Timeslots, talkgroups, and the separate roaming schemes that get confused with each other. Working notes, v1.1, 10 September 2026.
DMR is the mode with the richest commercial hardware pool, the only one amateurs actually roam on, and the one that can carry two simultaneous users on a multi-mode repeater where the other five carry one. It is also the mode where roaming gets muddled most often, because this page covers four distinct roaming schemes and they have nothing to do with each other.
The same four questions are asked of every mode, in the same order, so the seven parts stay comparable:
Same base as D-STAR: MMDVMHost on a Pi with a modem board. The difference is the gateway. DMR uses DMRGateway, also from G4KLX, and it does something ircDDBGateway does not: it lets one repeater connect to up to six DMR networks at the same time through rewrite rules, so BrandMeister, TGIF, DMR+ and an XLX reflector can all be live at once and the user picks by changing talkgroup.
The richest of the six. Motorola MOTOTRBO (XPR 8300 and 8400, later SLR series), Hytera (RD985, RD982), and cheap modern boxes like the Retevis RT97 and RT97P. BrandMeister documents connecting Motorola and Hytera commercial repeaters directly, alongside the MMDVM route. A great many amateur DMR repeaters are secondhand commercial Motorola hardware.
DMR has three tiers and Tier III is the trunked one. Amateur DMR is Tier II: "the licensed, conventional tier of the DMR standard. It is non-trunked, each repeater pair uses fixed frequencies," and it is "the basis of amateur DMR repeaters."
| Mode | Channel bandwidth | Modulation | Bit rate |
|---|---|---|---|
| DMR | 12.5 kHz | 4FSK, two slot TDMA | 9600 bps, 4800 symbols per second, two slots sharing it |
DMR chose to divide the time, not to narrow the RF. It occupies the full 12.5 kHz but carries two conversations in it. That is what "6.25 kHz equivalent" means: true per user, and not true of the signal on the air. D-STAR and NXDN took the other route and genuinely occupy 6.25 kHz. This one choice is the origin of the timeslots, and of everything downstream: two talkgroups at once, a CallHang timer, and two simultaneous users on a multi-mode repeater where the other five modes carry one.
"Two DMR slots of 4800 bps" is arithmetic, not a specification. No source states it as a spec figure. Per slot the real numbers are 2450 bps of vocoder plus 1150 bps of FEC. Do not print 4800 per slot as though ETSI said it.
Every mode has two different fields and they get confused constantly. An access field, which works like CTCSS and decides whether the repeater listens to you at all, and a routing field, which decides where your audio goes. DMR's color code is access, its talkgroup is routing. Keeping those apart is most of the answer, in every mode.
| Mode | Access field | Routing field | Range |
|---|---|---|---|
| DMR | Color code | Talkgroup, plus TS1 or TS2 | 24 bit talkgroup, 0 to 16777215 |
Only DMR has timeslots. DMR is two slot TDMA, so every talkgroup has to be assigned to TS1 or TS2. D-STAR, C4FM, NXDN and M17 are all single channel, and P25 Phase 1 is too. For the other five, "which timeslot" is not a question that exists, so a DMR operator moving to another mode will go looking for a setting that was never there.
The 24 bit talkgroup field is also the widest routing field of the six. P25's talkgroup and NXDN's destination ID are both 16 bit, and C4FM's DG-ID is two digits. The comparison table in part 7 puts all six side by side.
This is the one amateurs actually use. Roaming needs two halves: a network half, several sites linked together, and a radio half, something the radio can measure plus logic to move by itself. DMR's radio half is entirely radio side, so the network half becomes optional. That is the whole reason DMR roaming works on ordinary ham repeaters and NXDN's does not.
Anytone has two separate roaming schemes, which is why the subject gets muddled before anyone even reaches the other two.
Signal based roaming. You build a Roaming Zone holding Roaming Channels, one per repeater. The radio moves when it loses the repeater or when a timer fires.
GPS Roaming. A separate feature. Each roaming channel carries a latitude, longitude and radius, and "if the radio enters the Geo-Fence, the radio switches to that repeater." Geography, not signal.
