Foundations of Amateur Radio

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The evolution of software in radio ... Feb 05, 2023

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Foundations of Amateur Radio

The amateur community is nothing if not entertaining. Look at any discussion about a mode like FT8 and you'll discover people who describe it as the dehumanising end of the hobby. In the same thread you'll find an amateur who's been licensed longer than I have been alive who welcomes it using words like revitalising, more active, and the like.

If you're not familiar, FT8 is one of many weak signal digital modes that gained popularity over the past years during the most recent solar minimum when long distance HF propagation was challenging.

That example discussion was about the visible end of a mode like FT8, but there's an often overlooked all but invisible aspect of these modes that is much more significant, namely the popularisation of signal processing in software.

In many ways amateur radio is more about receiving than transmitting. This might not be obvious, but what's the point of transmitting if you cannot receive? Using software to do the listening makes for an interesting evolution that might be hard to grasp if I start digging into the fundamental algorithms that make this happen, instead let me describe a process that is easier to explain.

Imagine that there's a piece of software that knows how to decode digital signals. As the user of that decoding software, or decoder, you send audio into one end and callsigns and grid-squares come out the other end. How it does this isn't important right now.

We measure the quality of this decoder by how many times it correctly does this, in other words, how many times a correct callsign and grid-square comes out. The decoder can be improved by changing the way that the decoding process works. If the number of correct callsign and grid-squares that come out increases, the quality of the decoder is improved.

Now imagine that the decoder spits out the callsign 7N5EC with the grid-square OF78. This particular combination emerged as a WSPR decode on the 10th of December 2022. It was reported by AA7NM as a 100 Watt signal, 14,882 km away on the 40m band. The signal report was -30 dB.

If you know where OF78 is, you'll immediately spot a potential problem, if not, I'll help you out, OF78 is located near Perth in Western Australia. It's unlikely that a transmitted callsign in that part of the world starts with anything other than VK6. Mind you, a weather balloon with an odd callsign could theoretically be overhead in that location, but I've not yet heard of a 100 Watt transmitter on 7 MHz that someone hung from a weather balloon.

Another problem is that 7N5EC is a callsign that appears to be Japanese. It starts with 7N which is part of the Japanese callsign block, but the next symbol is the number 5 and at least according to the research I was able to do is not actually a currently valid callsign. The prefix 7N4 is allocated to the Kanto region on Honshu island, the largest island in Japan. 7N5 doesn't seem to be valid as a prefix. Ironically, that callsign will now exist on the Internet as soon as this article is published, but that's a whole other problem.

Either way, the chances of the combination of the callsign 7N5EC with the grid-square OF78 is unlikely to be correct. It gets even less likely if you consider that the callsign was reported only once in fifteen years and over 500 million WSPR decodes, I checked.

That means that if you updated the software to ignore that particular decode, you'd have improved the decoder by removing an incorrect combination. You could keep doing this by checking callsigns against grid-squares and against allocated callsigns and you'd have made a higher quality decoder.

Before you start arguing that this isn't fair, it's exactly the same process as the super check partial list does for people operating in a contest. The idea being that if you only recognise known contesting callsigns, you've got a better chance of making contact.

Think of it as a way of filtering out potentially incorrect callsigns. It still leaves the operator having the option to ignore the suggested callsigns and listen to what's actually coming in.

I realise that this is not how you would realistically improve a digital signal processing decoder, but it's an example of how changing the software can change the quality of a decoder and that was the point of this example. In reality you'd attempt to discover how this decode happened and what caused it to be wrong.

If you want to consider a more signal centric example, consider a decoder that starts with a first attempt at making a decode. With a single decode, it can then remove that known signal from the original audio and start another decoding cycle. You can repeat this as many times as you want until you end up with gibberish. Essentially this is an example of how a modern decoder can improve its performance.

This is why signal processing in software is so powerful and important and why FT8 and the rest of the digital firmament are here to stay. I should point out for those wondering, FT8 and WSPR are examples of simple messages, but there's nothing stopping us from using digital messages like this to exchange little bits of audio, or video, or something else. It's how mobile phones work today and at some point amateur radio is going to extend the envelope and come up with the next thing, it always has.

So, FT8, it's changing amateur radio, but not because we're glued to a screen having our computer talk to another one, but because it represents digital signal processing in software and it's just the beginning.

I'm Onno VK6FLAB

Path loss and very small numbers ... Jan 29, 2023

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Foundations of Amateur Radio

Sometimes you learn mind boggling things about this hobby, often when you least expect it. Recently I discussed having my 20 mW WSPR or Weak Signal Propagation Reporter beacon heard on the other side of the planet, in Denmark, 13,612 km away. That in and of itself is pretty spectacular, but it gets better if you consider just how weak the signal was by the time it got there.

In radio communications there is a concept called path loss or path attenuation. Until recently I understood this to mean the things that impede a signal getting from transmitter to receiver. That includes coax and connector losses, refraction across the ionosphere, reflection off the surface of the planet and diffraction around objects.

It turns out there is another factor called "Free Space Path Loss" to consider. It's loosely defined as the loss of signal strength between two antennas. The name sort of implies that something happens to the signal in free space, which is odd if you know that in space, radio waves, regardless of frequency, travel without loss and will travel pretty much indefinitely.

So what's going on?

To get started, think about a dome lawn sprinkler, one of those little round discs that sits on the ground with the hose connected to the side. You turn on the tap and the water sprays in all directions. If you're really close to the sprinkler when the tap is turned on you'll get sopping wet almost immediately, since most of the water will hit you directly. This is particularly fun in the heat of summer on New Years Day in Australia, not so much in the middle of winter on the other side of the globe.

