Hanging out with hotspots

Revised: May 2019, CC BY-SA = open in new tab ]
Most up-to-date version:  amateurradionotes.com/hotspots.htm

1) Overview

A personal, low-power hotspot (also known as a personal access point) is a combination of hardware, firmware, and software that enables a ham with a digital radio and internet connectivity to link directly to digital voice (DV) systems around the world. Hotspots can link to DMR talkgroups and reflectors, D-STAR reflectors, YSF rooms, QuadNet Smart Groups, and, in some cases, DV repeaters. Basically, hotspots are your own 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.

Colorado Digital Multiprotocol logoI particularly enjoy participating on the Colorado HD (Hotspot Discussion) net, a Colorado Digital Multiprotocol net held each Friday at 7:30p MTN:

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

Important! The regulations and best practices that apply to amateur radio—including use of frequencies, control of our stations, and on-air courtesy—also apply to our use of personal, low-power hotspots. It's our responsibility to understand and adhere to those regulations and best practices. My personal practice is that I power on my personal, low-power hotspots only when I'm monitoring and in control of them, adhere to my local band and frequency use plans, and leave adequate pauses between transmissions. For more about this, see Hotspot best practices.

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 an enthusiastic user. If anything needs correcting, please let me know.

1a) Background

This is an article about personal, low-power hotspots, specifically, personal access points1, not repeaters. For information about repeaters, see: Repeater Builders.

I've been playing around with personal, low-power hotspots since 2016. During the first year or so, I tried a bunch of devices and apps including the DVMEGA, BlueStack-Micro+, SharkRF openSPOT v1, DV Access Point (DVAP), and a couple DV4 products. While each of them taught me something, when I tried an MMDVM-based hotspot called the ZUMspot with an app called Pi-Star (discussed in more detail in the Playing with Pi-Star article), I discovered that the combination took the experience of personal, low-power hotspots to a new level.

The Multi-Mode Digital Voice Modem project was conceived in early 2015 by Jonathan, G4KLX, and developed by Jonathan and Jim, KI6ZUM. Jonathan wrote all the software, Jim created the hardware (and, eventually, the ZUMspot), and both worked on the firmware. Later, Andy, CD6JAU, took over working on the firmware. Andy also created the cross modes (DMR2YSF, DMR2NXDN, YSF2DMR, YSF2NXDN, and YSF2P25). Since they launched the project, a bunch of people around the world have integrated the MMDVM technology into the hotspots they're creating.

Note: There's a good presentation from Pacificon 2017 that contains an introduction to digital voice and multimode by Jim, K6JM, as well as a keynote about MMDVM by Jim, KI6ZUM: MultiMode Digital Voice: The Exciting New Trend in DV.

2) The components

A personal, low-power hotspot is like your own personal repeater and gateway computer. Similar to a repeater, it's capable of receiving and transmitting RF, though at a very low power level, typically, 10mW or 0.01 watts. Like a gateway, it's also capable of as connecting to the internet to send and receive data.

A typical personal, low-power hotspot is made up of some kind of radio/modem board with an antenna together with a small computer like a Raspberry Pi (some hotspots combine the two into a single board). The hardware typically includes built-in WiFi and/or an ethernet port, as well as various ports (USB, HDMI, etc.) and pins or through-holes that enable connecting peripherals like displays.

The radio/modem board component typically has firmware controlling its core functions, while the entire hotspot has software controlling its overall operation. Usually, both the firmware and software can be upgraded by the end user, enabling the hotspots to incorporate feature updates and fixes.

  1. Here's a closer look at some key personal, low-power hotspot topics:
    1. Radio/modem board
    2. Processing and connectivity
    3. Firmware
    4. Software
    5. LEDs
    6. Buttons
    7. Through-holes
    8. Cases
    9. Displays

2a) Radio/modem board

I'm most familiar with MMDVM-based hotspots, so I'll focus on them for this explanation. I had the good fortune to meet, via email, Dave, KC6N, who shared insights with me about how they work. What he pointed out made me appreciate these little boards even more.

ZUMspot boardHere's what I understood from Dave: The MMDVM-based personal, low-power hotspots have a radio/modem board with two primary chips, shown here on a ZUMspot. The radio and modem functions are distributed between those chips.

One of the primary chips is an Analog Devices ADF7021 Integrated Chip, a low-power 2FSK/3FSK/4FSK* transceiver. The ADF7021 generates RF signals and handles audio tones used by our digital radios to represent 1s and 0s.

The other primary chip is a microcontroller, a small computer on a single integrated circuit. It does the digital work, builds the packet frames, and programs and controls the ADF7021.

