Foundations of Amateur Radio

Foundations of Amateur Radio The other day I was playing around with RDS, or Radio Data System, it's a digital signal that's often embedded in a commercial broadcast FM transmission. Among other things it contains information about the station, its content, frequencies and potentially other useful information, such as traffic alerts. If you recall I've been working on 50 things to do with a Software Defined Radio and decoding RDS is one of those things. The decoding effort aside, I imagined a screen where you could see the RDS information, in real-time, as it was being transmitted by all the local FM broadcast stations. You'd see what music each station was playing, what their local clock thought the time was, how much they transmit other data and what they might do for emergencies, like say a Tropical Cyclone heading this way. It occurred to me that this would be an example of a fundamental difference between a traditional radio and a Software Defined Radio or SDR. Specifically, we're taught that you tune a radio to a frequency, it demodulates or decodes what's there and plays the sound, or digital information, or whatever is being transmitted, on that frequency. If you want to hear something else, you need to change frequency and the radio decodes that new frequency. If you have multiple channels to choose from, there are ways to automatically switch frequency, one after the other. One of my friends recently discovered an old scanner in a box and according to the specifications, it can scan 20 stations per second. If all 1,000 stations are programmed, it takes 50 seconds to scan them all. A lot can happen in that time. The traditional solution is having more radios. Ideally you'd have one for every frequency you care about. Cost aside, logistically this is not fun. Imagine having to power a thousand radios, or find the one where the volume isn't right, or even find space for them, or antennas. In the SDR world that's not quite how it works. Instead of tuning to one frequency, you essentially tune to a range of frequencies and then, using software, decode one or more of those frequencies, at the same time. Listening to multiple broadcast FM stations like that might not make a whole lot of sense, but what about decoding RDS, or listening to aviation frequencies, or local amateur radio repeaters, or multiple digital modes? While that might sound far fetched, a $50 RTL-SDR dongle can manage 2.5 MHz of bandwidth over USB, by comparison, my $1,000 Yaesu FT-857d can receive all of 200 kHz in Wideband FM mode, and only whilst tuned to the broadcast band frequencies. In normal AM or FM mode it's 10 kHz, so you'd need 250 of them to listen to the same frequency range. Again, just so we're clear, in analogue radio you need to change frequency to decode a different signal. In SDR you can simultaneously decode as many signals as resources permit. For example, I can make a simple GNU Radio flowgraph, a little program, that accepts a command line setting, in GNU Radio it's called a parameter block, and run it with a frequency I'm interested in. Then I can run another copy of the same program with a different frequency. Rinse and repeat and I have as many receivers as I need. While we're at it, you don't need to run the same program multiple times, you can run an FM decoder, a RTTY decoder, an AM decoder, all at the same time, as long as the frequencies you're looking at fit inside the bandwidth of the receiver you're playing with. Just so we're clear, this is one receiver, one antenna, one power supply, with as many decoders as resources allow. In other words, these two methods, analogue and SDR, are not the same. Am I glossing over things? Sure. With such a wide bandwidth comes susceptibility to interference and signal overload, also the RTL-SDR dongle doesn't transmit, although, in 2014 Ismo OH2FTG managed to change the centre frequency of his dongle 300 times per second, causing the on board oscillator to leak in a controlled manner, making a Frequency Shift Keyed or FSK transmission. Yes, I know, that's not quite up to the standard of a transmission coming from an 857d. You'll also need a computer, which you don't need to run an analogue radio, though truth be told, an analogue radio from the last couple of decades is pretty much a computer anyway. You can likely get away with a Raspberry Pi to process the data coming from an RTL-SDR dongle, so another $5, and yes, you'll need a monitor, keyboard, and a power supply. The point I'm making is that these two methods are not the same and in the evolving world of amateur radio, there's space for both. It also means that once you have this infrastructure, you can start experimenting with new radio technologies and approaches. Will it make my 857d and its siblings obsolete? Perhaps, but I doubt it. There's still plenty of valve radios going around, not to mention the spark gap transmitter at Grimeton in Sweden. In other words, this is growing the hobby, which ultimately is why I'm here. I will mention that it's not all hot cocoa and cookies. I've spent the past two days attempting to figure out why my very simple AM decoder isn't actually playing back the local ATIS or Automatic Terminal Information Service and why MacOS SDR applications don't include SoapySDR support, because of course they don't. Oh, yeah, I'm still trying to get my Proxmox server guest audio to work. I'm sharing this to make sure that you understand, that just like creating your own circuit board design and building it, there's plenty of experimentation to be done, problems to solve and challenges to meet, ultimately we're playing at the bleeding edge, at least it's not with sharp or hot implements. I'm Onno VK6FLAB