Measured from the AT-D890UV programming guide, section 12.7 Auto Repeater:
| Setting | Options |
|---|---|
| Repeater Check | Off, positive or negative offset frequency for TX only |
| Repeater Check Interval | 5 to 50 seconds |
| Repeater Check Recon. | 1, 2 or 3 times |
| Rep. Out of Range Times | 1 to 10 times |
| Rep. Out of Range Not. | Off, Bell or Voice |
| Auto Roam Start Cond. | Fixed Time or Out of Range |
| Auto Roam at Fixed Time | 1 to 256 minutes |
| Roaming Effect Wait T. | None up to 30 seconds |
| Roaming Zone | which zone is active |
"TX only" is the giveaway. The radio transmits. Every 5 to 50 seconds it keys the repeater's input, listens for the repeater to come back, and after a set number of failures declares itself out of range and moves to the next entry in the roaming zone. It is an active check, not passive listening.
The key point. The repeater needs no roaming feature for this to work. It only has to behave like a repeater and key up when the radio checks it. That is why DMR roaming works on ordinary amateur repeaters including homebrew MMDVM ones.
The active check is not the only route. MMDVMHost has DMR roaming beacons built in,
in the [DMR] section, and they are off by default:
| Setting | Default | What it does |
|---|---|---|
| Beacons | 0, off | Set to 1 and the repeater transmits roaming beacons |
| BeaconInterval | 60 seconds | How often, in timed mode |
| BeaconDuration | 3 seconds | How long each beacon lasts |
There are three modes, and MMDVMHost logs which one it is running as DMR Roaming Beacons
Type: network / timed / off. Network means the DMR network pushes the beacon
to the repeater. Timed means the repeater beacons on its own local timer.
Read from the current MMDVMHost source, version 20260713, in MMDVM-Host.cpp and
Conf.cpp. It is easy to miss because it is not in the DMR slot files where you would
look for it.
So an amateur DMR repeater can beacon. One config line. That puts the passive half of roaming within reach on ham bands for DMR, which is exactly what NXDN cannot do, and it is the single most actionable thing in these notes.
Roaming needs the radio to measure something. There are only two ways to guarantee there is something to measure.
Passive. The repeater transmits a beacon on a schedule
and the radio listens and compares.
Active. The radio transmits a probe on the repeater input and listens for the
repeater to answer.
Kenwood pairs its beacon with Active Site Hunt, where "the transceiver sends a Wakeup message to the repeater to prompt synchronization", governed by a Sync Wakeup Wait Time and a retry count. Motorola pairs Passive Site Search with Active Site Search. Anytone offers only the active probe, because a ham repeater historically does not beacon and its design cannot assume one.
An earlier draft of these notes said DMR and NXDN were exact inverses, one receive side and one transmit side. That was wrong on both counts and is corrected here. Kenwood's radio does transmit, and MMDVM's DMR repeater can beacon. The difference between the two modes is narrower and more specific than that: MMDVM implements the beacon for DMR and not for NXDN. It is an implementation gap, not a design philosophy.
Yes: Anytone AT-D878UV and AT-D890UV, Motorola XPR7550e, Motorola XPR5550.
No: TYT MD-UV380 and MD-UV390, Alinco DJ-MD5T and MD5TGP, and the older Anytone AT-D868UV. One source puts it plainly: budget radios at "the '$100' TYT MD380/390 level" do not support it.
So roaming is not a Motorola and Hytera exclusive, but it is not universal in amateur radios either. It is a higher end feature.
An operational cost worth knowing before anyone enables it. A roaming DMR radio is keying the repeater input every 5 to 50 seconds, for as long as it is switched on. A few roaming radios in a coverage area are unremarkable. A great many of them are not.
This turned up while proving the NXDN beacon is vendor design, and it matters because it is a second, entirely separate DMR roaming scheme that has nothing to do with Anytone's.
Kenwood's Site Roaming works on DMR Tier II Conventional as well as NXDN, and it is one implementation rather than two. The NXR-1700 Function Reference is explicit that the repeater "can only transmit a beacon on the channel configured as below: Channel Type: DMR or Mixed or NXDN," and the NXR-1700 spec sheet files "Site Roaming Using Beacon" under Digital, Common, not under a protocol heading. Kenwood's own DMR portfolio says it plainly: subscribers may "auto roam using site beacons with roaming based on RSSI."