Thanks, Dave, for taking the time to share your knowledge and patiently explain this to me; it's at times like these that I appreciate the amateur radio community the most. If you'd like to dive into all of us this a bit more deeply, Dave created a good presentation about all of this: Digital Voice for Amateur Radio.

Hint: A common issue with new hotspots is high Bit Error Rate (BER > 1%). If you experience this when transmitting, see the note: Fine tuning to reduce high BER.

[*] FSK = Frequency Shift Keying; 2FSK is used for D-STAR, and 4FSK is used for DMR, YSF, P25, and NXDN, which explains why cross-mode operation is possible between the latter four, but not so easily with D-STAR.

2b) Processing and connectivity

While the radio/modem board handles the tasks related to the radio signals, a small computer handles the rest of the processing tasks, as well as the internet connectivity tasks, and the hotspot's power processing.

Raspberry Pi 3 model A+A primary hotspot component handled by the computer is the Gateway, which communicates with the internet. For an MMDVM-based hotspot, that's handled by a computer like a Raspberry Pi that the radio/modem board is mounted on.

The MMDVM-based radio/modem boards can be mounted on and work well with a variety of Raspberry Pi models, most commonly the Zero W (very compact) and the 3A+ and 3B+ (faster and more powerful). They'll also work on many of the older models. Some MMDVM-based radio/modem boards are designed to work with other small computers like the NanoPi Neo, but those aren't as common. As I mentioned earlier, some hotspots incorporate both the radio/modem and computing components onto a custom single board.

My current favorite Raspberry Pi is the 3A+ because it is a nice balance between form factor size and performance. It's much faster than the Zero W, more compact than the 3B+, and also runs much cooler than the 3B+, while not much warmer than the Zero W. You do give up some ports with the 3A+ compared to the 3B+: there's only one USB port vs. four on the 3B+, and most importantly, there's no ethernet port, but that's fine for me as I use only WiFi for my hotspots. The RPi 3B is also a very good board.

Bud, W0RMT, posted a good article comparing the RPi 3A+, 3B+, and Zero W: Choosing a Pi for your Pi-Star hotspot.

2c) Firmware

The radio/modem's firmware controls its key functions. Many MMDVM-based modems use the firmware developed by Andy, CA6JAU (GitHub: juribeparada / MMDVM_HS). You can find the latest releases and release notes at ZUMspot/MMDVM_HS firmware. Other hotspots use their own firmware, which you can find on their own websites.

The ZUMspot/MMDVM_HS firware can be updated easily via Pi-Star (see Performing firmware updates via Pi-Star). To use Pi-Star's firmware updating script, you need to know the exact firmware update command to use, which you can learn from the manufacturer or vendor of your MMDVM-based hotspot.

2d) Software

Most of the MMDVM-based hotspots work really well with the Pi-Star app, and setup is relatively easy, especially because many of them can use Pi-Star's Auto AP feature for wireless network configuration (requires a recent RPi like the Zero W, 3B, 3A+, or 3B+).

For more information about setting up and running a hotspot using Pi-Star, see the Playing with Pi-Star article. At least one hotspot uses its own software, and a couple use derivatives of Pi-Star, which you can learn more about from the manufacturer or vendors of those hotspots.

2e) LEDs

You need to view the LEDs from the perspective of the hotspot:

2f) Buttons

Often, there are one or more push buttons on an MMDVM-based radio/modem board, for example, you might see:

2g) Through-holes

Radio/modem boards also have various sets of plated through-holes you can use to connect a variety of peripherals, for example, you might solder in a 4x1 straight or right-angle pin header connector that you can use to connect the cable from a display. A couple of the sets of through-holes you might see:

2h) Cases

Technically, you don't need a case for an MMDVM-based hotspot; I've used some of mine with just the bare boards, connected together with standoffs, and with some short standoffs beneath to provide feet. But it's really nice to put them in a proper case. Here are some examples of handmade and manufactured cases.

Handmade hotspot cases

I'm a woodworker, so for fun, I decided to make a few hotspot cases out of some mahogany thinwood I had left over from my woodworking projects, as well as a few other scraps. I ended up building several cases as I experimented with different combinations of RPi boards, batteries, displays, and shapes, before I settled on one design for my shack, a second for the desk where I do a lot of my research and writing, and a third and fourth for mobile use.

Shack hotspot

The setup for my shack hotspot is a ZUMspot mounted on an RPi 3B with an Alchemy Power Pi-UpTimeUPS, which uses type 18650 3.7V batteries for uninterrupted power.

ZUMspot connected to RPi3 and Pi-UpTimeUPS

Since Pi-Star can run headless, the hotspot really doesn't need any external ports other than one for power in. Basically, it 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. For this case, I made a simple box: 4.5″ wide × 4.7″ deep × 3.5″ high (mm: 114 W × 119 D × 89 H).

