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Foundations of Amateur Radio: Daily Summaries Delivered
by Onno (VK6FLAB)
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- 3 days ago4 min
Some days are like running in place ...
Foundations of Amateur Radio Recently I discovered that the antenna that I had connected to my WSPR or Weak Signal Propagation Reporter beacon was not a 40m antenna, instead, it turns out to be a 15m antenna. The how and why of that mix-up isn't particularly helpful, so instead I set out to remedy the situation. Step one was simple, go into the garage and pull out the antennas and check if I had forgotten about an 80m antenna. As it happens, I'd forgotten about a 17 megacycles antenna. At the moment I couldn't tell you if it was intended for Maritime or Amateur use, but it doesn't really matter, since I'm not permitted to use those frequencies for transmit and I was on a mission. Oh, I also discovered that you can dislodge two shelves with stuff on them by moving an antenna. Fun. So, 7 MHz, or 40m it is. The antenna mount is clamped with G-clamps to the side of a steel roofed framework that's bolted to the house. It's been there for about eight years or so. From time-to-time I change over the antenna depending on my mood. Today I wanted to move the mount and after taking it down decided that it could do with a little maintenance, least of which due to the fact that the feed-point connector had detached itself. I also needed to remove the ground wire, which turns out to be a bit of a palaver, since my socket wrench adaptor has gone walkabout and the 10 mm socket that fits into the next size is too large. Eventually I found an imperial socket with a matching wrench to undo the thing. Then I set about moving the mount to a new location, tucked inside a tree, so plenty of branches to poke me in the eye, or the belly, depending on which was handy at the time, and discovered that the steel beam was thicker, to the point that my G-clamps were 2 mm too small. So, I spent some quality time comparing hardware store offerings, finally found a bigger G-clamp for a reasonable price, but in the process discovered customer reviews and photos showing that the clamps fail if you hand-tighten them. Me being the "if you can move it, it's not tight" kind of person, figured that this would not work. Found F-clamps at a different hardware store and went on my merry way to get one. The hardware store was undergoing maintenance, so hammer drills and stuff everywhere, more fun. After getting back home I discovered that the new location was great in theory, but in practice it turns out to be less than spectacular, since the beam has a slight curve in it, making for a poor clamping surface and no place to put two clamps. Back to the original location. Using the new clamps, fighting for space, I realised that I could re-use the old clamps, so swapped them over. Then I got to the point of connecting the feed-point and discovered that my 40m antenna is missing the mounting thread and the all-thread inside the old antenna wouldn't budge, neither would any of the threads in the other two antennas. So, at this point, three hours in, I came to the realisation that this was going to be a 15m antenna or no antenna. So, 15m it is. There is one actual change. I discovered that the feed-point connector is actually an SO-239 socket and the connector to it was a standard banana plug which in turn was connected to a BNC connector, with the shield connected to ground. I realised that I could use a BNC to PL-259 adaptor instead to connect the RG6 coax to my antenna. This means that the coax is now directly connected to the feed-point, rather than through a weird cobbled together BNC-to-wire-split-thinga-ma-bob-contraption. It looks very pretty. Measuring the result also shows some changes. On both 40m and 15m the SWR is still the same, on 10m it's a little worse and on 2m it's significantly better. All in all, I think this is a perfect example of 17 steps backwards and 18 steps forward. I suppose it could be worse. I'll let you know how the beacon goes. Now, I should probably log this. Something like: "QTH HF antenna mount maintenance, nothing changed, 15m antenna, PL-259 to BNC adaptor to replace homebrew wire splitter. 3 hours." I'm Onno VK6FLAB
- 1 weeks ago8 min
Keeping track of your adventures
Foundations of Amateur Radio About a year ago I set upon a new adventure, to determine if the dummy load I own, traditionally seen as a device that doesn't emit any RF, to determine if it was in fact imbued with the ability to absorb RF, rather than share it around like an antenna might. At this point you might be shaking your head, but this wasn't embarked upon lightly. I had spent several years experimenting with lower and lower power levels and came to learn that even 10 mW can make it to the other side of the planet, 13,945 km away. In other words, extremely low power can, under the right conditions, make it across the globe. So, with that in mind I connected a dummy load to my WSPR beacon and configured it to transmit across each band between 80m and 10m and then set-up an RTL-SDR dongle to monitor those same bands as well as the remainder of the amateur bands within the range of the dongle. I did this because I wanted to make sure that if there was any chance of a harmonic appearing unexpectedly, there'd be a good chance I'd see it. Then for a year I did nothing. Well, not exactly, but we'll get to that. After downloading 16 months of WSPR reports I extracted all the records that had my beacon in it and separated them into two groups. Those that had VK6FLAB