Foundations of Amateur Radio While spending some quality time discovering what I don't know about GNU Radio, I explored the notion of attempting to at least understand a little more about how an FM signal works. Depending on your background, the letters FM mean different things. In amateur radio it's a way to encode information, generally audio, using something called frequency modulation. Outside the hobby, the letters point at commercial broadcast radio. While the two are related, they're not the same thing. In amateur radio use, FM is a single channel of mono-audio, however, in commercial broadcast radio, there's a whole lot more going on, interesting because it gives you ready-made access to a composite signal that's just complicated enough to be challenging without being so complex that you need to spend hours on understanding the thing. In essence, a commercial FM broadcast signal is multiple channels encoded in a specific and documented way. This is helpful, since you can compare the documentation against ready made examples and replicate the process for yourself. In case you're new here, I'm in the process of building a radio system, in software, using GNU Radio in a project called Bald Yak. Specifically, the Bald Yak project aims to create a modular, bidirectional and distributed signal processing and control system that leverages GNU Radio. It's called Bald Yak because by the time I'm done, the Yak is likely well and truly shaved. One of the easy things to forget when you're using GNU Radio Companion, is that the blocks you're connecting together on the screen into a flowgraph actually represent software, generated when you either build or run the flowgraph. This code is currently generated in either Python or C++, making me wonder, what does the code look like, and more specifically, what code would be needed to decode FM? It turns out that an old friend, the PySDR.org website has a whole chapter dedicated to this process. Chapter 18, the End-to-End Example, details how you can decode one of the channels embedded within a commercial FM broadcast, the RDS or Radio Data System signal. If you're not familiar, the PySDR.org website represents a whole book about software defined radio and python. It goes into as much or as little detail as you want, to explain how this whole software malarkey works, and takes you by the hand down the path of discovery. So, armed with a working example, I followed along the bouncing ball and made a working RDS decoder and I think, understood most of it. There's a few interesting wrinkles that I've contacted the author, Dr. Marc Lichtman, about and we'll see what comes of that. Here's the kicker. The author, who is also a senior member of the GNU Radio team, started with a GNU Radio flowgraph and reverse engineered what was happening to get to the point of the code that's available in PySDR.org Chapter 18. This is significant because it creates a relationship between the code I have in front of me and the code generated by GNU Radio, which means that when I start with a new flowgraph, not only do I know the steps required, I also know that the outcome is predetermined, as-in, I already know that there's a solution. Having professionally written software for over 40 years, I can tell you that this is not often the case. I realise that I can search the Internet for an RDS decoder flowgraph, but that's unlikely to get me to a better understanding of what GNU Radio is doing. Once I've clarified with the author, I'll add the code to my GitHub project, "Fifty Things you can do with a Software Defined Radio", specifically, "Receive road traffic information", since among other things, that's carried by RDS. As an aside, Rohde and Schwarz have a lovely YouTube video on the topic, "Understanding the Radio Data System", which is giving me a whole set of ideas about things we might attempt with amateur radio repeaters, but that's a story for another time. Meanwhile, have you considered what other signals exist on the RF spectrum that you might want to decode and how you'd go about this? I'm Onno VK6FLAB

Foundations of Amateur Radio How do you make a hole? That's a pretty straightforward kind of question, and by the time this sentence is finished, there's going to be at least as many answers as people who considered it. I didn't supply any parameters to this hole, so answers could include shovels, collapsing space, fire, a drill, or any number of other interesting approaches. If I narrowed it down to, say, a hole in wood, there'd still be plenty of options. Specifying the type of wood, the diameter and other parameters would further narrow down the selection of methods. What if I asked you: "How do you decode FM?" You might wonder if there's more than one way and I can assure you, just like with making a hole, there's plenty of ways to go about achieving this, even if I limit this to software implementations only. I must confess, when I recently set out to test my Soapy SDR library notions using a GNU Radio flowgraph to listen to FM radio, I searched the documentation, found a beginners tutorial and used the information there to make my first proof of concept FM receiver. I put it on GitHub and went about my business. After finally managing to hear the decode effort and being less than impressed, I started trying to understand the tutorial flowgraph. When I started looking at what would be needed to decode stereo FM broadcast radio, I discovered that there were several tutorials, examples and videos with slightly, or significantly different solutions to the problem. That's on top of the over a dozen standard FM related blocks supplied within GNU Radio. I then set about trying to discover the canonical implementation of an FM receiver and came up short. Instead I discovered even more implementations of FM receivers, each subtly different. You should know that there's a difference between how your local hit radio station does FM and how an amateur radio repeater does FM, let alone the local CB radio channels, satellite telemetry, wireless microphones or even hearing aids, so within the implementation of an FM receiver, there's additional complexity, which explains to some extent the variety of FM related blocks within GNU Radio. I think ultimately it's safe to say that there's an unlimited supply of implementations of an FM receiver within GNU Radio. It led me to ask, what is the .. for want of a better word .. "right" way and what does that actually mean? In GNU Radio, you string together blocks that process a signal. If you're familiar with flowcharts, the process is very similar. Unlike flowcharts on a piece of paper, in GNU Radio, or should I say, GNU Radio Companion, the tool you use to actually design flowgraphs, the little blocks represent underlying software and their connections represent how data flows between these bits of software. In other words, each block represents a series of programming instructions that process data and pass it on. It means that the more blocks you have in your flowgraph, the more instructions are running to process data. The more instructions, the more computing resources required. This is significant because in a complex system like this, we're likely to be doing more than one thing at a