Friday, December 30, 2022

Reducing RF noise from solar inverter by replacing capacitors

Old friend and new ham, Richard, VK3LRJ,  has been setting up his station at his off-grid property near me at Drummond. We put up an off centre fed dipole over the shed which houses the shack and also his solar and battery installation. The noise level was very bad.

The next step was to move the antenna away from the shed via a run of suspended coax. Noise was lower but still not great. 

We quickly identified that the culprit was the Australian Selectronic SE42 inverter. Richard spoke to the supplier and they suggested "servicing" the bypass capacitors. 

A high power inverter is an impressive piece of equipment. It seems that the electrolytic capacitors you can see on the left degrade after ten years and should be replaced. This has had a noticeable effect on the noise floor.

We also tried a noise canceller which did work better than it did for me in the suburbs, presumably because the sense antenna could pick up the noise signal effectively. 

The next step was to add an EMI filter in line with the mains coming out of the inverter on its way to the radio shack.

This has helped even more.

Richard says there are still noise "farts" at S3 but overall it looks much much better. We're going to run WSPR to compare with my place.

Thursday, December 15, 2022

Was a guest on ABC Download This Show - end of year wrap

A pleasure to be a guest once again on ABC RN Download This Show with star host Marc Fennell. Co-host Alice Clarke and I talked about the eventful year just passed in technology.

Marc has had a very successful year of radio and TV presentation and production.

You can listen to the show on radio or here.

Fast pin toggling on a Raspberry Pi Pico

Over the past few years I've built a few WSPR transmitters using an Arduino driving an Si5351 clock generator. They work well. I was thinking about the cheapest possible WSPR beacon transmitter and wondered if a Raspberry Pi Pico might be fast enough to toggle a pin at radio frequencies?

Although I've installed and tinkered with the native developer tools, I find the Arduino library convenient and familiar. 

The Pico has an interesting capability in that you can create little I/O state machines that run on the pins to take the bit banging overhead away from the CPUs. I found a nice library called RP2040_PWM by khoih-prog.

A few lines of code showed that it could easily generate RF. I tried on 7MHz. Here it is on 3MHz:

A decent waveform! Unfortunately to generate WSPR you need to be able to generate very small frequency steps and I wasn't able to do this with the library. Despite small changes in the float value of the frequency, the actual frequency would jump in quite large steps. I wrote to the author who explained:

"That sounds interesting project, but your concern, IMHO, is more accurate than what the RP2040 can provide.

The TOP register to control PWM is only 16-bit, giving 64K resolution can't provide the 1.4648 Hz increments in MHz range (nearly 32-bit resolution)"

The more obvious approach was to test if the Arduino library had extended the existing functions to fully use the extra speed of the 2040 chip.

I tried the tone() function but it wouldn't go up as high as 20kHz. (Worked at 10kHz and I didn't try to find the actual limit).

Next was simply toggling a pin in the loop() function.

The maximum is 862kHz. If I put the toggle code in a while(1) dead loop I could squeeze 957kHz out of it.


There is a PWM method in machine in Micropython for the Pico so I gave that a try. The code is super simple:

When run, this starts a PWM oscillator on GPIO16 that keeps going. There does seem to be a bit of jitter for some reason visible on the CRO:

The same problem remains, while you can generate frequencies well up into the MHZ, you don't have the fine grain control needed for WSPR generation. Looks like the Si5351 is a good way to go.

Tuesday, December 06, 2022

WSPR Watch 3.47 now in the App Store

A modest update to WSPR watch is now in the iOS App Store. This one moves a few settings around, makes it easier to see how to edit the list of past callsigns and provides an option for small dots on the graphs.

This was requested by someone with a lot of spots to display.

There are changes under the hood too. My networking code was quite old and I've started taking advantage of innovations in Swift to make the code cleaner and, perhaps even a bit faster.

I do have a niggling bug, sometimes the map freezes and I think this started with iOS 16.1.

Monday, December 05, 2022

Vertical wire antenna against ground stake for SDR reception

Now that I'm getting good at hauling wires up to the tops of trees I've hammered in a ground stake and raised a wire vertical high into my antenna tree. This makes an excellent broadband receive antenna.

I'm loving SDR++ and it works brilliantly with an AirSpy HF+ (I recommend the nightly builds). Recently I decided to wipe the shack Linux laptop and have switched over to Ubuntu Mate Linux. To get the AirSpy going I was pleased to see that I simply needed to do:

sudo apt install airspyhf

This is a much better experience than all the messing around with an SDRPlay device.

Saturday, November 26, 2022

Field trial of new QRP antennas from OzTenna

Richard, VK3TXD, kindly sent me a preview of two of OzTenna's new antennas for the QRP enthusiast. Now that the rain has stopped I took the medium duty EFHW and his 64:1 coupler out into the field and had good results.

