GopherTrunk as a scanner

Key takeaways GopherTrunk is the software that turns a bare SDR into a trunk-tracking scanner. Give it an SDR and one system’s control-channel frequency and type; it locks the control channel, reads the grants that channel hands out, follows each to its voice channel, and produces tagged per-call audio with logs and metadata — across P25, DMR, NXDN, TETRA, and more. It’s the same lock-and-follow behaviour as a hardware trunking scanner, but open, multi-protocol, and fully exposed for recording, alerting, and integration.

You’ve seen where GopherTrunk sits among SDR scanning software — a multi-protocol trunk-tracker on the top rung. This lesson puts it to work: what you feed it, what it does with a real system, and what comes out. Everything you learned about programming a trunked system and following a call is exactly what GopherTrunk does automatically — here it is in the flesh. The project home and the architecture overview go deeper than one lesson can; this is the scanner’s-eye view.

What you point it at

GopherTrunk needs the same three things any trunking scanner does, no more:

An SDR and antenna — the receiver that hands it raw samples, fed by a good antenna.
One control-channel frequency — the single frequency that unlocks the whole system, exactly as in programming a trunked system.
The system type — P25, DMR, NXDN, TETRA, and so on, so it knows which decoder to run.

From that one control-channel frequency it discovers the rest of the system by listening. And when you don’t have a control-channel frequency, its Hunt feature sweeps a band, detects carriers, identifies the protocol, and reports which one is the control channel — the search-and-discovery job, automated.

Locking the control channel

The moment GopherTrunk has the control-channel frequency and type, its first job is to lock that channel — tune to it, demodulate it, and start decoding the steady stream of signalling the control channel never stops sending. A good lock is the foundation of everything else; if the control channel isn’t decoding cleanly, nothing downstream works, which is why when decoding fails starts there.

Once locked, GopherTrunk is reading the system’s live bookkeeping: affiliations, registrations, and — the part that matters for scanning — the grants that assign a talkgroup’s call to a voice channel. It’s the same control channel a hardware scanner reads, decoded in the open.

Following the grants

This is trunk-tracking, and it’s the whole point. Each time the control channel grants a call — “talkgroup 1201, go to this voice channel” — GopherTrunk follows it: it tunes to that voice channel, decodes the digital voice, and plays or records the call, then returns to watching the control channel for the next grant. That control-channel-to-voice-and-back loop is precisely following a call across the system, running continuously and automatically.

Because it works from a wideband capture, GopherTrunk can follow more of a system at once than switching a single tuner around — several concurrent calls decoded in parallel from the same receiver, which is where software pulls ahead of a one-call-at-a-time box.

What comes out

The output is everything Unit 5 was about, produced for you:

Tagged per-call audio — each call as its own recording, labelled with system, talkgroup, unit, time, and frequency straight from the control channel.
A live call log and metadata — the searchable record from metadata & tagging, written as calls happen.
Hooks for the rest — alerting, feeds, and dashboards all draw on the same exposed stream of calls and metadata.

In other words, GopherTrunk isn’t just a decoder — it’s the engine that drives the whole logging, recording, and alerting apparatus you built earlier in the module.

Running it for real

For a quick listen you run it on your desk; for anything lasting you run it as the always-on post — headless, managed, and self-recovering. Because GopherTrunk is server-shaped software, that’s its natural home, and the deploying GopherTrunk guide walks through standing it up as a durable service rather than a program you babysit. The architecture overview shows how the pieces — receiver, control-channel decoder, grant follower, voice decoders, recorders — fit together, and the project home is where to start if you want to actually run it.

The next lesson assembles all of this — antenna, SDR, GopherTrunk, logging, and a dashboard — into one complete, worked monitoring setup.

Quick check: what does GopherTrunk do after it locks a system's control channel?

Recap

GopherTrunk turns a bare SDR into a trunk-tracking scanner across P25, DMR, NXDN, TETRA, and more.
You give it an SDR, one control-channel frequency, and the system type; its Hunt feature can find control channels you don’t have.
It locks the control channel, reads the grants, and follows each call to its voice channel — trunk-tracking, automated.
It outputs tagged per-call audio, a live log and metadata, and hooks for alerting, feeds, and dashboards.
Run it briefly on the desk or, for real, as an always-on post — see the architecture overview and deployment guide.

Next up: a worked end-to-end monitoring setup.

Frequently asked questions

What does GopherTrunk actually do?

It takes raw samples from an SDR, locks a trunked system’s control channel, reads the grants that control channel hands out, tunes to and decodes the voice channels those grants point to, and produces tagged per-call audio with logs and metadata. In short, it’s the software that turns a bare SDR into a trunk-tracking scanner across P25, DMR, NXDN, TETRA, and more.

What do I need to give it to start?

A supported SDR, an antenna, and one system’s control-channel frequency and type — the same details you’d program into any trunking scanner. From that single frequency GopherTrunk discovers the rest of the system by decoding the control channel, or you can let its Hunt feature find control channels you don’t have.

How is it different from a hardware trunking scanner?

Same behaviour — lock control channel, follow calls — but open and exposed. It’s multi-protocol, updatable, can follow more from one wideband capture, and lays every call’s metadata, logs, and audio open for recording, alerting, and integration. It’s the brain of the setup rather than a sealed appliance.