If you stand a couple of meters away, you'll still get wet, eventually, but it will take much longer, because most of the water isn't hitting you. If you stand even further away and assuming the water still gets that far, it will take even longer.

A small towel and a big towel will both take the same length of time to get wet if they're held at the same distance from the sprinkler, but if you wring them both out, you'll discover that the big towel captured much more water during the same time.

In radio communications we can combine these two ideas, the distance and the size of the receiver, to describe free space path loss.

The further away from the transmitter you are, the less signal is available to you to capture since much of the signal is not heading in your direction and the bigger your antenna, the more signal you receive. The bigger the antenna, the lower the frequency, which is why you'll discover that free space path loss is dependent on both distance and frequency.

To give you an idea of scale, the free space path loss for 28 MHz over 13000 km is about 144 dB.

While the name "Free Space Path Loss" implies loss of signal across the path in free space, the loss is not due to distance as such, rather it's caused by how much the signal is spread out in space. Similarly, there isn't more loss because the frequency is increased, it's that less signal is captured by the smaller size or aperture of the antenna required for a higher frequency.

So perhaps a better name might be Spherical and Aperture Loss, but then everyone would have to learn how to spell that, so "Free Space Path Loss" it is.

I'll point out that this is the minimum theoretical loss, in reality the loss is higher than this, since it also includes all the other parts of the path loss which are things that we can control, like coax and connector loss, and things we can improve by frequency selection, like ionospheric reflection and refraction which depend on solar conditions.

The one aspect of path loss that we have no control over is the "Free Space Path Loss", so perhaps that's why we don't talk about it very much.

I'll mention that in path loss calculations often antenna gain at the transmitter and receiver are used to reduce any path loss figures. If I have an antenna with 6 dB gain, then that reduces my overall path loss by 6 dB, which is why we spend so much time and effort figuring out what antenna to use when we get on air to make noise.

I mentioned that the free space path loss for my beacon between Australia and Denmark was about 144 dB. This means that my 20 milliwatt signal arrived in Denmark as a -131 dBm signal. That might not mean much, but that's the equivalent of about 80 attowatts. If you're not sure how big that is, 1 milliwatt is 1 quadrillion attowatts, a 1 with 15 zeros. Said another way, 1 watt is 1000 milliwatts, 1 milliwatt is 1000 microwatts. 1 microwatt is 1000 nanowatts, 1 nanowatt is 1000 picowatts, 1 picowatt is 1000 femtowatts, 1 femtowatt is 1000 attowatts.

It might come as a surprise, but these numbers are not unusual. Don't believe me? When your radio shows an S0 signal on HF, it is defined as -127 dBm, so we deal with tiny numbers like this all the time, we're just not quite aware of it on a daily basis.

Remember, my numbers are theoretical only, to give you an idea of scale. In reality everything in the path between the transmitter and receiver affects what ends up at the other end and might make the difference between hearing someone, or not.

I'm Onno VK6FLAB

What is the difference between handheld, mobile and a base radio? Jan 22, 2023

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Foundations of Amateur Radio

If you've ever been in the market for a new radio, and truth be told, who isn't, you'll find yourself faced with a bewildering array of options varying from obvious to obscure and everything in between. At the obvious end of the scale are things like price, bands and transmit power and at the other end are things like Narrow Spaced Dynamic Range, which you'll find explained by Rob NC0B on his sherweng.com website where he's been publishing receiver test data for many decades.

One of the more subtle options you'll need to consider are handheld, mobile or base radio.

This is harder than you might think, since radios are increasing in functionality every time you wake up and if you look long enough, you'll discover that they're getting smaller at the same rate. Once upon a time you could just look at the size of a radio and define it as belonging in one or other category, but that's no longer a useful distinction. For example, my PlutoSDR is a tiny device, fits in my pocket, but there's no way I'd consider it a handheld, or even a mobile radio.

You might think that a bigger box has more stuff inside, costs more and performs better.

For example, the Drake R-4C receiver and companion T-4XC transmitter require external power and were once rated by the ARRL as very good. In reality the Drake R-4C performed terribly in a CW contest, incidentally, that was what caused Rob to start testing radios in 1976. That receiver and transmitter manage to cover 80m, 40m, 20m, 15m and 10m and together weigh in at 14.3 kg. They're considered a base radio.

The Yaesu FT-817, runs on batteries, weighs in at just over a kilogram and can be carried with a shoulder strap. It comes as a single device and covers many more bands than the Drake transmitter and receiver do, it would be considered a mobile or even portable radio. Obviously it would be hard to jam a Drake into your car or strap it to your belt, but does that mean that you cannot use an FT-817 as the base radio in your shack?

In case you're curious, the slightly beefier brother to the FT-817, the mobile FT-857d, is sitting on my desk as my current base radio. Has been for years.

So why do manufacturers continue to make this distinction between handheld, mobile and base radio? One look at the nearest radio catalogue will tell you that it's not based on either performance or price, not even close. You can buy a handheld with more functionality for the same price as a mobile radio and that same is true when you compare a mobile radio to a base radio.

Radios vary in price from $20 to $20,000. A cynical person would suggest that pricing is based around extracting the most money from your pocket, but a more charitable explanation might be that physical size dictates things like the number of buttons you can fit on a radio, how many connectors can be accessed before the radio flies off the desk from the weight of the coax hanging off the box, how big is the display and other such limitations.

