Hanging out with hotspots

By Toshen, KEØFHS (Updated Aug 2018, CC BY-SA)

1) Overview

A hotspot (personal access point) is a combination of hardware, firmware, and software that enables a ham with internet connectivity to link directly to digital voice (DV) systems like DV repeaters, DMR talkgroups and reflectors, D-STAR reflectors, YSF rooms, QuadNet Smart Groups, and so on. Basically, hotspots act as your personal digital voice repeater and gateway, which can be really fun.

This illustration shows what it looks like for D-STAR:

Diagram of DV HTs connecting via personal access points to a reflector and a DV repeater

For someone like me who doesn't live within range of a digital voice repeater, a hotspot goes beyond being fun to being a critical key to accessing digital voice systems, a gift that opens doors to the whole wide world.

Overall, it's an exciting area of amateur radio that is evolving and progressing rapidly with some excellent work being done by some very innovative hams.

Disclaimer:  These are my personal notes and opinions based on my experience as a non-technical user playing around with hotspots, as well as by learning from what others are sharing. I'm not affiliated with any hotspot projects, except as a user. If anything needs correcting, please let me know.

2) Background

This is an article about personal hotspots, not repeaters. (For some extensive info about repeaters, see: Repeater Builders⩘ .)

I've been playing around with hotspots since late 2016, during which time I've tried a bunch of hotspot devices and the apps they work with, including the DVMEGA, BlueStack-Micro+, SharkRF openSPOT, DV Access Point (DVAP), and a couple DV4 products. While all the initial hotspots I tried are interesting and taught me something, ultimately they all had various limitations I didn't like:

And then …

I tried an MMDVM-based* hotspot called the ZUMspot with an app called Pi-Star⩘ , and all the rest of my hotspots got given away or tossed into a box and forgotten. For me, the combination of the ZUMspot and Pi-Star is taking digital voice hotspots to a whole new level. *Multi-Mode Digital Voice Modem

3) Zooming around with the ZUMspot

ZUMspot boardThe ZUMspot Pi Board by ZUM Radio is the same size as and works well mounted on a Raspberry Pi Zero W. It also can be mounted on the RPi 3B (a bit faster) and various other RPis.

It's a multi-mode digital voice modem that works with DMR and D-STAR (the two digital modes I use), and also with YSF, P25, and NXDN, as well as various DMR and YSF cross modes.

The ZUMspot also supports POCSAG, which is used to transmit data to pagers.

The ZUMspot pairs well with the Pi-Star app⩘ , and its firmware can be updated easily via Pi-Star (see the note Performing firmware updates via Pi-Star⩘ ). Set up is relatively easy, especially because it can use Pi-Star's Auto AP feature for wireless network configuration. It requires a digital-voice capable radio.

The ZUMspot is available from Ham Radio Outlet as a bare Board⩘  or a Kit⩘ . The kit includes a Raspberry Pi Zero WH and a microSD card preloaded with Pi-Star.

The ZUMspot is designed by Jim Mclaughlin, KI6ZUM, with firmware by Andy, CA6JAU (juribeparada / MMDVM_HS⩘ ), based on the Multi-Mode Digital Voice Modem (MMDVM) software by Jonathan Naylor, G4KLX (g4klx / MMDVM⩘ ).

3a) In case you're interested …

For fun, I decided to make some hotspot cases out of some mahogany thinwood I had left over from my woodworking projects. I ended up building a bunch of cases as I experimented with different combinations of RPi boards, batteries, displays, and shapes, before I settled on one design for my shack and another for mobile. In addition, I have a few other hotspots that are in nice cases from C4Labs⩘ .

The setup for my shack is a ZUMspot mounted on a RPi 3B with an Alchemy Power Pi-UpTimeUPS, which uses type 18650 3.7V batteries, for uninterrupted power. (Adafruit has a good battery tutorial⩘ .)

ZUMspot connected to RPi3 and Pi-UpTimeUPS

Since Pi-Star can run headless, the hotspot really doesn't need any external ports except for power in. It basically can be a black (or mahogany) box, optionally with on/off switches between the external power port and the UPS and between the UPS and the RPi, and maybe a display screen. In this case, I made a simple rectangular box case: 4.5″ wide × 4.7″ deep × 3.5″ high.

ZUMspot hotspot v2

The height of the case was determined by the stack of boards, which has a plexiglass base. The stack slides into the case, with the base sliding under a rectangle of wood to secure the stack in place.

