Foundations of Amateur Radio Podcast Por Onno (VK6FLAB) arte de portada

Foundations of Amateur Radio

Foundations of Amateur Radio

De: Onno (VK6FLAB)
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Starting in the wonderful hobby of Amateur or HAM Radio can be daunting and challenging but can be very rewarding. Every week I look at a different aspect of the hobby, how you might fit in and get the very best from the 1000 hobbies that Amateur Radio represents. Note that this podcast started in 2011 as "What use is an F-call?".℗ & © 2015 - 2025 Onno Benschop Ciencia Física
Episodios
  • There's promotion .. and then there's Amateur Radio

    There's promotion .. and then there's Amateur Radio
    Jul 19 2025
    Foundations of Amateur Radio In the community of radio amateurs scattered around the planet we have a habit of getting together with others to have fun in whatever shape that takes. The obvious ones are HAMfests, car boot sales, raffles and other amateur adjacent pursuits, but we also do things like licence training, weekly on-air nets, contesting, portable activations, climbing mountains, or hills, setting-up in parks, or lighthouses, we set-up on a field day, just for fun, and find excuses, sorry, reasons, for any number of other activities. Some of these are solitary affairs, but many are best enjoyed shared with multiple friends, both old and new ones. Having been a member of this community since 2010 I've come to observe an aspect of this community that is odd, to say the least. We organise all these events, but rarely promote it beyond a single email to three people, if that. It's almost as-if the average organiser thinks that their event permeates the community by magic osmosis. Even if there is any form of promotion, there's sometimes a date and time, but hardly ever does it show that time in UTC, even if it's a radio event, it's like we've forgotten that radio waves pass through time zones, or there is a misconception that everyone on the planet knows what your local timezone is, let alone if it's summer or winter time at the time of the event. So, what does promoting your event look like if you actually want people to know about it? For starters, you should consider who you want to have as a participant. A local HAMfest is unlikely to attract people from around the globe, but Friedrichshafen and Dayton are examples that contradict that notion. A VHF-only event might be intended for local amateurs, but what if it allows for satellite or digital contacts, like say via Allstar, IRLP or Echolink? Similarly, you might run a weekly on-air net, but have visitors from around the planet. The point being, that your audience might not be exactly what you initially think. In other words, there might be people playing from further afield. Consider that when you announce what time the event starts, and finishes. Speaking of finishing, adding an expected closing time is helpful for participants where only one member of the family lives and breathes amateur radio and the rest just want to get on with their respective lives, so consideration is welcome. Aside from telling your audience when and for how long the event goes, adding a location is not optional. You'd be surprised how many events say things like: "it's again in the usual location", or "we're at the community hall" without ever publishing an address. I can tell you, it's fun discovering that the name of the hall isn't unique. Now, for the big one. After putting the information together about the event itself, where and how do you announce it? For starters, on your own website, in whatever form that takes. It serves two purposes, announcing to the world what is happening, but it's also the definitive place where the right information is published. This is important because things change, get cancelled, moved, updated, whatever. Life isn't static, so you need to define a place where the official announcement lives. At this point I'd like to mention that this is often where promotion stops. It's easy to think that in your universe everyone you know is aware of your website, but that's just not true. A single place to publish is not the end of the process, it's the start. Then you need to use things like the local news broadcast, the national news broadcast, the international news broadcasts, contesting websites and calendars, social media, fediverse and whatever else you can get your hands on. You need to include it in your own club news, in club newsletters from other clubs, on the local amateur notice board, you need to talk about the event on-air, share it during on-air nets and if it's recurring, tell the world that it's going to happen again next year. Nothing here is revolutionary, it's not like launching a rocket into space, this is basic common sense and you too can do this. If you need help, ask. So, if you have an event that you want to have participants for, you need to make noise. Publishing the announcement at the local planning department in Alpha Centauri 50 years before the event is going to cause issues, as will defining the date for an annual event as: When the June solstice is on a weekday (Monday through Friday), the weekend following shall be the weekend of the event. When the June solstice falls on a Saturday or Sunday, that weekend shall be the weekend of the event, but only for the Winter field day, the Summer one requires you to count back four weekends, or forward, depending on if you're talking about the Spring or Summer event, and add one if it falls on the weekend. In case you're wondering. No, I didn't make that up. It's real. I'll leave you to ponder how you'd add such an event to your family calendar. ...
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    6 m
  • Decoding a signal ...

