Hanging out with hotspots

Updated: Mar 2019, CC BY-SA
Most up-to-date version:  hotspots.hamnotes.com Easy link: hotspots.hamnotes.com
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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 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 act as 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.

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.

Important! Be aware that the regulations and best practices that apply to amateur radio—including use of frequencies, on-air etiquette, and control of your station—also apply to your use of a personal, low-power hotspot. It's your 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 using them, adhere to my local band plan, and leave adequate pauses between transmissions. For more info, see the Code of Federal Regulations > Title 47 > Part 97 – Amateur Radio Service.

1a) Background

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

I've been playing around with low-power hotspots since 2016, during which time I've tried a bunch of devices and apps including the DVMEGA, BlueStack-Micro+, SharkRF openSPOT v1, DV Access Point (DVAP), and a couple DV4 products. For more info about these devices, see Other hotspots (below). While each of these taught me something, ultimately they all had limitations I didn't like:

ZUMspot and Pi-Star – And then I tried an MMDVM-based hotspot called the ZUMspot (discussed in more detail below) with an app called Pi-Star (discussed in more detail in the Playing with Pi-Star article). For me, the combination of the ZUMspot and Pi-Star is taking personal digital voice 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 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).

Note: There's a good presentation from Pacificon 2017 that contains an intro 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) Zooming around with the ZUMspot

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

    1. Overview
    2. What makes up a hotspot?
    3. A note about the LEDs, buttons, and through-holes
    4. In case you're interested
    5. Putting the vroom in zoom (going mobile)
    6. Other cases
    7. Nextion screen customizations
    8. Jump down to: 3) Other hotspots

2a) Overview

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 3A+ and 3B+ (faster), as well as some 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, and NXDN, as well as various DMR and YSF cross modes.
Pictured: ZUMspot V0.6 with the 1.3″ OLED display removed.

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

2a.1) Software

The ZUMspot pairs well with the Pi-Star app, and setup 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.

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.

2a.2) Firmware

The ZUMspot firmware can be updated easily via Pi-Star: Performing firmware updates via Pi-Star. For release notes, see: ZUMspot/MMDVM_HS firmware

2a.3) Version

ZUMspot V0.6 was released Jan 2019:

Unfortunately, initial availability of the new ZUMspot V0.6 is only with an attached OLED screen. Hopefully a bare board will be available soon.

2a.4) Availability

In the U.S., the ZUMspot is available from Ham Radio Outlet in two configurations: ZUMspot with attached 1.3″ OLED display or a ZUMspot with attached 1.3″ OLED display kit. The kit includes a Raspberry Pi Zero WH and a microSD card preloaded with Pi-Star. HRO also carries a variety of other ZUM Radio boards and accessories; just do a search at HRO on "ZUM Radio."

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

Caution: OLED displays are fragile. Don't press on them, they may crack.

2a.5) Support

2a.5) A note about the Raspberry Pi

The ZUMspot can be mounted on and works well with the Raspberry Pi 3A+, 3B+, Zero W, and several of the older models.

My favorite 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 runs much cooler than the 3B+ but not much warmer than the Zero W. You do give up some ports 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.

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

2b) What makes up a hotspot?

Low-power hotspots like the ZUMspot are sometimes referred to as radio/modem boards. But what does that actually mean?

I had the good fortune to meet, via email, Dave, KC6N, who shared some great insights with me about how hotspots work. What he pointed out made me appreciate these little boards even more.

ZUMspot boardHere's what I understood from my chat with Dave: These low-power hotspot boards have two primary chips, and the radio and modem functions are distributed between them.

One of the primary chips is an Analog Devices ADF7021 Integrated Chip, a low power 2FSK/3FSK/4FSK transceiver. (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.) 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.

The other component of a hotspot is the Gateway, which is what communicates with the internet. That functionality is handled by the Raspberry Pi computer that boards like the ZUMspot are mounted on.

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

2c) A note about the LEDs, buttons, and through-holes

A hotspot is like your own personal repeater and gateway computer. As such, it's capable of receiving and transmitting RF, as well as connecting to the internet to send and receive data. It has firmware it runs, and it also can run a display.

2c.1) LEDs

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

2c.2) Buttons

There are two push buttons on the board.

2c.3) Through-holes

You can use the plated through-holes to connect various 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.

2d) 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, a second for the desk where I do a lot of my researching and writing, and a third for mobile.

