The Contester In Me...
vor 2 Tagen
6:01Foundations of Amateur Radio So, I have a confession to make. I'm a contester. I'm not ashamed of this. While I'm in a confessing mood, I'll also mention that I've not participated in many contests in the past few years. This is not for the want of desire, but for the lack of motivation to fix things in my shack that are fundamentally broken. On the weekend I participated in a local contest. I took part for six hours, got on-air and made noise, made about 30 contacts, had a ball. I wasn't playing to win, though I did use the opportunity to refresh and hone some of my rusty skills. The next day I spent much too long converting my log into something that the contest organiser asked for. I also discovered that there was a duplicate entry in my log, not something which I'd expect with only so few contacts, but a reflection on the tool I was using to create my log. I started writing down what I learnt from the experience, operating from my own shack, documenting what worked and what didn't. I commented on several things relevant to me, but to give you a flavour, my operator position is terrible because I'm logging on my main computer and the radio is side-on when I'm facing the computer. The sun was shining directly into my eyes when facing the computer. Holding a microphone I didn't have hands-free, I still don't have an auto-keyer to save my voice, my foot pedal didn't work and my data interface was on loan to another amateur. As I said, these things are specific to me. Logging was worse. It didn't quite bring me to tears, but as the contest went on, it became a problem. I started to write down what was wrong with the tool I was using with a view to submitting patches to fix it when I realised that it wasn't actually built as a contesting logging tool, so I stopped and instead started writing a new list, one that describes what a good contesting tool looks like. It builds on a decade of using different tools and participating in contests in all manner of different situations, from special portable event activations, through to the annual top-tier contests run from a purpose built contest station and everything in between. So, what does the ideal contesting tool look like, for me? It needs to be cross platform, as-in, I should be able to use it on whatever computer I have access to, my Linux workstation, a Macintosh Laptop, an Android phone or tablet and while I'm at it, Windows and iOS and I think it should be able to run on a Raspberry Pi. In other words, there shouldn't be a situation where you cannot run the tool because you have some random combination of operating system or CPU that the developer doesn't support. It must be open source. By that I mean, the code should be available to the entire community. There are too many stories of great tools dying or being held hostage by individuals or small groups. The tool should continue to exist and be usable regardless of the participation of the original developer. Users should be able to fix things, add functionality, change themes, whatever. You should be able to customise it because not every contest needs the same information. For example, the John Moyle Memorial Field Day, a contest run every year during March in Australia requires that VHF and UHF contacts record the maidenhead locator, a four or six character message that designates the location of the station. This is used to calculate distance between two stations and award points accordingly. Such a requirement isn't needed in most other contests. Some contests are considered friendly contests, like the Remembrance Day contest in August. It's common to exchange your name, details about your station and have a chat. You'd be unpopular if you used that approach for the Oceania DX, the CQ World Wide or the CQ WPX contests. In other words, some fields are expected for some contests, but not for others. The tool needs to be able to show if a contact is valid by whatever means the rules for a particular contest decide. It needs to automatically log the time, keep track of previous entries and know about the super check partial list to validate partial callsigns. The user needs to be able to use either a keyboard or mouse, or both, to do all the common contesting data entry. No dependency on crazy keyboard shortcuts, no requirement to click the mouse to make an entry, in other words, the tool needs to be able to get out of the way of the contester. I think it needs to have a plug-in system to accommodate different rules and it needs to be able to export data in whatever format the contest organiser expects. You should be able to use it without needing to be connected to the internet during the contest, it should be easy to update and have the ability to keep a station log for all the contacts ever made. It would be great if it could also import existing logs so you can start to consolidate older logs. Having spent quite some time looking for such a tool and failing, I've come to the conclusion that there's only one thing for it, I'm going to have to write my own tool and it would be great if you could help by sharing your opinion on the matter. At this point I'm looking for suggestions on what you think is needed for a great contesting tool. I realise that for some, pen and paper is sufficient, and I'm not trying to dissuade you from using that, I've used it myself on more than one occasion, rather, I'm asking if you can think of things that it should do out of the box, things that are basic functionality that you would like to see as part of the design. You can find the project on my vk6flab GitHub page, comment on Reddit, or you can drop me an email, [email protected] Look forward to hearing from you. I'm Onno VK6FLAB
What's with a negative SNR?
