QRP-Labs QMX excellent for portable operations

I've been staying in Tasmania this week, on the north coast, near Devonport and naturally I wanted to bring some sort of radio gear along. The QRP-Labs QMX recently added the ability to transmit sideband. I've had a few contacts with this and reports are good. The QMX (and QDX) are particularly good at FSK modes like WSPR I think due to the direct synthesis rather than audio mixing.

My travel case is quite small and fits everything I need including a pill bottle microphone.

The station was set up overlooking the ocean with a 29' wire pretty much just resting on some bushes.

Operation was on 40m at first but 20m was the standout. I was heard as far away as Europe in the first transmission.

I'm embaressed to admit that the very compact tuner was purchased from China and is clearly a copy of the QRP Guys' Ununtenna Plus. I have ordered the real thing which they say has much better quality toroids in it. The design is good and it's the most compact antenna tuner I can carry with me.

The QMX has a built in tuning mode with SWR display but I find nulling the LED on the tuner is easier.

At first I tried operating inside the house with the wire running out through a metal sliding glass door but I couldn't get it to tune. I think the close coupling to large metal earth threw things off. Operating outside was pleasant and signals were very good.

Moorabbin Hamfest a blast again this year

The Moorabbin & District Radio Club Hamfest must be one of the biggest in Victoria and it's always a good excuse to pick up some parts and catch up with friends.

My feeling was that it was a bit smaller than last year but still worth a visit. I purchased a Bird power meter with a fault (but it came with the needed part). A few pushbuttons and a vintage morse key being sold from an SK estate by Drew. A few impressions of the show:

The in-line power/SWR meter I bought was said to be faulty due to a burnt out diode. The Seller supplied me with a replacement and said he hadn't got around to fixing it.

When I got it home, I opened it up and tested both diodes and they seem to be OK. Attaching a transmitter and it seems to work. I'm not too concerned about calibration so I'm happy with the purchase. It came with 2x N to BNC adapters which are probably worth what I paid for the whole thing.

I headed off early to visit VK3ZZC who's unwell at the moment. We wish him all the best for a speedy recovery. Great to catch up with Drew VK3XU, Peter VK3YPG, Nigel VK3DZ, Dave VK3ASE, Peter VK3YE, Chris VK3AML, Jim VK3ZKK, and others.

Technology talk on ABC Radio

Artificial Intelligence continues to revolutionise our lives. Predictions from experts state that AI will likely automate or transform 50% to 60% of jobs. 

How long until it takes over our lives or jobs completely? 

Also self-driving trucks on the road and we bid farewell to Skype.

Peter Marks, a software developer and technology commentator from Access Informatics, joined Philip Clark on Nightlife to discuss the latest news in technology. 

https://www.abc.net.au/listen/programs/nightlife/nightlife-tech-talk-with-peter-marks/105261180 

AI in FreeDV presentation at the Bendigo Technology Festival

The Bendigo Amateur Radio and Electronics club today held their first Bendigo Technology Festival. It was an ambitious affair with information and sales tables and a series of technology talks.

The Macedon Ranges Amateur Radio Club had a table with information for potential new members. 

ALARA, WIA and many others had tables and there was quite a bit of gear for sale at excellent prices.

I presented a talk on how AI is being used in the new versions of FreeDV.

Congratulations to the organisers and I hope they do it again.

RF Noise Bridge for antenna tuning?

An early electronics project for me was to construct an RF noise bridge. This remarkably simple device, combined with a receiver, let me measure resistive and reactive impedance by adjusting for a null in the noise on the receiver.

I'm putting together a compact station for portable operation and it occurred to me that a noise bridge might be a good way to adjust an antenna tuner used to match an end fed wire in a tree. Sometimes it's hard to find the resonant point.

I tried this with a random wire, a Z match and a QMX transceiver (with the recent SSB software). It was not a good way to tune up, partly because of the QMX's excellent AGC.

To see what's going on I hooked up an SDR as the receiver, so I can see the noise over a broad bandwidth:

The antenna is an off centre fed dipole and the tuner is a simple L match. The dip can be seen above up the top end of 40m after tuning. A traditional antenna analyser confirms the tuning:

So it does work but is difficult compared to other options such as minimising an LED on the Z-match or using a NanoVNA. 

I wonder if I'm not doing this correctly. I'm not seeing what I would characterise as a "deep null".

The Palomar bridge is a nice bit of gear and I rather like the warning on the back of the manual:

They have an article about using the noise bridge for antenna tuning. Oh, and this story is another example of Betteridge's law of headlines.

Rotary encoder in MicroPython

Sample code for rotary encoder handling that I've found seems to double step with my encoder. I guess there's other that have half steps or something. Anyhow, here's how I've been doing it and it's working just fine.

CLKPin.irq(trigger=Pin.IRQ_FALLING, handler=rotary_callback)

def rotary_callback(pin):

"""Interrupt handler for rotary encoder falling edge"""

global frequency

if DTPin.value() == 1:

frequency += int(math.pow(10, step_power))

else:

frequency -= int(math.pow(10, step_power))

setFrequency(frequency)

So, the interrupt triggers just on the falling edge of the clock pin and then looks to see if the data pin is high (for clockwise) or low (counter-clockwise).

A full project is stored here.

Thonny alternative for MicroPython - MicroPico

Recently, I've been enjoying developing embedded projects on an RP2040 zero board using MicroPython. The RP2040s are fast and cheap and the zero board is much more compact than the Pi Pico but has more than enough I/O for my needs. (Actually, all the I/O is there if you need it).

MicroPython is a wonderful language and I like the fact that the source code is on the device so I can always find it again.

The normal way to develop MicroPython is Thonny. It's fine but the editor is rudimentary compared the modern code editors with completion and AI suggestions.

Recently I've discovered the MicroPico extension for VSCode and it is working pretty well.

The environment does all the things I need including showing the files on the board, letting me run the current file, stop it, and use the REPL console.

Most impressive is the AI code completion which often stuns me with its guesses about what I was about to type. (The suggestion is the italic stuff after time. below).

MicroPico doesn't do the firmware install but that's quite easy on the RP2040 (hold the boot button and plug in). 

The files stored on the device are shown in the "Mpy Remote Workspace" area on the left and a project folder is above. You can drag files up or down between areas but it moves the file. To copy a file on macOS you option-drag as is the normal convention here.

I wish single step debugging was available for MicroPython but if I'm debugging pure python algorithmic code it can be debugged locally if needed.

There are other MicroPython extensions for VSCode but this one seems to work quite well for me.

Low cost display and rotary encoder board for VFO building

As part of my objective to take the SolderSmoke DC receiver forward to be a double sideband transceiver I've been messing about with an Si5351 based VFO. The CPU is an RP2040 Zero board which I program in Micropython. I've just bought a couple of these handy boards that include a 1.3 inch OLED display, a rotary encoder and two extra push buttons.

No documentation comes with it but the edge pins are nicely labeled on the back.

When I hooked it up and tried my existing code, written for an SSD1306 OLED, the display showed mostly noise. It turns out the boards with a larger, 1.3 inch, display require the SH1106 driver which I found here. Both drivers subclass the Micropython Framebuffer class which is a very interesting thing in its own right.

The display / encoder board has nice big mounting holes on the corners as you can see.

I paid AU$6.79 each for the larger display version on AliExpress. For you in America I guess they'll be about $100. ;-) The board seems to be widely available and is called "0.96/1.3-inch OLED Display Module With Button EC11 Rotary Encoder IIC Interface LCD Screen"