The "medium duty" antenna is quite easy to put in the portable case but if you want even less to carry OzTenna has a "light duty" version as well:

The "coupler" is particularly notable as it includes both a 64:1 unun with a 1:1 balun in the same compact case. Mine was supplied screwed to a wire winder but I removed to make it more compact.

Here's my current "go box". All fits very neatly.

It's great to see some products being created for the QRP operator here in Australia. The OzTenna products are well thought out and nicely put together. Check their website for details.


Richard gave an interesting presentation to the EMDRC club on the topic of Unun efficiency with half wave end fed antennas and shares some of his very interesting research.

Thanks to VK2BLQ for the tipoff.

Friday, November 25, 2022

Creality Ender 3 v2 stopped printing

I've been having a good time with the Creality Ender 3 v2 3D printer here but today something weird happened and it refused to print.

At the end of a print the control panel became unresponsive and I had to power off the printer. I cleared settings and next time I tried to print neither the nozzle or bed heating started. It said it was trying to heat to 0, but I didn't notice that clue until much later.

Various forums suggested checking cables or that the motherboard might have failed. Other's suggested re-flashing the firmware. I tried a few different versions of the firmware, clearly not right for my printer as they included auto bed levelling which my printer doesn't have.

After flashing the interface came up in Chinese and my first thought was that I had the wrong file but it turns out you can set the language to English in the settings "Control" area.

In the end I flashed firmware 1.2.1 and navigating around I noticed that the bed and nozzle temperatures were set to zero. I changed them to 200C and 60C and tried printing again. This time the nozzle and bed came up to temperature but no printing started.

I'm working on a small job for Ralph, VK3ZZC, who asked for some caps for all his BNC sockets.

Earlier I'd got the cap working well and I used the slicer to duplicate the object so I could print six at a time. This was the first time I'd used the object duplicate feature in the slicer. 

It turns out that this gcode was upsetting the printer. I went back to just printing one and all is again working as expected.

So... if your printer stops don't assume it's hardware. I was pretty depressed thinking my new toy had died so quickly. All worked out in the end.

3D Printed spacers for KX3 in box

I purchased a LiPo battery pack from Paul Paton, VK3AHM, at the Rosebud Radio Fest and it triggered the desire to make a portable setup for my KX3. In the past I've put it in a waterproof box (Pelican case clone) with cubic foam spacers but it's not very efficient. My 3D printer can't print a large enough object to do this in one go so I divided the task up in to separate modules. Here's the result.

The cutout below the tuning know reflects the small speaker's audio up which helps quite a bit. Other segments on the left and above have holes for access to the sockets for power and microphone.

What you see here is my first attempt and I'm pretty happy with how it went. Obviously there can be improvements such as better fitting with the sloping sides of the case interior.

Wednesday, November 23, 2022

Radio Australia Book "Australia Calling"

This review was written for ABC Alumni.

Radio Australia was founded in 1939 by Prime Minister Robert Menzies to project the perspective of Australia during the second world war. At the time propaganda, what we might now call “fake news”, was being broadcast in our region by the Japanese, Russians and Germans.

Shortwave transmissions could be received with low cost, low power receivers and were difficult to censor locally. It was estimated that millions of suitable radios were in the field.

After the war, Radio Australia pivoted to sharing Australia’s outlook and appealing to people who might like to do business with Australia or even migrate here. 

Radio Australia was relatively free to run programs sometimes critical of the Australian government and thereby demonstrating the freedom of independent media in a democracy. This freedom of reporting was, at times of conflict or coups, very annoying to local strongmen. The fact that Radio Australia had programs in local languages gave it a direct line to the people.

The book, Australia Calling – The ABC Radio Australia Story, by Dr Phil Kafcaloudes includes many accounts of times when balanced information, from an Australian viewpoint, played a part in informing people on the ground in places like Timor-Leste, Solomon Islands, Bougainville and notably Fiji.

The broadcaster’s favour with our government has ebbed and flowed and funding levels have changed over time, leading to many changes in resources and programming. 

While brand recognition of Radio Australia was very strong and positive throughout the Pacific, the service was virtually unknown within Australia and despite strong support by some politicians, it came to be seen as disposable by those wielding the razor.

Looking back, the glory days of high power shortwave broadcasting seem like a golden era but at the time we despaired at the difficulty of measuring the audience, many of whom were isolated and unable to even write in (although millions did). Today, with internet streaming and local FM relays, measuring the audience is easier but the vulnerability of local transmission or internet-based delivery to being cut either by natural disasters or local politics is surely a step backwards.

Phil Kafcaloudes’ book is a fine piece of work, brimming with high quality photographs of smiling staff. Stories of people who have learned English by listening and the avalanche of letters that arrived at times are tempered with tales of dramatic changes in direction and the trauma of savage cuts.