7:00Foundations of Amateur Radio We describe the relationship between the power of a wanted signal and unwanted noise as the signal to noise ratio or SNR. It's often expressed in decibels or dB which makes it possible to represent really big and really small numbers side-by-side, rather than using lots of leading and trailing zeros. For example one million is the same as 60 on a dB scale and one millionth, or 0.000001 is -60. One of the potentially more perplexing ideas in communication is the notion of a negative signal to noise ratio. Before I dig in how that works and how we can still communicate, I should point out that in general for communication to happen, there needs to be a way to distinguish unwanted noise from a desired signal and how that is achieved is where the magic happens. Let's look at a negative SNR, let's say -20 dB. What that means is that the ratio between the wanted signal and the unwanted noise is equivalent to 0.01, said differently, the signal is 100 times weaker than the noise. In other words, all that a negative SNR means is that the ratio between signal and noise is a fraction, as-in, more than zero, but less than one. It's simpler to say the SNR is -30 dB than saying the noise is 1000 times stronger than the signal. Numbers like this are not unusual. The Weak Signal Propagation Reporter or WSPR is often described as being able to work with an SNR of -29 dB, which indicates that the signal is about 800 times weaker than the noise. To see how this works behind the scenes, let's start with the idea of bandwidth. On a typical SSB amateur radio, voice takes up about 3000 Hz. For better readability, most radios filter out the lower and upper audio frequencies. For example, my Yaesu FT857d has a frequency response of 400 Hz to 2600 Hz for SSB, effectively keeping 2200 Hz of usable signal. Another way to say this is that the bandwidth of my voice is about 2200 Hz, when I'm using single side band. That bandwidth is how much of the radio spectrum is used to transmit a signal. For comparison, a typical RTTY or radio teletype signal has a bandwidth of about 270 Hz. A typical Morse Code signal is about 100 Hz and a WSPR signal is about 6 Hz. Before I continue, I should point out that the standard for measuring in amateur radio is 2500 Hz. This is significant because when you're comparing wide and narrow signals to each other you'll end up with some interesting results like negative signal to noise ratios. This happens because you can filter out the unwanted noise before you even start to decode the signal. That means that the signal stays the same, but the average noise reduces in comparison to the 2500 Hz standard. This adds up quickly. For a Morse Code signal, it means that turning on your 100 Hz filter, will feel like improving the signal to noise ratio by 14 dB, that's a 25 fold increase in your desired signal. Similarly, filtering the WSPR signal before you start decoding will give you roughly a 26 dB improvement before you even start. But there's more, since I started off with claiming that WSPR can operate with an SNR of -29 dB. I'll note that -29 dB is only one of the many figures quoted. I have described testing the WSPR decoder on my system and it finally failed at about -34 dB. Even with a 26 dB gain from filtering we're still deep into negative territory, so our signal is still much weaker than the noise. There are several phenomena that affect the decoding of a signal. To give you a sense, consider using a limited vocabulary, like say the phonetic alphabet, or a Morse character, the higher the chance of figuring out which letter you meant. This is why it's important that everyone uses the same alphabet and why there's a standard for it. To send a message, WSPR uses an alphabet of four characters, that is, four different tones or symbols. Another is how long you send a symbol. A Morse dit sent at 6 words per minute or WPM lasts two tenths of a second, but sent at 25 WPM lasts less than 5 hundredth of a second This is why WSPR uses two minutes, actually 110.6 seconds, to send 162 bits of data, lasting just under one and a half seconds each. If that's not enough, there's a processing gain. One of the fun things about signal processing is that when you combine two noise signals, they don't reinforce each other, but when you combine two actual signals, they do. Said in another way, signal adds coherently and noise adds incoherently. To explain that, imagine that you have an unknown signal and you pretended that it said VK6FLAB. If you combined the unknown signal with your first guess of VK6FLAB and you were right, the unknown signal would be reinforced by your guess. If it was wrong, it wouldn't. If your vocabulary is small, like say four symbols, you could try each in turn to see what was reinforced and what wasn't. There's plenty more, things like adding error correction so you can detect any potentially incorrect words. Think of it as a human understanding Bravo when the person at the other end said Baker. If you knew when to expect a signal, it would make it easier to decode, which is why a WSPR signal starts at one second into each even minute and each symbol contains information about when that signal was sent, which is why it's so important to set your computer clock accurately. Another is to shuffle the bits in your message in such a way that specific types of noise don't obscure your entire message. For example, if you had two symbols side-by-side that when combined represented the power level of your message, a brief burst of noise could obliterate the power level, but if they were stored in different parts of your message, you'd have a better chance of decoding the power level. I've only scratched the surface of this, but behind every seemingly simple WSPR message lies a whole host of signal processing magic that underlies much of the software defined radio world. These same techniques and plenty more are used in Wi-Fi communications, in your mobile phone, across fibre-optic links and the high speed serial cable connected to your computer. Who said that Amateur Radio stopped at the antenna connected to your radio? I'm Onno VK6FLAB
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Acronym not found ...