I'm not being glib when I use the word charitable, since much of modern transceiver design revolves around software which can pretty much fit in any box. Using external computers, neither buttons nor a display are needed, leaving external connectors, which if we're being really honest could all fit in a box that would fit in your pocket.

At this point you might wonder if handheld, mobile or base has any meaning at all. As I said, in most cases it doesn't. There's really only one place left where this matters, and that's when you have access to strictly limited space and power if you need to put the radio in your pocket or cram it into your car.

For your home shack, the distinction is unhelpful for most, if not all, amateurs.

Don't believe me? The Yaesu FT-710 currently ranks fourth on Rob's Sherwood Engineering Receiver Test Data List. It's a quarter the size of the top radio and it's sold as a "Base/Portable Transceiver". Yaesu calls it "Compact". It might not fit in the dashboard of my car, but it will fit on the folding table we use during field days.

That isn't an exception either. The Elecraft KX3 is the smallest radio on the first page of Rob's Receiver Test Data list. It fits in your pocket.

Before you start collecting statistics for each radio, I should point out that the more you know about this hobby, the harder this process becomes, so be careful. That said, if you have a massive list of anything to choose from, a new amateur radio, pet food, car, what to have for dinner, whatever, here's a process that will guarantee a result.

It works by eliminating one item at a time until you're left with your preference.

To start, grab the first two items on your list and pick the best one between the two. Ignore everything else, just those two items. You're going to fret about the definition of "best", but don't worry, since every time you do this, you'll have a different idea. All you're doing is saying, all things being equal, between these two options, which one do I prefer. No need to describe why, just pick one. In picking one, you've removed one option from the list.

Now, compare the winner to the next item on the list, again, ignore everything else and pick one and remove the other. Keep doing this until you run out of items. You'll end up with the single option that wins, for whatever reason, from the entire list.

Now, about that radio. All I need is the next paid project.

I'm Onno VK6FLAB

What should we be learning? Jan 15, 2023

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Foundations of Amateur Radio

It's an immersive effort to create an article every week, so much so, that I've only just discovered that I passed the 600 article mark some time ago. I'd open up a bottle of something celebratory if I thought it warranted the effort, but I'd rather talk about amateur radio and what I've learnt since becoming licensed in December of 2010.

This hobby, this community, the activity of amateur radio keeps surprising me in unexpected and exciting ways. I know that there is a part of the community that thinks of this as a dying hobby, but with every fibre in my being I know this to be wrong. We explore, test, build and learn at every opportunity. Put any two amateurs in contact with each other, either physically or over the air and you'll soon witness an exchange of ideas, of things that bring joy, hints of the next thing and the next.

The inspiration for my writing comes from all manner of places. For example, here's an opinion recently shared by someone on social media:

"Basic antenna modeling using software should be included in ham radio licensing exam syllabus if it's not currently." [sic]

As opinions go it's one of the tamer ones I've come across, but it's not unique in any sense of the word. I've heard it described bemoaning the missing knowledge of new digital modes or the need to upgrade my license, or the idea that the introductory license should come with a fixed expiry date. You might have heard similar ones, phrased along the lines of a missing attribute that new licensees should be required to learn or know about before they can call themselves amateurs.

It's also completely unhelpful.

Let me explain why.

I'll start with an analogy. When was the last time your driver's license expired because you didn't upgrade it due to new road rules, new vehicle types, new car accessories or speed limits? In case you're confused, the answer is: never.

Does amateur radio cause death and mayhem in the community? No.

Do cars?

So, in the scheme of things, even if amateur radio can be used to help save lives, it's not an activity that's generally considered life threatening. You could argue that radio amateurs could cause life threatening interference, and technically they can. So can any user of any piece of radio equipment, CB radio, mobile phone, Wi-Fi, you name it. Even a half asleep electronics student in their first year of high-school could do this. The skill isn't specific to radio amateurs.

So, what is this about, the requirement for antenna modelling, or some other missing skill, and why does our community keep getting flooded with such, frankly, nonsense?

In my opinion, it's the same phenomenon that laments the loss of Morse code, the fact that we lost the 11m band, that we're playing with FT8 instead of AM, that we prefer integrated circuits to valves. The world is a flowing feast and amateur radio is along for the ride. Stand still and the world moves on.

Should amateur radio licensing change?

Absolutely!

It should move with the times. It should lower the barrier to entry at every opportunity. It should explore the possible, not the requirements of a select group of people who decry the dumbing down of the hobby and want to pre-load every license exam with things that are absolutely irrelevant to the turning on of a radio and making noise.

Will amateurs benefit from knowing that antenna modelling software exists? Sure they will. Just like they'll benefit from knowing about valves and Morse code. That doesn't mean that they should be part of the exam process. I want new amateurs, no, all amateurs to be curious, to ask, to discover, to explore and to want to know stuff, not because it's a requirement to get a license, but because it's beneficial to their amateur journey.

Every week I come up with a different way to look at our hobby because this hobby is so divers. I've used the phrase a 1000 hobbies in one. So far I've just scratched the surface, some 600 weeks in. We'll see where we're at when I've held my license for another decade or so.

So, have at it. What is missing from the current exam and why should it be included?

I'm Onno VK6FLAB

Where does propagation data come from? Jan 08, 2023

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Foundations of Amateur Radio

One of the many questions that new amateurs ask is, "When should I get on-air, and on what band?" The often-heard reply is just to get on-air and make some noise. As time goes by, the importance of this seems to fade in favour of using HF prediction tools. Some amateurs never venture beyond that point, relying almost exclusively on technology to determine if they should turn on their radio or not.

