Thursday, June 30, 2022

DMR in Australia - what I've learned

DMR digital radio is intriguing but confusing. I live at a location where I can't reach any DMR repeaters so I'm using a pi-star hotspot to access global talk groups.

The hot spot provides a local radio link to my TYT MD380 handheld and connects to the DMR network. There are several networks available in Australia:

  • VKDMR - the official network that includes most repeaters
  • FreeDMR - an alternative network apparently objecting to the control by repeater operators
  • Brandmeister - this seems more global than the others
  • VKMultnet - VK2 based connects to VKDMR, Brandmeister, C4FM and P25
After trying the first three, I've settled on Brandmeister. I like the way talk groups are configured through a web interface on the site rather than a rather cryptic "options" string in pi-star. You do need to register and set a password but this was all pretty easy.

Brandmeister including many active track groups such as 91 which has traffic pretty much 24/7.

The radio's programming is done by editing its "code plug". There's no real code, it's just configuration settings. Initially, I downloaded a code plug which had every repeater in Australia in it but I found the number of settings in there overwhelming and so I started from scratch with a minimum setup for my needs through a hotspot.

DMR is designed for commercial use and many of the features are not used for ham radio and many of the terms are alien. 

On the MD380 you choose a "zone" which is typically a set of channels for a repeater or a hot spot.

Here's my process to add a talk group or contact to a zone for my radio.

I'm using the excellent editcp (edit code plug) on Linux.

First I add a group or personal Contact.


Next I add an "RX group". I'm not sure if this is necessary.


Now I create a Channel that combines the contact and RX group.


Finally I create a zone and add the Channels to it.


Then upload the code plug to the radio.

The Zone, in my case "HomeSp" is chosen via the menu and then the knob on top selects between talk group or contacts.

I'm using the third party MD380 Utils firmware so I have some extra features such as showing more information about who's talking and promiscuous mode where I hear everyone even if not on that talk group.

Private calls

Adding another station's DMR ID as a contact and (via the steps above) adding it to a zone gives me the ability to call that station privately. I think this only works if we're both on the same DMR network. Ross EX0AA and I have been able to speak using this mechanism with good success.

Activity

You can get s sense of the activity on Brandmeister via the LastHeard page. You can listen in via the Brandmeister Hoseline. (Click on a box with a red outline).

Finally

I am really just starting to figure this stuff out. Please comment with corrections or clarifications - I'm sure to be mis-understanding this rather confusing world.

Thursday, June 23, 2022

Guest on ABC RN's Download This Show

Facebook pointed out that I've been appearing on Marc Fennell's Download This Show for over ten years. Since COVID and my move to country Victoria, I'm a remote guest but you probably wouldn't know as a listener.

This week:

"After 27 years Microsoft has retired Internet Explorer, a product which transformed the way people engaged with the web. A timely end, or gone to soon?

Plus, new data reveals that Australian border force searched more than 40,000 mobile devices in five years. Can they all be justified?

And, Instagram introduces parental controls to a curb mental health crisis."

The show airs a few times on ABC Radio National or you can listen here.

Tuesday, June 07, 2022

Built the QDX from QRP Labs

The QDX v3 kit arrived yesterday and today I've finished the build.


This transceiver is tiny, about the size of a playing card deck. It does FSK modes on four bands: 80, 40, 30 & 20m. Five watt output and a great receiver from what I can see so far.

The QDX connects to a computer with a single USB cable that comes up as a sound card and does TS-440 compatible CAT control - so very convenient for possible field use.

It can be built for 9 or 12V operation - I went with 12V as I have it more available.



The assembly manual is the best I've ever followed. Clarity and detail with lots of handy tips from Hans. The board comes with all the surface mount components already soldered in place so the main job for the constructor is a few diodes, capacitors, transistors and winding the toroids. 

Page 34-76 of the assembly manual describes the design and could be a book on its own rivalling the recent Software Defined Radio Transceiver Book by Peter & Purdum.

I took my time and had a break after a few toroids. One of the joints didn't connect but following Hans' advice to check continuity found this problem at the time. On initial power up I blew a 25A fuse - which was a bit alarming - but I think it was my DC connector shorting. All was fine with another connector.

Running with wsjt-x on Ubuntu Linux 22.04 got immediate spots on each of the bands (shown here in WSPR Watch).



There is diagnostic software built-in that can be operated via a serial (over USB) terminal. Here is the low pass filter band sweeps on my unit. I'm interested to know if this looks normal or should I perhaps remove a turn from the 80m low pass filter for example?





Here's my portable operations configuration. The QDX is the smallest part:



I can't recommend this kit too highly.