Which DMR hotspot to choose in 2026: simplex or duplex, MMDVM, Jumbospot

If this is the first time you've heard of a DMR hotspot — it's a small device that turns an ordinary digital radio into an internet-connected node. The hotspot receives the radio's signal over the air from a few metres away, packs the voice into IP packets, and sends them to the network's server over Wi-Fi or Ethernet. The reverse path works exactly the same way. Without a hotspot, a DMR radio only works on a direct channel ("simplex") or through a repeater. With a hotspot you get access to any network in the world — including the private, closed DMRhub network.

Simplex or duplex: the real difference

Most amateur hotspots run in simplex mode: a single frequency is used both to receive from the radio and to transmit back. The radio and the hotspot "talk" in turns, just like a walkie-talkie with a single PTT button. It's cheap, simple, and completely sufficient for personal use at home or in the office. For more on the modes, see the article "Simplex and duplex: which to choose".

A duplex hotspot has two independent radio paths: a receiver on one frequency and a transmitter on another. This lets it receive and transmit at the same time — and, more importantly, support both DMR time slots simultaneously. In practice you need duplex if you want to emulate a full repeater for several users indoors, or to monitor two time slots in parallel. For a single operator at home, duplex is overkill. For a detailed board comparison, see the article "Duplex hotspot: when you actually need one".

Board types: MMDVM_HS_Hat, Jumbospot and Dual Hat

The "brain" of any hotspot is a board based on the MMDVM project running MMDVM_HS firmware. The schematic is open, so there are dozens of similar boards on the market. Let's go through the main ones.

MMDVM_HS_Hat

The original design by Juan Parada (CA6JAU) — the MMDVM_HS_Hat. The board plugs straight onto the 40-pin header of a Raspberry Pi (hence "Hat"). It uses the ADF7021 chip from Analog Devices. It works on UHF (430–450 MHz) and VHF (144–148 MHz) frequencies depending on the version. This is a simplex board: a single transceiver. It's considered the reference implementation — the firmware is optimised specifically for it.

Jumbospot

Chinese clones of the MMDVM_HS_Hat sold under the "Jumbospot" name (sometimes just "MMDVM HS Hat" without the prefix). They are identical to the original by schematic, but the quality of the TCXO and assembly varies. The price ranges from 10 to 25 dollars. Most of them work fine, but you do come across units with an unstable frequency oscillator — and that's when BER errors start. For more on choosing a board, see "HS Hat vs Dual Hat".

MMDVM_HS_Dual_Hat (duplex)

The duplex version — the MMDVM_HS_Dual_Hat — contains two ADF7021 chips. One receives, the other transmits. It uses the same Hat form factor but draws noticeably more current. For personal use without the need for two time slots at once, it's a premium you pay with no benefit.

Why the TCXO matters so much

The ADF7021 chip has no automatic frequency control (AFC) for the 4FSK mode that DMR uses. This means frequency accuracy depends entirely on the clock oscillator — the TCXO (temperature-compensated crystal oscillator). The MMDVM standard is a TCXO at 14.7456 MHz with an accuracy no worse than ±2.5 ppm. If the oscillator is worse, not only the frequency offset suffers but the data rate too. This cannot be fixed in software. The result is a high BER (bit error rate) and a distorted or unreadable signal.

A good board with a quality TCXO needs minimal calibration after its first power-up. For details on the process, see "TCXO and frequency accuracy" and "Calibrating the hotspot".

Raspberry Pi: which version to choose

Hat boards are compatible with most Raspberry Pi versions that have a 40-pin header:

• Raspberry Pi Zero W / Zero 2W — the most compact and cheapest option. The Zero 2W is faster and more stable than the Zero W (4 cores). Perfect for a fixed home hotspot.
• Raspberry Pi 3B / 3B+ — more power, better Wi-Fi. A good choice if you plan to run extra services.
• Raspberry Pi 4 — overkill for a hotspot, but it works.

For most use cases, a Pi Zero 2W + MMDVM Hat is the optimal choice: compact, cheap, and runs for years without overheating. The microSD card matters too — more on choosing one in "Choosing a microSD for your hotspot".

Ready-made boxes vs DIY builds

The market offers so-called "all-in-one" hotspots — devices with a Pi Zero, an MMDVM board, and a flashed image already assembled in one enclosure. They're sold under brands like AURSINC, RADIODDITY and others. The upside is convenience. The downside is the premium price, a closed enclosure, and sometimes outdated firmware.