time, so preserving resources is important, if only to ensure that there's time available to process the next sample. As a result, there's a difference between implementing an FM receiver with two blocks, or with ten blocks. You might conclude that two blocks is more efficient, but that might not be true. For example, two blocks processing 2,000 samples per second each, are processing 4,000 samples per second in total. A block that converts the 2,000 samples into 200 samples, followed by nine blocks processing 200 samples per second each, is processing 3,800 samples in total. All things being equal, the ten blocks together are handling less data per second, so overall it's potentially using less resources. I say potentially, because it might be that one of those blocks is using a massive calculation, consuming more resources than all the other blocks put together, ultimately, each block is software, so whatever it's doing is using resources. So. How would you go about choosing between two implementations or algorithms, which was the "better" one and how is "better" defined? My first pass at this, is to use standard testing files and using the algorithms under consideration to process them. Run the tests multiple times, keep a record of how long they take and then attempt to measure how much the original input signal differs from the processed output signal. At the moment I have no idea how you might compare signals, other than to invert one and combine them to see if they cancel each other out, which means they're the same, or not, which means that they're different. For my sins, in trying to think of a way to do this I realised that the way I implement this radio contraption needs to be able to deal with test files and potentially multiple different implementations of a decoder. It also means that I have some more thinking to do. Ideally, there needs to be a concept of meta information, like the radio source, the tuned frequency, the bandwidth, gain, and likely more so I can set the parameters once and re-use these across whatever else is part of the flowgraph. It should be possible to use a test file just as simply as a Soapy SDR compatible radio. It should also be possible to hear the audio, or save it to a file, or decode an embedded signal, or all at the same time. In other words, it needs to be flexible. Luckily, GNU Radio is really a collection of libraries built precisely for this task. I'd love to hear your thoughts on the matter. I'm Onno VK6FLAB

Foundations of Amateur Radio Still excited from my minor victory in discovering a missing puzzle piece associated with the project I'm working on, I spent the past week introducing my head, if not literally, at least figuratively, to the surface of my desk in a traditional head-desk troubleshooting move that you might be familiar with. I suppose it's an improvement on the "Bear with a Toothache" approach. In short, the Yak is losing hair .. rapidly. You might be wondering why I'm telling you about it, since in the land of milk and honey nothing ever goes wrong and all the answers are presented on a silver platter, except when they're not. Within the amateur radio community, it appears to me that the inclination to fiddle is ingrained and widespread. Given that the hobby is all about experimentation and learning, that's not a bad thing, but there are times when this behaviour can be counterproductive. Specifically when you're troubleshooting. Faced with a problem, there are times when a systematic approach is warranted. For some, the first time they come across this phenomenon is during the practical test component of their amateur radio license. Presented with a station, they're asked to determine why it's not working. The problem might be a power supply that isn't plugged in, or a disconnected antenna, the mode button set to FM, the squelch closed, the RF gain set to zero, generally something simple. Those inexperienced in the art of troubleshooting are more likely than not inclined to try everything, sometimes all at once, in the hope that one of the changes will magically fix the issue, but in reality, often making the problem worse. There is a better way. I'm mentioning this because this skill applies to many aspects of life and in the decades that I've been here, it's not something I was ever taught. It's funny to think that a quote from nearly a century ago applies to this skill: "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." The salient point being "eliminating all which is impossible". In other words, you're not finding the problem, you're eliminating all the things that are not the problem. Another way is to think of it as finding all the things that don't need fixing. While that might sound weird, in deeply interdependent systems like an amateur radio station, or a computer, that approach can help you find the root cause of an issue and with it the path to a potential fix. Of course, this process invites you to examine where the issue might exist. Experience will teach you that you need to start small and grow the net, rather than cast wide and narrow it down. That's not to say that you need to stop paying attention to the bigger picture. In the example of an inoperative station, you might discover that the lights in the room are out and that this coincides with the radio being off. In other words, trying to discover if the antenna is disconnected makes little sense, since there is no power to the radio. In my case, I'm balancing my efforts between maintaining an existing system whilst attempting to deploy a new one to replace it. I'm working on several related issues on multiple fronts. Their common theme is audio, though the specifics differ depending on which computer I'm looking at. Then there's the installation and ongoing care and maintenance associated with keeping GNU Radio running. It's a balancing act because while this is happening, I still need to look for work, respond to email, deal with the regulatory requirements for accounting and tax returns, not to mention the myriad projects I have going on at any given time. At this point I could go into deep and disturbing detail about the technology issues I'm juggling and I could even justify it by pointing out that a problem shared is a problem halved, but truth be told, I'm not sure you're up for a treatise on the comings and goings of forced system security updates and arising bugs, and just so we're clear, this is not the company who brought us a talking paperclip, it's the one who gave rise to companies called "Orange" and "Lemon". On the GNU Radio front, there's a snake based installer that happily installs two incompatible libraries for the same application, causing it to fail, and a beer related one that fails to install dependencies. At least I can use 'apt-get' on a real system. That said, juggling problems and all, I did manage to actually hear an FM station being decoded across the network. It did help that I actually connected the antenna to the radio, and I'm ignoring the audio buffer under-runs, or over-runs, depending on the weather, or some other unknowable variable, but I suspect that's all part of the learning I'm in the middle of. Hopefully, the hair will grow back soon. I'm Onno VK6FLAB

