Also known as: trunked radio, trunking
Trunked radio is a system architecture in which many user groups share a small pool of frequencies, with a computer assigning a free channel to each call for its duration and reclaiming it afterward.1 A control channel coordinates the whole system.
How it works
When a user keys up, their radio requests a call on the control channel, which issues a channel grant pointing the talkgroup to a free voice channel. Because real traffic is bursty, a few channels can serve many groups.
Relevance to SDR
To monitor a trunked system you decode the control channel first, then follow grants — exactly what GopherTrunk does for P25, DMR Tier III, and others.
Sources
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Trunked radio system — Wikipedia, on trunking architecture and control-channel coordination. ↩