If you search the internet for "current HF conditions", you'll end up with dozens of sites boldly claiming to provide precisely that information, some even using the label "Real-Time". You'll find instructions from countless self-proclaimed "experts" on how to read propagation conditions from their favourite site. There's even widgets that you can install on your website displaying propagation data per amateur band with helpful labels like "Band Closed" or showing conditions as "Poor", "Fair" or "Good". Some of these widgets even include an embedded time-stamp to prove just how "current" the information is.

If that's how you decide to activate your amateur station, like I once did, I have some questions.

Where is this information coming from, is it accurate, and when was it last updated?

To give you an idea of just how complex this question is, consider visiting two popular websites, solarham.net from Canada and spaceweatherlive.com from Belgium. On their home-pages, you'll find all manner of numbers, charts, photos, events, notifications, alerts, and warnings, each related in some way to HF propagation and the condition of the Sun.

Sounds great, excellent resources, job done.

Well, no.

Let's start simple. Location.

Leaving aside where the site's owner is or where the servers are, both potential sources of confusion, consider where you are and where the remote station is that you're trying to contact. Now compare that with the propagation data location. Do you know where the measurements came from and if they're relevant to you?

What about data currency?

For example, if you can see the Sun, you can count the number of sunspots since that data comes from physically looking at the Sun. Mind you, can someone count the number of sunspots at night? It's not a trick question. The Sun isn't overhead for everyone all the time, and the data from any particular observer will be out of date at night. When was the count updated? Is it still actually current, let alone real-time? Obviously, not everyone uses the same data source either.

In case you're wondering, why are we counting by eye in the space age? It turns out that, since Galileo more than 400 years ago, it's the most long-term, reliable way to keep data consistent between observers and instruments, both of which often last only one or a few solar cycles, and it's also cheap!

What about equipment changes and failures in data gathering?

Geomagnetic activity isn't global; it's measured using a device called a flux-gate magnetometer. Measurements from specific instruments scattered around the globe are combined into the planetary, or Kp index. You'll discover that locations used change over time, and when instruments are down, the numbers are estimated, but you won't see that unless you actually find and explore the source data.

It's not just solarham.net and spaceweatherlive.com; it's pretty much every single site that shows any form of HF propagation or space weather information. Even sites based in a specific country, like the Australian Space Weather Service, have many instruments scattered around Australia. If you happen to be near an actual instrument, where "near" is anything less than 500 km away, how do you know if that instrument was actually online when a measurement was made?

Even if the instrument near you is working, is the data relevant to the receiving station on the other side of the planet?

If you look closely at the sites giving out current HF conditions, you'll discover that most of these don't even tell you where the data comes from, let alone if any of it was estimated to come up with their current reported values or recommendations.

If you start searching for historical information, this problem gets bigger. You'll find many sites that claim to have data, but are invariably underfunded, are rife with broken links, out-of-date servers, and moved, deleted, and abandoned pages. If you unearth a dataset, you'll discover that everyone uses a different standard to record their measurements.

How do you even know if combined measurements are coming from the right column? Think I'm kidding? There are documents with warnings about different formats, calculations, and dates on which these changed. Aggregating this data is challenging, at best.

So, is there a better way?

Yup. You're not going to like it. "Get on-air and make noise!"

I can hear you groaning from here. It's not all bad. You can run your own beacon to see the conditions at your location. It's what started me down the path of installing a WSPR, or Weak Signal Propagation Reporter, beacon and leaving it running 24/7. Currently, I'm focused on very weak, 10 mW signals. So far, it's been reported 3,685 km away.

If you visit the VOACAP or Voice of America Coverage Analysis Program website, you'll find a visualisation of how FT8 propagation worked between ITU zones between 2017 and 2019. It's not current, but it's an excellent way to see how propagation data can be derived from actual contacts.

What we really need are more beacon transmitters and online receivers.

I'm Onno VK6FLAB.

What's the weakest signal that WSPR can decode? Jan 01, 2023

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Foundations of Amateur Radio

In 2016, Daniel EA4GPZ, documented how to discover the weakest signal that could be decoded using several weak signal modes, including WSPR, or Weak Signal Propagation Reporter. This is an interesting question because as you might recall, I've been experimenting with very weak signals coming from my shack. To date, my 20 milliwatts has been heard over 13 thousand kilometres away.

When you tune to a weak station you'll often hear both the station or desired signal as well as interference or background noise. The stronger the signal, the less noise you perceive. The weaker the signal, the more noise. You can express the relationship between the power of these two, the signal and the noise, as a ratio. If the power levels are the same, the so-called signal to noise ratio or SNR is 1:1. A higher ratio, like 2:1, indicates that the power of the signal is higher than the noise and a lower ratio, like 1:2 indicates that the signal is lower than the noise.

If you express this ratio in decibels, you'll end up with positive numbers where the signal is stronger than the noise and negative numbers where the signal is weaker than the noise and zero when they're the same. If I tell you that the signal report for my WSPR decode from Denmark was -28 dB, it means that the noise was much stronger than the signal.

For today I'm going to leave alone just how WSPR can report a negative signal to noise ratio and still successfully decode the signal, even though the signal appears to be buried in the noise.

That said, in this experiment, we're trying to learn something else. Using the technique detailed by Daniel, we test using different, known, signal to noise ratios to discover at what point the WSPR decoding process breaks down. This might help me understand if I can reduce my beacon output power even further and still anticipate a good chance of being decoded successfully.