7:12Foundations of Amateur Radio Our community is full of TLAs, or three letter acronyms. Some of them more useful than others. For example, I can tell you thank you for the QSO, I'm going QRT, QSY to my QTH. Or, thanks for the chat, I'll just shut up and take my bat and ball and go home. Acronyms arise every day and it came as no surprise to spot a new one in the wild the other day, SHF. It was in a serious forum, discussing antennas if I recall, so I didn't blink and looked it up. Super High Frequency. Okay, so, where's that? I'm familiar with VHF and UHF and as radio amateurs we're often found somewhere on HF, that's Very High Frequency, Ultra High Frequency and High Frequency if you're curious. Turns out that the ITU, the International Telecommunications Union has an official list, of course it does. The current ITU "Radio Regulations" is the 2020 edition. It's great bedtime reading. Volume one of four, Chapter one of ten, Article two of three, Section one of three, Provision 2.1 starts off with these words: "The radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table." When you look at this table you'll discover it starts with band number four and ends with band number twelve, between them covering 3 kHz to 3000 GHz. In position ten you'll see the designation "SHF", covering 3 to 30 GHz, centrimetric waves. A couple of things to note. The list starts at band four. There are of course frequencies below 3 kHz. The list ends at twelve, but there are frequencies above 3000 GHz. You'll also note that I'm not saying 3 Terahertz, since the ITU regulations specify that you shall express frequencies up to 3000 GHz using "gigahertz". Interestingly the same document has a provision for reporting interference where you can report using Terahertz frequencies, so I'm not sure how the ITU deals with such reports. Another thing to note is that this table doesn't actually define what SHF means. It's nowhere in the radio regulations either, I looked. I'm not sure where the words Super High Frequency came from. There is an ITU online database for looking up acronyms and terms. That leads to a document called "Nomenclature of the frequency and wavelength bands used in telecommunications", which also doesn't use "Super High Frequency" anywhere. That said, using the ITU band four, where its definition starts, the VLF band, or Very Low Frequency, followed by LF, Low Frequency, MF, Medium Frequency, the familiar HF or High Frequency, VHF, UHF, then SHF and beyond that, EHF, Extremely High Frequency and THF or Tremendously High Frequency, yes, Tremendously High. There's a report called the "Technical and operational characteristics and applications of the point-to-point fixed service applications operating in the frequency band 275-450 GHz". It introduces the term "THF which stands for tremendously high frequency" but adds the disclaimer that "this terminology is used only within this Report." Seems that there are plenty of documents on the ITU website using that same definition, so I'm guessing that the cat is out of the bag. THF by the way is defined as being for 300 to 3000 GHz frequencies. By the way, the ITU TLA finder exposes that THF stands for Topology Hiding Function. Where's a good acronym when you need it? Speaking of definitions, I came across the definition of a "taboo channel" which according to the ITU is "A channel which coincides with the frequency of the local oscillator in the single super heterodyne receiver which is tuned to an analogue channel." Anyway, we still have a way to go. Below band four, less than 3 kHz, we have ULF or Ultra Low Frequency, SLF, Super Low Frequency and ELF, Extremely Low Frequency, which is defined as band one, between 3 and 30 Hz. Below that, some have suggested TLF, or Tremendously Low Frequency which apparently goes between 1 and 3 Hz with a wavelength between 300,000 down to 100,000 km. Others have suggested that this is an internet meme, but so far it seems to me that it has just as much legitimacy as any of the other wordings, since it appears that the ITU explicitly excludes such definitions, even if internal documents introduce terms from time to time. It did make me wonder, what comes after Tremendously High Frequencies, Red? Turns out, yes, well, infra-red pretty much follows on from Tremendously High Frequencies. If you think that's the end of it, think again. The IEEE, the Institute of Electrical and Electronics Engineers has its own definitions, of course it does. Unfortunately they decided that you need to pay for their standard. It was first issued in 1976 "to remove the confusion". There's an xkcd comic called "Standards", number 927 if you're looking. It goes like this: Situation: There are 14 competing standards. 