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 plexiglass 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 (on a subsequent Nextion, I actually removed the connector altogether and soldered directly to the board, which was easier).

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, I used the LoveRPi Power Switch, which includes a green status LED showing when it's on (important in a black box scenario). It also includes three rubber caps for the switch (green, red, and black).

LoveRPi Power Switch

An alternative switch that I have used for some of my other hotspots is the CanaKit PiSwitch.

The cables and switches, which I attached to the case with hot glue, determined the depth of the case. Here you can see them crammed into the remaining space. (It's amazing how, as electronic components keep getting smaller and smaller, the plugs and cables have become some of the bigger and bulkier parts!) The case piece with the glued-on switches fits into the cases's back opening.

The stack of boards anchored inside the box

The power switches and the single port (a micro-USB power input) are located on the back of the case. The cable with the black switch controls power between the power input and the UPS. The cable with the green switch controls power between the UPS and RPi.

The back of the box with the power switches

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.

Writing desk hotspot

I keep another hotspot on my writing desk so I can test things out as I'm researching new features.

The back of the box with the power switches

One thing I realized is that I have no problem using my hotspots when I'm in another room with a thick wall in between, which means I really don't need to have the antenna sticking out of the box. So my goal was to make something clean looking with the screen at an angle for easier viewing when I'm typing. It has a ZUMspot + RPi 3A+ on the inside, with a 3.2″ Nextion enhanced display.

Mobile hotspot

The design for my mobile hotspots was influenced by two goals: a desire for compact simplicity and a hunger for operating time. I decided on a minimalist design: just an MMDVM-based radio/modem board mounted on an RPi Zero W in a box for protection 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:   3.37″ × 2.50″ × 1.75″
External battery: 4.60″ × 2.80″ × 0.90″
Deck of cards:    3.60″ × 2.60″ × 0.70″

Jan 2019 update: Once Pi-Star 4, which supports the Raspberry Pi 3A+, became available, I upgraded my mobile hotspot to a combination of the RPi 3A+ and an MMDVM_HS_Hat with a ceramic onboard antenna. See MMDVM_HS_Hat devices below for a look at that hotspot case.

Manufactured hotspot cases

Even though I like making some of my own cases, I also use some manufactured cases for test hotspots. For hotspots based on the RPi Zero W, 3B, and 3B+, I use the MMDVM cases made by C4Labs in Tacoma, Washington.

ZUMspot + RPi Zero WH
C4Labs case for a simplex hotspot with the RPi Zero W form factor

ZUMspot + RPi 3B+
C4Labs case for a simplex hotspot with the RPi 3B/3B+ form factor

For the new RPi 3A+, I use the Adafruit Pi Model A+ Case Base and Lid, which has room for an MMDVM-based radio/modem board inside. I drill a hole in the lid for the antenna, if needed, and a larger hole in the base so I can add a heat sink to the chip that's on the bottom of the RPi 3A+. I also found that it helps to sand the catch at the back of the case (on the GPIO header side) to make it easier to snap the 3A+ in place.

Adafruit Pi Model A+ Case
Adafruit Pi Model A+ Case

2i) Displays

MMDVM-based hotspots can run various displays. The most common are Nextion displays in a variety of sizes and the smaller OLED displays.

I personally prefer the Nextion displays. My Nextion display 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 for the different modes 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, just the mode logo and the data.

ZUMspot hotspot v2 D-STAR screen

Thanks to Rob van Rheenen, PD0DIB, 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.


3) The hotspots

These are the hotspots I use, or have tried or heard about, in alphabetical order.

  1. The ZUMspot is my favorite MMDVM-based, personal, low-power hotspot board:
    • It's a dependable, high-quality board designed by Jim, KI6ZUM, who is one of the earliest participants with Jonathan, G4KLX, in the Multi-Mode Digital Voice Modem (MMDVM) project.
    • It uses firmware by Andy, CA6JAU, who is also one of the earliest participants in the project.
    • It's versatile, supporting a wide variety of modes including DMR, D-STAR, YSF, P25, NXDN, various DMR and YSF cross modes (DMR2NXDN, DMR2YSF, YSF2DMR, YSF2NXDN, YSF225), and POCSAG (for digital voice paging).
    • It's compact, fitting and running well on a Raspberry Pi Zero W.
    • It's widely adopted, so it's easy to find online or on-air help.
    • Updating its firmware from within Pi-Star is easy via a single-line command:
      sudo pistar-zumspotflash rpi
    • It has through-hole connectors right on the board for directly wiring in either a Nextion or OLED display.
    • It's relatively inexpensive, especially given its quality.
    • I'm especially happy with the Apr 2019 release of the ZUMspot-RPi Board 3 v0.6, which includes a pre-installed Nextion display header connection.
  2. That said, there are several other good quality hotspot boards available that are worth considering as well.
  3. Disclaimer:  Once again, 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 an enthusiastic user. If anything needs correcting, please let me know.
    1. Amateur Radio Toys
    2. D2RG – something new coming?
    3. DV dongles
    4. DVMEGA
    5. JumboSPOT (a.k.a., J-Hat)
    6. LoneStar MMDVM devices
    7. MMDVM_HS_Hat devices
    8. Nano-Spot
    9. SharkRF openSpot
    10. ThumbDV
    11. ZUMspot
    12. Others