Foundations of Amateur Radio A little while ago I discussed a lovely article by programmer, artist, and game designer "blinry" called "Fifty Things you can do with a Software Defined Radio". This week it occurred to me that I could use their article as a framework to further explore my 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. For that to happen, I need a solid understanding of GNU Radio and its ecosystem. While I've been playing with it off and on for a decade or so, I have yet to build anything substantial for the simple reason that there was a puzzle piece missing. Last week I discovered it .. by accident. One of the fundamental things I'm attempting to achieve is the creation of a system that doesn't care which radio device you're using. In case you're wondering, I'm doing this because there is a proliferation of device specific software that cannot keep up with the influx of new hardware, doesn't consider the growing use of network connected radios, forced by increased RF noise levels in many communities across the world, not to mention, connecting increasingly expensive computing hardware to lightning rods. If everything goes to plan, it should be possible to use the project with any radio device. This is easier said than done. In GNU Radio this complex issue is addressed by having different blocks that represent different devices. You'll find receiver specific source blocks and equivalent sink blocks representing transmitters. While that's all fine and usable, it means that if I were to publish, say an FM receiver flowgraph, essentially a collection of blocks representing software that implements an FM receiver, I have to decide how I want to deal with the specific device. Do I select an RTL-SDR dongle as the device in my flowgraph and let you figure out how to make it work on the HackRF or the PlutoSDR sitting in your shack, or do I make it completely hardware agnostic, requiring you to wire it all together for your specific situation? Neither is desirable, or simple. Added to this is the problem that trying to make this work using a traditional analogue radio would cause more issues, since there isn't a Yaesu FT-857d block, nor is there one for an Icom IC-7400, let alone something from last century. Someone with some GNU Radio experience might point out that there are source and sink blocks for an audio device, which would allow you to plug one of those radios into a sound card and access the receiver, or transmitter, that way. While that would work, it requires that the radio is physically connected to a computer that's running GNU Radio. It would also give you all manner of headaches attempting to change frequency in the same way as you could using an RTL-SDR dongle. There are several ways to get remote radio control working across a network. For example, using 'rigctld' and 'Hamlib', we can change frequency on over 300 analogue radios, but even if you do, you'll discover that getting the audio across the network creates a whole range of new issues, not to mention that GNU Radio doesn't talk to Hamlib compatible radios. This is why many remote radio solutions are implemented as remote desktop sessions to a computer that is physically connected to the radio. While attempting to solve a completely unrelated challenge last week, I came across 'SoapySDR', described as a vendor and platform neutral SDR support library. Essentially it's a project that allows an application to interact with different devices without needing to support individual radios. This allows an application developer to write their software to support SoapySDR and from then on benefit from its ability to talk to lots of radios in a variety of different ways. For example, one of the in-built features is called 'SoapyRemote' which allows you to connect to a SoapySDR radio and interact with it across a network. Specifically, you can send and receive, as well as control the radio, essentially bundling together both the audio and control signals. SoapySDR also includes a tool called 'soapy-audio'. While documentation is sparse, it appears to support Hamlib, which means that you can, at least theoretically, connect a low powered computer, like for example a $5 Raspberry Pi Zero, to your analogue radio and access and control it across the network. Best part? It's supported by GNU Radio and many other applications. I've started creating a repository with the "Fifty Things you can do with a Software Defined Radio", one directory per thing, that will contain the bits needed to run inside GNU Radio and across the network to any SoapySDR compatible hardware. Now, before you get as excited as I am, there's a few hurdles. I'm not yet sure of the status of soapy-audio, but it looks promising. I have the bits sitting on my computer and I'm working through them. For example, I'm not sure if the current implementation supports transmit. I also have anecdotal evidence that Hamlib support is incomplete, but I don't yet know to what extent. I anticipate some coding in my future. I suspect it will be the equivalent of building a new SoapySDR module, but time will tell. I can tell you that I'm running an RTL-SDR dongle connected to a low-power computer and I can connect to it across the network with GNU Radio on my workstation and run a proof of concept FM receiver flowgraph. There's no reason for either computer to be in the same room, let alone the same country. You'll find the project on my VK6FLAB GitHub page. I plan to work my way through the 50 items and discover what I don't know about GNU Radio. Feel free to play along. I'm Onno VK6FLAB