as the reporting station and those that didn't. Both contained a significant number of signal reports. After doing some analysis, charting the efforts and discovering other phenomena, I can report back a little of what I learned. The dummy load does radiate, but I only saw reports from the dongle which is in the same room. I have already talked about this and at the moment the working theory is that the coax between the beacon and the dummy load radiates, or the beacon itself does, or something else, because the RTL-SDR dongle is clearly and accurately decoding WSPR signals. I'm not sure how I'd go about verifying where the radiation is coming from exactly or if I'd need equipment that I don't have or know about. That said, somewhat to my surprise, the signal reports were not static, varying considerably by as much as 40 dB. Notice that we're talking about a signal that is being, at least ostensibly, transmitted into a dummy load and being received on an external antenna. The signal reports don't appear particularly affected by time of day or band, that said, there's a visible range of reports across the year, but it's hard to observe anything definitive since most of September and October is missing. At this point I cannot tell you why that's the case. More on this in a moment. I did notice that some odd things happened to reports throughout the year. For example, on 40m, the reports were significantly poorer in the first half to 2025. 17m and 15m on the other hand were worse in the second half of the year. On the 25th of April here in Australia we're permitted to change our callsign to use AX as a prefix, so my VK6FLAB callsign would be AX6FLAB. On that day I configured my beacon to use 40m and connected it to the antenna for the first time in a year. I had several reports across the Great Australian Bight over 2,000 km away. At midnight UTC the next day I changed the callsign back to its normal VK prefix and changed the bands to use 80m, 40m, 15m and 10m, and left it connected to the antenna. While the antenna is a mono-band antenna, I wanted to know if it would still radiate on bands it wasn't intended for. Turns out that yes, it does, very nicely in fact. Since activating it like this, I've been heard by 79 different stations, as far away as 15,649 km in the United States, and in Antarctica as well as across Europe and several reports in Africa, the bulk in the Asia Pacific. Something curious though. I noticed that there were no reports on 80m and only a few on 40m. Pretty evenly split are reports on 15m and 10m. This was odd to me, since I would have told you that the antenna is a 40m mono-band antenna. You might recall, built by Walter VK6BCP (SK), I was given several antennas that are essentially helically wound verticals. I've used these ever since. I was adamant that I'd changed my antenna to 40m. After scratching my head for a bit, I decided that measuring might be a good idea. I discovered that the SWR, the Standing Wave Ratio, a traditional measurement of antenna effectiveness, on 80m is infinite, it's high on 40m, over 3 to 1 on 15m, just on 3 to 1 on 10m and similar on 2m. In other words, this is probably a 15m antenna. Now here's some things to observe. Based on reports across Australia, this antenna still radiates my 200 mW beacon on 40m, even though the SWR is 17.5 to 1, yes, you heard that right. This by way of noticing that the SWR has a relationship with how your antenna functions, but you might know, a dummy load has a perfect SWR of 1:1, in other words, the SWR is one way of characterising your antenna, but clearly it's not the final w
- 2 weeks ago6 min
Dealing with Complexity
Foundations of Amateur Radio Several years ago, I forget exactly when, I was gifted a device called a "Wio Terminal". It's a micro-controller in a box with a screen, buttons, Wi-Fi, Bluetooth and a boat load of sensors, ports and more. It's intended for experimentation and truth be told, exactly the right gift for a geek like me. It even has rubber feet to stop it from sliding off the desk, well, slow it down at least! The thing is, it remained sealed in its box until this week, when I finally gathered enough unrelated information, something I often refer to as "puzzle pieces", to understand what this device might do and how I might use it. Given that I'm talking about amateur radio, and not software development, I'll only mention that I got my initial "hello world" working and observe that I have some radio projects in mind for it. What this experience revealed to me was that complexity is hard, not to mention frustrating, and not limited to my adventures with computers. Let me elaborate. In amateur radio the answer to a great many questions is a phrase I've used before: "It depends", a valid, but ultimately immensely irksome response. Over the years I've attempted to dig into what exactly "it" depends on, with varying levels of success. While Earth rotates on its axis, that answer is unlikely to change, but I think I can make it potentially less aggravating, and here's how. When you come across a question where the answer is: "It depends", stop worrying about exactly "what" "it" depends on, instead, keep the question in mind whilst you go about your life. Looking back at my Wio Terminal experience, that's exactly what I did. While there's the frustration of not being able to report to my friend that I'd done anything useful with it, by having it float around my desk, albeit still in the box, I regularly noticed it, and when going about my day I'd continue to gather puzzle pieces that eventually hit a critical mass. In other words, whilst gathering