DMR and hotspots

What is DMR?

DMR “Digital Mobile Radio”. This description applies to the system designed by Motorola. Such a description could of course apply to the Yaesu Fusion system, or the Icom D-Star system, as all of these are digital systems, and all can have a mobile implementation. And there are others…

 As such the commercially available hotspots will work with any of these systems, and in some cases, will actually “transcode”. i.e. you could use a DMR radio with a hotspot and access a Fusion system. In fact, the latest (expensive) incarnation of the Shark Openspot allows transcoding between many modes, D-Star included. So if you only have a D-Star radio, you could go on DMR or Fusion… The Pi-Star, whilst not so comprehensive, does transcode between some modes, and is about 20% of the price of a Shark Openspot 3…

This guide is intended to assist in the setting up of a Pi-Star hotspot, as these are readily available at a low price, provided you are willing to assemble it yourself. The Openspot is not discussed, simply because adequate documentation and support exists elsewhere.

So what is a “Pi-Star”?

This is a hotspot, which uses a modem, attached to a Raspberry Pi zero W. Note the “W” at the end of the name, that is vital, when you go to buy a Raspberry Pi Zero W, as it denotes that the Raspberry Pi has inbuilt WiFi. Those without the “W” suffix don’t, and are no good to us.

So now you have a computer, (for that is what a Raspberry Pi is, a small, single board computer, “SBC”), you need a “modem hat”. Search ebay for “mmdvm -duplex –repeater” and you should see a small rectangular PCB. A square one is not what you need…

Note that if you want to use a bigger screen, you do not need the OLED screen, and can buy a modem board only for a lot less. I have a 3.5 inch Nextion screen, and I use it on a Raspberry Pi 3b, (which uses USB ports). I have a feeling it will work on a Pi zero, but I have not done it… I also believe that unless you connect the bigger screen via USB, the “touch screen” aspect does not work.

Now…  Caveat No 1. If you buy the modem board, OLED screen, and case, you will still need to buy the Raspberry Pi Zero W, and assemble it all together. No particular pitfall in that. BUT…  If you assemble it outside of the case, and then power it up, you COULD have the pins “one hole out”. The modem board plugs onto the top of the Raspberry Pi SBC. Assemble it incorrectly, and you WILL be buying a new modem board. If you get it “one hole out”, it won’t fit the case…. So FULL assembly before power!

You can use other Raspberry Pi SBCs, I have built them using a Pi3b. But you will be using a different box, and the possibility of incorrect assembly will exist. I have a box with two hotspots in it, and a five inch 40 pin IDE cable from SBC to modem hat for each. Looks nice, works well. After I replaced a couple L  Yeah, you just KNOW what I did…

So let us assume that you bought a modem and case etc, and you have the Raspberry Pi zero W. What else do you need?

1) a power supply, 5V at 1 amp. (2.1 amps for a Pi3b. A Pi4 is overkill and needs 3 amps).

2) A Micro SD card. 8Gb is more than adequate.

The software you need is available from https://www.mw0mwz.co.uk/ and near the top of the page is a button “Projects”. You can access the software from there, and what you need is:

Pi-Star_RPi_V4.1.0_26-Mar-2020.zip

While in there, watching a video regards the setup may be helpful: 

You also need a radio, and a digital ID if you don’t already have one. That page gives details of how to obtain an ID, and you will need a copy of your Amateur Radio licence.

Also on that site is a “WiFi builder. The idea is that you put in the ID of your router, and its password, and you get a file come down that then allows you to log into the Pi-Star after you built it. The file you get is in plain text, and is called wpa_supplicant.conf, so you can put in any ID, and any password (“psk”), and then edit the file with the correct values. (You will easily see within the file where you need to substitute the correct values, or you could just trust the site and input the correct values).

When you have built the micro SD card with the software, (done on a Windows machine and very simple), you put the wpa_supplicant.conf in the ROOT of the card. When ready, the card goes into the slot on the Raspberry Pi, and it is then powered up. Initially, it is very slow, so be patient. Even swapping screens is agonising, but after it has settled down, subsequent operations are fine.

What else will you need?

An account on the Brandmeister server is recommended. Extra security for your hotspot is one benefit. Better control over incoming traffic is another. www. https://brandmeister.network/ will allow you to set up an account.

I am happy to help folks set up a hotspot, there is a lot of configuration, and I would do it by looking at my system, and talking to you while you are setting yours up. For that reason, it would not be helpful to include further details here. The good news is that once set up, you can back up the config from within the software itself, and if it all subsequently goes “orrible”, you rebuild a fresh card, use the wpa-supplicant.conf, and then go in and restore from the backup. And it all works again!  J

I have a hotspot dedicated to talk group 144650. There is no “official” setup to it, just use it, and as you know we use 144.650 BHRC on Zello. Could be that this gets used as more of us get DMR.  I also monitor “Florida Gulf”, TG 31670. It is a long story as to why I use this, suffice to say that its use was offered to myself and my American friends by Jim, AA0NO, who set it up. Sadly, Jim is silent key, but I named the channel in my radio in his honour, hence my radio shows “FG AA0NO-01” .

Hopefully, this has “wetted” your appetite, I’ll be pleased to help.

73 de Stan, G4EGH.

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