Foundations of Amateur Radio How to go about documenting your setup? Possibly the single most important thing that separates science from "fiddling around" is documentation. Figuring out how to document things is often non-trivial and me telling you that "unless you wrote it down, it didn't happen" only goes so far. If documentation isn't your thing, what about "I broke something and I don't know how it was before I fiddled" as an incentive instead? Recently I had cause to explore how to document how my station is configured. To give you a sense, the microphone is connected to a remote-rig, which is connected to a Wi-Fi base station, over Wi-Fi to a Wi-Fi slave, to another remote-rig, to the radio body, to the VHF port, through two coax switches, a run of RG213, to an antenna. When receiving, it goes from the antenna, to a run of RG213, through two coax switches, to the VHF port, to the radio body, to a remote-rig, to a Wi-Fi slave, to a Wi-Fi base station to a remote-rig, to the remote head, to a set of headphones. Of course, at this point I've written it down, so, job done .. right? Well, what about the data connection, the external speaker, the remote head display and other goodies, say nothing of the duplicate devices with similar names. All in all, the FT-857d has something like eleven ports, each remote-rig has ten, so just wording it is a start, but hardly qualifies as documented. What if we drew a picture instead? At this point you could pull out your crayons and start scribbling on a sheet of butcher's paper and that would be a fine start, but it would be difficult to share with me or anyone else and updating it would be a challenge, let alone versioning it. As it happens, we're not the first people to have this issue. In the 1980's and 1990's researchers at Bell Labs were trying to figure out how to draw graphs and from that work a language, 'DOT', since everyone is a fan of the "DAG Of Tomorrow", and a series of tools, which today are known as 'Graphviz', made the visualisation of relationships possible without the application of coloured wax on dried cellulose fibre. In my other, computing job, I had cause to visualise the relationship between a million or so nodes, allowing me to discover a specific node that was directing all traffic, where I could insert my debugging code, but it was only possible thanks to these free and open source tools. While the DOT language isn't particularly complex, it occurred to me that for someone not conversant with the syntax, we can start even simpler with a CSV text file that shows the relationships between each device and convert the CSV to DOT and in turn to a picture. For example, I documented the relationship between the radio and the antenna by adding five lines to a CSV file, essentially, FT857d to VHF port to VHF coax switch to VHF grounding switch to RG213 to antenna. In all, to document everything except power, since I haven't decided how I want to describe it, I used a CSV with 47 lines. On the face of it, that might sound ridiculous, but I can tell you, it shows all the sockets on the FT857d, all the sockets on both remote-rig devices and the relationships between them. With it anyone can duplicate my set-up. Having previously spent some quality time learning various aspects of the DOT language, I figured I could write a little script to convert CSV files to DOT, but being of the generation of software developers with the attitude, "Why write something if someone else already did?", I discovered that Reinier Post at the Eindhoven University of Technology has a delightful collection of scripts, including one appropriately named 'csv2dot'. Written in Perl, the only language that according to some looks just as impenetrable before and after encryption, the tool works as advertised and makes a DOT file that you can then visualise using Graphviz. Of course there's Python scripts lying around that claim to do the same, but I wasn't keen to install the kitchen sink just to try them. Instead I made a quick little Docker file that you can find on my vk6flab GitHub repository that will walk you through this, complete with my example, so you have a starting point. Now, I used this here to describe my station, well, one part of it, but it can easily extend to document your entire station, and because we're talking about text files that contain the information, anyone with a copy of a text editor can update the file when things change, since that's where the real magic happens. So, what are you waiting for, documentation? I'm Onno VK6FLAB

Foundations of Amateur Radio Just under a year ago I started an experiment. I set-up a beacon for WSPR, or Weak Signal Propagation Reporter, transmitting at 200 mW into a dummy load using eight bands between 80m and 10m. I also set-up an RTL-SDR dongle, connected to an external 20m HF antenna and made it monitor 18 amateur bands between 630m and 23cm. I left this running 24/7 for most of the year, though there were times when I detached the antenna due to local thunderstorms and there was a seven week period where there were no reports. It's highly likely that I forgot to reconnect the antenna, but I don't recall. For this analysis I used the online WSPRnet.org database where I uploaded my spots as they were decoded. I noticed that there are reports that I have locally that are not in the database, though I'm not sure why. They're incomplete and not in the same format and merging these is non-trivial for reasons I'll discuss. Lesson learnt, the "rtlsdr-wsprd" tool needs to be patched to output the data in the same format as is available from the online database and I need to actively log locally. The results are puzzling, at least to me right now. Let's start with the low hanging fruit. There are no reports of my WSPR beacon being received by anyone other than me. That doesn't guarantee that nobody heard me, just that nobody reported that they did. In the database there's just over six thousand reports of my station receiving a WSPR transmission from my beacon during the past year. The reports cover all bands, though not equally. The 80m band represents 6 percent of reports, where 40m accounts for 20 percent. The reported SNR, or Signal To Noise ratio, varies significantly across the data. For example, the 12m band shows a range of 42 dB. Digging into this does not reveal any patterns related to date, time of day, season, other band reports or any other metric I was able to imagine. In my exploration, missing records and time-zone differences aside, I discovered that the local data does not appear to match the database. For example I have records where the software