apparently unrelated, facts, skills, articles, example code, cables, computing resources, how-to documents, forum posts and the like, including having discussions with others, eventually I had enough to realise that I had the answer to my question that wasn't "It depends", instead, I had a clear, well, clearer, understanding of what kinds of things I needed to achieve to make progress. Now I'll be the first to acknowledge that this journey isn't always a gentle stroll in the woods, "bear with a sore tooth" has been levelled more than once, but the point remains, figuring out how things work isn't a linear process and once you are aware of that, life becomes, well, at least in my mind, more interesting. Again, what does this have to do with amateur radio? Well, let's look at some innocuous questions that an amateur might ask: "What radio should I buy?", or "What antenna should I get?", or "Given the current propagation, can I make a contact with my friend on the other side of the planet?" The answer to each of these questions is: "It depends." If you have been in this community for a time, you'll understand some of the things "it" depends on, but the longer you are here, the more aware you become of other things "it" depends on, in other words, your understanding of the problem reveals that there are more considerations at play that might not be immediately obvious. At some point you'll get to the next unhelpful response in amateur radio: "Try it and report back." Equally annoying, since, at least on the face of it, you'll invariably be left with the feeling that nobody cares, least of all the person you asked. While I'll acknowledge that this is sometimes the case, on the whole, the response really reveals that there are too many unknown variables to form any coherent overview. That said, as the person answering, providing a range might be helpful to at least get a sense of what space to play in. What I mean by that is, sometimes figuring out what needs to happen involves multiple considerations which each impact on the solution in subtle and different ways. When you're learning about a problem, you might not know what those considerations are, but as time goes by, while you're presumably collecting puzzle pieces, your awareness increases. During the week, I saw a post by Christophe ON6ZQ announcing a tool called "HF Propagation Lab" (https://on6zq.be/prop), described as "A browser-only teaching instrument for amateur radio operators. It explains what live space-weather numbers suggest, how each band may react, and which ionospheric mechanism is probably doing the work. It is a teaching model, not a substitute for beacons, skimmers, WSPR, or listening on the air." What this tool does is give you a feel of the propagation landscape you're playing in, what variables impact in what way, in your ability to make contacts. In other words, it's a way to learn about the unknown variable
- 3 weeks ago5 min
What does amateur radio bring to your life?
Foundations of Amateur Radio The other day I went for a walk around the block for the first time in a while. It's something I did for a time and then for several reasons, mostly to do with health, didn't. For me it's the mental equivalent of having a shower with the added benefit of not having to dry my hair, in other words, it's a place I go to with the intent of generating shower thoughts. During my walk, away from the forces pulling me in all manner of directions, none of which have anything to do with amateur radio, away from my keyboard, away from my screen, away from technology challenges, although I'll admit that my phone was in my pocket, I took about twenty minutes to walk and daydream, to follow my thoughts and to see where they'd end up. I got to this point because sitting at my desk I was getting nowhere trying to put together my thoughts in any sequence at least resembling coherence. While it's happened before, it's not something that occurs often. The day before I'd started writing, almost as-if possessed, about what amateur radio means to me, but during my walk I started wondering about the people who leave this hobby and the community embracing it. I've often said that F-troop is a weekly net for new and returning amateurs, both people who have a license that's still hot off the printer, and others who have one typed up on an IBM Selectric, signed with a quill, ink faded with age, paper yellowed by sunlight, potentially with coffee mug rings on it, stashed somewhere in a drawer. I wondered about those returning amateurs and asked myself about the nature of leaving a hobby. It occurred to me that people leave for many different reasons, and it would be foolhardy to consider that all of those reasons are controllable by our community. While bullying and arguments exist, each responsible for their share of people leaving, it seems to me that some amateurs leave because there's too much other stuff going on in their lives, things that actively or passively prevent amateurs from participating. This is difficult for me to relate to because for me, amateur radio is an intrinsic part of my life, in that it often quietly shapes how I view the world and learn from it. I see it when I notice a television antenna pointing in the wrong direction, when I install a new Wi-Fi router somewhere, when a signal is lost to a manned mission around the Moon, when I open the garage door and when I read that researchers at the National Institute for Standards and Technology, better known as NIST, have developed a new method for creating chips that process photons similarly to how traditional chips process electrons which