Foundations of Amateur Radio

When you join the community of radio amateurs, or when you briefly look over the shoulder of the nearest devotee, you're likely to discover that this is a hobby about a great many different ideas. Over the years I've discussed this aspect of our community repeatedly, talked about the rewards it brings you, about the camaraderie, about communication, learning, research, soldering, disaster recovery, public service, and all the other thousands of activities that this hobby represents to the world.

While all those things might be true for some, they're not true for everyone. Many amateurs get excited about antennas, some immediately, some eventually. The same can be said for all the other points of what we think of when we discuss our hobby with others.

Recently I saw a random comment on social media from a person who was having issues with their mobile phone on their property. I considered and ventured an opinion about what might be the cause and how they might go about discovering what was going on.

I debated about how I signed off. It's a recurring dialogue, should I reveal upfront that I'm a radio amateur, or should I leave that to be discovered at a later date? In my experience, the wider society has a, let's call it a rocky relationship with our hobby. With the decrease in profile and numbers comes an increase in misconception about who it is that we are, and what it is that we do.

At some level, there's an understanding that at some point this was an activity that grandpa might have engaged in, or it might be someone preparing for the end of the world, seeing our community as the way forward when all else fails, not at all helped by that slogan being used by a vocal amateur radio body, the ARRL.

Given that, as I saw it, the issue was related to radio interference or a weak signal, I signed off, for better or worse, "Source: I'm a licensed radio amateur", and crossed my fingers.

This started a discussion about the issue, which revealed that the person was having other problems with other communication tools in their remote village. I don't want to go into the specifics, because it's not about what their issue is, where they live and what other resources they might have access to, or not. It's about us, radio amateurs, because of course it is.

Aside from the cringe associated with my sign-off, if you have suggestions on how to improve it, I'm all ears, I had a take-away that I thought was worth discussing. As I'm beginning to suspect, it's about the fundamental nature of our hobby, what it is and what it does.

Troubleshooting.

Let me say that again. Amateur Radio is fundamentally about "troubleshooting", in other words, systematically finding and fixing complex problems.

So, let's explore this.

If you consider we're all about communication in difficult environments, I'd point out that getting that message across is an exercise in troubleshooting.

If you lean towards learning, then consider deciding what to study and why, more troubleshooting.

If you suggest it's about soldering, what happens when you poke the leg of a component into the wrong hole? Do I really need to say it?

Every time you think you've nailed down the intangible nature of our hobby, you can point at troubleshooting. Don't get me wrong, it's about having fun too, but you and I both know that fun is balanced by frustration, again, you guessed it, troubleshooting.

In our increasingly technical, interconnected and complex world, the ancient pursuit of amateur radio is teaching you an invaluable skill, over and over again, all but inevitably: "The art of troubleshooting".

So, next time you are asked why we should be doing this thing, why we are obsessed with this hobby, why we spend many hours, dollars and effort, it's all about finding out why something doesn't work as expected and funnily enough, the more you do it, the better you get.

For radio amateurs, troubleshooting is our superpower.

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently I started an experiment I plan to run for a year. Using a WSPR beacon and a dummy load I'm transmitting 200 mW, 24 hours a day across all bands supported by my hardware, in this case it covers 80m, 40m, 30m, 20m, 17m, 15m, 12m, and 10m. The aim of the experiment is to determine if, and to what extent my dummy load can be heard outside my shack. Why? Because I've not seen anyone do this and because a dummy load is widely believed to not radiate, despite evidence to the contrary.

Together with the transmission side, I've also configured an RTL-SDR dongle, initially with the telescopic antenna it came with, now, since my HF antenna isn't being used by the beacon, I'm using it instead. It's about five metres away from the beacon, outside. It's a helically wound whip resonant on the 40m band built by Walter VK6BCP (SK). It's what I've been using as my main antenna for the past seven years or so.

While I'm telling you this, my beacon has been heard by my dongle 1,182 times across all eight bands. Some of those reports were from inside the shack, some from outside, some while I was monitoring a single band, and for the past week or so, I've been monitoring all the bands supported by "rtlsdr_wsprd", 18 in all. Purposefully, this includes some bands that I'm not transmitting on, because who knows what kinds of harmonics I might discover? The receiver changes band every half hour, so over time when I monitor a band will shift across the day, this is deliberate. I don't know when a stray transmission might suddenly appear and this will give me the best chance of hearing it, short of using 18 different receivers.

At this time, my beacon hasn't been heard by any other station. I'm not expecting it to, but that's why I'm doing this experiment in the first place.

I'm not in any way reaching any sense of "DX on a dummy load", but it got me thinking. My beacon can be heard, albeit by me, from five meters away. So it's radiating to some extent. I've already discussed that this might come from the patch lead between the beacon and the dummy load, or it could be the dummy load itself, or some other aspect of the testing configuration. Regardless of the situation, there is a signal coming from my beacon that's wirelessly being heard by a receiver.

