A patched group is treated as if every member talkgroup were one — voice on any patched member is rebroadcast to the others. Patches are configured per-system by SCN admin staff.