3a) Amateur Radio Toys

By Winters Huang, BI7JTA.

Huang is quite passionate about amateur radio and hotspots. He has designed a variety of boards, and also puts a lot of energy into the Amateur Radio Toys website and blog, as well as his Facebook group and Twitter account. He also provides friendly support for his hotspots.

ZW_SPOT HAT for RPi Zero WI run one A.R.T. hotspot based on the simplex MMDVM_HS_HAT_RPiZW (a.k.a., ZW_SPOT HAT) by BI7JTA and VR2VYE.

Because I've had good success with onboard antennas, I ordered a custom version with a RainSun onboard ceramic antenna, but it still has an SMA antenna mount, too, and since they are on isolated circuits, either can be used.

It has an RPi Zero W form factor, though I have it mounted on an RPi 3A+.

I run a second A.R.T. hotspot based on the simplex hotSPOT for RPi (a.k.a., RPi hotSPOT with Cool FAN) by BH7NJF and BI7JTA. I have it mounted on an RPi 3B+ in the "official" RPi 3 case. (I had to tweak the case a little bit to make everything fit, but once tweaked, it works fine.) I also drilled an opening in the bottom of the case so I could mount a heat sink on the chip that's on the bottom of the RPi 3B+.

RPi hotSPOT with Cool FAN

The RPi hotSPOT with Cool FAN has the form factor of an RPi 3A+, but this is a great board to run on an RPi 3B+ because of its very quiet but effective built-in fan, which helps keep the hotter 3B+ running cooler. When I'm running the hotspot, I keep the case cover off; at other times, I keep it on to keep the dust out. Bonus: the RxOffset needed no adjustment!

Nano hotSPOT(BlueBox) for MMDVMI also previously tried the simplex Nano hotSPOT(BlueBox) for MMDVM. It's very compact and works well, though it's slow, presumably due to the specs of the NanoPi NEO computer it uses. Amazingly for its compact size, it has a built-in OLED display, a fan, and even full-sized ethernet and USB ports (the USB port can be used for a WiFi dongle).

Amateur Radio Toys also makes a Duplex hotspot board and a repeater board, though I haven't tried those. The boards come in a variety of configurations: as bare boards or with various cases, and with optional Nextion or OLED displays.

The RPi-based simplex boards use standard firmware by Andy, CA6JAU (juribeparada / MMDVM_HS). To update the firmware via Pi-Star:
sudo pistar-mmdvmhshatflash hs_hat

The Radio/Modem Type for the RPi-based simplex boards is:
STM32-DVM / MMDVM_HS - Raspberry Pi Hat (GPIO)

Website: Amateur Radio Toys by BI7JTA. Ordering is easy and shipping is fast.
GitHub: bi7jta

3b) D2RG – something new coming?

Digital Radio Research Group logo
Apparently in production: An MMDVM-HS-AMBE hat, with an onboard DVSI AMBE3003™, to make transcoding on the RPi possible.

Digital Radio Research Group
See also: https://mmdvm.blogspot.com/


By Guus van Dooren, PE1PLM.

DVMEGA DUALThe DVMEGA comes in single-mode (UHF) and dual-mode (VHF/UHF) versions, both of which can be mounted on Raspberry Pi computers, and there are other models as well.

The DVMEGA also can be mounted on a BlueStack board. With firmware 3.07 and later, the DVMEGA can support D-STAR, DMR, and YSF. Requires a digital voice-capable radio.

Works well with Pi-Star, and once you've soldered the firmware update jumper wire in place for Pi-Star, it's easy to update via Pi-Star's command line as well. It's also possible to update the firmware when the DVMEGA is mounted on a BlueStack board (with the jumper wire soldered to different pins) and connected to a PC. For firmware info, see the note DVMEGA firmware update.