That's the same as what you'd hope to achieve with any antenna.

So, in what way are an antenna and a dummy load different, and in what way are they the same?

Whenever someone asks this, the stock answer is that an antenna radiates and a dummy load doesn't. My experiment, 20 days in, has already proven that this distinction is incomplete, if not outright wrong.

Even so, if we take it on face value, and we say, for argument's sake, that a dummy load doesn't radiate and an antenna does, then how do we materially distinguish between the two? How does an antenna compare to a dipole, Yagi or vertical antenna and where does the isotropic radiator fit in this?

The best I've come up with so far is a spectrum line comparing the various elements. Let's say that at one end of the spectrum is a dummy load, at the other is an isotropic radiator, to refresh your memory, that's the ideal radiator, it radiates all RF energy in all directions equally.

Somewhere between the two ends is a dipole. We might argue if the dipole sits equally between a dummy load and an isotropic radiator, but where does a Yagi or a vertical fit in relation to the dipole?

Also, if you turn a Yagi in the other direction, does it change place?

So, perfect this notion is not, but here's my question.

What's the measurement along the axis between the dummy load and the isotropic radiator? It's not SWR, since the ideal antenna and a dummy load share the same SWR, unless this line is a circle that I don't know about. It might be Total Radiated Power expressed in Watts, but that seems counter intuitive. It would mean that in order to determine the effectiveness of an antenna we'd need to set-up in an anechoic chamber, basically a warehouse sized room where incoming radiation is shielded to some predetermined standard.

Do we measure gain using a VNA and call it a day, or is there something else going on? Remember, we're attempting to quantify the difference between a dummy load and an antenna.

In case you're wondering, I'm asking the question.

In the 15 years I've been part of this community, I've never seen any coherent response. The Internet seems to return a variation on the radiation vs. not-radiation pattern, but so far I've not seen anyone quantify this, or perhaps I haven't understood it while it was staring me in the face. I even checked the syllabus for the three license classes in Australia. The single reference that the regulator appears to specify is that at the introductory level you are required to, wait for it, recall that when testing a transmitter, a non-radiating load, or dummy load, is commonly used to prevent a signal from being radiated.

Very illuminating. Obviously my dummy load is of the wrong type, the radiating variety. Which begs the question, if there's an ideal radiator, is there a theoretical ideal dummy load that doesn't radiate in any way, and if so, how far away on this line is it from my actual dummy load?

Over to you. What are your thoughts on this? Better yet, got any references?

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently Glynn VK6PAW and I had the opportunity to play radio. This isn't something that happens often so we try to make the most of it. For our efforts we had plenty of frustrations, to the point where we were joking that I should rename this to "Frustrations of Amateur Radio".

That was until we heard something weird on-air. All setup shenanigans forgotten, we marvelled at the experience.

I was playing around on the 10m band, trying to hear people making noise and potentially our first contact for the field day we were participating in, when I heard something odd. Two stations talking to each other, but the audio was strange. It was like they were doubling up, the same audio played a fraction of a second later, until that moment, something I've only ever heard in a radio studio whilst editing using a reel-to-reel tape machine with separate recording and playback heads.

Having just started using a digital only radio, at first I thought this was an artefact of the radio. I took note of the frequency, 28.460 MHz and told Glynn about it. After we moved the telescopic vertical antenna to the analogue radio, we discovered that this was in fact real, not caused by the radios, no doubt a relief to the proud owner of both radios, Glynn, who was thinking more clearly than I. He took note of the callsigns, Dom VK2HJ and Yukiharu JE1CSW. Looking back now, an audio recording would have been helpful.

At the time I suggested that this might be a case of long path and short path signals arriving at our station and being able to hear both. If you're not sure what that means, when you transmit, an antenna essentially radiates in all directions and signals travel all over the globe. Some head directly towards your destination, the short path, others head in exactly the opposite direction, taking the long way around Earth, the long path.

You might think that the majority of contacts are made using the short path, but it regularly happens the other way around, where the long path is heard and the short path is not. As you might know, radio waves essentially bounce up and down between the ionosphere and Earth and it might happen that the signal arrives at the destination antenna, or it might happen that it bounces right over the top, making either short path or long path heard, or not.

In this case, both arrived clearly audible.

It wasn't until I sat down on the couch afterwards with a calculator that I was able to at least prove to my own satisfaction that this is what we heard.

So, what were those calculations and what was the delay?

The circumference of Earth is roughly 40,000 km. RF propagation travels at the speed of light, or about 300,000 km/s. It takes about 0.13 seconds or 130 milliseconds for a radio signal to travel around Earth.

At this point you might realise that 40,000 km is measured at the surface, but ionospheric propagation happens in the ionosphere, making the circumference at the very top of the ionosphere about 45,000 km, which would take 150 ms.

There are several things that need to line up for this all to work.

