Which Modes Actually Cross?

The interoperability truth table — what really happens to your voice when you bridge one digital mode to another.

Your Rosetta Stone tells you the number to dial. This tells you what actually happens to your voice when it gets there. Every cross-mode connection comes down to one question: do the two modes speak the same vocoder? If they do, the voice bits pass straight through. If they don't, something has to transcode — and whether that needs a hardware dongle depends entirely on which codecs are involved. Pick a mode, or tap any cell.

Pass-through (same vocoder) Transcode — software only Transcode — needs AMBE hardware

Tap a mode or a cell to see exactly what happens to the audio.

Operator note: on the URFJET reflector, N6JET runs the AMBE transcoding in hardware (2× DVStick 33), so in practice all six modes cross on the transcoded modules — the grid shows what it takes to bridge each pair, which is why some are effortless and some need the dongle.

Note on the “needs AMBE hardware” cells: DVSI’s AMBE and AMBE+2 were long proprietary, so transcoding them meant a hardware stick (DVStick / ThumbDV). The core patents have since expired and software AMBE emulation now exists, but a hardware AMBE transcoder is still the common, reliable route — which is why it’s marked that way here.

The short version

Same vocoder = free. DMR, Fusion (C4FM), and NXDN all speak AMBE+2, so they pass straight through to each other — no transcoding, cleanest audio.
D-STAR is the odd one out. It uses the older AMBE (not AMBE+2), so even reaching DMR — its closest cousin — needs a hardware transcode.
P25 and M17 are the open pair. IMBE and Codec 2 are open / patent-expired, so bridging them is software-only — no dongle.
Anything touching an AMBE-family codec (AMBE or AMBE+2) is the row that costs money to bridge.