A note about the form factor: The DVMEGA has an odd form factor. Its GPIO connector is sized for 10 pins (2 rows of 5 pins) and it has a standoff in an odd place on the opposite side from the pins, between the pins and the antenna mount. I'm guessing this may have matched some older RPi, but it's a bit awkward on the current RPi 3B/3B+/3A+ boards. The standoff acts as a pivot point, so that if you touch the antenna, the GPIO connector tends to pull up off the pins. To partially solve this, I took a full GPI0 connector, cut off 5 rows, pulled the pins out of the rest, and mounted that on the remaining GPIO header on the RPi, which gives the DVMEGA a bit more stability.

Guus also recently released a couple new products: the DVstick 30, a thumb drive with an onboard AMBE-3000™ Vocoder chip, and the DVMEGA Cast, an AMBE-3000™ based multi-mode IP radio for DMR, D-STAR, and YSF.

Website: DVMEGA. Twitter: Guus van Dooren.


DVMEGA DUALBy Ruud Kerstens, PE1MSZ.
[ For use with DVMEGA ]

A companion board for the DVMEGA. The DVMEGA RPi board can be paired with the BlueStack-Micro+ instead of an RPi, which enables a bluetooth connection to an Android or iOS phone running BlueDV or a serial connection to a Windows computer running BlueDV.

When powered by a portable battery pack, the BlueStack + DVMEGA combo provides a mobile solution that can be used with D-STAR, DMR, and YSF radios:

DVMEGA & BlueStack in custom case
I made a case for the BlueStack-DVMEGA duo
out of some mahogany scraps

For more about this mobile solution, see: Just can't wait to get on the road again.

The BlueStack board also can be used to facilitate a DVMEGA firmware update. For more info, see the note DVMEGA firmware update.

Website: pe1msz.nl. Supplier: Combitronics.

BlueDV apps

By David, PA7LIM.
[ For use with DVMEGA (and other scenarios, too) ]

BlueDV app
David makes some really fun and innovative apps. He's continuously trying new things and pushing boundaries. BlueDV can be run on Android and Windows (experimental versions also available for iOS, Linux, and RPi), and is a good solution for a mobile hotspot using the BlueStack-Micro+ paired with a DVMEGA.

Note from David's website: "I am not a company! I just wrote the software for fun! (I have no commercial link with DVMEGA, Combitronics or others.) Hope you have a lot of fun with the software!" Note from me: Thanks, David!

Website: BlueDV. Twitter: David PA7LIM.

3d) DV dongles

By Robin Cutshaw, AA4RC, and Moe Wheatley, AE4JY, Internet Labs, Inc.
[ Older, limited designs. ]

DVAPThe DV Dongle and DVAP were among the earliest personal hotspots available (my first hotspot was a DVAP). They can be connected to a PC running Windows or a Mac.

The DVAP requires a D-STAR radio, the DV Dongle uses a DVSI AMBE-2000™ chip, and the newer DV3K uses a DVSI AMBE-3000™ chip.

At the 2017 Hamvention, they announced an upcoming "DV Air" product with built-in Bluetooth, WiFi, and ethernet, but as of spring 2019, I haven't found any further information about it.

When running their own software, these dongles work with only DPLUS (REF) reflectors, intentionally block access to XRF, DCS, and XLX reflectors, and don't support DMR, YSF, or P25 modes. I've read that some people use Pi-Star instead, but I don't have any experience with that.

Websites: DV Dongle, DV3K Dongle, and DVAP Dongle.

3e) JumboSPOT (a.k.a., J-Hat)

By ???

My personal recommendation is to stay away from these boards, which are unauthorized, lower-quality clones of the original German MMDVM_HS_Hat boards designed by Florian, DF2ET, and Mathis, DB9MAT. It's not clear who makes these boards (they originate in China), and it's even possible that there is more than one manufacturer.

While some people have had good luck with these boards, others have had considerable problems, especially with the inconsistent quality of the TCXO chips used, which at best can mean large RxOffsets (I've heard of people having to set the offset in the many thousands range), and at worse can mean a bricked board.

These boards are often sold by vendors who have no association with amateur radio, and some don't provide the hams who purchase these boards with any support, not even for defective boards.

3f) LoneStar MMDVM devices

By David, N5BOC, with firmware by Andy, CA6JAU (juribeparada / MMDVM_HS).

These boards well made of quality components, and they use good design techniques.

LoneStar MMDVM Simplex

LoneStar MMDVM Simplex with ceramic antennaA well-designed, four-layer board with a YAGEO 432 MHz ceramic antenna (as well as SMA through-holes), and a large ground plane sandwiched in the middle, which results in well-isolated signals. Supports OLED and Nextion displays.

From the website:

… this board has its own dedicated 3.3V regulator and does not pull voltage off of the noisy Raspberry Pi 3.3V line like all other simplex board do. This board is now a 4 layer board with LARGE ground planes for 3.3V and GND sandwiched in the middle. This acts as one very large decoupling cap the side of the entire board. Also this isolates signals between TOP side and BOTTOM side. Speaking of that all of the Analog RF signals are on the TOP side only and the high harmonic digital signals are all kept isolated on the BOTTOM side. Making this board much more stable.