Propagation aside, the distance between all three stations needs to be such that the number of hops between each combination is a whole number so we can all hear each other.

As it happens, the distance between Perth in Western Australia and Maebashi City in Japan is pretty close to the distance between Goulburn in New South Wales and Japan, and the distance between Goulburn and Perth is roughly half that.

Using back of napkin trigonometry, it appears that 27 hops around the planet are required to make this happen. That's five hops between Perth and Japan, and between Goulburn and Japan, and two hops between Goulburn and Perth, and 27 hops between Perth and Japan the long way around.

Given that the F2 layer where the 10m signal is refracted exists between about 220 km and 800 km, we can estimate that the total delay for the long path is at least 144 ms.

That doesn't really translate into anything you might relate to, but at 8 wpm a Morse code dit takes 150 milliseconds, which gives you a sense of how long the echo delay is. In other words, it's something that you can absolutely hear without needing to measure it.

There are other implications.

WSPR signals are used to test weak signal propagation. Stations around the globe report on what they can hear and when. For this to work, the signal need to be synchronised, something which is commonly implemented using something called NTP, or Network Time Protocol. It can achieve a time accuracy of 10 ms. GPS locked WSPR beacons can achieve an accuracy of 40 nanoseconds.

In other words, if we know that the beacon and the receiver are time synchronised, we can probably detect if the signal arrived using a short path or a long path. The WSPR decoder tracks the time between when the signal arrived and 2 seconds past an even minute as perceived by the receiver. Gwyn G3ZIL wrote an interesting document called "Timescale wsprdaemon database queries V2" on the subject of the data format used by wsprdaemon, a tool used to analyse WSPR beacon transmissions. If this is something you want to play with, check out wsprdaemon.org

From our adventures there was plenty to take away. Stay curious, go portable, take notes, practice putting up an antenna, keep a log, laugh and have fun, and last but not least, get on air and make noise.

Before I forget, make sure your mate brings a pen for logging when your own trusty scribble stick suddenly gives up the ghost for no apparent reason. I knew there was a reason I prefer pencils.

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently I received a question in relation to the Bald Yak project. If you're not familiar, "The Bald Yak project aims to create a modular, bidirectional and distributed signal processing and control system that leverages GNU Radio."

I know that I've said that several times now and I suspect I'm going to say it several more times before we're done. I was asked about a specific radio and if this project could make it use a frequency that the supplied software didn't cover.

The answer is deceptively simple and if you know me at all, you know what's coming: "It depends". As with many things, what it depends on is not fixed. I'll come back to the question, but I'm making a diversion past a magical place, the local hardware store. You can buy everything you need to build a house with the caveat that some assembly is required. GNU Radio is similar for building a signal processing system, but, wait for it, some assembly is required.

In the context of GNU Radio this means that you'll need to collect all the bits and wire them together, fortunately you're unlikely to need Personal Protective Equipment or access to a First Aid Kit, unless of course the idea of playing with computers gives you palpitations, in which case I'd recommend that you go see your doctor.

One of the less obvious things you'll come across with GNU Radio is how to bring signal processing into the physical realm, in other words, how do you get a signal into your computer, known as a "source", and get it out, called a "sink".

The ability to talk to physical hardware arrives in roughly three different ways. Let's call them, "native", "library", and "abstraction". Native access requires that GNU Radio already knows about the hardware out of the box. Library access requires that the hardware manufacturer has provided software libraries, also known as drivers, allowing GNU Radio to communicate, and finally, abstraction is where a third party has written a library that knows how to talk to hardware from different manufacturers.

The distinction between these is almost arbitrary, for example abstraction might require a driver from a hardware manufacturer. Similarly, because all this software is open source, native can include software from other projects, like the RTL-SDR blocks from Osmocom, Open Source Mobile Communications, and UHD blocks written by Ettus Research, which in turn can be seen as an abstraction.

As I said, some assembly required.

I will point out that this provides a great deal of flexibility, albeit at the cost of complexity, there's still no such thing as a free lunch.

At this point you might shake your head and run away. I get that, it can be daunting. Before you do, consider the scenario where you have a working system and you upgrade your hardware. In a GNU Radio world you'll need to figure out how to configure the new hardware and then all your other stuff will continue to work.

The alternative is upgrading each of your applications to connect to your new radio and in doing so, run the risk of making your old radio obsolete, even if you are collecting them .. let's say for posterity rather than hoarding .. because radio amateurs never hoard anything .. right?

Back to the original question. Can GNU Radio make a radio use frequencies that the software that came with the radio cannot? As I said, "it depends".

First of all, the hardware needs to actually be able to support the frequency. Then someone needs to have written a library to use that frequency, then GNU Radio needs to be able to use that library.

That said, the chances of that happening are much higher than the chance of the hardware manufacturer rolling out this feature within your lifetime. Before you start yelling at me, yes, this is manufacturer dependent, some provide open source tools, many still don't.