The stack of boards anchored inside the box

The display fits into the opening in front of the stack of boards. To reduce the footprint of the display, I soldered wires directly to its back rather than using the connector that plugs into its side. Since I'm using those same soldered wires to connect the display directly to my PC for programming via a USB to TTL UART CH340 Serial Converter, I also didn't need to leave space or cut a slot for inserting a microSD card into the display. That means I can fit a 3.5″ display into a space that's nearly the same size as the width and height of the stack of boards.

Back of Nextion display showing wiring

For the on/off switches, the best option I could find is the LoveRPi Power Switch, which includes a green status LED showing when it's on (important in a black box scenario). It includes three different colored rubber covers for the switch.

LoveRPi Power Switch

The cables and switches determined the depth of the box. Here you can see them crammed into the remaining space. The case piece with the switches exposed screws into the back opening.

The stack of boards anchored inside the box

The power switches and the single port (the micro-USB power input) are located on the back of the case. The cable with the green switch controls power between the UPS and RPi. The cable with the black switch controls power between the input port it provides and the UPS, which it's plugged into.

Theoretically I could leave the UPS powered on all the time, but ever since we had a (fortunately relatively small) fire in our home several years ago that was caused by an electrical short sparked by some poorly done wiring by a previous owner, I've been a bit paranoid about leaving things on when I'm not using them.

The back of the box with the power switches

3b) Nextion screen customizations

My screens are a customization of the Nextion_ON7LDS⩘  screens. My goal was to be able to look at the display from anywhere in my shop and tell at glance what's being received, so I made the screens look quite different from one another, with colors related to their logos. I also like simple, calm screens, so the different text fields are displayed in various subtle colors, and there are no other eye candy embellishments.

ZUMspot hotspot v2 D-STAR screen

Thanks to Rob van Rheenen, PDØDIB, the Dutch ham and digital voice enthusiast who moderates the Nextion Ham-Radio Screens⩘  Facebook group, and who generously provides excellent tutorials and mentoring. Thanks also to the hams who are sharing inspiring designs and support in the group.


Conclusion: While I enjoyed learning how to program the Nextion display, in the end I don't really look at it all that much and don't think a display is in any way a necessary component for a hotspot using Pi-Star. That said, I found it worth it to add a display simply because doing so broadened my knowledge about hotspots and electronics. And it's fun.

3c) Putting the vroom in zooming around

The design for my mobile hotspot was influenced by two goals: a desire for simplicity and a hunger for operating time. I decided on a minimalist design: just the ZUMspot + RPi Zero W protected in a box and powered by a rugged external RAVPower 10050 mAh portable charger, which gives me a full day's capacity.

Minimalist ZUMspot mobile hotspot

I added a right-angled micro-USB adapter inside the box to make plugging in easier (the plugin port aligns better with the port on the charger), as well as to reduce wear and tear on the RPi's micro-USB port. The mahogany case fits nicely on top of the battery, attached with Soft Touch Velour cinch straps.

Size comparison

                 Width   Depth  Height
Shack hotspot:    4.50″ × 4.70″ × 3.50″
Mobile hotspot:   3.25″ × 2.50″ × 1.75″
External battery: 4.60″ × 2.80″ × 0.90″
Deck of cards:    3.60″ × 2.60″ × 0.70″

A good video about setting up a ZUMspot with Pi-Star

Don Arnold, W6GPS, has a good video out: ZUMspot setup with Pi-Star for the Kenwood TH-D74⩘ . In the first half of the video, Don explains the general initial configuration of a ZUMspot using Pi-Star. In the second half, he explains setting up the Kenwood TH-D74A for use with a hotspot.

3d) C4Labs cases

C4Labs⩘  in Tacoma, Washington makes some nice cases for ZUMspots mounted on either the RPi Zero W/WH or the 3B/3B+. Even though I like making cases, I also use several of their creative cases. C4Labs ZUMspot cases⩘ .

ZUMspot + RPi Zero WH
ZUM-PI Zero case

ZUMspot + RPi 3B+
ZUM-PI3 case

4) Other hotspot hardware and software

Alphabetical list of some other hotspots and apps I've tried or heard about:

5) Be wary of cheap clones!

There are some really good quality, cutting-edge hotspot modem boards available right now. And then there are the clone boards called JumboSPOT (a.k.a., J-Hat). It has been challenging for me to find info about them, but from what I've learned so far, they appear to be inferior unauthorized copies of an early MMDVM_HS_Hat.

From what I have read in forums, a significant number of people have problems with the JumboSPOT. In particular, it uses cheap versions of the oscillator/TXCO chips, which can cause some serious issues, up to bricking the board.

