If you've spent any time around DMR, you've heard of the big networks. What's less obvious is the plumbing that lets those networks exist and talk to one another. A lot of that plumbing is HBlink3. (New to DMR networking? Start with How a DMR Network Works. To see how many networks are built on this software, see the tour of the wider DMR world.)
HBlink3 is open-source software that acts as a routing hub for DMR traffic. Think of it as a small switchboard: DMR systems connect to it, and it decides which conversations get passed along to which other connections. It doesn't transmit on the air itself and it isn't a radio — it's a program running on a server that moves digital voice data between the systems plugged into it.
The “HB” stands for HomeBrew, after the HomeBrew protocol — the common language that MMDVM hotspots, repeaters, and DMR servers use to talk to each other over the internet. Because HBlink3 speaks that same protocol, anything that already speaks HomeBrew DMR can connect to it without modification. That's the quiet genius of it: HBlink3 didn't invent a new world, it gave hams a way to build their own pieces of the existing one.
Every connection in HBlink3 plays one of two roles, and this is the one idea worth holding onto. A master waits for others to dial in — when you point your hotspot at a DMR server, that server is acting as a master. A peer does the dialing — it reaches out and connects to someone else's master.
The power move is that HBlink3 plays both roles at once. It can be a master that your hotspot connects into, while simultaneously being a peer that connects outward to a larger network. That dual nature is exactly what makes it a bridge: connections come in one side, go out the other, and HBlink3 ties them together in the middle.
Connecting systems is only half the job. The other half is the routing rules — the part that says “traffic arriving here on this talkgroup should be passed along to there.” Without rules, you'd just have a pile of systems plugged into the same server but not actually hearing each other. When someone keys up a talkgroup on one connection, HBlink3 checks it against the rules and forwards the audio to every other connection the rules say should receive it — and only those. The rules are what turn a switchboard full of plugged-in cables into actual conversations.
Three reasons come up again and again. Some run HBlink3 as a private DMR server — a place for a club's hotspots to meet without depending on anyone else's infrastructure. Some run it as a bridge, joining talkgroups on different networks so a conversation can span them. And some run it as the backbone of something bigger: a single HBlink3 instance can hold dozens of simultaneous connections, each governed by its own rules, quietly stitching together a personal corner of the DMR world.
The big idea
However it's used, the idea is the same — DMR linking doesn't have to belong only to the big networks. With one piece of free software and a small server, any ham can run their own switchboard.
A noncommercial hobby reference compiled by N6JET, gathered from public sources and shared freely for anyone interested in amateur digital voice.