There are alternative ways to access different frequencies.

The PlutoSDR is a computer and radio in a box. You can connect to it, change some settings and have it access a whole lot more frequencies. In some ways it's like adding or removing jumpers on a traditional circuit-board.

Another approach is to use an up- or down-converter. Essentially a piece of hardware connected between antenna and radio that translates frequencies to different bands. A down-converter allows you to use the 23cm band on a radio that's only capable of 70cm. Similarly, an up-converter allows your 70cm radio to hear HF signals. If you see a symmetry here, you didn't imagine it. You need both to transmit and receive, sold together in the same box as a transverter.

Just so we're clear, the radio is still using the 70cm band, but the RF coming in and out of the antenna connected to the transverter is on a different band entirely. It's why my Yaesu FT-857d has three menu options, 89, 90 and 91, to adjust the display to show the actual RF frequency. As an aside, you could use this functionality if your radio is off frequency by a known amount.

As I've said before, GNU Radio is a powerful tool. It contains many different moving parts, the system is complex and unwieldy, but with it comes the promise of doing some amazing stuff.

The whole point of the Bald Yak project is to make this all accessible to the wider amateur community, not just computer geeks and software radio nerds.

If you have questions, feel free to drop me a line.

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently I made a joke about operating your station with a dummy load in response to John VA3KOT operating their station with the craziest antenna they ever used.

It got me thinking about the ubiquitous "dummy load" as an antenna.

Since becoming licensed I've spoken with several amateurs who tell a similar story, one comes to mind immediately, Lance VK6LR, now SK, who told me that they managed an unexpected 2m contact with another station using a dummy load, across the city. There's various versions of this doing the rounds, incandescent light bulbs used as both dummy load and antenna, coiled up roll of coax, everyone has a story to tell.

Having spent several years proving that you can in fact use 10 mW and be heard on the other side of the planet, 13,945 km away, it tickled my fancy to think about what would happen if I replaced my antenna with a dummy load on purpose, as a test.

For the past two or so months my WSPR beacon has been transmitting every ten minutes on the 15m band. It was heard 3,493 km away. Interestingly, even in that short amount of time, the radiation pattern of my antenna as seen on the "wspr.live" website shows a similar outline to the 10m transmissions I've been doing since late 2021.

The number of total spots wasn't nearly as significant. I added a local receiver to my shack, just to prove that I was in fact transmitting, but there were plenty of days without a single external report, this in contrast with my 10m experiment where most days I had at least one or more reports from outside my shack, most of them outside my state.

In other words, not every band gets the same kind of report. My license restricts me to the 80m, 40m, 15m, 10m, 2m and 70cm bands. The two antennas I've used so far are essentially limited to a single band, unless I start tuning it every time I change bands.

As you might recall, I purchased a Hustler 6BTV antenna several years ago. Unfortunately, it's still sitting in the box. Climbing on my roof has not been an option for several years, but its time will come. The purpose of getting that antenna was specifically so I could use WSPR across multiple bands and see how propagation was in my shack in real-time without needing to rely on external forecasts or predictions.

Switching to a dummy load has several benefits and impacts.

First of all, it's not something I've seen anyone do. Then there's the idea of band hopping without needing to re-tune. The idea of radiating into something that's not supposed to radiate, is something that makes me smile.

Given that each band has a different level of propagation, which ones should I choose? I could pick all the ones I'm licensed for, but that would leave out the WARC bands and the ever popular 20m band.

What if I ignored convention and transmitted on all bands supported by my WSPR transmitter? Remember, I'm transmitting into a dummy load. By all accounts this should not radiate. It's taken as gospel by the amateur community that it doesn't.

So, using a dummy load, one that's rated at 15 Watts between DC and 150 MHz, feeding it with 200 mW, or 23 dBm, my WSPR transmitter is currently merrily pinging away across 80m, 40m, 30m, 20m, 17m, 15m, 12m and 10m.

If all goes to plan, nobody will ever hear this.

That said, I can hear the uproar from here.

What's the point? You're illegally transmitting on bands you're not licensed for. I'll report you to the regulator.

Here's the point.

The community and the regulator both state that the dummy load is the approved method for testing equipment. It's implied that the equipment will be happy and there will be no radiation. I'm testing and monitoring that assumption.

I'm using all bands because if conventional wisdom is right, nobody will hear this. On the other hand, if conventional wisdom is wrong, there will be reports from bands where there are many people monitoring.

I'll note a couple of other things.

There's a patch lead between the WSPR transmitter and the dummy load. It's about 200 mm long. It's the shortest one I have. It was terminated at the factory and connects the SMA output of the WSPR transmitter to the SO-239 on the dummy load. Theoretically it might radiate. Perhaps this is where other transmissions into a dummy load emanate from, perhaps not.