RxOffset: The LoneStar MMDVM Simplex I received didn't require any RxOffset, and it stated that on the box, so it looks like he tests the individual boards before he ships them out.

Radio/Modem Type:
Firmware upgrade script:
sudo pistar-mmdvmhshatflash hs_hat

A final note about aesthetics: This is a beautiful board, crispy laid out, with a lustrous deep blue finish. While that isn't an essential element of a radio/modem board, it is nice, and I appreciate the craftsmanship, care, and sense of aesthetics that went into designing and making this board.

Website: Tindie N5BOC store: LoneStar MMDVM Simplex

LoneStar MMDVM Daul with SMA antennasLoneStar MMDVM Dual

I haven't tried this board, but just from what I see on the website, it's obvious that David has done some clever work to make a duplex board with quality components and good design practices with a Raspberry Pi Zero W form factor, making it the only duplex board I've seen that is this compact. Quite an accomplishment! Also supports both OLED and Nextion displays, and the C4Labs DRZ-1S case is designed specifically for this board, and it also has enough space inside for an optional OLED display.

Website: Tindie N5BOC store: LoneStar MMDVM Dual.
Note: It can be a bit challenging to order these boards via Tindie. Tindie has a weird waiting list system. When the boards are out of stock, which is most of the time, the only thing you can do is sign up to be on a waiting list. When a batch of boards is released, everyone on the waiting list is notified, and then the people who respond first get to buy a board. So even if you've been on the waiting list for a long time, there no guarantee you'll get a board when they're released unless you respond very quickly to the email announcing they're back in stock.

3g) MMDVM_HS_Hat devices

By Florian, DF2ET, Mathis, DB9MAT, and Andreas, DO7EN; based on work by Jonathan, G4KLX, Jim, KI6ZUM, and others, with firmware by Andy, CA6JAU (juribeparada / MMDVM_HS).

While it's not exactly a sexy name, the MMDVM_HS_Hat line of boards from Germany is top notch (and shouldn't be confused with the unauthorized, lower-quality clones known as JumboSPOT or J-Hat).

These boards handle D-STAR, DMR, YSF, P25, and NXDN, as well as the YSF and DMR cross modes, and POCSAG (Florian and Mathis are very active in POCSAG-related development). A digital-voice capable radio is required.


By Florian, DF2ET, and Mathis, DB9MAT.

MMDVM_HS_Hat with ceramic antenna I have revision 1.6 of this board, which uses the 12.288 MHz TCXO chip (the older versions used the 14.7456 MHz chip). It comes in two versions, one with an onboard ceramic chip antenna and another with an SMA socket for an external antenna. Works well with Pi-Star, and its firmware can be updated easily via Pi-Star's command line. You can see which TCXO chip your board has in the Radio Info module of the Pi-Star dashboard.

While it can be a bit challenging to get ahold of one of these, the quality is very good, so I found it well worth the effort. Otherwise, if you're good at assembling electronics, you can build your own. There's a pre-configured Mouser cart for several versions, including one for MMDVM_HS_Hat version 1.6.

Contact email: mmdvm@df2et.de.
MMDVM_HS_Hat on GitHub: mathisschmieder / MMDVM_HS_Hat.

Jan 2019 update – Once Pi-Star 4, which support the Raspberry Pi 3A+, became available, I upgraded my mobile hotspot to a combination of the MMDVM_HS_Hat with a ceramic onboard antenna produced by Florian, DF2ET, and Mathis, DB9MAT, mounted on an RPi 3A+. The RPi 3A+ is more compact and runs cooler than the RPi 3B+, while being a lot faster than the RPi Zero W.

MMDVM_HS_Hat + RPi 3A+ mobile hotspot

Size comparison

                 Width   Depth   Height
Mobile hotspot:   3.00″ × 2.90″ × 1.75″
External battery: 4.60″ × 2.80″ × 0.90″
Deck of cards:    3.60″ × 2.60″ × 0.70″

Bonus: For my new mobile hotspot, I also left the RPi 3A+ USB port accessible so I can plug in an external Nextion display if I want.

Nextion test unit plugged into MMDVM_HS_Hat mobile hotspot

(For my two Nextion test units, I simply made cases out of their boxes.)


By Florian, DF2ET, Mathis, DB9MAT, and Andreas, DO7EN.

This newer duplex board also uses the 12.288 MHz TCXO chip.

The dual boards have one immediate advantage over the simplex hotspots, which is that you can transmit even when your radio is in the middle of receiving. This means that you can easily unlink from a busy talkgroup like TAC 310 even when the hams using the TG don't leave gaps between their transmissions.