Many of the vendors of the cheap knock-off clones appear to not even know much about amateur radio; instead, their focus seems to be making a quick buck. Many also don't provide much support to the hams buying their products.

The hams creating the genuine hardware, the firmware it runs, and the MMDVM software are personally contributing to the amazingly rapid innovation we're seeing in the digital voice space right now.

At first glance, the clone boards may seem to be a bargain because they're a few bucks cheaper than the original boards. But spending a few extra bucks on one of the original boards is probably worth it; not only do you get quality components and better support, you also get the satisfaction of supporting the innovation that is happening in our hobby.

6) A shout out to the innovators and enablers

In general, hotspots really put the amateur in amateur radio. For the most part, the creative innovation driving this branch of amateur radio forward is being done by passionate hams around the world with day jobs and families who are pursuing various projects in their spare time.

The upside is that we get this really innovative playground to mess around in; the downside—or, depending on how you look at it, another upside—is that this really is an amateur endeavor: things don't always work; there are some rough edges; updates sometimes break stuff; it can take a while for new features that many people want to get implemented; sometimes the only way to make something work is with a soldering iron, a bit of cussing, and a lot of stubbornness; and some features aren't fully documented so it can take a lot of trial and error to figure them out. In other words … lots of fun to be had for an adventurous amateur!

Here are some of the hams driving all of this forward:

Jonathan Naylor, G4KLX

Jonathan operates in a technical stratosphere way above my head. What I can comprehend is that he has been creating important digital voice-related solutions for years, which he makes freely available to the hams who are innovating in this playground and helping to make amateur digital voice radio so exciting.

The fact that he does this as a side project is truly amazing. (In a video of a talk he gave about MMDVM, he mentioned how at one point his job took him away from home during the week for a period of time to a place that had few disturbances. This, he said with a somewhat mischievous grin, made it possible for him to spend his evening doing something useful … which turned out to be MMDVM!)

Here's what Pi-Star's Andy Taylor says about this:

There are some more special people who we all owe a debt of gratitude for their willingness to release their software for free. Jonathan Naylor (G4KLX) for his most excellent DStarRepeater, ircDDBGateway suite, and more recently MMDVMHost and DMRGateway. These applications form the core of what makes Pi-Star what it is, and without these excellent applications Digital Voice for Amateurs would be an entirely different and barren landscape.

Here's a video of one of Jonathan's talks: MMDVM⩘ , 2017. For more info, see: GitHub g4klx⩘  and MMDVM Yahoo group⩘ .

Andrew Taylor, MWØMWZ

Andy's work has made a huge difference to the thousands of us who use Pi-Star to run our hotspots and repeaters. If this were his full-time job, I still wouldn't understand how he manages to crank out so much code as he keeps updating Pi-Star with the latest cutting-edge features and advances. The fact that he does this as a side project and somehow still manages to find time for his real full-time job, his family, and his studies totally baffles me. Website: www.pistar.uk⩘ .

José Uribe (Andy), CA6JAU

Andy makes the firmware that powers many ZUMspot and MMDVM_HS-based boards. If you ever hear a rumor about some awesome new feature or functionality, check out his GitHub page; chances are he'll already have a release ready with it ! GitHub: juribeparada/MMDVM_HS⩘ .

The tinkerers

There are tinkerers in countries all around the world who are designing boards and wielding soldering irons faster than any of the legendary six-shooter gunslingers of the Old West.

Jim McLaughlin, KI6ZUM, is one of them. He worked closely with Jonathan and Andy on the original MMDVM project, and is the guiding hand behind the ZUM Radio products. There are several others listed in the Other hotspot hardware and software section above. And there are many more I've read about (try searching Twitter for MMDVM!), and I'm sure there are even more I haven't yet heard about.

For someone like me who thinks it's a pretty amazing accomplishment when I manage to solder on a GPIO header without melting the whole board … well, let's just say I'm in awe!

The mentors

There are a bunch of hams hanging out in forums and groups around the internet answering question, solving problems, and giving guidance for all the various aspects of digital voice and hotspots. For the Pi-Star project, this includes Craig, W1MSG, who also makes the tutorial videos, Adrian, MØGLJ, and Andrew, M1DNS, as well as many others. Thanks to all the hams who are helping out in this way; I really appreciate the opportunity to learn by reading your posts!

And all the other enablers

Finally, a shoutout to all the clubs and individuals who are putting up repeaters, reflectors, servers, gateways, bridges, and other equipment, as well as providing trainings for how to use it all.


Thanks for making it possible for all the rest of us to enjoy the rich variety of systems and features that are now available in the digital voice playground!

Pi-Star ≫