NXDN is the narrowest of the digital voice modes, and its reflectors are among the simplest. Where an XLX or URF reflector is a big building of lettered rooms, an NXDN reflector is a single room with a number on the door. This is a plain-language explanation of what an NXDN reflector is, how your radio reaches one, and how the wider NXDN network hangs together.
An NXDN reflector is a server that acts as a central meeting point for NXDN radios. Hotspots and repeaters connect to it over the internet, and everyone connected can hear everyone else. It does one mode — NXDN — and nothing else, which makes it far simpler than the multimode reflectors elsewhere on this site. The software comes from Jonathan Naylor’s NXDNClients package (and a maintained fork in DVReflectors), and it’s free and open under the GPL.
This is the key difference from XLX and URF. Those reflectors are divided into modules A through Z — many rooms in one server. An NXDN reflector isn’t: each reflector is a single talkgroup, identified by a number. You don’t pick a module once you’re connected; the reflector is the room. To be in a different conversation, you connect to a different reflector.
On the RF side, your handheld talks to a repeater or hotspot as usual. The linking is handled by a companion program called NXDNGateway, which runs alongside the MMDVM software on that hotspot or repeater. The gateway knows how to find reachable reflectors because it reads a shared list — the NXDNHosts.txt file — that’s distributed through the NXDN community and updated automatically in Pi-Star and WPSD.
Selecting a reflector
Because a reflector is just a talkgroup number, choosing one is as simple as keying that number in from your radio (or picking it in the hotspot dashboard). The gateway looks the number up in the hosts file, connects you, and after a period of inactivity it drops the link again — the same dynamic idea used across digital voice.
On its own, one NXDN reflector is an island. The amateur NXDN community links many of them into a wider network known as NXCore (sometimes seen as WW-NXCore). An individual reflector can be configured to link up to NXCore, so that traffic is exchanged between systems rather than trapped on a single server — this is how a call on one reflector can reach operators well beyond it. NXCore is community-run and has been rebuilt and improved over the years as NXDN’s amateur following has grown.
NXDN uses the AMBE+2 vocoder — the same codec family as DMR and YSF. That shared language matters when reflectors are bridged to other modes: NXDN, DMR, and YSF can be joined without transcoding, because their radios already speak the same digital tongue. Bridging to D-Star (AMBE), P25 (IMBE), or M17 (Codec2) is where transcoding hardware or software comes in — the story told in Understanding URF Reflectors, which carries NXDN as one of its six modes.
An NXDN reflector is light enough to run on a small VPS. You compile the reflector software, choose a talkgroup number, and decide whether it’s public or private. A private reflector just needs its details added to the local hosts file on each participating device; a public one gets its number and address added to the shared list so anyone can find it. Optionally, you link it to NXCore to join the wider network.
NXDN reflector software descends from the same source as most of amateur digital voice: Jonathan Naylor, G4KLX, whose NXDNClients repository provides the gateway, the reflector, and a parrot (echo-test) server, all under the GPL. A widely used fork lives in nostar’s (Doug McLain, AD8DP) DVReflectors, which bundles the NXDN, P25, and YSF reflectors together. The NXCore network that interlinks reflectors is a separate, community-run effort maintained by NXDN enthusiasts. As with the rest of this family, it’s all open source and run free of charge for the amateur community.
A noncommercial hobby reference compiled by N6JET, gathered from public sources and shared freely for anyone interested in amateur digital voice.