I discussed the idea of measuring the emissions from a dummy load with a fellow amateur versed in testing much more sensitive equipment. We were not able to come up with a way that would be simple to do by any amateur. If you have ideas, feel free to share.

I'm likely going to cop flack from those who think I'm doing something illegal. You cannot have it both ways. Either I'm transmitting legally or a dummy load isn't a suitable testing tool. Unless instructed by the regulator to cease, I'm confident that I'm operating precisely within the obligations and requirements of my license which encourages me to test and monitor interference, which is literally what I'm doing.

One other point. Until now my WSPR transmitter has paused for eight minutes between transmissions, transmitting once every ten minutes, or six times per hour. It was the default as I recall. I've changed that to transmitting every cycle on a different band. This means that every 16 minutes, the same band will get activated. It also means that because 16 minutes doesn't fit neatly into an hour, the band will move over time, which I think is a good thing. The frequency hopping appears to be round robin, so no grey-line changes, but feel free to correct me.

I don't know what this will do to the transmitter and if it will sustain this. I haven't asked Harry SM7PNV, but if it cooks itself, I'm sure that I can order a new one and mark it down as a lesson learnt.

So, have at it. Point your receiver at VK6 and see what you can hear. I expect to keep this running for a year and see what we learn.

I'm Onno VK6FLAB

Foundations of Amateur Radio

When you joined the global community of radio amateurs you did so with a perspective that represented, at the time, what you thought the hobby was and how it operated. Since then, years, months, even days ago, that perspective has shifted in both subtle and obvious ways.

One of my local amateur radio clubs, Ham College, was specifically formed to provide amateur radio education and license exams. It's where I went to get my Foundation license in 2010 and it's where many of the local amateurs have been taught over the years.

For years I've been semi-regularly visiting Ham College during their Foundation course sessions. The purpose of my visit is to share what it's like to be an amateur, what things you don't really know about before you get licensed, and what things to look out for when you are.

In general I talk about how to find the rest of the community, what you can expect and what to do with your license once you pass the exam. I try to cover the highlights without overwhelming the audience who technically are not yet amateurs at the time I'm sharing my thoughts.

I talk about the endless variety of amateur radio activities, from activating anything that's not moving, or anything that is, depending on the level of adrenaline required, through contesting, camping and bushwalking, antennas, endless antennas and electronics.

I talk about low power versus high power, and about community expectations in relation to upgrading to a "real" license. In case you're wondering, a "real" amateur license is any amateur license, including the Foundation license I hold, the introductory license. In my view, ultimately, this is your hobby, where you decide when and how much you want more responsibility and decide to pursue what this means for you.

I discuss that the amateur radio community is global, attracting people from all walks of life, from submariners to scientists, from tow truck drivers to teachers, aged from nine to ninety, across all languages. I also touch on some of the less fun aspects of our hobby, specifically bullies.

Over the years you've heard me discuss diversity, equity and inclusion in our community and also how there is a vocal minority who make it their mission to present obstacles to anyone who is different in any way. As I've said previously, the only antidote against this intimidation is to call it out and make your views heard, "this is not in the spirit of amateur radio", rather than change the dial and move on. In case you're wondering, changing the dial does nothing to address the issue and has a lasting effect on anyone else on frequency who might feel, or worse, has been, threatened by the bully.

I also point out that this obnoxious behaviour is an exception, even if you feel personally attacked, and what you might do and whom you might talk to. For the record, my door is always open.

Another example of what I discuss is the local amateur news and the weekly net for new and returning amateurs, F-Troop, midnight UTC on Saturday for an hour, a place where you can ask questions and discuss your issues with a supportive international community of amateurs.

As you can tell, I'm not shy in voicing my opinion. Although I set myself a limit of 15 minutes, of late I've been wondering what other things might be of interest to someone who is just taking their first steps on their amateur radio adventure, hours away from taking their exam.

What kinds of things would you have liked to know when you started your amateur journey? Get in touch, my address is [email protected].

Don't be shy, express your opinion, it's the only thing that changes the world. What do you want the amateurs of tomorrow to know today? How would you equip yourself if you had the chance to start again?

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently I received a lovely email from Michele IU4TBF asking some pertinent questions about the Bald Yak project. If you're unfamiliar, the Bald Yak project aims to create a modular, bidirectional and distributed signal processing and control system that leverages GNU Radio.

The short answer to how I'm doing getting GNU Radio to play nice with my computer is that I have bruises on my forehead from banging my head against the wall. When I get to success I'll document it. To be clear, I'm not sure what the root cause is. I suspect it lies between the GNU Radio developers, the people making packages and the manufacturer of my computer. I'm the lucky one stuck in the middle.

A more interesting question that Michele asked was, for Bald Yak, what is the A/D and D/A requirement for making GNU Radio talk to an antenna?

This is a much deeper question that meets the eye and I think it serves as a way to discuss what I think that this project looks like.