can generate a rainbow of colours, though they didn't use the letter "u" to describe them. While those examples might be somewhat obvious, amateur radio is also there when I see someone share a tiny electronic paper screen on social media and I consider how I might use that when I go portable. It's there when I'm walking in a park and when I'm looking at a beach, it's there when I see metal artworks or painters poles at the local hardware store and when I watch a movie with radios anywhere on screen. It's there when the topic of physics arises and when some electromagnetic phenomenon occurs. Like radio waves and air, it's pretty much part of my daily existence. I will add that this same depth of connection exists between me and computers. Watching "Flight of the Conchords" I cannot help but notice that Murray's computer keeps changing and that I miss the Commodore Vic 20 sitting behind him surrounded by ever changing New Zealand tourism posters. In other words, I cannot imagine ever not having radio or computers in my life. I'm mentioning all this because my experience isn't universal. While I'm sure that I'm not alone in this deep affinity, the community as a whole invariably ranges between people who could take or leave the hobby at a moment's notice and those who couldn't live without it and beyond our community there are people who are, depending on your perspective, blissfully or woefully, unaware of our existence. All this to say, your experience of this hobby is not the same as that for everyone else, neither is your experience of life. This is revealed more clearly in what we think the hobby means, whether or not FT8 is a blessing or a curse, contesting is ridiculous or amazing, why 40m is better than 20m or vice-versa and if the hobby died when the ITU stopped requiring Morse code, or saw a rebirth. It should be obvious by now, but I think it's important to be explicit. Amateur radio is your hobby. It's what it means for you. Not for your mate, not for me, not for the people in your club, the local email list or social media. Just you. So, use this as an opportunity to think about this, in my not so humble opinion, absolutely amazing hobby and what place it has in your life. I'm Onno VK6FLAB
- Apr 18, 20263 min
You don't need an excuse to make noise!
Foundations of Amateur Radio The other day I came across a post on mastodon.radio by Keith W6KME announcing the resumption of the Micro Field Day, spelled using the 12th letter of the Greek alphabet, Mu. This was news to me, since I didn't know they'd stopped, let alone existed at all. Being the curious type, I stopped to investigate and discovered an initiative that could, and in my not so humble opinion, should, be replicated all over the planet. Essentially an informal monthly gathering of amateurs with their portable set-up, ranging from hand-held radios through lightweight backpack gear suitable for SOTA or POTA, or Summits or Parks on the Air, to car portable stations where your vehicle acts as the carry mule and perhaps the base of your antenna. In other words, it's for anyone who brings along their radio to play or if you're not yet ready to do that, come and participate as you feel inclined. So, what of the resumption, you ask. It turns out that the activity became so popular locally that some parks required paid bookings and insurance, which is somewhat challenging if you're not actually an organisation. The closest I've ever come to a Micro Field Day is when we celebrated a milestone anniversary for the weekly F-troop net that has now been running for over 15 years. The Bored Net Group website has plenty of information about what they get up to during a Micro Field Day, Random Metal Objects On The Air, shared club activities, picnic lunches, and activations at local lakes, landmarks and other places of interest. I'd also like to make a point here about documenting your activities so the rest of the community can learn from your experience and the Micro Field Day isn't the only, or even the first activity that the group organised. Special mention to Zak N6PK who started hosting the BORED net four times a day during the COVID-19 pandemic lockdown in March 2020. You'll find the full story when you check out their site at theborednet.net for that and oodles more inspiration. While I'm perfectly happy sitting at home behind a computer reading research on the resource comparison between half a dozen algorithms for calculating a Fast Fourier Transform, that's not the only thing that amateur radio represents. When I started running F-troop there was no place for new and returning amateurs to gather and ask questions and share their experiences. Today the log shows at least one new callsign for each week we've been on-air, representing nearly a thousand amateurs who activated their transmitter and shared their experience. There is no organisation behind F-troop, it's a couple of amateurs who regularly turn up and participate to act as a welcoming voice into the diverse community that represents amateur radio. In other words, it started because I felt like it and it continues because people keep coming back. The Micro Field Day is exactly the same in that it was started to scratch an itch. I'm making this explicit because some amateurs appear to be under the impression that they'll need a local club or organisation to organise activities for them. I'm here to tell you that you can start such an activity with your friends. Ultimately, where do you think clubs come from? So .. what are you waiting for? Get on-air and make some noise! I'm Onno VK6FLAB
- Apr 11, 202610 min
What's in an S-unit?