To conduct his experiment, Daniel used the then current version of WSJT-X, version 1.7.0-rc1 and I'm using the current version today, 2.6.0-rc5 to repeat those tests. You might ask why I'm not taking Daniel's word for it and just using his findings. The process to decode a WSPR signal is all software and can be improved with better methodologies and algorithms. It's not unreasonable to think that in the years since Daniel's experiments things have changed, hopefully improved.

So, how does this work?

If you generate and attempt to decode one hundred different files, you can use the number of times that you count your callsign in the decode list as a percentage of success. If all of your files decode properly, the decode percentage is 100%. If only half of them are decoded successfully, it's 50% and so-on.

Similarly, if a different callsign, locator or signal power is decoded, you can count those as a percentage of false decodes. This is important because noise coming from the ionosphere can corrupt any signal. I should point out that because we know in advance what the decoded signal should be, since we created the message, we can actually count the ones that don't match what we sent. In the real world it's very hard, if not impossible, to do this, unless each transmitter also starts recording their efforts so data cleaning can be done after the fact.

A false decode happens when the software decodes a message and the result is not what was sent. Due to the way that WSPR works, this is not a case of a single character error and as a result the whole message is corrupt, wrong callsign, wrong grid square and wrong power level.

Just how prevalent this issue is, has to my knowledge so far not been discussed. Over the past year I've been working with the entire WSPR data set, nearly 5 billion reports, and mapping the data to explore just what's going on behind the scenes. Based on the raw data every single grid square on the planet has been activated. Of course this is not really the case, since there's plenty of parts on Earth where we haven't yet turned on a WSPR beacon.

Back to our experiment.

Two tools are used, "wsprsim" to generate an audio file and "wsprd" to decode it. Both come with WSJT-X and when you build the application from source, you get them as part of the process. The generator takes several parameters, one of which is the desired signal to noise ratio. If you ask it for a signal to noise ratio of -20 dB, wsprsim will generate the appropriate noise and the desired signal, combine them and build an audio file. You can then use wsprd to decode that file. If you repeat this many times, you end up with some data.

How many times?

Well, I probably went a little overboard. I generated a set for each SNR reading between 0 and minus 50 dB in 0.01 dB increments and then generated one hundred for each of those. At the point where the process broke down I doubled the resolution further to get a better idea of what was going on. About three quarters of a million tests. It took a while.

What did I learn from this?

First of all, false decodes happen at every signal level. I saw the first false decode at a signal to noise ratio of -0.07 dB. This is significant because it means that even at excellent signal levels there is a percentage of incorrect reports which explains why I'm seeing that result in real world data. When you start playing with really big numbers, even if the error rate is low, with enough data, it starts to matter. In my tests I saw an error rate of 0.03%. This means that there's at least 1.5 million false decodes in the current WSPR data set, likely more because wsprsim cannot emulate the real world of ionospheric and local noise.

On the flip-side, I also saw an overall success rate of nearly 94%. At -29 dB things start to change. Until then the decode is 100% successful, then it starts to decline to 0 at about -34 dB. Comparing Daniel's results directly, he saw 34% success at -30 dB, I'm seeing 95% at that same noise level. At -31 dB Daniel saw 6%, I'm seeing 75%. I don't see 34% until we get down to -31.6 dB and 6% at -32.4 dB. This indicates that the software has improved over the years.

It also means that with a signal report of -28 dB from Denmark, I've got a few dB to play with. I've now reduced my output power by another 3 dB, making it 10 mW. Point your antennas at VK6 and see what you can hear on 10m.

I'm Onno VK6FLAB

One Volt ... Dec 25, 2022

Show notes

Foundations of Amateur Radio

Have you ever asked yourself a question that turned out to be a rabbit hole so deep you could spend a lifetime exploring and likely never come out the other end?

I did. Yesterday.

What's a Volt?

This came about when I started exploring how to measure the power output of my WSPR or Weak Signal Propagation Reporter beacon. According to the specifications the output level is 23 dBm or 200 milliwatts.

If you read the fine print, you'll discover that the power output actually varies a little depending on which band you're on, for my specific transmitter it says that the output on the 10m band is 22 dBm, or 158 mW.

That comes with a disclaimer, that there can be some variation on individual transmitters of about 1 dB. So, on 10m, my output could vary between 21 and 23 dBm, or between 125 and 200 mW. With my attenuator connected, the output could be between 12 and 20 mW, and that's assuming that my attenuator is exactly 10 dB, it's not.

Measuring anything means to compare it against something else. To give you a physical example. If you look at a tape measure, the distance between the marks is determined in the factory. The machine that prints the lines is configured to make the lines just so. In the factory there will be a specific master tool that determines how far apart the lines are in that factory. That tool is called "the standard". The process of lining up the standard with the machine making the lines is called "calibration".

If you build a house on your own with just that tape measure, everything should work out fine, but if you have a mate help you and they bring their own tape measure, from a different factory, their lines might not quite match yours and the fun begins.

If you don't believe me, as I've said previously, pull out all the tape measures and rulers around your house and see just how much variation there is.

In my house, well, my CNC, there's a standard that came with my micrometer kit. It specifies physically how long 25mm is. I also have a 50mm and a 75mm standard. When I compare the 75mm with the 50mm and 25mm together, they're the same within one hundredth of a millimetre. It's likely that it's better than that, but I'm still learning how to hold a micrometer and not have it overheat and stretch while I'm measuring. Yes, temperature changes the size of things.

The point is, in my CNC world, my current standard sits in my micrometer box. At some time in the future I might want to improve on that, but for now it's fine.