Ultimately in the digital realm, to receive, an analogue antenna signal needs to be converted to digital using an Analogue to Digital or A/D converter, and to transmit, the reverse uses a Digital to Analogue or D/A converter to make an electrical signal appear on your antenna.

The specific A/D or D/A converter determines what you can do. The sampling rate of such a converter determines what frequencies it can handle, the sample size determines the range of signals it can handle. You can compare it with a video screen. The sample rate determines how many pixels on the screen, the sample size determines how many colours in each pixel.

The sample rate of an A/D converter is measured in samples per second. If the device only has one channel, you could think of this as Hertz, but if there are multiple channels, like say a sound-card, the sample rate is likely equally divided across each channel.

You might have a sound card capable of 384 thousand samples per second, or kilo-samples, but if it supports simultaneous stereo audio input and output, only 96 of those 384 kilo-samples will be allocated to each channel and only half of those will actually help reconstruct the audio signal, leaving you with 48 kHz audio. In other words, the advertised frequency response might not have a direct and obvious relationship with the sample rate.

At the moment I have access to a few different A/D and D/A converters. The simplest one, a USB audio sound card, appears to do up to 192 kilo-samples at 16 bits. The next one, an RTL-SDR tops out at a theoretical rate of 3.2 million or mega-samples at 8 bits. The Analog Devices ADALM-PLUTO, or PlutoSDR handles 61.44 mega-samples at 12 bits.

Now, to be clear, there are other limitations and considerations which I'm skipping over. Consider for example the speed at which each of these devices can talk to a computer, in this case over USB. I'm also going to ignore things like mixers, allowing devices like the RTL-SDR and PlutoSDR to tune across frequency ranges that go beyond their sample rate.

Each of these three devices can convert an analogue antenna signal into bits that can be processed by GNU Radio. All of them can also be used to do the opposite and transmit. Yes, you heard me, several amateurs figured out that an RTL-SDR can actually transmit. Credit to Ismo OH2FTG, Tatu OH2EAT, and Oscar IK1XPV.

The point being that whatever Bald Yak looks like, it will need to handle a range of A/D and D/A converters. As I've said previously, I'm aiming for this to work incrementally for everyone.

This means that if you have a sound card in your computer or an $8 USB one, this should work and if you have an $33,000 NI Ettus USRP X410 lying around, this too should work.

Also, if you have an X410 lying around not doing anything, I'd be happy to put it to use, you know, for testing.

So, kidding aside, what about the rest of the Bald Yak experience?

GNU Radio works with things called blocks. Essentially little programs that take data, do something to it, then output it in some way. It follows the Unix philosophy, make each program do one thing well, expect the output of every program to become the input to another, design and build software to be tried early and use tools rather than unskilled labour.

Amateur radio transceivers traditionally use electronics blocks, but if we move to software, we can update and expand our capabilities as the computer we're using gets faster and the GNU Radio blocks evolve, and because it's all digital the computer doesn't actually have to be in the same box, let alone the same room, it could be in multiple boxes scattered around the Internet.

So, the idea of Bald Yak is a collection of blocks that allow you to do radio things. You might have a separate box for each amateur radio mode, AM, FM, SSB, RTTY, CW, WSPR, FT8, FT4, Q65, but also modes like Olivia, FreeDV, SSTV, Packet, PSK31 or Thor. Instead of having to figure out how to wire these modes into your radio and your computer, the infrastructure is already there and you just download another block for a mode you want to play with.

We'll need to deal with variables like which A/D and D/A converter is being used and what their limitations are. We'll also need to build a command and control layer and probably a few other things.

I'm considering a few other aspects. For example, GNU Radio is mostly run with text files. We might distribute those using something like a web store. GNU Radio is proving hard to install, perhaps a LiveCD is the way to go. We'll need to come up with a base level of functionality and the documentation to go with it. I'm still contemplating how to best licence this all, specifically to stop it from being exploited. Feel free to get in touch if you have ideas.

I'm Onno VK6FLAB

Foundations of Amateur Radio

Have you ever come across a solution to a problem that you sort of knew you had, but didn't really appreciate until that moment? I had one of those recently. To set the scene, fair warning, we're not going to solve this today, we're still very much shaving yaks, but there's plenty to take away.

So, the scene.

I'm hosting my weekly net. It's going well. All the internet links are up and running again, thanks to the hard work behind the scenes of several unsung heroes, I can name a few, Bob VK6ZGN, John VK6RX and Rob VK6LD, but there are plenty of others whom I don't know and who have yet to stick up their hand to say, I was there. Regardless, thank you.

Anyway, I'm hosting my weekly net, F-troop. A curious thing is occurring. Two of the stations are emitting a tone during their transmission. I'm pretty hot on how things sound, so I ask. We talk about it for a bit when Allen VK6XL comes in and tells us that according to his spectrum analyser it's a 1 kHz tone with harmonics and it's on all transmissions, just audible on two.