    Decoding a signal ...
    Jul 12 2025
    Foundations of Amateur Radio Recently I was given some radio data captured on the 40m band. Using a piece of software called "Universal Radio Hacker", I attempted to decode it. At the time I thought that this might be Morse code, since then I've been told by someone who has been using Morse longer than I've been alive, that it isn't. I shared the data on my VK6FLAB GitHub repository where you can download it and see what you learn, and perhaps repeat what I did, or better still, improve on it. Over the years I've talked a little about how Software Defined Radio or SDR works, essentially it's a glorified Analogue to Digital converter, much like the sound card in your computer, which does the same, albeit at a much lower frequency. As it happens, you can represent the signal that comes into your radio antenna as a series of values. Essentially, the stronger the signal, the bigger the number, the weaker the signal, the lower the number. Let's talk about the characteristics of this signal. It consists of two parallel signals, in opposition to each other. The first signal jumps intermittently between 7 kHz and 40 kHz, where the second jumps between -7 kHz and -40 kHz. The recording is marked 7.06 MHz, so if we think of that as the central frequency, the whole signal sits between 7.02 and 7.1 MHz. This 80 kHz wide signal is not something you'd typically be able to hear using a standard amateur radio receiver which tops out at about 3 kHz bandwidth. It's so wide that you couldn't even hear more than one of the four tones at the same time. Randall VK6WR, who supplied the recording, spotted it on a waterfall display showing a chunk of radio spectrum, in fact, a $25 RTL-SDR dongle could receive this signal. Aside from the fact that this is a really wide signal, well at least in traditional amateur radio terms, it was interesting in that it was heard on the 40m band. As it happens, just after I shared my initial exploration, I was told by several other amateurs that they had heard the signal. I even saw it on a WebSDR in India and attempted to record it, but failed. As it happens, a few weeks ago, I was playing with something called "CAN Bus", or Controller Area Network, a technology that was designed in 1983 and is used all over cars for things like sensors for speed, engine temperature, oxygen level, detonation timing and anything else that's happening inside a car. You might know the end-user view of this called OBD2 or On Board Diagnostics, second generation. I was looking into it because my car has been acting up and I've been trying to track down the root cause. Anyway, I learned that CAN Bus is implemented using something neat, "differential signalling", where two wires each carry the same, but opposite signal, so they can be combined to ensure that in an electrically noisy environment like a car, the information still gets where it needs to go. Seeing the radio signal Randall shared, reminded me of this. Noise immunity is a useful attribute in digital HF communication, so I can understand why it was done like this, but it also means that either signal was sufficient to start to decode the information. We can use Universal Radio Hacker to show us only half the signal using a band pass filter. I then decided that the 40 kHz frequency was "on" and represented by a "one" and the 7 kHz frequency was "off", represented by a "zero". Of course that's entirely arbitrary, there's no reason that it cannot be the other way around, but for our purposes it doesn't matter at this time. That said, we don't yet have enough to decode the actual signal. We need to figure out how long each switch, or bit, lasts, because two zero's side-by-side or two ones side-by-side would look like a long "off" or a long "on". Using that logic, you could also say that the shortest possible duration for a 40 kHz or a 7 kHz tone would represent a single "one" or a single "zero". Of course, this is a simplified view of the world. For example, the data file contains more than thirteen and a half million bytes. Half of those are for the I in I/Q, the other for the Q. I'm purposefully glossing over a bunch of stuff here, specifically the notion of so-called I/Q signals, that's for another time. In computing a single byte can represent 256 different values. It means that if the signal is represented by a single byte, a voltage from the antenna at maximum amplitude can be represented as 255 and the minimum amplitude as 0. As it happens, voltages go up and down around zero, so, now we're only using half a byte, 127 for maximum, -128 for minimum. If we use two bytes, we get significantly more resolution, -32,768 as the minimum and 32,767 as the max. A little trial and error using another tool, "inspectrum", told me that the data was organised as two bytes per sample. Which brings the next point. How many samples per signal? Said differently, we're measuring the antenna voltage several times per second, let's say twice per second. If ...
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    8 m
  • Antenna modelling with genetic algorithms.