Foundations of Amateur Radio The other day fellow amateur Randall VK6WR raised an interesting question. Using his HP 8920A RF Communications Test Set, which you might recall from our adventures in measuring radio harmonic power in 2023, that report is on my Github repository, but I digress, Randall wondered if the signal strength he was seeing on several radios were the same and discovered that in fact they were not. It made Randall ask who set the standard and following on from that, what does this look like in the real world? In 2014, episode 149 of the series "What use is an f-call?", I published an article titled "The simple S-unit". In it I referred to a standard for S-units defined in 1981. Unfortunately, I didn't provide any references, so, armed with more than a decade extra experience, Randall encouraged me to investigate. Twenty seconds into my search, I discovered IARU Region 1 Technical Recommendation R.1, which has four statements related to the topic at hand. Under the title "STANDARDISATION OF S-METER READINGS" it states that: 1. One S-unit corresponds to a signal level difference of 6 dB, 2. On the bands below 30 MHz a meter deviation of S-9 corresponds to an available power of -73 dBm from a continuous wave signal generator connected to the receiver input terminals, 3. On the bands above 144 MHz this available power shall be -93 dBm, 4. The metering system shall be based on quasi-peak detection with an attack time of 10 msec +/- 2 msec and a decay time constant of at least 500 msec. So. Job done, right? Yeah, nah, not so much. The web page I quoted from is linked from the Wikipedia S-meter entry and was archived in 2005 and at the time existed on a Swedish domain in the home directory of Kjell SM7GVF. The page has two additional interesting things, the words "Brighton 1981" and "Torremolinos 1990", both of which refer to IARU conferences. The reports for these meetings are online. In searching for any reference to the definition of the S-unit, the 1990 report shows that resolution "83-1" had the status of "Action completed", whatever that means. The 1981 conference document has all manner of interesting references, including "Log Forms and Summaries for International Contest Use", "Meteor Scatter qso procedure" and the definition of the standard way to determine Morse Code speeds using the word "PARIS" followed by a 7 bit word space, to name three. The one we're interested in is called "BM/134 - S-Meter Standards", appearing on page 33 and 34 of the 1981 report. It's a photocopy, so you can see the text from other pages superimposed. I'm making this observation because this is essentially a standards document, intended to be adhered to by industry and the amateur community. It gets better, or rather .. worse. The text that is referenced by Wikipedia uses numbers for the four elements, where BM/134 uses letters. The third item in BM/134 says that it applies for "bands above 30 MHz", but the document I just quoted appears to be unique in saying that it applies to "bands above 144 MHz". The fourth item, dealing with the way that the meter responds has been altered on BM/134. The text "+/- 2 ms and a decay time" are in a different font and at an angle. Worth noting that the change includes "ms" twice, rather than "msec" as the unit for milliseconds used elsewhere. Searching for a phrase within the standard, I discovered the Region 1 HF Manager Handbook v7.01, which appears to include the S-meter standard in chapter 11.1.2, but closer inspection reveals that the fourth item is missing, the one about quasi-peak detection. This is significant because the S-meter standard is based on a CW signal, not an SSB signal, which fluctuates. There's no reference as to where or when this was removed or by whom. These changes are repeated in subsequent versions of the HF Managers Handbook. There's other differences too, instead of using millivolt and microvolt as shown in the original BM/134 standard table, all units have been converted to millivolt for no discernible reason. The new table, including typo, is also copied everywhere. While we're at it, the original standard contains the letters "V", "E", "R", "O", "N" at the top. They don't show in the HF Managers Handbook either. This is curious, since last time I checked, those letters signify an organisation that at least some here will recognise, the "Vereniging voor Experimenteel Radio Onderzoek in Nederland", known to the the people who don't speak fluent Dutch, as the peak body for amateur radio in the Netherlands, VERON. Searching its website does not reveal their contribution to this standards document, which I have to say, is par for the course, much of our amateur radio history is poorly documented or archived, if at all, something which I've spent plenty of my time attempting to remedy over more than a decade, one article at a time. Moving on. The
- Apr 4, 20268 min
Where is the spark .. gap?
