Thursday, July 28, 2022

New open source SDR available from HFSignals - sBitx

I've been following the progress of an open source SDR transceiver, the T41-EP, from Albert Peter and Jack Purdum for some time. It's a great contribution but the author's understanding of how open source normally works is a little unusual.

By contrast, Ashhar Farhan, VU2ESE, of HFSignals, exemplifies best practice. 

HFSignals new SDR transceiver, the sBitx, is available to early adopters. The radio has a large graphical touch screen that shows a waterfall. Inside there is a standard Raspberry Pi which is set up as the software development environment - great idea!

Here's my video of unboxing the sBitx, tuning around and having a not great first contact.

Later, on a different (more resonant) antenna, I did not have RF feedback trouble. It might be that the SWR is quite critical. The operation manual says "At times, with high enough gain and high SWR, RF can get into the mic and cause self-oscillations. Monitor the modulation on the display if you are setting the mic above 50 to be sure that it doesn’t happen."

"The sBitx is a 40 watts, fully open source, high performance HF SDR transceiver with in-built popular modes like the FT8, RTTY, PSK31, etc."

Design paper.

The source code and circuit diagrams are here on GitHub.

Operating manual.

Assembly manual.

There is discussion about the sBitx in the Bitx20 group (which should probably be re-named).

Having a computer inside that can be internet connected opens up all sorts of interesting possibilities for this platform.


Since the original unboxing video, where audio stopped, I have updated the software to 1.1 and that problem hasn't re-occurred.

On the RF feedback... I was using my off centre fed dipole. Reading the ARRL Handbook I saw that command mode suppression on the feed line is "essential". This has now been added. I guess my normal (commercial) radio is more forgiving.

Tuesday, July 26, 2022

QDX with Fldigi on Ubuntu 22.04

The QDX works brilliantly with WSJT-X but I have struggled to get it working with Fldigi on Linux.

I'm pleased to report that I just had an Olivia 8/250 contact over a distance of 732km with VK2BLQ using Fldigi on Ubuntu 22.04.

Thanks to KJ7LVZ for the tip to install Pulse Audio Volume Control (from the Ubuntu App Store). That let me adjust and monitor send and receive audio levels.

In Fldigi I set the audio devices both to "pulse".

In the QDX settings I set the audio cycles to 1 (down from 480) as suggested by G3SPL. The larger number of samples is fine for slow changing modes like WSPR or FT8 but not good for fast modes like Olivia. Also I increased the receive gain to 75, up from 60 (I think), so I could see something on the waterfall in Fldigi.

Here's the Pulse Audio Volume Control window:

While I'm here, I've been using `screen /dev/ttyACM0` to configure the QDX but it's difficult to send ^Q as that's used for XON/XOFF. The trick is to type ^AQ. Hans, it might be good if there was another key to exit a menu than ^Q as I think many serial terminals might use ^Q for flow control.

Thursday, July 21, 2022

Updated QDX Firmware to 1.04 - working very well on WSPR

The QDX is a tiny FSK mode transceiver from QRP Labs which works amazingly well. This week, new firmware was released which improves transmit a little. I've been running it on 40m here and results are very good.

My friend Stephen, VK2BLQ, is 800km away in Sydney and he received my 3W at +18dB last evening.

I have a theory that direct generation of RF for digital modes in rigs like the QDX produces a cleaner signal than you get by mixing audio up to RF in a sideband radio and so decodes are better.

At a similar time I had a transmit cycle that was spotted by 45 stations around the world.

 Changes in 1.04:

  • Resolution to the Rev3 PCB "popping" issue (RF discontinuities during TX).
  • Audio streamed to the PC during Transmit is now set to zero (silence).
  • 50 millisecond transmit timeout on cessation of audio from PC (protects QDX e.g. if PC crashes).
  • No CAT command TX timeout (configurable enable and timeout duration).
  • Removed unnecessary 48ksps clock domain sync PC vs QDX.
  • Enables PTT output connector, with grounded and +5V outputs individually controllable by band.
  • 12kHz IF offset is removed when you enable IQ Mode.
  • Transmit is disabled when you are in IQ mode. 
  • Gain is now in dB.
  • Gain is now configurable per band.
  • New "Band Configuration" screen where you can configure the list of supported bands.

The firmware upgrade process couldn't be easier. You interrupt the power up cycle and then re-plug the device. It mounts as a disk drive and you drag over the firmware.

After running for a few days on 40m I see I'm #3 on the WSPR Challenge for receiving. 

Hard to beat Phil, VK7JJ though!

Thursday, July 07, 2022

Live PV solar monitor

If you have solar photo voltaic panels it's good to know how much is being generated so you can choose when to use power such as the tumble dryer. Using power locally, from the panels, is much more economical than receiving the feed-in tariff and buying power back at other times.

In a previous home we installed a PV solar system that had a Fronius inverter. I was impressed with the low RF noise emitted by this product and pleased to find that it had a JSON producing web service endpoint that I could poll to see how much power was being generated.

At our new home there is a system with micro-inverters and an Envoy controller. The micro-inverters do produce noticeable RF noise but bear in mind that this is a very low noise location so I might be a little sensitive to it.

It turns out that this system also has JSON producing web services. The system, once I figured out how to connect to our Wifi, has a web interface at http://envoy.local 

By enabling Developer mode in the browser I was able to see that the web page calls back to endpoints including:

  • home.json
  • production.json
  • Inventory.json
  • info.xml
  • dba.json
I haven't explored them all, but production.json gives me the data I need.

Here's a snippet showing how I get the generated power and the used power from the content returned from production.json

DynamicJsonDocument doc(3072);
DeserializationError error = deserializeJson(doc, payload);

if (error) {
USE_SERIAL.printf("Json error");


// Extract current power generated from the Envoy controller JSON

long genWattsNow = doc["production"][1]["wNow"];
long useWattsNow = doc["consumption"][0]["wNow"];

Using a nifty M5StickC device, which has an ESP32 and a little LCD display, I've stuck together sample code for an http client and Json parser to display the currently generated power and the currently used power. I'm happy to share the code but honestly, there's not much to it beyond the HTTP sample code.

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.


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).


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.