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. From the Pi-UpTimeUPS product page: "Pi-UpTimeUPS protects the Raspberry Pi from brown-outs as well as power failures preventing unwanted downtime. Pi-UpTimeUPS accepts power input from an external power source and charges its batteries at the same time it provides clean uninterrupted power to Raspberry Pi." (Adafruit has a good battery tutorial.)

ZUMspot connected to RPi3 and Pi-UpTimeUPS

Note: In Mar 2019, I swapped in a RPi 3A+ to take advantage of its cooler operating temperatures.

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 (for a subsequent hotspot, I actually removed the connector altogether and soldered directly to 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 includes three different colored rubber covers for the switch. (An alternative, which I have used for some of my other hotspots, is the CanaKit PiSwitch.)

LoveRPi Power Switch

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. 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

A hotspot for my writing desk

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 there is no reason for me 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. ZUMspot + RPi 3A+ on the inside, with a 3.2″ Nextion enhanced display.

2e) Putting the vroom in zoom (going mobile)

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.

Jan 2019 – Once Pi-Star 4, which support the Raspberry Pi 3A+, became available, I upgraded my mobile hotspot to a combination of an RPi 3A+ and the MMDVM_HS_Hat with a ceramic onboard antenna produced by Florian, DF2ET, and Mathis, DB9MAT. See MMDVM_HS_Hat devices below.

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″

2f) Other cases

Even though I like making cases, I also use some other cases for test hotspots.

For hotspots based on the Raspberry Pi Zero WH and 3B+, I use the creative ZUMspot cases made by C4Labs in Tacoma, Washington.

ZUMspot + RPi Zero WH
ZUM-PI Zero case

ZUMspot + RPi 3B+
ZUM-PI3 case

For the new Raspberry Pi 3A+, I use the Adafruit Pi Model A+ Case Base and Lid, which has room for the ZUMspot board inside. I drill a hole in the lid for the antenna, and a larger hole in the base so I can add a heat sink to the chip that's on the bottom of the 3A+.

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

2g) 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, 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.


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 Nextion display simply because doing so broadened my knowledge about hotspots and electronics. And it's fun.

3) Other hotspots

  1. Some other hotspots I've tried or heard about:
    1. DVMEGA
    2. BlueStack-Micro+
    3. BlueDV apps
    4. MMDVM_HS_Hat devices
    5. SharkRF openSpot
    6. Hotspots by BI7JTA
    7. Nano-Spot
    8. MMDVM DUPLEX in Pi Zero Form Factor
    9. ThumbDV
    10. DV dongles
    11. DV4 devices
    12. Something new coming? D2RG
    13. Others

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.


By Guus van Dooren, PE1PLM

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.

DVMEGA-DUAL in FLIRC caseI have my DVMEGA-DUAL mounted on a RPi 3B in an aluminum FLIRC case, which I modified by removing the built-in heatsink and drilling an antenna hole. Makes for a nice, rugged hotspot.

I recently upgraded this hotspot to Pi-Star V4, and so far it is working just fine.

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.

3b) BlueStack-Micro+

[ 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 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.

3c) BlueDV apps

By David, PA7LIM
[ For use with DVMEGA ]

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!" Thanks, David!

Website: BlueDV.

3d) MMDVM_HS_Hat devices

By Florian, DF2ET, Mathis, DB9MAT, and Andreas, DO7EN; based on work by Jonathan, G4KLX, Andy, CA6JAU, Jim, KI6ZUM, and others.
[ It can be challenging to order these boards. ]

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 low quality Chinese clones … see below: Be wary of cheap clones).

These boards handle D-STAR, DMR, YSF, P25, and NXDN, as well as 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.

Currently, this MMDVM_HS_Hat simplex board is on version 6, 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.

MMDVM_HS_Hat with ceramic antenna

While it can be challenging to get ahold of one of these, the quality is good, so I found it worth the effort; however, it's not clear whether they intend to keep working on this form factor. If you're good at assembling electronics, you can Build your own MMDVM_HS_Hat. There's a pre-configured Mouser cart for several versions, including one for MMDVM_HS_Hat version 1.6.

Jan 2019 – 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 nice thing about the RPi 3A+ is that it is more compact than the 3B+ while being a lot faster than the Zero W.

RPi 3A+ based ZUMspot 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 optionally can plug in an external Nextion display.


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 have produced 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_Hat on GitHub: mathisschmieder / MMDVM_HS_Hat.
MMDVM_HS_Dual_Hat on GitHub: phl0 / MMDVM_HS_Dual_Hat.
Twitter: Flo (DF2ET) and Mathis Schmieder.

