What it is, why it is so small, and how to get one.
If you are coming to NXDN from DMR, the first thing you will notice is that your DMR ID does not fit. Type it into the radio and it will be rejected, or silently truncated, or simply refuse to work. This is not a bug. NXDN uses a different number entirely, and it is a great deal smaller than you expect.
The number that identifies your radio on an NXDN system is a Unit ID, almost always abbreviated UID. This is not slang — it is the term used by the protocol itself. The NXDN Technical Specifications define Source Unit ID and Destination Unit ID as the addressing fields carried in every transmission.
You will see it under several names depending on where you are looking, but they all mean the same thing:
Kenwood’s own manual glosses one term with the other: “NXDN ID (Own unit ID) can be used to identify the transceiver in an NXDN System.” Same field, three names.
Here is the part that surprises everyone. An NXDN Unit ID is a 16-bit number, and the usable range is:
00001 to 65519
That is one to five digits, and there is a hard ceiling. Nothing above 65,519 exists as far as the protocol is concerned. Sixteen bits gives you 65,536 possible values, and the top handful are reserved for special use — hence the odd-looking limit.
Your DMR ID is a 24-bit number, typically seven digits, and a US ID like 3140123 is roughly forty-eight times larger than the biggest number NXDN can hold. It will not fit, and no amount of fiddling will make it.
The accepted convention, endorsed by the registries, is simple: use the last five digits of your DMR ID, provided the result is 65,519 or below. If your DMR ID is 3140123, your NXDN UID becomes 40123. If the last five digits land above the ceiling, request a shorter number instead.
NXDN IDs for amateur radio are issued by RadioID.net — the same organization that issues DMR IDs. They took over NXDN ID assignment in 2020; older guides may still point you at a separate NXDN manager site, which is out of date.
You need a valid amateur licence, exactly as with a DMR ID. The process is the same; only the ID type differs.
| Radio / software | Where to find the field |
|---|---|
| Kenwood CPS (KPG-111D) | Edit → NXDN → Unit ID (Own) |
| Anytone CPS | NX Setting → Unit ID (Own) |
| Kenwood ProTalk (menu) | NXDN ID Setup |
| Pi-Star / WPSD hotspot | Configuration → NXDN → NXDN ID |
On the Anytone, note that there is also a Base ID field — put the same number in it. And set Air Alias Name to your callsign, for reasons explained below.
Because the number space is so small — 65,519 slots for the entire world — duplicate UIDs happen. Two hams on opposite sides of the planet can quite legitimately end up with the same number, and the registries acknowledge this openly.
The fix is OTAA — the Over-the-Air Alias. This is a separate field that transmits your callsign alongside the number, so the receiving station sees who you actually are rather than a five-digit integer that might belong to someone else entirely.
Set your alias to your callsign and leave OTAA enabled. On a mode where the ID space is this cramped, the alias is doing more work than the number is. Note that not every NXDN radio supports it — Kenwood does; some Icom models do not.
NXDN has three separate identifiers and they get conflated constantly:
| Term | What it identifies | Analogy |
|---|---|---|
| Unit ID (UID) | Your radio — who is talking | Your DMR ID |
| Group ID | The talkgroup you are calling | A DMR talkgroup |
| RAN | Radio Access Number — the code that lets you into a repeater | A CTCSS tone, or a DMR colour code |
A wrong RAN means the repeater ignores you entirely. A wrong Group ID means you are talking on the wrong channel. A wrong Unit ID means people see the wrong name. All three are worth getting right, and only one of them requires registration.
Unlike DMR — where a registered, valid ID is mandatory, and Brandmeister will simply refuse to pass your traffic without one — many amateur NXDN systems do not check the UID at all. You could set it to 1 and be heard perfectly well on a good number of repeaters.
So why bother? Two reasons. First, courtesy: your ID and alias are what appear on other operators’ displays, and turning up as an anonymous 00001 is the digital equivalent of not identifying. Second, gateways and reflectors increasingly do care — anything that bridges NXDN to another mode, or logs activity, or displays a last-heard list, needs a real number attached to a real callsign to make sense of you.
It takes ten minutes and one registration. Do it properly.