Digital Voice Modes Compared

Six digital voice modes share the amateur bands — D-STAR, DMR, C4FM (Fusion), M17, P25, and NXDN. They solve the same problem in different ways, and the differences are easiest to see side by side. This chart lays out how each one is built; the individual guide pages go deeper on any single mode.

	D-STAR	DMR	C4FM (Fusion)	M17	P25	NXDN
Origin / developer	JARL (Japan); Icom	ETSI (Europe)	Yaesu	M17 Project (open-source hams)	APCO (USA public safety)	Icom & Kenwood
First appeared	~2001	2005	2013	~2020	1990s	~2006
Modulation	GMSK	4FSK	C4FM (4FSK)	4FSK	C4FM / CQPSK	4FSK
Access method	FDMA	TDMA (2 slots)	FDMA	FDMA	FDMA (Ph 1) / TDMA (Ph 2)	FDMA
Channel width	6.25 kHz *	12.5 kHz	12.5 kHz	9 kHz	12.5 kHz	6.25 or 12.5 kHz
RF bit rate (gross)	4.8 kbit/s	9.6 kbit/s (4.8 ×2)	9.6 kbit/s	9.6 kbit/s	9.6 kbit/s	4.8 kbit/s (6.25 kHz)
Voice codec	AMBE (~2.4 kbit/s)	AMBE+2	AMBE+2	Codec 2 (open, 3.2 kbit/s)	IMBE (Ph 1) / AMBE+2 (Ph 2)	AMBE+2
Access code	— (callsign routing)	Color Code (0–15)	DG-ID (0–99)	CAN (0–15)	NAC	RAN (0–63)
User identity	Callsign	DMR ID (numeric)	Callsign	Callsign (in stream)	Radio ID (numeric)	Unit ID (numeric)
QSOs per channel	1	2	1	1	1 (Ph 1) / 2 (Ph 2)	1
Registration required	Yes (gateway / trust)	Yes (DMR ID)	No	No	No	No
Codec type	Proprietary	Proprietary	Proprietary	Open source	Proprietary	Proprietary
Repeaters on the ham bands	Common (full-duplex; Icom)	Very common (full-duplex)	Common (full-duplex; Yaesu)	Rare — full-duplex hardware scarce; mostly hotspots	Uncommon (full-duplex; surplus + MMDVM)	Uncommon (full-duplex; surplus + MMDVM)
Amateur ecosystem	REF / XRF / DCS reflectors; Icom radios	BrandMeister / TGIF; huge radio market	Wires-X + open YSF / FCS / YCS; Yaesu radios	mrefd reflectors; open hardware; few repeaters	MMDVM + reflectors; surplus commercial radios	MMDVM + reflectors; surplus IDAS / NEXEDGE

On a phone, swipe the table sideways to see all six columns.

Notes

* D-STAR channel width. D-STAR is specified around 6.25 kHz, but its occupied bandwidth measures wider in practice — closer to 10 kHz — so it isn’t as narrow as NXDN in the real world.
P25 phases. The figures above describe Phase 1, which is what nearly all amateur P25 uses: FDMA, one conversation per 12.5 kHz channel, IMBE vocoder. Phase 2 adds two-slot TDMA and the AMBE+2 vocoder, but it’s a public-safety feature rarely seen on the ham bands.
NXDN width. NXDN runs either 6.25 kHz (narrow) or 12.5 kHz (wide); amateur use is typically the 6.25 kHz mode, the narrowest of the group.
“Registration required” means a central sign-up before you can use the network or gateway — a DMR ID number for DMR, a gateway/trust registration for D-STAR. The others carry your identity in the signal itself, with nothing to register.
Repeaters vs. hotspots. Every mode’s repeater is a full-duplex machine — that’s what a repeater is. The real difference is availability: five of the six have mature, easy-to-source full-duplex repeater hardware, while M17’s full-duplex platforms are still scarce, so it lives largely on simplex hotspots rather than hilltop repeaters. That’s why M17 stands out in the row above.
Codec matters for bridging. DMR, C4FM, and NXDN all use AMBE+2, so they interconnect without transcoding. D-STAR (AMBE), P25 (IMBE), and M17 (Codec 2) each speak a different codec, so bridging to or from them needs transcoding — see Understanding URF Reflectors.

Go deeper on any mode

Each mode has its own guide, its “how the repeater works” page, and a history: D-STAR · DMR · C4FM · M17 · P25 · NXDN.

New to digital voice? The Rosetta Stone for the Digital Modes maps every concept on this page across all six modes — and The Digital Cliff explains why digital sounds perfect right up until it vanishes.

A noncommercial hobby reference compiled by N6JET, gathered from public sources and shared freely for anyone interested in amateur digital voice.