5.2.2. Portable DMR HotSpot

I love DMR as a system, however using repeaters while on the road really doesn’t work well. You are sharing the two time slots with anyone else on the repeater, and if you aren’t making a conversation then someone else might switch the repeater to a different talkgroup without you noticing.

So I wanted a portable hotspot. Pi-Star seems like the right thing, however it’s somewhat time consuming to pair it with the phone. I have to enable hotspot on the phone, and hope the pi-star finds it. Often repeating the process a few times. I just want to jump in the car and go. So I ended up putting a 4G USB dongle on a pi-zero so it’s nicely self contained.

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5.2.2.1. Parts list

  • Pi-Zero WH (Wireless and Headers)
  • MMDVM duplex board
  • 2000mAh battery
  • Adafruit 1000c USB charger board
  • OTG cable
  • Right angle USB adapter
  • 4G Huawei Unlocked E3372
  • 2x SMA connectors

I designed the box using openScad and then printed on my 3D printer, took about 2 hours to print the black, and 2 minutes to print out the transparent diffuser for the board LEDs.

Not strictly necessary but I didn’t want the antennas on the face of the hotspot, so I unsoldered the SMA connectors from the duplex board and made some very short RG58 to SMA pig tails which I fixed to the top of the box.

I’ve since put right angled adapters on as well so it all folds flat for easy storage.

The Battery lasts for a few hours, and there’s a micro USB port to recharge.

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Pi-star out of the box supports this USB dongle, in fact it shows up as an ethernet device so it just works. You can even use the pi-star as a hotspot for WiFi too, though I don’t plan to do that.

I’ve used a GiffGaff SIM card for the moment, put £10 credit, not a goodie bag. So the credit will just slowly run down, hopefully over a few months. DMR doesn’t take a lot of data, and as we’re all not travelling much at the moment. Once this money runs out I’ll see about maybe making a monthly payment.

5.2.2.2. Why a duplex board?

Well with duplex you can access both timeslots. Two people can have two conversations at once. It also means that if you do have a chatty channel and you want to switch to a different one, it’s possible to do so.

I tend to use one timeslot for monitoring channels and the other for talking. Again that way if one slot is busy I can still get out using the other.