14?! Ridiculous! We need to develop one universal standard that covers everyone's use cases. Yeah! Soon: Situation: There are 15 competing standards. Anyway, the IEEE designates that after UHF comes L or Long wave, followed by S, or Short wave, then comes C, the compromise between Short wave and X or cross or Exotic. Then there's Ku, Kurtz Under, K, Kurtz, and Ka or Kurtz above, Kurtz being the German word for Short. There's the V band and the W band which follows the V band. Had enough yet? NATO, the EU and the US define these using letters of the alphabet. And broadcasters use Band Numbers which link up to nothing in particular. I wonder if the measure of a society is just how many different ways can be used to describe the same thing. Perhaps we should have stopped at Hertz or Hz, which was established in 1930 by the International Electrotechnical Commission, as an expression of the number of times that a repeated event occurs per second, in honour of Heinrich Hertz. One more three letter acronym, the International Electrotechnical Commission is better known as the IEC. I wonder if the ITU is taking suggestions, ginormous, utterly, inordinately, awfully and humongously seem like perfect opportunities for future expansion. I'm Onno VK6FLAB.
Antenna Testing Day ...
5:41Foundations of Amateur Radio Last week I went outside. I know, it was a shock to me too. The purpose of this adventure was to test an antenna that has been sitting in my garage for nearly a year. Together with a friend we researched our options and at the end of the process the Hustler 6BTV was the answer to our question. Before the commercial interest police come out of the woodwork, I'll point out that I'm not providing a review, good or bad, of this antenna, it was the antenna I purchased and went to test. Between the two of us we have three of these antennas. I have the idea to use one as a portable station antenna and another as my base station antenna. Glynn VK6PAW intends to use his as a base station antenna. To set the scene. The antennas came in quite large boxes, just over six bananas long, or more than 180 cm. When they arrived I opened my boxes and checked their content, then sealed it all up and put the boxes on a shelf. Last week Glynn proposed that we set one up and see what we could learn from the experience. You know that I love a good spreadsheet, so planning went into overdrive, well, I put together a list of the things we'd need, starting with the antenna and ending with sunscreen to protect my pasty skin from the fusion experiment in the sky. In between were things like an antenna analyser, spare batteries, tools, imperial, since apparently there are still parts of the world that haven't gone beyond barley measurements. I jest, they authorised the use of the metric system in 1866. My list also included a magnetic bowl to capture loose nuts and washers, you get the idea, anything you might need to test an antenna in the field. Our setup was on a rural property where we had lovely shady trees and oodles of space to extend out a 25m radial mat. We tested many different set-ups. I won't go through them all, but to give you an idea of scale, in the time we were there, we recorded forty different antenna frequency scans. The 6BTV antenna is suitable for 80m, 40m, 30m, 20m, 15m and 10m. We tested with and without radials, raised and on the ground and several other installations. We learnt several useful things. For starters, sitting on the ground with radials the antenna measurements line up pretty well with the specifications and with a suitable base mount to protect the plastic base the portable station antenna is usable out of the box. Any variation on this will result in change, sometimes subtle, sometimes less so. For example, we came up with one installation where the SWR never dropped below 3:1. That's with the antenna on the ground without any radials in case you're wondering. Other things we learnt were that manually scanning each band is painful. When we do this again we'll have to come up with a better way of measuring. The aim for my base antenna is to install it on my roof, bolted to a clamp on the side of my metal pergola. This means that we're going to have to do some serious tuning to make this work for us. It might turn out that we'll start with installing the antenna at Glynn's QTH first, but we haven't yet made that decision. Other things I learnt are that I had actually put together the base clamp when I checked the boxes a year ago, so that was a bonus. The magnetic bowl saved our hides once when a spring washer fell into the lawn. The hose-clamps that come with the antenna require a spanner, but there are thumb screw variations of those that I'll likely use for my portable setup. Other things we need to do is learn exactly how the traps work and how adjusting them affects things. In case you're unfamiliar with the concept of a trap, think of it as a radio signal switch that lets signals below a certain resonant frequency pass and blocks signals above that frequency. In other words, a 10m trap resonates just below 28 MHz. It lets frequencies below 28 MHz pass, but blocks those above it, essentially reducing the length of the antenna to the point where the trap is installed. One test we did was to only use the base and the 10m trap. We discovered that this doesn't really work and that the metal above the trap, as-in the rest of the antenna, isn't just for show, even though it's on the blocked side of the 10m trap. Given that I