Also known as: patch, multigroup, multi-group, megagroup, simulselect
A patch (or multigroup) is a dispatcher-created link that temporarily joins two or more talkgroups so that a single transmission is heard by all of them at once.1 The trunking system announces the patch on the control channel, and thereafter a group call to any member talkgroup is delivered to every group in the patch. It is how a dispatcher glues separate units — say fire and EMS, or two adjacent districts — into one temporary net without reprogramming any radio.
How it works
A dispatcher builds a patch at the console by selecting the talkgroups to join. The console tells the trunking controller, which distributes the patch definition to the sites and advertises it on the control channel. When any member group keys up, the controller issues channel grants so that all member groups — which may be on different voice channels at different sites — receive the same audio. The patch persists until the dispatcher tears it down; it is a temporary, console-controlled grouping, not a change to any radio’s programming.
A closely related construct is the multigroup (sometimes megagroup): a pre-defined “supergroup” ID that expands to a fixed set of member talkgroups. A patch is typically ad-hoc and dispatcher-built on the fly, whereas a multigroup is configured in the system and invoked by a single ID, but both produce the same on-air effect — one transmission, many groups.
In practice
For a listener, patches are important because they change who is talking to whom. A call that appears on TG 205 may actually be part of a conversation that started on TG 101; without knowing the patch is in place, the two look like unrelated traffic. Systems announce patch/multigroup membership on the control channel precisely so radios (and consoles) stay consistent, which means a monitor can reconstruct the grouping too. Patches are common during large incidents, mutual-aid operations, and events that pull together agencies that normally run on separate talkgroups.
A patch can also span audio types and even systems. A console may patch a trunked talkgroup to a conventional channel, to a telephone line, or to a talkgroup on a neighboring system, acting as a bridge so users who could never otherwise hear each other share one net. When that happens, the identity a monitor sees on the trunked side is only part of the conversation — the other participants live outside the trunked signalling entirely. This is why patches are as much an interoperability tool as a convenience: during a multi-agency incident, a single patch can be the only thing letting fire, police, and EMS on three different radio systems talk on one virtual channel.
A further wrinkle is dynamic regrouping, a related console power in which the system temporarily reassigns radios to a new group — sometimes forcing selected units onto a special talkgroup and even locking their selector so they cannot leave it. Where a patch links existing groups so their traffic is shared, dynamic regrouping moves units into a newly imposed group. Both are announced over the control channel so the affected radios comply, and both are temporary states a dispatcher sets up and later tears down. For a monitor the two can look similar on the air, and telling them apart depends on reading the specific opcodes involved.
Relevance to SDR
Because patch and multigroup definitions are broadcast on the control channel, GopherTrunk can parse them and understand that several talkgroups are temporarily linked. That lets it present a call correctly — showing that traffic on one talkgroup is being delivered to the others in the patch — rather than as unrelated events. It also helps a scanner avoid double-tasking receivers: if three patched groups share the same audio, the monitor need only follow one voice channel to hear the whole net.
Real systems with these features include P25 (patch/regroup and dynamic regrouping) and Motorola trunking (dispatcher patch and multigroup). GopherTrunk reads the grouping passively from control-channel signalling; it recovers the structure of the conversation as metadata, and the audio it can play back still depends on the traffic being unencrypted.
Sources
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Trunked radio system — Wikipedia, on dispatcher patches and multigroup/regroup features in trunked systems. ↩