decoded my beacon ten times in the same time-slot, but none of them exist in the database. For others, there's only one matching record, which leads me to believe that the WSPRnet.org database only accepts the first report for any given combination of timestamp, transmitter and receiver, but I have yet to confirm that. So, let's talk about getting more than one result for a specific time-slot. As you might know, a WSPR signal is transmitted every 120 seconds, starting at the even minute. Each transmission lasts 110.6 seconds. The decoder will make several attempts to decode multiple, potentially overlapping signals. It is my understanding that the way this happens is by essentially removing a known decoded signal and then attempting to decode what's left, repeating until either there's no more signals to decode, or time runs out, since there's probably only really 9.4 seconds in which to do this. Potentially this means that a faster computer will decode more signals, but I've not actually tested that, but it's probably something worth pursuing. Back to our decodes. If the first decode is removed from the received data and the next decode gives you similar information, same callsign and maidenhead locator, with SNR and frequency differences, then you might imagine that there's so much of it there that the only way that might happen is because the receiver is overloaded. I'm still looking into this, because if that's the case, then we'd need to determine if the receiver was always overloaded, or only sometimes. It's curious, since there's over a thousand other signals being received from other stations, several over 18,000 km away, so it's not like the receiver is completely swamped. Another hypothesis is that the decode is coming from a different band, like a harmonic. This is potentially caused because from a band and timing perspective, the receiver isn't linked to the transmitter in any way. The transmitter hammers away 24/7 one band after the next, switching every two minutes, the receiver listens for half an hour on a band, then randomly picks the next, until it runs out of bands and starts again. The receiver is listening on more than twice as many bands as the transmitter operates on, but that doesn't mean that it cannot hear the transmitter on a harmonic of one of the bands. Again, I don't know if this is the case, or if something else is happening. One thing I'd expect, is to see reports on other harmonics outside the bands that the transmitter is using, but I'm not seeing that. Perhaps the overload is limited to just the band we're actively monitoring and the other signals are coming in regardless of the overload. I'm still trying to determine if that's the case. As I said, merging the data from the two sources is non-trivial, time-zones and formatting are not the same and I'm not in the mood for manually fixing 2,500 or so records, not to mention attempting to determine which SNR is real for the multi-decodes. So, what did I learn? For starters, the world didn't come to a sudden and laborious stop when I transmitted into a dummy load. The experiment was interesting and worth doing. I should test using shorter runs until I've determined the mechanisms involved. For example, one amateur suggested that I might be decoding information that's coming in via the coax, rather than from an antenna. That said, doing so would also require significantly more effort to incrementally analyse this data, so I'd have to find ways to improve my workflow. The SNR is all over the place, not something that I expected. All bands are represented in the data. There does not seem to be any relationship between date, time, other stations and the signal strength seen for the local transmission. I need better record keeping. No doubt there's more. If you have questions, feel free to comment. The experiment also leaves plenty of questions. Why do the SNR values vary so much? I can't imagine that the variation relates to propagation, since we'd have reports from other receivers, so is it something else, even though we're talking about equipment that's indoors, are we observing variations in electronics temperatures for example? Alternatively, if the measurements represent overload of the receiver, why don't we see other harmonics and how is it possible that we can receive and decode very weak signals from other stations? If the signal is arriving via an unexpected path, like the coax, rather than the antenna, what could we do to stop that from occurring and what effects does it have on our current dataset, and could we account for those effects? I suppose, leaving the ultimate question for last: Is the data that I've collected over the past year useful, beyond potentially "this is not how you do this", or is it essentially meaningless? I'm Onno VK6FLAB

Foundations of Amateur Radio The other day a fellow amateur revealed that they qualified for membership of the QWCA, the Quarter Century Wireless Association .. twice over .. there may have been some innocent whistling involved. During the ensuing discussion it emerged that it all started with a crystal radio set built together with dad, which triggered a whole lot of memories and made me consider just how you'd get into the hobby of amateur radio today. I think it's important to notice that amateur radio is a hobby. There are public service and emergency communication aspects to the experience, but it's essentially a hobby. It's supposed to be fun. I'm mentioning this because that might get obfuscated when I tell you that in order to actually be a radio amateur, you need a license. This license is required because when you transmit, radio waves don't know about international borders, don't know about interference, don't know about priorities and other aspects of our deeply interconnected world. Think of it as a way to formalise your responsibilities. Note that I said "when you transmit". You don't need an amateur radio license to listen, which you can do right now using all manner of online tools in your web browser, "WebSDR", "KiwiSDR" and "shortwave listener" are useful search terms if you're inclined. Getting an amateur license is not difficult. There are many amateurs who were licensed as a teenager, or even younger. It sets you up for life and amateur radio license in hand, you can start transmitting on dedicated amateur frequencies or so-called "bands". A license is required in every country and how that specifically happens in your country will require that you do