intend to use my base antenna as my main WSPR transmission point, I need to adjust things so the antenna works best on WSPR frequencies. I intend to use a tuner for when I want to work outside those frequencies. One unexpected lesson was that the awning that Glynn attached to his vehicle was an absolutely essential item. I don't think I'll ever go portable again without one. Life changing would be an understatement. I'm investigating if I can fit one to my vehicle. Having had some health issues over the past months I was anxious about going outside and being somewhat active. I paced myself, protected my back, took regular breaks, sat down a lot, drank litres of water and slept like a baby that night. No ill effects, very happy. As a bonus, I even transferred our measuring data to a spreadsheet. I can't wait to see the results of our next adventure. Oh, we did connect a radio. Heard a beacon in Israel, heard a QSO in Italy, listened to WWV on 10 MHz and almost missed the bliss of not having to tune or switch when moving from band to band. What have you been up to in the great outdoors? I'm Onno VK6FLAB
Are all spiky antennas the same?
6:19Foundations of Amateur Radio The world is filled with antennas. You'll find them on towers, buildings, cars and on your next door neighbour's roof. They come in an astonishing variety, to the point where you might start thinking that antennas are a fashion accessory that vary with the season and if you start digging through the history books you'll come across designs that dial that variety up to eleven. Possibly the most visible antenna today is the television antenna and when you start noticing them, the more variation you'll discover. Their basic shape consists of a vertical pole, the mast, with a horizontal pole, the boom. Attached to the boom are various different shapes, or elements, that often vary in length according to some pattern. The shape is designed to collect as much electromagnetic radiation from a particular direction, or in the case of a transmitter, focus as much energy as possible into one direction. This focus is called gain. The more focus, the more gain. One of the oldest designs for this kind of antenna, still in use today, is the Yagi-Uda or Yagi antenna. It was invented in 1923 by Shintaro Uda at the Tohoku Imperial University in Japan and popularised to the English speaking world by his boss Hidetsugu Yagi who claimed to be the sole inventor in his Japanese patent application. He went on to file similar patents in Germany and the United States. Gain for a Yagi varies depending on design. Generally more elements means more gain. Sometimes you'll see a Yagi with weird shorter elements along the boom. This is a design to make the antenna work across multiple frequencies. Another way that this can be achieved is by adding traps along an element. They look like a thick stubby tube at some distance along an element. You can have more than one of these to allow for more frequencies. These improvements allow for several Yagi antennas to share elements and boom space, essentially combining several independent antennas into one. It can be tricky to discover in which direction a Yagi is pointing, but essentially the boom indicates the direction and the end with the shortest element is the front. There's another type of antenna that to the casual observer looks similar. It's called a log periodic dipole array, LPDA or log periodic antenna. It was invented in 1952 by John Dunlavy whilst he was contracted to the United States Air Force. He wasn't credited because it was classified as "Secret", later changed to "Restricted". In 1958 Dwight Isbell built a log periodic antenna as an undergraduate student at the University of Illinois at Urbana-Champaign. He was part of a larger team that included Raymond DuHamel, John Dyson and Robert Carrell. Later Paul Mayes developed a variant that improved performance. Before I dig in, I'll also note that this antenna caused all manner of legal issues that are still in force today. The so-called Blonder-Tongue Doctrine states that a patent holder isn't permitted to re-litigate the validity of a patent that has been held invalid previously. It was a result of the University attempting and ultimately failing to protect its patent for the widely copied antenna design. Reading about this is a fascinating discovery in how a single Judge can make a massive impact on law and society. The log periodic antenna is designed in a way that to the uninitiated looks very similar to a Yagi antenna. It's based on the idea that you can design an antenna made up from independent dipoles that are spaced in such a way that they form an antenna where each dipole radiates to take advantage of its neighbours. Generally a log periodic antenna looks like a triangle. Often the elements are on two separate booms, alternating side-to-side, or you'll see a zig-zag structure that causes the antenna signal to alternate side-to-side. One characteristic of an antenna is called bandwidth. It's a measure of how many frequencies it can operate on within the constraints of the antenna. The wider the