There is a good machine on a good hill near you, and almost nobody uses it. The board that would make it multimode costs less than a duplexer — but the board is not the hard part.
A repeater group keeps a machine alive for years. Site rent, power, batteries, a duplexer that took a decade to pay for. And the traffic quietly drains away, until the repeater identifies faithfully to nobody at all.
Meanwhile the digital operators in town are all on hotspots — ten milliwatts on a desk, talking to Australia — and they have no reason to key up a local machine, because there is nothing local to key up.
Both halves of that are fixable with one board.
An MMDVM repeater board — the Repeater Builder STM32‑DVM is the reference design — is a hotspot board with the radio taken off. There is no RF chip on it. Instead it wires directly into the radio you already own: audio in, audio out, PTT.
Repeater Builder describe it in exactly the terms that matter here: it gives new life to analog repeaters by allowing them to become digital capable.
One board. One cable. One Raspberry Pi. The repeater on the hill stays exactly where it is.
All five modes, from one board. DMR, D‑STAR, Fusion, P25 and NXDN — because that is simply what MMDVMHost does. The analog machine on the hill becomes a multimode digital repeater, and the radios that reach it are the ones people already own.
The radio does not move. Everything new hangs off its accessory port — and only one thing on this drawing costs money forever.
This is the first objection, it is always the first objection, and it deserves a real answer rather than a shrug. Nobody wants to be the trustee who filled a beloved FM machine with digital noise.
They will not hear it.
The proven arrangement uses CTCSS as the sorting mechanism. The software is told to expect a tone on all analog traffic — that is how it knows FM from digital. It then transmits that same tone on all analog output. The analog users set tone squelch, and their radios never open on digital traffic. A digital lockout keeps the analog side quiet while a digital QSO is running.
To the FM regulars, the machine behaves exactly as it always has. They gained nothing and lost nothing. Someone else gained a repeater.
Here is the part the enthusiastic write‑ups skip.
Most repeater groups are already paying to keep the machine alive — site rental and power, month after month, funded by dues and donations from a membership that is not getting any larger. That budget is not comfortable. It is met.
Adding digital adds another recurring bill on top of the ones already being paid. Not a one‑time purchase like the board or the Pi — a permanent new line item, on a budget that had no slack in it to begin with.
That is the conversation that stops this project, and it stops it in the treasurer’s report rather than at the workbench. Any trustee reading a page like this one deserves to see it stated plainly rather than discover it later.
But the requirement is tiny. This is voice at a few kilobits per second. Not video. Not streaming. A digital repeater is one of the lightest internet loads you could put on a hill — so “we need broadband up there” is the wrong way to frame the problem, and framing it that way makes the bill far bigger than it needs to be.
Ways this actually gets solved:
And the honest fallback: a digital repeater will run with no internet whatsoever. It simply becomes a local digital repeater — no talkgroups, no reflectors, no network. Which, for most people, removes the entire reason to have built it.
If the site cannot be connected affordably, this project will not do the thing you wanted it to do. Better to know that on day one than after the cable is soldered.
| The job | How hard, honestly |
|---|---|
| The cable | This is the wall. There is no universal pinout — it is specific to your radio, and it is a soldering job. Everyone who has done this says the same thing. |
| Flat / discriminator audio | The radio must give unfiltered audio, and be set to flat. Commercial Motorolas and Kenwoods generally will. Not everything does. |
| Aligning the pots | Tedious. Budget real patience. This is where enthusiasm goes to die. |
| Analog FM in software | The soft spot. FM support has been the weakest part of the stack — which is why the arrangement people actually run pairs MMDVM for digital with SVXLink for analog. |
| Board choice | V1 and V2 do DMR, D‑STAR, Fusion and P25. V3 adds NXDN. V4 adds the FM controller. Buy current. |
This is not a thought experiment. Joshua L. McAdam, VK4JLM, in Australia, interfaced an MMDVM to a Kenwood TKR‑850 and runs the result as a full multimode repeater — every MMDVM digital mode, plus analog FM, plus EchoLink, on one machine.
His stated reason for building it was to encourage further digital activity in an area that had none, and to replace his low‑power hotspots with something that actually covered ground.
Which is precisely the argument this page is making.
There are thousands of sound analog repeaters on good hills doing very little. The hardware to make one multimode is cheap, the analog users need not lose a thing, and the radios to use it are already in people’s hands.
The board is not the obstacle. Making the cable is a weekend’s work.
The obstacle is one more line on a budget that was already tight — and that is a conversation for the club, not the workbench.