a little research. Most countries have a so-called "peak body", an association that represents amateur radio to their government, it's a good place to start. In Australia where I live, it's called the Wireless Institute of Australia or WIA. In the United States, it's the ARRL, the UK it's called the RSGB. Searching for "amateur radio peak body" and your country should get you there. If you're stumped, your national telecommunications regulator is often another good place to find information, ultimately you'll be obtaining your amateur license from them anyway, even if they don't actually run courses and exams, though some do. Essentially what you're looking for is, where you need to go to get an amateur license and what's involved. As far as I know, most of this infrastructure is run by volunteers, fellow radio amateurs, even if there's a fee involved. You should also know that amateur licenses generally come in different flavours or levels. For example, in Australia there's currently three levels of license, Foundation, Standard and Advanced. The USA has Technician, General and Extra. The UK has Foundation, Intermediate and Full. The Netherlands has Novice and Full. In other words, what it's called and how many levels there are is country dependent, as are their requirements. I'll also mention that whatever license level you pursue, it's your hobby. You get to decide if, how and when you look for more responsibilities with a higher level of license. It might surprise you to know that I hold the basic Foundation license in Australia. I've held it since 2010. So-far I've yet to have a need to pursue anything further, despite regular "encouragement" to "upgrade" to a "real" license. You do you. It's your hobby. Some countries allow all of this to happen online, others require that you use pen and ink in person in a dedicated classroom, and everything in between. If you are hard of hearing, blind, or unable to physically attend, there are often specific tools and processes available to help you, make sure you ask. As an aside, I will mention that, as in life, there are people in this community who are less than welcoming and will go out of their way to be obnoxious, obstructionist or worse. Fortunately, while vocal and destructive, they are in the minority. Don't let their behaviour dissuade you from participating. You'll find amateurs all over the planet who will welcome you into the community with open arms. There are thousands of local amateur clubs, online resources and of course potentially a couple of million radio amateurs at the other end of your antenna. It's important to understand that the journey into amateur radio is different for everyone. For many long term amateurs the experience came from a family member or neighbour. While that route still exists, it's much less common as an introduction as it used to be. I first came across it as a teenager during a sea scouting event called JOTA or Jamboree On The Air. Whilst memorable, it wasn't until two more amateur radio interactions, decades apart, that I finally got to the point of actually discovering the hobby. For your journey, just being here, today, right now, is already a start. Welcome, it's nice to have you here. You've found the community! What are you waiting for? I'm Onno VK6FLAB

Foundations of Amateur Radio Building a shack makes a number of assumptions about your situation and to make it abundantly clear, it's not the only way to enjoy the hobby of amateur radio. Visiting clubs locally and remotely, being a member of a club, visiting other amateurs, setting up your station in a suitcase or a backpack, on a bicycle, in a car, on a bus, or in a boat are some of the many other avenues open to you. That said, there is something magical about building your own shack. It has the ability to transform your hobby and if you have the opportunity, I can highly recommend it and I'd like to encourage you to consider the notion. As I've said previously, there is plenty of exploration and learning associated with putting one together. After you've spent some time reflecting, planning, designing, sourcing, building and testing the environment where you do amateur radio, you're likely to reach a point where you'll refer to that space as "your shack". You might even come to think of it as your shack, rather than a collection of trade offs that you've constructed in the best way you know how. Inevitably, you'll wonder what to do next. Several things come to mind. Creature comforts is probably the most obvious, a push to talk foot pedal, or a desk microphone, either on a stand or hanging from a boom, an audio mixer, a couch, a soldering station, a microwave oven, a fan, or air conditioning, in other words, plenty of opportunities for improvement and enhancement. Then there's computing, something that might interest you, or not. It offers the ability to explore a whole different side of amateur radio, from logging through to digital modes, from weak signal propagation to tracking satellites, the possibilities are endless. Your shack is also potentially a communal place where you can meet with your friends to share the experience. It's a place for contemplation, for relaxation, for "being" an amateur. All of it is open to you as possibility, an excuse to improve and enhance. The thing is, that too will come to a point of, let's call it "completion", and you're left with more questions. Amateur radio is inherently experimental in nature, that's the whole point of the pursuit. Your licence gave you access to the playground, your shack is that playground. Now it's up to you to play. Of course what playing looks like is unique to you. Over the past 15 years I've been describing what playing looks like to me, and from the over 3 million downloads last year from my website alone, not to mention the newsletters, rebroadcasts, podcast inclusions, other streaming services, news reports, social media and messages I've received, they've encouraged you to explore and investigate this wondrous activity. The point is, the shack you just completed isn't finished and hopefully it never will be. Whichever one it is, the first one, the one after that or the next one, your shack is a place where you can experiment, learn, discover, test, fail, succeed, challenge and enjoy the hobby of amateur radio. It's not the only place where you'll find this hobby, but it's your place. So, have at it. I'm Onno VK6FLAB