A DIY build (Pi + Hat + case) gives you full control over the components, the ability to replace any part, and the freedom to choose the OS image you want. The cost of a build on a Pi Zero 2W + a quality Hat + case is comparable to ready-made solutions, with greater flexibility.

Display: OLED or Nextion

Many boards ship with a 0.96" OLED display — a small screen that shows the callsign, frequency, and active time slot. It's enough for basic indication. More on this in "An OLED on your hotspot".

A more informative option is the Nextion: a 2.4–3.5" colour touchscreen that shows a full summary — recent QSOs, RSSI, BER, time. A Nextion display costs from 15 dollars. If the hotspot sits on your desk and you glance at it often, the Nextion is worth the money. For a detailed comparison: "A Nextion display for MMDVM".

Power and enclosure

A Pi Zero draws about 0.5–1 W at idle, a Pi 3B+ up to 3 W. A 5 V / 2 A power supply is the minimum for stable operation. Don't skimp on power: voltage drops lead to Pi freezes and spurious reboots. More on this in "Powering the hotspot".

A plastic or aluminium case is advisable to protect the board from dust and accidental shorts. Many aluminium cases also double as a heatsink for the Pi 3/4. For the antenna, the stock rubber "duck" from the kit is usually enough indoors, but if you want coverage in the yard, swap it for a GP antenna. Read: "An antenna for your hotspot".

Software side: Pi-Star, WPSD or the RadioStar image

The historic standard is Pi-Star, a web interface on top of Raspbian/Debian. Setup is manual: you enter the DMR ID, frequency, Color Code, network password, and master address. Each network needs its own profile. It works, but it requires understanding what you're entering. More on Pi-Star in "Configuring Pi-Star".

WPSD is a modern alternative with actively updated code and DMRGateway support out of the box. The interface is fresher and updates come more often. A comparison: "Pi-Star vs WPSD".

For users of the DMRhub network there's a third path — the RadioStar image. It's a ready-made image for the Raspberry Pi (based on MMDVM) in which all parameters — DMR ID, frequency, Color Code, authorization secret — arrive from the portal automatically on first registration. No need to dig into config files by hand. Bonus: OTA firmware updates, automatic frequency calibration, built-in display indication. Read more: "The RadioStar image" and "Migrating from Pi-Star to RadioStar".

Working with the DMRhub network

A RadioStar hotspot connects to the private DMRhub network — with its own talkgroups, private voice calls by DMR ID, and DMR-SMS. Voice calls are processed by a server-side AMBE vocoder, so audio quality doesn't depend on the radio's internet link — only on yours. Working behind NAT is no problem: a hotspot behind NAT works normally via UDP hole punching. Frequency-use rules in Russia are summarised on the "Frequencies and the law" page.

Checklist: what to buy and what to watch for

• An MMDVM_HS_Hat board with a TCXO ≥ 2.5 ppm (don't go for fully unbranded ones with no specs)
• A Raspberry Pi Zero 2W (or 3B+ if you need the power)
• An A1-class microSD card, 8–16 GB (Samsung, SanDisk Endurance)
• A 5 V / 2 A PSU with a good cable (not a phone USB charger)
• A ventilated or aluminium case (with a heatsink for the Pi 3/4)
• The kit's OLED display or a Nextion 2.4" — optional
• The stock antenna for indoors, or a GP antenna for outdoors

Common beginner mistakes

• Wrong radio frequency. The radio and hotspot frequencies must match. For personal use on the 70 cm band, 430–440 MHz is typical — see "Frequencies and the law".
• A poor TCXO. The board works, but the BER is high — voice breaks up or isn't received. Fix: swap the board or calibrate the offset.
• Weak power. The Pi reboots under load. Check the PSU and cable.
• Wrong Color Code. The DMR connection won't establish if the radio's Color Code doesn't match the hotspot's. More on this in "Color Code in DMR".
• Operating on the same frequency as a neighbour. If there's another hotspot nearby, use different frequencies or ESSIDs. Article: "Multiple hotspots in one location".

Verdict: what to choose in 2026

For the vast majority of users, the sweet spot is a simplex MMDVM Hat with a TCXO on a Pi Zero 2W. Under 40 dollars in components, compact, and runs stably for years. You only need duplex if you're building a home repeater for a group of people.

If your goal is to connect to the DMRhub network without fiddling with config files by hand, the choice is obvious: assemble the hardware and install the RadioStar image. The portal hands out the DMR ID, sets the frequency and Color Code, and then the hotspot appears in your account ready to go. OTA firmware updates arrive automatically. On top of that, you get access to the network's talkgroups, DMR-SMS, and private calls right in the Android app.