Foundations of Amateur Radio The thing I love most about this amazing hobby of amateur radio is the sheer size of the community and the depth of knowledge that comes with it. Case in point, the other day I mentioned the spark gap transmitter at Grimeton in Sweden. A few hours after releasing my comments into the void I received a message from Paul SA7CND who lives, wait for it, 153 km from the transmitter. He's been on-site while it was running, transmitting on 17.2 kHz. Paul pointed out that the Grimeton transmitter is not a spark gap transmitter at all. It's actually an Alexanderson alternator, an entirely different beast, and all the more interesting for it. Invented by Swedish electrical engineer and inventor, Ernst Frederick Werner Alexanderson, he received a patent for it in 1911 whilst working for General Electric. He died in 1975, aged 97 with 345 patents to his name. Before I dig in, because you know I will, the transmitter at Grimeton was officially opened on the 1st of December in 1924. Built to increase Swedish independence after World War I revealed its vulnerability to foreign controlled transatlantic telegraph cables. Serving as a telegraphy station capable of transmitting traffic across the Atlantic ocean the station was in regular service until 1996. Unlike its scrapped brethren, the Grimeton transmitter is currently operated several times a year as a functioning transmitter using the callsign SAQ. Announcements are made on the station mailing list and the website at grimeton.org, but generally on Alexanderson Day in July and Christmas Eve in December. You'll need to tune to 17.2 kHz, something you can do with a sound-card, or with an SDR. Sound-card you say? Yes. Not for audio, but for RF. Connect an antenna to the microphone centre-pin input and have at it. Note that this will likely be highly susceptible to noise, so filtering and experimentation are to be expected. There's several tools around to play with this, GNU Radio, Quisk, SuperSID and SAQrx. Also, there's plenty of other VLF, or Very Low Frequency stations to listen to. I should probably add this as a 51st thing to do with SDR, but I digress. Back to Grimeton. As the last remaining functional Alexanderson alternator transmitter, it was added to the UNESCO World Heritage List in 2004. You can visit and see first hand what radio history looks like. As I said, if you pick your day, you can even watch it working. Failing that, there's plenty of YouTube videos showing the entire process, it's an absolute monster. There's even an amateur radio shack on-site with the callsign SK6SAQ. The website says that it's open sporadically, so I'd recommend you contact them before heading to Grimeton. I'll note that at the time that this station was being commissioned in 1924, it was already being superseded by valve oscillators, which brings me to how it works. Depending on where you live, you're likely familiar with the 50 or 60 Hz alternating current associated with household electricity. In 1891, Irish experimental physicist Frederick Thomas Trouton pointed out that if you could run an alternator at high enough speed it would create an alternating current at radio frequencies, said differently, creating a continuous wave at radio frequencies. Much experimentation followed and many giant shoulders supported this effort. It goes a little like this. Use an electric motor designed to spin at 900 revolutions per minute. Connect it to a gearbox. Connect that to a rotor with multiple poles. Then run the motor with a clutch to vary the speed. If that's not enough, to produce high power, the clearances between rotor and stator have to be kept to a millimetre. Then there is cooling and lubrication to consider, not to mention dealing with thermal expansion and contraction of a fast spinning and closely toleranced disk. At Grimeton, the whole transmitter weighs in at 50 tonnes, pretty much the opposite of portable operation. The rotor at Grimeton is a 1.6 meter diameter disc with a 7.5 cm thick edge with 488 slots milled into it, each filled with brass. The motor at Grimeton runs at just over 711.3 revolutions per minute, the gearbox has a ratio of 2.973 and the whole contraption generates 17,200 Hz. If you get the sense that you're balancing an elephant on top of a needle, you're almost there, but if you consider that keying the transmitter changes the load and currents, it's more like an elephant being shoved by a train, balancing on top of a needle. At Grimeton, the motor is loaded by one of three liquid resistors, which each consist of a two metre high container filled with water and baking soda. The liquid level is controlled by separate pumps, varying the resistance. Whilst transmitting, a second liquid resistor is added, reducing the resistance to regulate the speed of the motor to maintain the overall speed and the associated frequency. The resistors generate heat which is fed through a
- Mar 28, 20267 min
Bald Yak 18: Everything Everywhere All at Once?
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 Grimet
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About Foundations of Amateur Radio
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?".
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