Foundations of Amateur Radio On your amateur radio journey, you'll likely discover that many transceivers run on 13.8 volt DC, give or take. For example my FT-857d requires 13.8 volt plus or minus 15 percent, with a negative ground, and a current draw of 22 ampere, more on that later. In other words, the power supply needs to be between about 11.7 and 15.9 volts, the same voltage that runs most vehicles with some wiggle room for fluctuating alternator charging cycles. While some radios will absolutely fit in your car, there's plenty where that just isn't the case, even though they're set-up for a 13.8 volt power supply. You might think of it as an anachronism, a few steps removed from spark gap transmitters, but there's more to the story. Most residential power grids run on AC power, at varying voltages and frequencies between 50 and 60 Hz. Across the world there's eight different AC voltages in use between 100 and 240 volts. Some countries use more than one combination and I haven't even looked at three phase power. Perhaps 13.8 volt DC isn't looking quite as odd. With this revelation comes the need to actually have 13.8 volt available in your shack. Converting your grid power to something you can plug your gear into requires some form of transformation, typically achieved with a power supply. Efficient, cheap and plentiful, the switch mode power supply is the most common. Built to a price, they're also often noisy, not just the fan, but noisy from a radio emissions perspective. Amateur radio has very sensitive receivers and as a result you can often hear, or see if you have a waterfall display, RF birdies, a sound reminiscent of a budgie whistling, every 100 kHz or so across the whole radio spectrum. Not something most other equipment cares about, so you're often left to fend for yourself in figuring out how to deal with this phenomenon. There's plenty of filtering techniques and circuits to be found and some of them even work, but for my money, I'd spend it on a power supply that doesn't make noise in the first place. A regulated power supply maintains a constant output voltage or current, regardless of variations in load or input voltage. An unregulated power supply can wander all over the place. Adjustable power supplies allow you to set the voltage, amperage, or both, sometimes with knobs, sometimes using external controls. At this point you might decide that this is all too hard and you want to do away with all this complexity and use a Sealed Lead Acid, or SLA battery, after all, that's what the 13.8 volt is based on, but then you'll need to charge it. Similarly, picking any battery technology requires some form of charging. Another word for charger is: power supply, often a switch mode one, and likely not filtered in any way that matters to you, since batteries, and for that matter solar power inverters, are unlikely to care about RF birdies. I will make mention of linear power supplies. When I started on this journey, this was the strong recommendation from my peers as the most desirable option. Although they're significantly less efficient than switch mode power supplies, only 30 percent versus better than 80 percent, from an RF perspective, they're extremely quiet. Of course, the lack of efficiency reveals itself in the form of heat, which necessitates the application of cooling, from a fan, often a very noisy fan. One potential source of power supply is a computer power supply unit or PSU. Before you go down that route, consider that they're intended for installation inside a case, often generate various voltages at very specific current draws and are not typically known for being RF quiet. After weighing up all the variables, I chose a laboratory grade switch mode current limiting adjustable power supply. It's set to 13.8 volt and it sits on my desk doing its thing. Rated at 1 to 15 volts at 40 ampere, it's now as old as I am in amateur radio terms, well and truly a teenager, it's also overkill, by quite a margin. Remember when I mentioned that my FT-857d is rated at drawing 22 ampere? As a QRP or low power station I typically use my transmitter set to 5 watt, but even when others use it at full power, I have never ever seen it draw more than 12 ampere. That's not to say that it can't draw 22, I've just never seen it. As a benefit of having such a massive overkill in the specifications of my power supply, I can power more than one radio and not notice. Not that they're all transmitting at the same time, or using more than 5 watt, it just doesn't matter. I previously discussed setting a standard for coax connectors in the shack, the same is true for deciding what to pick for power supply connectors. In my case I chose Anderson Powerpole connectors. Pins come in 15, 30 and 45 ampere ratings, are genderless and housings are available in many different colours. When I say genderless, it means that you can join two identical connectors. Within my shack, I use the RACES or ARES Powerpole wiring standard and every single 13.8 volt connection uses it. If I get new gear that uses some other connector, I'll cut the power supply wire in half and terminate both the power supply and the cut off cable using Powerpole connectors. That way my gear will connect to my own power supply and I'll have a universal adaptor cable when I need it. Over the years I've collected an impressive array of adaptors using this method and it's helped immensely when sharing gear with other amateurs. Word of warning, make sure you get positive and negative the right way around when you join your Powerpole connectors, and make sure that you have the red and black housings the right way around too, you can thank me later. If you do this more than a few times, I'd recommend that you spend the money on a proper crimping tool. It makes the experience So. Much. Better. To avoid many of the pitfalls of interference whilst connecting power and coax to the same radio, try hard to avoid running both in parallel, or worse, joined to each other. Instead, attempt to run them in different directions and only cross at right angles if you have to. One thing to consider is the ability to switch everything off immediately. To that end I have a power switch on my desk that isolates all power to the equipment. You'll notice that I have not said anything about grounding or earthing, that's on purpose. Your laws and mine are not the same. Similarly, information you'll find online rarely, if ever, describes the jurisdiction it applies to, so, look at your own rules and implement accordingly. I'm Onno VK6FLAB