For me, a shortwave listener since childhood, most moving is the story and image of Nigel Holmes who “seems to be equally proud and distraught as he presses the last button on a huge panel and watches the light go out [on shortwave transmission], ending nearly 80 years of Australian broadcasting history”.

At the ABC Friends Victoria Christmas dinner in November, I took the opportunity to ask the Minister for Communications, Michelle Rowland, if there were any plans to re-invest in shortwave. She reminded us that it was the ABC’s decision, under MD Michelle Guthrie, to end that mode and that it would be considered as part of future plans. The decision to cut shortwave broadcasting was, of course, in the context of cuts to the ABC and additional costs required to roll out DAB+ transmissions in major population centres.

Even if Radio Australia’s direct influence has waned in recent years, it has had a lasting influence on journalists and media in the region. Many RA staff have trained and mentored the current generation of program-makers throughout the region and the standards and practices of our programs have set an example to emulate.

Phil Kafcaloudes moved from domestic ABC duties to present the breakfast program on Radio Australia for almost a decade. He seems genuinely proud of what he was a part of and presents a warm and engaging account.

Australia Calling – The ABC Radio Australia Story was commissioned and published by the ABC.

Monday, November 21, 2022

Rosebud Radio Fest - excellent

This year's Rosebud Radio Fest was a first for me. It was a very well organised event with a wide range of equipment to buy and excellent talks to attend. At entry there was a welcome from some ladies from ALARA.

An interesting talk on pinpointing and reporting noisy power poles:

Fascinating talk about the new open VHF+ digital mode M17:

Peter Parker, VK3YE, was there with his amazing pedestrian mobile setup:

I caught up with old friends including recent licensee, Richard, who has been preparing since around 1980:

My congratulations to the organisers who did a fabulous job.

Guest commentator on ABC Download This Show

Is it ever the rational to pay a hacker's ransom? Controversially, I make the case that sometimes it is. I'm a guest again on Marc Fennell's "Download This Show". You can listen here.

As an aside, I have appeared on ABC shows quite a few times over the years. My commentary stems from a perspective as a software developer - so I hope I bring are deeper technical understanding than some other speakers. People sometimes ask me if we prepare and if we know what we'll be asked? Yes and generally yes. 

I keep my notes for each appearance and a count of documents indicates that I've done 325 of these so far, probably more.

Saturday, November 12, 2022

E-Field antenna works much better in the bush

Many years ago, when I lived in Suburban Sydney, I built an e-field or "probe" antenna. 

The benefits of these antennas is their small physical size and broad band operation including down to very low frequencies.

My home made one was disappointingly noisy. I purchased the PA0RDT mini whip and while well made, it was similarly noisy at that location. 

These days I'm at a low noise location and thought I'd give it another go.

It's certainly much better here than it was in the city but does pick up electrical noise particularly at low frequencies.

Power is fed up the coax from a little injector box that runs on 12V. For a while I ran it in to an AirSpy HF+ using SDR++ in the server mode (note that you need to get a nightly build for this feature to be there). Here's a look at 40m from a remote machine:

I'm not sure what those bands of noise are but I think they're related to power mains noise of some sort.

To test the low frequency receive performance, I set up WSJT-X to band hop 160m, 630m and 2200m. No luck on 2200m but I did receive spots from a station in VK5.

Amazing to receive a 1W signal on 475kHz from 1,380km away! Most spots were on 160m.

I'm finding that all antennas work better in the bush than they do in the city.

Attaching a wire to the top of a squid pole with a 3D part

My 3D skills are improving. This morning I was out testing an end fed half wave supported by a squid pole and a tree. Attaching a wire to the top of a squid pole is troublesome. The top segment is too flexible so I tend to use the second segment but attaching a wire to the tube is difficult and although duct tape works - it's messy. I've considered dog clips but don't want to squeeze the tube and risk it cracking.

I had an idea - a cylinder with a hole for the wire which can be dropped over the end of the squid pole.

It's a simple object and the 3D print is strong enough for QRP use. Marvellous to be able to think of an object and make it in just a few minutes.

Wednesday, November 09, 2022

3D printed case for TTGO ESP32 board

Starting to see some useful products from the 3D printer. I've designed and printed a nice case for the TTGO ESP32+LCD boards I like using around the house. The box and lid were designed in TinkerCad and printed on the Creality Ender 3 v2.

Not perfect but good progress for me. Here's the board sitting in the case part.

The case makes my solar monitor and K index displays look rather snappy.

My approach was to measure the board with vernier caliper and use those measurements in the 3D design. To get the lip of the lid to fit snugly into the lower case I sized it down 0.5mm on each of the 4 sides. It's a very tight fit and sure to vary by printer but it's working for me.