Another advantage of the dual boards is that you can use both time slots, for example, you can use two DMR radios, one linked via TS1 and the other linked via TS2, to listen to both linked talkgroups simultaneously.

Just as with their simplex board, they produce these high quality dual boards infrequently and in small batches, but again, I found it worth the effort and patience to get ahold of one.

Note: There is a known DMR timing synchronization issue with some duplex hotspots and radio combinations. Bud, W0RMT, has a good post on the Pi-Star User Forum about adjustments that can be tried to address the issue.

Contact email: mmdvm@df2et.de.
MMDVM_HS_Dual_Hat on GitHub: phl0 / MMDVM_HS_Dual_Hat.
Twitter: Flo (DF2ET) and Mathis Schmieder.

3h) Nano-Spot

Nano-SpotBy Mark Guidbord, K7IZA.

The Nano-Spot is a plug-n-play device. It includes built-in WiFi, RF and WiFi antennas, and an OLED display, all in a durable extruded aluminum case. Runs Pi-Star. Requires a digital radio and supports D-STAR, DMR, YSF, and P25.

I haven't tried this hotspot, but if you're looking for all-in-one hotspot hardware, it may be one that is worth checking out.

One thing to be aware of is that it uses custom firmware and I think it also uses a custom version of the Pi-Star software, so you are dependent on Mark as to when new versions are available, and may even need his assistance for some of the updating.

Website: Micro-Node.

3i) SharkRF openSPOT

By Ákos Marton, HG1MA, and Norbert Varga, HA2NON.

SharkRF openSPOT 2The openSPOT version 2, released Oct 2018, includes in its case both a built-in antenna and WiFi. It works with D-STAR, DMR, YSF, P25, and NXDN radios, has some cross-mode capability, and also handles POCSAG. It uses its own, quite good, browser-based software. This is one of the hotspots that combines the radio/modem and computer onto a single board. From the reviews I've seen, I can tell it's a very fast hotspot.

I used the openSPOT V1 and thought it worked quite well, though it supported only wired ethernet connectivity. I'm glad to see that V2 has built-in WiFi.

Website: SharkRF

3j) ThumbDV

By Bryan Hoyer, K7UDR, Basil Gunn, N7NIX, John Hays, K7VE, and Dennis Rosenauer, AC7FT.

ThumbDVThe ThumbDV is a USB device with a built-in AMBE chip, so it can be plugged into a computer that has a microphone and speaker, and doesn't require a digital radio. I haven't tried this hotspot so can't share much about it. Apparently it can support D-STAR, DMR, and YSF, depending on the hotspot software used. I even heard someone on a net who had the ThumbDV plugged directly into his Android phone (I'm guessing using BlueDV software). Sounded just fine.

While there is still stock of this board as of early 2019, they appear to be more focused on other projects now.

Website: NW Digital Radio ThumbDV

3k) ZUMspot

Designed by Jim Mclaughlin, KI6ZUM, based on the MMDVM work by Jonathan Naylor, G4KLX (g4klx / MMDVM), and others, with firmware by Andy, CA6JAU (juribeparada / MMDVM_HS).

ZUMspot boardThe ZUMspot-RPi 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 3A+ or 3B+ (faster), as well as most of the older 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, NXDN, and POCSAG, as well as various DMR and YSF cross modes.

ZUMspot board - Nextion connectionThe high-quality, dependable ZUMspot is my favorite MMDVM-based, personal, low-power hotspot board. I'm especially happy with the Apr 2019 release of the ZUMspot-RPi Board 3 v0.6, which includes a pre-installed Nextion display header connection.

The ZUMspot-RPi v0.6, which was released Jan 2019, includes these changes:

Availability: In the U.S., the ZUMspot is available from Ham Radio Outlet in a couple configurations:

HRO also carries a variety of other ZUM Radio boards and accessories; just do a search at HRO on "ZUM Radio."

There also are a variety of C4Labs cases designed specifically for the ZUMspot board, for use with RPi Zero W or RPi 3B/3B+ computers, and optionally with OLED or Nextion displays.

In the U.K., the ZUMspot-RPi v0.6 is available from ML&S (Martin Lynch & Sons).

ML&S also carries a variety of other ZUM Radio boards.

Support: You can find support for the ZUMspot in a couple of places: the Official ZUMspot and ZUM Radio Products Group on Facebook, and the ZUMspot section of the Pi-Star User Forum.

A good video: ZUMspot setup with Pi-Star for the Kenwood TH-D74 by Don, W6GPS. In the first half of his 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.

