A normal hotspot transmits about ten milliwatts. A DMR handheld transmits five watts. What if the handheld were the hotspot?
A hotspot is a tiny radio bolted to a Raspberry Pi. The RF board — a ZUMspot, a JumboSpot, any MMDVM board — puts out roughly 10 milliwatts. The people who wrote the firmware describe their own hardware in exactly those terms: a few milliwatts, short range, indoors.
Everyone who owns one knows what that means in practice. It covers the room. It might cover the house. Walk out to the garage and you are gone.
The obvious fix is the wrong fix. Do not hang an amplifier on a 10 mW hotspot. These boards have little or no output filtering, so an amplifier will faithfully amplify your spurious emissions along with your signal. Worse, you would be transmitting far further than you can hear — a hotspot already transmits better than it receives — so you would end up shouting across town from a station that still cannot hear anyone answer.
There is a better answer, and it is elegant: throw the RF board away and let a real radio do the job.
The open‑source OpenGD77 firmware — the work of VK3KYY and F1RMB — can put a supported DMR radio into hotspot mode. Connect that radio to a Raspberry Pi with its ordinary USB programming cable, tell Pi‑Star that the radio is the modem, and the Pi stops talking to a 10‑milliwatt chip and starts talking to a real transceiver.
The numbers are not subtle. A conventional hotspot: about 10 mW. A DMR handheld in hotspot mode: 5 W. Roughly five hundred times the power — and it costs nothing but firmware, because you may already own the radio.
The whole argument is in the box that isn’t there.
| Part | Notes |
|---|---|
| A supported radio | The Baofeng DM‑1701 is the practical choice — still sold new, dual band, 5 W. |
| OpenGD77 firmware | Free, open source, actively maintained. Replaces the factory firmware. |
| A Raspberry Pi | A Zero 2 W is plenty, running Pi‑Star or WPSD. |
| The USB cable | The radio’s own programming cable. That is the entire interface. On a Zero 2 W you will want a micro‑USB OTG adapter. |
| No MMDVM board | This is the point. There is no RF board anywhere in this build. |
OpenGD77 runs on a specific list of radios, and that list is not the same as the list you can buy. Two current models are the ones worth your money:
| Radio | Why |
|---|---|
| Baofeng DM‑1701 also sold as DM‑1701B |
The practical pick. Dual band, 5 W, inexpensive, sold new direct from the manufacturer. Sellers now print OpenGD77 Available in the product title — which tells you how mainstream this has become. |
| TYT MD‑UV380 also MD‑390 / Retevis RT‑3S |
Still in TYT’s current catalogue and widely stocked. Dual band, 5 W. The same firmware, the same hotspot mode. |
The answer is a semiconductor story, and it is worth knowing before you shop.
The GD‑77 — the radio the whole project is named after — went out of production because of a CPU supply shortage. The processor simply stopped being available.
The MD‑UV380 and RT‑3S use a different processor, one that is still in supply. That is the entire reason TYT can keep building them, and the entire reason they are still on the shelf while others are not.
Buy the radio while you can. Manufacturers redesign models out of compatibility without announcing it, and a chip shortage can end a model overnight. OpenGD77 cannot support hardware that no longer exists. If this build appeals to you, do not wait for the perfect moment.
The entire configuration is two choices, one on each side.
On the Pi — in Pi‑Star’s Configuration page, set Radio/Modem Type to OpenGD77 DMR hotspot (USB).
On the radio — go to Options → General options, set hotspot to MMDVM, and confirm with the green key.
Plug in the USB cable, and the Pi finds a modem exactly where it expects one.
The screenless GD‑77S has no menu, so it enters hotspot mode by holding SK1 while powering on.
Power is the headline. The receiver may be the better story.
Ordinary hotspot boards are deaf. Their receivers cope badly with even small frequency errors, which is why hotspot owners spend so much time on frequency calibration — and why a hotspot carefully tuned to one handheld often works badly with the next one out of the bag.
A hotspot built from a real radio does not have this problem. It has a real radio’s front end and a real radio’s tolerance for the small frequency differences between transceivers. The calibration ritual largely goes away. You are no longer nursing a chip; you are using a receiver that was designed to be a receiver.
The limit: this is DMR only. The Pi‑Star modem type says so in its own name. You will not run D‑STAR, Fusion, M17, P25 or NXDN on it. This is a DMR hotspot with a real radio’s power and a real radio’s ears — a different tool from a ZUMspot, not simply a better one.
A hotspot is a simplex station on a frequency shared by convention rather than by coordination. At 10 milliwatts nobody notices you. At 5 watts you are a genuine signal covering genuine distance, sitting on a channel your neighbours may also be using.
A conventional hotspot is a set of compromises wearing an antenna: a radio chip chosen to be small and cheap, with the power and the deafness that follow from that.
Putting a real radio in its place does not overcome those compromises. It simply declines to make them. The transmitter and the receiver were always going to be better, because they were built to be a radio rather than an accessory.
You give up five modes to get it. If you live on DMR, that may be no loss at all.