KJ7NZL → Robert V. Bolton

Building My Own LoneStar Electronics MMDVM Hotspot

Digtial voice

If you’re reading this post on my new LoneStar Electronics MMDVM hotspot, then you no doubt decided to explore the option of buiding one yourself after noting the price of some of the commercially available hotspots. For example the Zumspot form Ham Radio Outlet retails between $150 - $160, and that’s not including a case to safeguard it. And let’s not forget about BridgeCom Systems who absolutely rape you on the price of their SkyBridge Hotspot; $299 is rip off.

So, “What did you build and what did it cost?” you ask. I built a simple small form MMDVM hotspot using the LoneStar MMDVM Simplex Board. Combined cost for the build is $140, and if you want the OLED screen you can add on another $10 for a total $150. Now before you start complaining there are Jumbospots on eBay for $75, let me remind you that those are made from questionable components. If you want to purchase one of these, fine but don’t be surprised if it underperforms or completely dies on you. That’s the price you pay for not paying full price.

Background #

Before we dive into the build, allow me give you a little background of my motivations behind this project and my requirements. To begin with, I believe the cost of commercially available hotspots is too high provided the quality of components used. Second, I didn’t like any of the available options on the market.

I think the OLED screen that’s attached to most MMDVM boards is ridiculously small. During my research on hotspot cases, I came across the line of cases from C4Labs with either 2.4” or 3.5” Nextion screens. This intrigued me because they are so much bigger than the OLED screens attached to the MMDVM boards. Bigger is better right?! Well… it turns out the screen is just a novelty and doesn’t provide any functionally beyond displaying which room/reflector/talkgroup you’re connected to and the callsign of the current person speaking. My Yaseu FT3D already does this for me. I asked around and couldn’t find anyone who thought it was a must have feature. Knowing this, I decided that I didn’t need either the OLED or Nextion screen. However, I still want the option to attach a screen to my hotspot should I change my mind in the future.

One of the biggest complaints against hotspots is the accusation that it isn’t real ham radio because most users operate them within ten feet of themselves. Personally I don’t care what you’re opinion on this topic is, the fact of the mater is that I’m going to be within ten feet of my hotspot when I employ it. With such limited distances between the users and their hotspot, I challenge the need for SMA connectors attached to the MMDVM board. The connectors are just soldered onto the board with nothing more to secure them in place. Luckily the MMDVM board I want to use comes with a ceramic antenna surface mounted onto the board. No need for me to worry about breaking the solder joints on a SMA connector.

With that out of the way, let’s move onto the parts utilized for this build.

Parts List #

LoneStar MMDVM Simplex Board #

LoneStar MMDVM Simplex Board

LoneStar MMDVM Simplex Board

The most essential component of a hotspot is the MMDVM board. I want the most superior performance and quality for my hotspot, so I don’t want to compromise by buying a cheap MMDVM board. The LoneStar MMDVM Simplex Board, designed by N5BOC David Dennis, is considerable more expensive than other MMDVM boards, however it’s constructed of higher-quality components and has the following features:

  • It 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.
  • The board is a four layer PCB with large ground planes for 3.3V and GND sandwiched in the middle of the PCB. This acts as one very large decoupling cap the size of the entire board. Also this isolates signals between top side and bottom side.
  • 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. It should also make it more sensitive on receive.

C4Labs JRZ-1S Case #

C4Labs JRZ-1S Case

C4Labs JRZ-1S Case

I like this case; it’s modest yet does the job very well once it’s completely together. As an added touch of class, I went with the wood inlays. I also sanded the sides of the case with 400 grit sandpaper to give it that frosted glass look. I appreciate how it turned out. The actual case is engineered very well with the components fitting in securely inside. Interestingly enough one layer of the case does include holes drilled in it to support the prongs of an SMA connector. It’s a thoughtful touch, but I’m keenly uninterested in trying to find out how well they work.

Raspberry Pi Zero WH #

Raspberry Pi Zero WH

Raspberry Pi Zero WH

Nothing extremely exceptional about this other than I purchased it from Adafruit. I went with the Zero WH instead of the Zero W, because I don’t know how to solder very well and didn’t want to ruin the thing. One of these days I need to force myself to learn and become better.

The Finished Build #

Custom LoneStar MMDVM Simplex Board Hotspot

Custom LoneStar MMDVM Simplex Board Hotspot

Here’s the finished hotspot. If you look in the top right-hand corner above the heatsink, you’ll recognize the ceramic antenna. With the hotspot located in my basement, I’m nevertheless able to connect to it will my Yaesu FT3D running 300 mW. Should I want to ever want to attach a screen I can because there are connections present for the Nextion and OLED displays. The only gripe I have remains the location of the micro-USB port on the Pi Zero. If you couldn’t determine from the photo the case is upside down. Well, I can’t do anything about that so, I’ll have to live with it. Overall I’m impressed with the build quality of the hotspot and look forward to using it for years to come.