The standard that I have was at some point calibrated against another standard. That standard was in turn calibrated against another standard and so-on. Eventually you end up with an SI unit of 1 meter as defined by the International System of Units. In case you're wondering, it's defined as the length of the path travelled by light in vacuum during the time interval of one second. One second is defined in terms of the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom. I know right, runs right off the tongue. I can't help myself, that frequency is 9,192,631,770 Hz.

Oh, this system is also subject to change. In 2019 four of the seven SI base units were redefined in terms of natural physical constants, rather than relying on a human artefact like the standard kilogram. This is an ongoing process. For example, in 1960, the meter was redefined as a certain number of wavelengths instead of a physical bar in a vault in Paris and there was also not just one bar, there were 30. National Prototype Metre Bar no. 27 made in 1889 was given to the United States and served as the standard for defining all units of lengths in the US between 1893 and 1960 - yes, perhaps surprisingly, the USA is metric, really. One inch used to be defined as "three grains of barley, dry and round, placed end to end lengthwise" but since 1959 is defined as exactly 2.54 centimetres or 0.0254 meters.

Back to power output on my beacon transmitter. Assuming for a moment that I had an actual tool available to measure this, I'd still be comparing my tool against another standard.

Let's imagine that I could measure the power output of my beacon with an oscilloscope. When the oscilloscope says 1 Volt per division. How do I know that it really is? If you start reading the calibration steps, you'll discover that they state that you need to connect your scope to a reference, another word for standard, and that's if you're lucky. Some documents just wave their hands in the air and say something like "push the auto calibrate button".

The Volt is defined as the electric potential between two points of a conducting wire when an electric current of one Ampere dissipates one Watt of power between those points. The Ampere definition involves counting elementary charges moving in a second. It's in the order of a 10 with 19 zeros. Not to mention that there's also a definition of how much an elementary charge is. You get the point, this is a rabbit hole.

So, now let's pretend that I have a calibrated oscilloscope. Let's say that our oscilloscope is calibrated within 1 dB. Cool. So I plug in my beacon and measure, what?

I'll end up with a reading, that's plus or minus 1 dB of "reality". In my case, perhaps I read 22.5 dBm. That means that it could be as low as 21.5 dBm or as high as 23.5 dBm, or between 141 and 224 mW. So, it's within specifications, great, but I don't actually know what the actual output power is.

Another way to look at this is to use a measurement to determine if the power is within specification or not. I'm guessing that Harry already did that test before he put my beacon in the box and shipped it to me.

Long story short, I'm no closer to knowing just how much power is coming out of my beacon, but I'm still working on finding a friend with a calibrated tool that might give me something a little more precise than fail or pass.

You know that there's a saying about turtles all the way down? I think it's rabbits myself.

I'm Onno VK6FLAB

Which way did it go? Dec 18, 2022

Show notes

Foundations of Amateur Radio

Propagation, the art of getting a radio signal from one side of the globe to the other, is a funny thing. As you might know, I've been experimenting with WSPR or Weak Signal Propagation Reporter and for about a year running a beacon on 10m. Out of the box my beacon uses 200 mW to make itself heard. I couldn't leave well enough alone and I reduced the output power. Currently a 10 dB attenuator is connected to the beacon, reducing output to a notional 20 mW. I say notional, since I haven't actually measured it, yet.

With so little power going out to my vertical antenna, a homebrew 40m helical whip, built by Walter VK6BCP (SK), and tuned to 10m with an SG-237, it's interesting to discover what's possible.

Last night my signal was heard in Denmark. Picked up by Jorgen OZ7IT, 13,612 km away. That report broke another personal best for me, achieving 680,600 kilometres per Watt. I was stoked!

I shared a screen-shot of my report with friends. One friend, Allen VK6XL, asked a very interesting question. "What makes you think it was short path?"

Before I go into exploring that question, I need to explain. If I was to fly from Perth to Sydney, the popular way to travel is across the Australian Bight, over Truro, north of Adelaide, clip the northern tip of Victoria, over the Blue Mountains to Sydney. The distance is about 3,284 km. This route is known as the great circle route, more specifically, the short great circle route.

It's not the only way to travel.

Instead of heading East out of Perth, if I head West, I'd fly out over the Indian Ocean, Africa, the Atlantic Ocean, the Americas, the Pacific Ocean and finally arrive at Sydney. That journey would also follow a great circle route, the long great circle route. It's about 37,000 km long. You might notice that I wasn't very specific with either the path or distance. There's a reason for that. None of the tools I've found actually provide that information, other than to point out that the entire circumference of the planet is about 40,000 km and that it's not uniform since Earth isn't a perfect sphere.

You might be asking yourself at this point why I'm spending so much energy worrying about taking the long way around and how that relates to my 20 mW WSPR beacon.

In amateur radio we refer to these two travel directions as the short-path and the long-path.

Radio signals travel along the curvature of Earth bouncing between the Ionosphere and the surface. How that works exactly is a whole different topic, but for the moment it's fine to imagine a radio signal skipping like a stone on water. As a stone skips a couple of things happen. If the angle at which it hits the water is just right, it will continue on its journey, get the angle wrong and you hear "plop". Every skip is slightly lower than the previous because the stone is losing a little bit of energy. Every time the stone touches the water it creates a splash that ripples out in a circle from the place where the rock hit. These ripples also get weaker as they increase in diameter. Consider what happens if you skip a rock across concrete or sand instead of water and if you really want to geek out, there's also wind resistance on the rock.