This starts a conversation about spectrum analysers when Allen mentions that he's using an audio spectrum analyser, a piece of software running on his computer. The software has a copyright from 1999 and based on the documentation I saw, has lots of excellent functionality. I might even be able to run it on a Linux machine using WINE, but that's an adventure for another day.

Randall VK6WR points out that I could use the spectrum display on Audacity. This is a much more current piece of software, but it's not intended for real-time use, it's what I use to edit the audio after recording my podcast. Not even sure if the spectrum display can show during recording, I've never tried.

In the past I've used SoX, the Swiss Army knife of sound processing to create sonograms, but that too isn't real-time.

Then it hits me. I have a real-time tool. I've been playing with it for weeks. GNU Radio. Surely it has a spectrum display, and indeed it does, several.

So, I already have a tool, purpose built for processing signals, that can do all the things I'm looking for and some I've not yet imagined.

Before I proceed, I'll remind you that we're in the middle of the Bald Yak project, so named because by the time we're done there won't be much hair left, if any. In case you're unfamiliar, the Bald Yak project aims to create a modular, bidirectional and distributed signal processing and control system that leverages GNU Radio.

So, boldly clicking about, I set on the notion of making a block called "fosphor" work. Depending on which description you use, it's an Open Source, GPU-accelerated FFT and Waterfall display tool. What that means is that it uses a graphics processor to do the heavy lifting and has the ability to show signal levels across frequencies and on a waterfall display. Apparently it's a block for RTSA-like spectrum visualisation. I'm fairly sure that doesn't mean Railway Technical Society of Australasia or has any relationship with Reverse Total Shoulder Arthroplasty or the Road Transport and Safety Agency of Zambia.

I'll admit that I didn't see the GPU part of that description until several days later. Had I seen it at the time, I would likely have carefully backed away and shelved the idea, but that's all water under the bridge.

To cut to the chase, I have yet to make this show a single pixel. I smelled trouble for the first time when I discovered a post asking if anyone had gotten this to work on a current release of Debian.

I came across a lovely post by what appears to be the author helping some hapless user, and I'll confess that's the camp I'm currently in, to make it work. I have no doubt that I can make it work, but that's going to take some effort.

Now, at this point you might ask me why I wasted your time with this tale of woe?

Well, the answer is simple. This is what "Yak Shaving" looks like. You solve a thousand little problems, one at a time, and if you manage to keep track of what you're doing and why, you can get stuff done.

This applies here, but it also applies in your life, in radio, in antenna building, in making a contact, in participating in a contest, in activating a park.

Each activity reveals myriad issues that you'll each need to resolve. The more practice you have at this, the better you'll get. I will point out that for me it's not without stress. When I go though intractable problems I'm often as grumpy as a bear with a sore tooth whilst my brain is running like a hamster in a wheel generating kilowatts of power.

This too shall pass.

Oh, because I know it's bothering you. RTSA, Real Time Spectrum Analyser, obvious, right?

I'm Onno VK6FLAB

Foundations of Amateur Radio

Recently I built a first attempt at a noise cancelling circuit, on my couch, in GNU Radio, without holding a soldering iron and running the risk of the room smelling like burnt chicken, because if you believe the Internet, sometimes holding a hot piece of metal by the hot end is not the best way.

The idea behind the circuit, or more accurately, flowgraph, is that you take a signal from two sources, invert one, combine them, and they cancel each other out. If the signal with the noise only contains noise, then you can, at least theoretically, remove the noise from the actual signal.

Before you think that I'm inventing something new, I'm not. I'm merely attempting to recreate the same notion I came across decades ago, where you combine the signals from two microphones, preferably identical, reversing the wiring in one and talking into a microphone whilst holding the other one away from your mouth.

I did essentially the same thing using RF signals from two RTL-SDR dongles.

Randall VK6WR pointed out that, aside from misusing the word "mix", which in electronics really means multiply, but in audio means combine, Randall suggested I use "add" and "subtract". I'm still working out how best to name things, because we're talking about audio and RF, sometimes at the same time. Perhaps that's where I went wrong. I'm currently using "combine" as my technology neutral word, but I'm happy to take suggestions.

All that was the side show, because as Randall points out, doing this in RF is much harder than in audio. This is already something I knew. At the time I didn't really know how to get two different but the same sources of audio to experiment with, so I started in the deep end at the RTL-SDR dongle side.

Now, armed with the encouragement from Randall I built a horrible thing, which is easy when you just drag and drop blocks on a screen. I built two independent FM decoders that use the exact same parameters, so they're tuned to the same frequency, they're amplified and tweaked identically. The only difference is that they each decode a different dongle. I then piped each of those into my magic noise cancelling circuit and tried again.

Aside from dealing with hardware restrictions, causing things like buffer under-, and over-run, that's when the computer isn't processing all your samples, or is getting ahead of itself and is running out of samples, I can make audio come out of the speaker in my computer. I can prove that there are two signals, by setting the amplification of either to zero, and still get sound from the other source, however, noise cancelling, no matter what I tried, didn't work.