Repeaters: NXR-1700 and NXR-1800, but only with the KWD-NX10-DCK licence that adds DMR at all, and the DMR-only TKR-D710 and TKR-D810. Note the NXR-700, NXR-800, NXR-5700 and NXR-5800 are NXDN only and do not do DMR.
Subscribers: NX-1200 and NX-1300, and the NX-5000 series, both of which document DMR site roaming directly. The NX-3000 series lists both features separately without tying them together.
There is no roam list as such. It lives under Scan. The parameters are:
The numeric ranges are dealer-gated like the beacon interval. Field values reported by one commercial installer: 200 ms link delay, 2 second dropout, 2 second dwell, Quick off, Standard at minus 100 dBm. For calibration, Motorola's equivalent threshold defaults to minus 108 dBm with a range of minus 80 to minus 120.
The DMR standard settles this as flatly as the NXDN one does. TS 102 361-1's scope clause lists what the document does not cover, and roaming is named in that list:
The present document will not provide the specification or operational detail for system implementations which include but are not limited to trunking, roaming, network management, vocoder, security, data, subsystems interfaces and data between private and public switched telephone networks.
Site broadcasts do exist in DMR, in TS 102 361-4, which is the trunking protocol. Tier III only. Nothing in the standard covers Tier II conventional roaming. Kenwood concedes the point itself: "Site roaming features are unique to each manufacturer, although compatibility does exist." It names no manufacturer.
Nobody has, and the cost is the reason to look closely. Putting DMR on an NXR-1700 needs the KWD-NX10-DCK licence per repeater. The IP network that links the sites is a separate paid option, the KWD-NX10MSK, at roughly 206 pounds a repeater.
But there is a real clue worth chasing. On the NXR-1700 spec sheet, "Multi-Site Conventional IP Network" carries a software-option marker and "Site Roaming Using Beacon" does not. And the repeater reports a Beacon Operating Status of Master, Member, Local or None, with no Kenwood document anywhere defining those words. If Local means a repeater beaconing on its own timing with no IP peer, roaming might work with zero IP licences, just uncoordinated beacons at each site. That is undocumented and would have to be tested on hardware.
Tier III is the trunked tier. It needs a pool of frequency pairs with one given over to a control channel that transmits continuously, the Tier III gear is commercial only, and trunking exists to solve congestion that amateur repeaters do not have. The full argument, which applies equally to NXDN and P25, is in part 7.
Every amateur trunked system found in this search is DMR, and two unverified leads on the subject were never read, so treat that as what was found rather than as what exists. At least two Motorola Capacity Plus systems have run on ham bands in Canada: VA3UEC in the Niagara region of southern Ontario, first site on air December 2021 and expanding to Hamilton and a rapid deployment site, and a five site system in central Alberta from 2024 around Red Deer County, Olds and Stettler County. There is also dmrtc, an open source DMR Tier III trunked controller written for amateur and educational use by Adrian Musceac, YO8RZZ, which works alongside MMDVMHost and DMRGateway.
Two caveats that matter. Capacity Plus is Motorola's proprietary pseudo trunking, automatic timeslot and channel assignment across a pool of repeaters, and it is not ETSI Tier III with a dedicated control channel. And both operating systems are documented only on RadioReference, so that is one origin each.
DMR is the exception, again. Because DMR has two timeslots, a DMR-locked repeater can carry two simultaneous users. D-STAR, C4FM, NXDN, P25 and M17 are single channel, so one user each. That is worth knowing before anyone concludes the repeater is broken because two people got in on DMR and only one can on YSF.
DMR also owns the only timer no other mode has. MMDVMHost's CallHang, 3 seconds, DMR only, reserves the slot for replies on the current talkgroup before anyone else may key. Its TXHang default is 4 seconds. And the reason a digital repeater sends morse every ten minutes is a DMR problem specifically: DMR carries no callsign in the data stream that an ordinary listener can decode, and Part 97 still requires the station to identify. The rest of the timers are in part 7.
Beacons=1, or of
a radio roaming on one.