Custom Designed Premium DMR Hotspots

Projects, Testing and Research

Ham radio is all about solving problems and experimenting with new ideas and equipment. Personal DMR is no different. It is just a different set of challenges and on a smaller scale than HF or repeater operations. We're always testing or trying new things to make DMR better and some of them are detailed here.
Hotspot Battery Power
If you own a hotspot, you probably don't just leave it sitting on your desk. Hotspots are perfectly happy running about anywhere you want to use them. But they need power. Of course, you can always plug it in to an accessory outlet in your car, but most new cars these days cut power to accessory outlets about 5 minutes after turning off the ignition.

Internal batteries would be difficult for small hotspots because they just don't have the capacity for more than a few hours of operation, and most of the time it is just an hour or two. That's okay for short term backup, but not for all-day use.

Our DMRspot and most other Raspberry Pi Zero based hotspots run very efficiently on common cell phone charging batteries. So this gives us lots of options. The problem is that these batteries are usually much larger and heavier than the hotspot itself. And, you have to attach the hotspot and battery with heavy duty rubber bands or velcro unless you want them flopping around.
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We wanted a portable system that would last for a minimum of 8 hours, be fairly compact, solid, and could use and readily available batteries from a name brand manufacturer.

For this prototype, we used an Anker PowerCore+ mini 3350mAh Lipstick-Sized Portable charger battery. These are readily available on Amazon for $24. In our tests, this battery lasted for 11-1/2 hours with about 90% of that time in standby (listening) mode. These batteries also come in several colors so the battery and DMRspot can be color matched in many cases.

We designed a holder that would securely hold the DMRspot and battery, and while it is a little clunky looking, it works great. We added a 9" right angle power cable and it is all reasonably compact. The DMRspot and battery stay securely in their openings and you can move it from place to place without anything flopping around. The battery comes out easily and can be swapped with a fresh one if needed.

While not exactly pocket-sized, it suits the purpose. There are smaller batteries available and we are experimenting with other prototypes. But there are a couple of issues that we have no choice but to live with. Unfortunately, the smaller the battery, the shorter the run time will be. And, we don't like messing around with cheap batteries from dubious manufacturers.
WiFi and Mobile Operation
One of the best thing about DMR hotspots is their small size and the ability to go mobile virtually anywhere you have access to a WiFi network, including cellular networks. Hotspots like our DMRspot use Pi-Star, and Pi-Star has some distinct advantages here.

Pi-Star lets you define any number of WiFi access points in it's configuration file which allows you to switch seamlessly between networks when you are moving around. So, for example, you can be at home using your home WiFi, get in your car and use your cellular phone WiFi, and go to work and use your work WiFi when you get there. Pi-star switches quickly from one network to the other as you change locations.

Another popular hotspot is the OpenSpot 2. When we received ours we had a lot of difficulty getting WiFi to work correctly. In fact it took two days of work, and it required the developer to provide an update. We had really bad problems getting it to connect to our Netgear Nighthawk which is a stand-alone mobile cellular hotspot/router. Not only would it not switch automatically when changing locations, it initially would not connect at all. A patch from the developer fixed the problem and the OS2 now connects, but still has difficulty changing automatically when we change from our home WiFi to mobile. And the OS2 only allows you to define four WiFi networks. So if you regularly have access to more than four WiFi networks, you are out of luck.

The OpenSpot 2 is a cute little hotspot and engineered very well. But hotspots running Pi-Star blow its doors off when it comes to WiFi operation. Not only does Pi-Star allow you to define numerous WiFi networks, It will automatically find an available WiFi network you have pre-configured and switch seamlessly every time and do it quickly.