    Antenna modelling with genetic algorithms.
    Jul 5 2025
    Foundations of Amateur Radio

    Recently I was helping a friend erect their newly refurbished multi-band antenna and during the process we discussed the notion of tuning an antenna that's high in the air. They made a curious response, in that they'd tuned the antenna on the ground before we started.

    I asked how this would work, since as I understand the process, this changes things once it gets in the air. They assured me that while the actual SWR might change, the frequencies at which it was resonant would not.

    This was news to me because I've been putting off erecting my own multi-band 6BTV antenna mainly because I didn't really want to face having to erect it, tune it, lower it, modify the elements, erect it, tune it, etc., all whilst standing on the steel roof of my patio. Would this phenomenon be true for my antenna?

    It occurred to me that I could test this idea, not only for my antenna, but for other antennas as well. In my minds-eye, I saw a video displaying the pertinent attributes of an antenna, SWR, gain, radiation pattern, and whatever else I could think of, animated with the modifications of things like height and ground radials.

    If this sounds familiar in some way, it's because I've been here before. This time the outcome was slightly different, since I found a tool that can optimise antennas using a genetic algorithm. What I mean by that is an automated process where you can test variations of a thing, in this case antennas. Rather than design each antenna and test it, you essentially generate antenna designs and tweak them to determine the best one. Then you use that to generate the next series of designs. Rinse and repeat until you have what you're looking for. There's a whole field of computer science dedicated to this and unsurprisingly the rabbit hole goes deep.

    The tool is called "xnec2c-gao" and it's written by Maurizio DC1MDP. The name of the tool hints at its nature, working in combination with "xnec2c", written by Neoklis 5B4AZ and maintained by Eric KJ7LNW, you'll find links to both tools on the xnec2c.org website.

    How the two tools work together is a beautiful dance. The antenna modelling tool, xnec2c, can read an antenna definition file and detect if it changes, at which point it can redo the simulation, which it can output to another file. The genetic algorithm optimisation tool, xnec2c-gao, can detect the changed output and update the antenna definition file, and the process repeats. Which brings me to a pro-tip, for this to work, you need to configure xnec2c to do two things, detect the changed definition file, and write the output to CSV, both of these options can be found in the "Optimization Settings" menu, just so you don't spend an hour banging your head against the desk.

    Between the two tools, the antenna definition evolves and you end up with a design optimised for your purpose. The default does this for SWR and gain. Mind you, I tested a multi-band dipole which managed to find some interesting designs, but didn't pick them because a low SWR combined with a high gain, for reason't I don't yet understand, wasn't considered better than a high SWR with a high gain, so there's some work to be done. As a software developer I have a sneaking suspicion that it's adding the two, rather than picking the highest gain combined with the lowest SWR, but I haven't confirmed that. As I said, deep rabbit hole.

    While we're not yet at the video display stage, for the first time I can get a sense that this might come to pass. There's plenty of work to be done. For example, the antenna display on xnec2c during the process seems broken, there's no way to output gnuplot files during the process, and capturing the various charts in real-time will require work, but all that seems if not easy, at least possible.

    Meanwhile, I'm attempting to locate an antenna definition file, preferably in .NEC format for my 6BTV antenna, so I can use this combination of tools to discover if tuning it on the ground will work and while I'm at it, discover if the installation I'm working on will give me something worthwhile.

    I realise that this is well beyond "try it and see", but my body isn't up to climbing up and down ladders 17 times in a day and I think that getting a feel for what might occur is a good way to learn.

    When was the last time you climbed on a roof and what did you do to avoid it?

    I'm Onno VK6FLAB
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    5 m
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