Here's the models in TinkerCad:

I've made them public. Case. Lid. TinkerCad is a little frustrating to use and I'm looking around for alternatives. I wish OmniGroup would do a 3D version of OmniGraffle.

Saturday, November 05, 2022

Home 3D printing notes

A few months ago I purchased a low cost 3D printer. I had just one project in mind but that was enough to get me started. The Creality Ender 3 v2 is excellent value for money and I've had good success with it.

Bed levelling is important for the success of prints. I had it right for a while but it drifted off which led to some prints not adhering to the base. A YouTube video suggested that replacing the wire springs with machined springs to improve the stability. At $8 for 10 it was not a big investment.

Here's a new spring along side the ones that came in the printer:

You can see how the spring is used to push the base plate up from the adjustment knob.

The new springs are slightly taller than the originals so I had to slide the print head limit switch up a bit. Doing this upgrade has helped me better understand the printer.

It's a week later and I've just had to re-level the bed. I would have to say that replacing the springs has not been the miracle cure I was hoping for. 


I started by using Blender for 3D design. It is great but overkill for this sort of thing. Several people mentioned Tinkercad which is a web based, but free, solution. I miss some of the advanced features but it is easier to use. Recently I made a little box to hold a TTGO ESP32+Display board:

Here it is in Tinkercad:

To be honest a 3D printer at home is a bit of a solution looking for a problem but no ham radio station is complete without an official station callsign statue:

There's a lot to learn about designing and printing 3D objects but my experience so far has been very positive. 

It's silly but sometimes I feel sorry for the printer when I send it a complicated job to print.

We live in an amazing age.

Thursday, November 03, 2022

Drone to raise antenna using bait drop servo

I've been raising antennas by running a line over tree branches. Various techniques have been used including an arborist's throw, a squid pole, and tying a line to a drone. The last method invariably ends with the drone's rotors getting tangled in the line on the way down. 

Recently I discovered little remote control releases, apparently meant for dropping fishing lines. It's hard to know what to search for but this one is titled "Universal Remote Thrower Hanger Airdrop System Fishing Bait Deliver Life Rescue for DJI/FIMI RC Drone Quadcopter Accessories" - wow.

This device works but the servo is tiny and quite weak.

This approach seems promising and I hope to try it out with a real antenna raising soon.

Tuesday, November 01, 2022

WSPR Watch app for iOS updates

I've updated WSPR Watch in recent weeks.  It's a free app for iOS that pulls data from WSPRnet and other sites so that you can conveniently check propagation on your phone or tablet.

Recent changes include:

* Fixed a layout issue triggered when a spot doesn’t have a tx grid square

* Handle small displays with large text better

* Searches now persist over to maps and graphs. This is handy for plotting propagation between two grid-squares for example.

* User can edit band colours in settings

* Shows bands in list headers

* Displays Grid Square codes in spot list

* Can now search for callsign or grid square

* Buttons in info alert to search for TX or RX Grid square

* Refresh buttons on map and graph view

The most interesting new feature is that searches in the spot list used to be cleared when you switched to the map or graph view. Now these searches persist. I use this when I'm using WSPR spots to see the best time for a voice contact to a specific place. Now I can run WSPR for 24 hours and search for the target grid square, then go over to the graph and see a plot of signal to noise ratio.

Round spots are received, triangles are reports of my transmissions.

In recent versions I've been adding more information into the spot list display and I hadn't realised that there's users who have small screen phones and they increase the text size. Thanks to feedback, and screenshots, sent in I was able to duplicate the problem and have improved things somewhat.

The colours used for each band has always been controversial. Initially I copied those used on WSPRnet but some people were not satisfied so recently I added the ability to customise band colours.

Thanks to all those who reported issues or sent suggestions. I don't have any monitoring in the app but downloads indicate quite a large user population these days. If you like the app, please consider leaving a review.

Wednesday, October 26, 2022

GA-800 Active loop receive antenna

I purchased a small (26cm) active loop antenna called a GA-800.  So far quite impressed. 

The bottom part has a re-chargeable battery with USB-C charging.

Interesting to note that for best reception in a window, the plane of the loop should face out.

Reception with the loop is significantly stronger than when using the whip antenna on the radio.

The loop can be separated from the power base part if desired. I'm sure it would work even better in a remote configuration.

Friday, October 21, 2022

BOM re-branding work

The re-branding of the BOM to The Bureau of Meteorology, hereinafter to be referred to The Bureau is reported to be costing $220,000. But what about all of us developers who use their excellent APIs? My little K index reporter used to look like this during startup:

Never fear, we've pulled the team in and made the necessary changes:

But of course the website and api URL domain names still have "bom" in them so we're standing by for any breaking changes. ;-)