3l) Others

There are other hotspots available that I've seen or heard about, and likely still others that I haven't:

4) Shout out to the innovators and enablers

In general, hotspots really put the amateur into 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 pouring their energy into these various projects in their spare time.

The upside is that we get this really innovative playground to play 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!

A hearty thanks to all the innovators, tinkerers, mentors, and enablers for making it possible for the rest of us to enjoy the rich variety of systems and features that are now available in the digital voice playground! 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!)

Jonathan is particularly passionate about opening things up so hams can participate fully in the hobby, not just as end users of systems and hardware. From his talk at Pacificon 2018: "A closed system in the face of an equivalent open system will never win."

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 are a couple videos of Jonathan's talks: MMDVM, 2017; The Road to the MMDVM, Pacificon 2018. See also: GitHub g4klx and MMDVM Yahoo group.

Andrew Taylor, MWØMWZ

Andy's work has made a huge difference to the thousands of us around the world 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 leaves me awed. Website: www.pistar.uk; Github: Andy Taylor.

José Uribe (Andy), CA6JAU

Andy makes the firmware that powers many ZUMspot and MMDVM_HS-based boards, as well as some of the cross-mode gateways. 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 Hotspots section above. There are more who I've read about (try searching Twitter for MMDVM!), and I'm sure there are even more who I haven't heard about yet.

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 impressed!

Here's a video of one of Jim's talks: Multimode Digital Voice Modem, Pacificon 2018.

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 produces tutorial videos, 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.

And a special thanks to a team here in my home state, led by Bud, W0RMT, and Jimi, N7VDR, who created the Colorado Digital Multiprotocol group and the associated Colorado HD (Hotspot Discussion) talkgroup, 31088. They've built a multiprotocol reflector project to interconnect various digital modes.

Colorado Digital Multiprotocol logo

So far, they've brought together DMR, D-STAR, NXDN, YSF, P25, and Allstar. Exciting! For more info, see Colorado Digital Multiprotocol Reflector Gateway.

Their multiprotocol Colorado HD net—which is a really great net—is held each Friday at 7:30p MTN:

They also have a Telegram group: Colorado Digital Multiprotocol.

5) Final notes and footnotes

  1. Part of the fun of playing with hotspots is learning so much.
    1. How I gain experience for writing these notes
    2. Hotspots: an opportunity to learn
    3. Footnotes

5a) How I gain experience for writing these notes

I regularly use a variety of hotspots configured in various ways to test things like updating and upgrading, different options, as well as routine use. My current radio/modem boards include:

Hotspots galore

Most of my hotspots are based on the Raspberry Pi 3A+ (current favorite) and 3B+. While I like how small the RPi Zero W is and still have a hotspot based on it that I test with regularly, I'm spoiled by the speed of the RPi 3A+/3B+ boards.

I run several Nextion displays (3.2″ and 3.5″), which I enjoy even if I don't find them necessary. I've also tried OLED units, though I don't like them much.

In addition to experimenting with my various hotspots, I read lots of online information related to hotspots, including tons of forum posts. As much as is practicable, I test what I write about, and I try to always note it when I mention something that I haven't personally tested.

5b) Hotspots: an opportunity to learn

Before I started using hotspots, I didn't know much of anything about digital voice (D-STAR and DMR were confusing concepts to me, and I hadn't heard of YSF, P25, or NXDN), didn't know the difference between a vocoder and a modulator or a reflector and a gateway, didn't really know how to solder, didn't know what a TCXO* chip is, had only heard about but had not tried the Raspberry Pi computer and its Linux-based Raspbian operating system, didn't know what SSH is, and didn't know the difference between a pub and a GitHub.

Now I'm happily playing around with a couple different digital voice modes on a variety of Raspberry Pi models, soldering pin headers onto boards (my joints won't win any prizes, but hey, they work!), SSH'ing into the Pi-Star image and editing files with the Nano editor, figuring out what it means when a TCXO chip is bad, visiting GitHub regularly for a pint … um, I mean to read release notes, and learning more new stuff all the time.
[*] Temperature-compensated Crystal Oscillator

In the grand scheme of things I'm still a novice, but it's so great to be able to play around with something that offers so many opportunities to learn about so many different things!

5c) Footnotes

[1] Hotspots vs Personal Access Points – When I first started playing around with hotspots a few years ago, there tended to be more of a distinction between "hotspots" and "personal access points" (see the article Hotspots vs Access Points? by Jim, K6JM). While both perform a similar function—bridging radio and the internet to extend a local digital voice setup—hotspots tended to refer to higher-power devices, while access points referred to lower-power (~10 milliwatts) devices meant primarily for personal use. As the growth of the lower-power devices exploded over the past couple years, the term personal access point has pretty much disappeared, and now the term hotspot is commonly used to refer to the lower-power devices, too.

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