3e) SharkRF openSPOT

By Ákos Marton, HG1MA, and Norbert Varga, HA2NON

Nano-SpotThe 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 browser-based software.

I used the openSPOT V1 and thought it worked very well, though I didn't like it that it supported only wired ethernet connectivity, so I'm glad to see that V2 has built-in WiFi.

Website: SharkRF

3f) Hotspots by BI7JTA

Nano hotSPOT

Huang Winters, BI7JTA, is quite enthusiastic about amateur radio. I tried his simplex Nano hotSPOT blueBOX. It's very compact and works well, though it's slow, presumably due to the specs of the NanoPi computer it uses.

He also makes a Duplex hotSPOT for RPi as well as other products.

Website: Amateur Radio Toys by BI7JTA.

3g) Nano-Spot

By 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 hotspot hardware, it looks like one that may be worth checking out.

Website: Micro-Node.

3h) MMDVM DUPLEX in Pi Zero Form Factor

By David, N5BOC
[ It can be challenging to order this board. ]

I haven't tried this board, but it looks to be well made of quality components with a very small form factor for a duplex board.

I didn't like it that David made and sold a clone of the MMDVM_HS_Hat by Florian, DF2ET, and Mathis, DB9MAT, without first getting their okay, but it appears to me that he has done some clever, original design work on this new duplex board.

Website: Tindie N5BOC store

3i) ThumbDV

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

The 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.

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

Website: NW Digital Radio ThumbDV

3j) DV dongles

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

The DV Dongle and DVAP were among the earliest personal hotspots available, can be connected to a PC running Windows or a Mac. The DV Dongle uses a DVSI AMBE-2000™ chip and the DVAP requires a D-STAR radio. 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 autumn 2018, I haven't found anything further 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.

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

3k) DV4 devices

By Uli Altvater, AG0X/DH6SAB, and Torsten Schultze, DG1HT
[ Older, limited designs. May be discontinued. ]

Another one of the earlier personal hotspots that was available, the DV4mini was a USB stick that could be plugged into a PC running Windows or Linux, or a Raspberry Pi. The DV4home, released later, was a standalone digital voice device that had two AMBE chips as well as its own screen, microphone, and speaker.

While I know people who have used and liked the DV4 devices, I personally found both the DV4mini and the DV4home V1 clunky to use when I tried them in 2016/2017. The DV4home's rotary knob was particularly poorly implemented—I found it almost unusable—and I've heard similar feedback from someone using V2. I also didn't like its bias for the DMR+ network. Too bad, because I had high hopes for using the DV4home as my digital base station. All their current products appear to be out of stock, and their social media activity ceased in Jan 2018.

Website: Wireless Holdings.

3l) Something new coming? D2RG

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

3m) Others

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

4) 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), which are unauthorized copies of the original MMDVM_HS_Hat made by Florian, DF2ET, and Mathis, DB9MAT.

From what I have read in forums, a significant number of people have problems with the JumboSPOT. In particular, they seem to sometimes use inferior versions of the oscillator/TCXO chips, which can cause some serious issues.

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

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

At first glance, the clone boards may seem like a bargain. But the original boards are worth it: not only do you get quality components and better support, you also get the satisfaction of supporting the innovation that is advancing our hobby.

5) 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 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 like Jim McLaughlin, KI6ZUM

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 hotspots 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 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.

6) Some final notes

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

6a) 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 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 a 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 (Temperature-compensated Crystal Oscillator) chip is bad, visiting GitHub regularly for a pint … um, I mean to read release notes, and learning more new stuff all the time.

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!

6b) 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 the ZUMspot, the MMDVM_HS_Hat (by Florian, DF2ET, and Mathis, DB9MAT), the MMDVM_HS_Dual_Hat (by Florian, DF2ET, Mathis, DB9MAT, and Andreas, DO7EN), and the DVMEGA DUAL.* I focus on the DMR and D-STAR modes, and Pi-Star.

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 couple hotspots based on them that I test with on a regular basis, I'm spoiled by the speed of the RPi 3A+/3B+ boards.

I run several Nextion displays, 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. I try to always note it when I mention something I haven't personally tested.

[*] I no longer use the BlueStack-Micro+, openSPOT, Nano hotSPOT blueBOX, DVAP, or any of the DV4 products.

6c) 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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