A complex equivalent dance affects a radio signal when it propagates between two stations. For success, enough radio energy needs to reach the receiver for it to be decoded. For our signal to make it to the other side of the globe it must bounce between the Ionosphere and Earth's surface. Every bounce gets it closer to the destination. Each time it loses a little bit of energy. This loss happens at the Ionosphere, at the surface and in between through the atmosphere.

To give you a sense of scale, my signal report from Jorgen in Denmark was -28 dB. It started here in Perth as 13 dB, so we lost 41 dB along the way. We're talking microwatts here. I'll note that I'm avoiding how this is exactly calculated, mainly because I'm still attempting to understand how a WSPR signal report actually works since it's based on a 2,5 kHz audio signal.

As I said, enough energy needs to make it to the receiver for any of this to work.

There's an assumption that less distance means less energy loss. It's logical. A shorter distance requires less hops and as each hop represents a specific loss, less hops means less loss.

But is that really true?

There's nothing stopping my beacon signal from taking a different route. Instead of travelling the short-path, it can just as easily head out in the opposite direction. Theoretically at least, my vertical antenna radiates equally in all directions. The long-path is mostly across water between Perth and Denmark. What if hops across the ocean were different than hops across a landmass? Turns out that they are in several ways. For example, there's less energy loss in a refraction across the ocean, how much less exactly is still being hotly debated. Much of the data is empirical at the moment.

It gets better.

What if I told you that the report was near to sunset? At that time there's a so-called grey line phenomenon related to how the sun stops exciting the Ionosphere and how different layers of the Ionosphere start merging. As a result the angles of refraction across the Ionosphere change and longer hops are possible.

What if the long-path took less energy to get to Denmark than the short-path did?

Would Jorgen's decoder care?

If that's the case, my signal didn't travel 13,612 km, it travelled twice that and I'd have well and truly cracked a million kilometres per Watt.

So, is there a way we could know for sure?

Well, yes and no.

For starters we'd need beacons that transmit at a very precise time. Then we'd need synchronised receivers to decode the signal. A signal travels 3,000 km in a millisecond, so we're going to need something more precise than the timing set by NTP or the Network Time Protocol used by your home computer. If we used GPS locked transmitters and receivers we'd be working in the order of 50 nanoseconds and be in the range of 15m accuracy.

That would allow us to calculate the physical distance a signal travelled, but that's not the whole story.

What happens if your signal travels all the way around the globe, or if some of it reflects back, so called back scatter, like the ripples from a stone coming back towards you, and that signal travelling back past you to the receiver? There's endless variation, since the planet isn't round with a flat surface nor is the Ionosphere.

So, do we know if my report was a long-path or a short-path? Not really. Based on the time of day, there's a good chance that it was a long-path report, but only if we actually measure the delay between send and receive will we have data to make a better assurance than "possibly" or "probably".

As I started, propagation is an art.

I'm Onno VK6FLAB

Morse is dead ... long live Morse! Dec 11, 2022

Show notes

Foundations of Amateur Radio

One of the oldest means of electronic messaging is Morse code. Developed by Alfred Vail and Samuel Morse and sent for the first time on the 24th of May 1844, Morse code changed the way we communicate.

For nearly a century it was required to become a licensed radio amateur until in 2003, the International Telecommunications Union or ITU left it to the discretion of individual countries to decide if a budding amateur needed to demonstrate their ability to send and receive in Morse. With that decision many thought that the end of Morse code was only a matter of time.

They were wrong.

Turns out that use and progress of Morse code continues at a surprising rate. Searching for scholarly articles on the subject, you'll discover that it's used, for communication by quadriplegics, for information exchange between IoT or Internet of Things devices, as a way to secure information combining DNA and Morse code, as a method for gesture recognition, as a research tool for psychologists interested in learning methodologies, for training neural nets, for REM sleep research and plenty more.

Learning the code is an activity that sparks joy or dread, depending on whom you ask. For me it's been a decade of anticipation with little to show for it.

How to learn is a question that prompts as many answers as there are people within earshot and most of those disagree with each other. If you do ask, you'll discover that there are dozens of websites that offer to teach you, podcasts and audio files, bits of paper, buzzers, software and video, images and cheat sheets, the list is endless. You'll also discover two terms, Koch and Farnsworth. Both are intended means of learning. You'll find proponents of both methods wherever you look. You'll also hear from people who learnt the Army way, whatever that means, there's people who were taught not to send before they could properly receive, those who were taught the opposite and everything in between.

There's discussion on the topic, heated even, but very little in the way of actual hard data. There's some research. In 1990 the Keller Method from World War 2 was explored. The method involves playing a Morse letter, followed by a gap where the student is expected to write the letter, followed by a voice prompt of the letter. Interesting, were it not for the fact that it looked at nine students and only at their ability to master the alphabet.

In 1960, 310 airmen were subjected to 14 tests to determine their ability to learn Morse. No idea what the research outcomes were, since the Journal of Applied Psychology doesn't appear to share their research unless you pay for it.

There are reports of actual science behind the Koch method of learning, but I wasn't able to find it, though it's repeated often. It's only with the introduction of computers that actually using this method of learning has become practicable and recently popular.

As you might know, I've been attempting to learn Morse code for a while now. I've tried many different things, including Farnsworth, Koch and others. I publish versions of my podcast as Morse code audio only. They're published every week and there are a few people who listen.

I also attempted to make stereo audio files with a computer generated voice in one ear and a Morse word in the other, I generated flash cards, I tried learning the code as dits and dahs, but in the end, nothing really worked for me.