Then I decided to simplify, rather than trying to cancel out "the Heat is on", word of honour, I'm not making that up, that's the song that was playing, I went back to basics starting with a tone. I fed the same tone into the noise cancelling block twice, once as signal, once as noise. Magic, the cancelling works.

I also learned that changing the frequency of the noise and changing it back gets you into all kinds of problems and even if you send the same tone, one shifted in phase by a known amount, getting the two to cancel each other out is non-trivial.

You might think that this was all a complete waste of time and if you're just driving past it looks like a swollen electrolytic capacitor about to burst your bubble, but it's not that bad.

Here's what I learned from this little adventure.

I can make hierarchical blocks out of flowgraphs. This is important because at some point all the functionality associated with Bald Yak will likely end up being implemented like this. I also learned that such a block can contain user interface elements, which means that we can build blocks that know how to do stuff and tweak how they operate without having to build a user interface every time we use such a block.

I learned that we can implement an idea that would be hard using physical components and test it really quickly, in this case my available time was the limiting factor, not the testing. If I'd done this with components I'd still be trying to figure out where to get them from, let alone turn up the heat. Another bonus is that I didn't spend a single dime and I can dispose of it with the click of a button, rather than trying to figure out how to recycle components and circuit boards.

I also learned that the idea as I built it doesn't work quite as I expected and that things that I didn't anticipate, like changing the frequency, buffer under-, and over-runs, impacted my efforts in unexpected ways. There's a delay between making a change on the user interface and the effect becoming audible, and I learned I can make a dongle work on my computer and that installing GNU Radio is a challenge at the best of times.

In other words, even though I'm unlikely to use the noise cancelling efforts in their current form, there was plenty I learned from the experience.

From my perspective, this was a success. What have you experimented with and learned?

On a completely unrelated matter, long overdue, and music to the ears of some, can you spell SKCC, I've finally put all the Morse Code versions of my podcast on a thumb drive and plugged it into my car. During the week I've managed to listen to about two hours of Morse. While I don't know most of the letters of the alphabet, I can still detect letter and word boundaries.

I'm Onno VK6FLAB

Foundations of Amateur Radio

As you might recall, recently I stumbled on an excellent list of 52 weekly challenges put together by Fabian, DJ5CW and friends. You can find it at hamchallenge.org. As I've previously mentioned, it contains activities right across the amateur spectrum, from designing a QSL card to making a contact on 80m or 160m, with everything in between. It's an excellent tool to set a weekly goal to achieve and I recommend that you have a go.

It's not the only interesting tool around.

Amal VU3FTH and Steph Piper, whom you might know as MakerQueen AU, have put together an "Amateur Radio Skill Tree". It's a collection of hexagonal tiles, each with a skill, displayed together in an attempt to track what you know and could know about amateur radio. The idea is that you print it out and colour in each tile as you complete it. You'll find things like "Explore D-Star", "Build a cw key", "Teach a friend about Amateur Radio", and plenty more. Can you get four activities in a row and which skills could do with more effort? There are 68 tiles ready for your colouring pencil .. Bingo!

The Radio Amateur Training Planning and Activities Committee, better known as the RATPAC, put together an "Amateur Radio Challenges Checklist for 2025" and published it on mastodon.radio. It's a list of bands, modes, activities, builds and clubs that help you track what you've been up to throughout the year. While we're here, I should mention that the RATPAC in their words "comprises Amateur Radio Operators of a wide variety of backgrounds and experiences", and hosts two weekly Zoom meetings so anyone can participate in the talks published on the ratpac.us website. If you're unable to attend, you'll find the presentation on YouTube.

Over the years I've been part of this amazing hobby, I've been telling anyone who will listen that there is plenty to do and see in our community, a thousand hobbies in one. The tools I've mentioned represent around one hundred and fifty activities and pursuits, but hidden behind each one is plenty to explore. For example, hamchallenge asks you to spend week 21 creating a GNU Radio flowgraph. That topic alone could fill a decade worth of exploration if you were so inclined. Similarly, one of the Skill Tree tiles is "Study RF propagation", something which you might realise is easier said than done. The RATPAC checklist has a tick box for "Work 100 countries", not something you're likely to achieve in an afternoon.

My point is, you can do as much or as little of this as you like, to what ever degree floats your boat. As you might know, I'm deep in the weeds with GNU Radio and I expect to stay there for plenty of time to come, but you are under no obligation to follow me down the rabbit hole. In other words, it interests me, but it might not do the same for you.

One final comment. None of these activities require you to upgrade your license, well, other than the Skill Tree tile "Upgrade your radio license". You can do most if not all of the activities I've shared with any amateur license and plenty of it can be done without a license at all.

So, what are you waiting for?

I'm Onno VK6FLAB