About a month ago I came across a video on YouTube by Electronic Notes. It contained the Morse alphabet as audio and flashed the letter visually on the screen whilst the audio was playing. There's also a video with numbers and a combination of the two.

It gave me the idea for something entirely different to try and in preparing to talk about this, it turns out that there's even research to suggest that I might be on to something. I discovered that in 1994, sixty healthy people were tested to determine if learning Morse code in a rehabilitation setting was best achieved using visual, auditory or a combination of both. The research conclusion was that the combination works best.

My idea is a video that shows an individual word whilst Morse code for that word is heard. There's no dits and dahs on the screen, just the word, written in English, and the Morse code for the word. The speed is 25 Words Per Minute, or WPM, and it's played with a side-tone of 600 Hz. Each video is an entire podcast, lasts about 30 minutes, and plays at full speed.

I'm already beginning to notice that some words sound like a sound blob in much the same way as when I learnt a new language, so I'm hopeful that this will finally get me on my way.

It's early days and the video channel is an experiment, so please comment to share your thoughts on the experience.

Who knows, I might have introduced a new way to learn.

Now all we need is some research to compare it to other methods, Koch, Keller, Farnsworth and Onno, hi hi.

You'll be able to find this article on YouTube too, "Morse is dead ... long live Morse!"

I'm Onno VK6FLAB

Attenuators, the missing link... Dec 04, 2022

Show notes

Foundations of Amateur Radio

Having been able to call myself an amateur for over a decade, it might come as a surprise to you that it wasn't until a couple of weeks ago that I thought about attenuators for the first time. They're a curious tool and once you come across them, you'll never be quite the same.

Before I dive in you should know that an amplifier is an active tool that makes things bigger and an attenuator is a passive tool that makes things smaller. To look at, attenuators are diminutive to say the least. The ones I have in my kit look like barrel connectors, a male and female connector and seemingly not much else, but looks can be deceiving and I'll mention that shape isn't universal.

The purpose of an attenuator is to reduce the power of an RF signal by a known amount, preferably without distortion or any impedance mismatches. When you go out hunting and gathering, your choice of connector is the first obvious selection, but soon after you'll be asked for a frequency range, an impedance, a power level and an attenuation level, so let's take a look.

I have some attenuators with N-type and SMA connectors. There's options for every connector under the sun, so consider what you're using with your gear and remember to think about your measuring equipment connectors as well. In my case my shack is pretty much SMA the whole way, but a friend had some broadcast N-type attenuators and I was unable to resist.

The next thing is impedance. In my case 50 Ohm, but there's options for other choices like 75 Ohm for TV based attenuators.

The purpose of an attenuator is to reduce power. It does so by converting power into heat and more power handling means more heat. Too much heat and the attenuator starts letting out the magic smoke, so consider how much power your RF source is generating. Putting out 5 Watts? Then make sure that you don't connect a 1 Watt attenuator to that radio.

Now for the attenuation level. It's described in dB or decibel. At first the numbers look bewildering, but pretty soon you'll be familiar with how it hangs together. A 3 dB attenuator will halve the signal, so a 10 Watt signal will be reduced to 5 Watts and a 200 mW signal will be reduced to 100 mW.

If you have a 6 dB attenuator, it will halve again, so 10 Watts becomes 2.5 Watts and 200 mW becomes 50 mW.

A 10 dB attenuator is a little more than 9 dB, so you could try something along the lines of a bit more than half again, but you don't need to. 10 dB attenuation is essentially moving the decimal point. A 10 Watt signal with 10 dB attenuation becomes 1 Watt. A 200 mW signal becomes 20 mW.

If you have a 20 dB attenuator, it moves the decimal point two places, 10 Watts becomes 0.1 of a Watt, or 100 mW and 200 mW with 20 dB attenuation becomes 2 mW. You can connect two attenuators together and combine their values by adding them together. For example, combining a 10 dB attenuator with a 3 dB attenuator makes for 13 dB attenuation which moves the decimal point and then halves that.

All that's fine and dandy, but what's the point?

Well, imagine that you want to measure the actual power output of your radio. If you were to pump the minimum power level of my Yaesu FT-857d into a NanoVNA you'd blow it up, but if you added say 20 dB attenuation, that 5 Watt would become 0.05 Watts or 50 mW which is half the power rating of the NanoVNA. If you're not confident that your radio is actually putting out 5 Watts, you could add 30 dB attenuation and have a safe margin at an expected output of 5 mW.

I mentioned that attenuators don't all look like an innocent barrel connector. That's because if you have to attenuate something with higher power levels, you'll need a way to dissipate heat, in much the same way as a dummy load has cooling fins, higher power attenuators can come with cooling fins too.

On the inside of this contraption is a simple circuit made from three or four resistors which combine to attenuate your signal. If you're inclined to build your own, there are plenty of online calculators to be found that show how to put an attenuator together.

One thing I've skipped over is the frequency range. Most of us are having fun with HF, VHF and UHF, generally below 1 GHz, so most attenuators will be fine, but if you are playing at higher frequencies you should take note of the frequency range specified for the attenuator.

While on the subject of frequency range. You can easily measure the actual performance of an attenuator using a NanoVNA. Connect Port 1 to Port 2 through your attenuator and using the magnitude trace you can see just how much attenuation it provides. Be sure to set the intended frequency range and calibrate without the attenuator before measuring.

Now that I know about attenuation, I cannot imagine a life without, but to be fair, I was in blissful ignorance for more than a decade, so this might not apply to you, yet, but one day perhaps you'll find yourself thinking about adding some attenuation to your tool kit.

I'm Onno VK6FLAB

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