bandwidth, the more frequencies you can use with the same antenna. A Yagi antenna typically operates within about four percent of the design frequency. If you combine multiple Yagis by adding traps or different length elements, you'll end up with several frequencies, each with a similar range. A log periodic antenna on the other hand is designed to be used across a large range of frequencies. In shortwave broadcasting there are log periodic antennas that operate between 6 and 26 MHz. In more common use today you'll find log periodic antennas used for higher frequencies. It's not unusual to find log periodic antennas that operate between 400 and 4000 MHz. For even more confusion, you can share the boom of a log periodic antenna with a Yagi antenna as is popular in fringe television reception areas. Some other things to note are that for a Yagi most of the elements are passive and only one is generally a driven element, in a log periodic antenna all elements are driven. For a Yagi antenna, more elements means more gain, whereas for a log periodic antenna it means more frequencies. I'll also point out that there are experiments where the frequency range for Yagi antennas is being increased to more than twenty percent of the main frequency by varying the design. Much of this is achieved by using computer simulations to test many different virtual antennas until one promising design pops out. This optimisation technique can also be applied to log periodic antennas resulting in very interesting shapes that look nothing like the antennas you see on the roof today. I've completely skipped over how these antennas are actually fed, as-in, how is the coax connected to the antenna. That's a whole different topic of conversation worthy of many hours of research and discussion. Next time you look at a spiky antenna you should be able to discover if it's a Yagi or log periodic, or both and why. I'm Onno VK6FLAB
Some Amateur Radio ABCs ...
4:30Foundations of Amateur Radio A is for Antenna, the eyes and ears of any amateur station. You'll spend eighty percent of your life attempting to get twenty percent improvement for any antenna you'll ever use. B is for Balun, bringing together the balanced and unbalanced parts of your antenna system. C is for Coax, the versatile conductor that snakes into your station, one roll at a time. D is for Dipole, the standard against which all antennas are measured, simple to make, simple to use and often first in the many antenna experiments you'll embark on in your amateur journey. E is for Electron, source of all things RF, the beginning, middle and end of electromagnetism, the reason you are an amateur. F is for Frequency, the higher you go, the faster it happens. G is for Gain, measured against a baseline, you'll throw increasing amounts of effort at getting more, one decibel at a time. H is for Hertz, Heinrich to his mother, the first person to transmit and receive controlled radio waves in November of 1886 proving that James Clerk Maxwell's theory of electromagnetism was correct. I is for Ionosphere, the complex and ever changing layers that surround Earth which led radio amateurs to discover HF propagation in 1923. J is for JOTA, the Jamboree On The Air where radio amateurs, guides and scouts come together on the third full weekend of October to share global communications. K is for Kerchunk, the sound caused by the local repeater that brings a smile to the operator and a grimace to the listener, created by pushing the talk button and not saying anything. L is for Logging, the only way you'll ever remember who you spoke to and when and the perfect excuse for bragging to your friends after you managed to collect contacts all over the globe. M is for Modulation, adding information to a radio signal by varying the amplitude, frequency, or phase. N is for Net, a social excuse for getting on air and making noise with your friends. O is for Oscillator, making repeating currents or voltages by non-mechanical means. P is for Prefix, the beginning part of an amateur callsign that identifies your country or region of origin. Q is for QRP, the best way to make just enough noise to make yourself heard, low power is the way to go! R is for Resonance, the point where a circuit responds strongly to a particular frequency and less to others, used every time you tune a radio or an antenna or both. S is for Shack, the space you call home, where you live your radio dream. The size of the corner of the kitchen table, the back-seat of your car or a purpose built structure with never enough space, no matter how much you try. T is for Transceiver, a single box that contains both a transmitter and receiver that share a common circuit. U is for UTC, Coordinated Universal Time, the only time zone that radio amateurs should use for any activity that goes beyond their suburb. V is for VFO, the Variable Frequency Oscillator that provides radio amateurs with frequency agility, the means to listen anywhere, any-time. W is for Waterfall, which displays radio signals across multiple frequencies at the same time. X is for XIT, Transmit Incremental Tuning, changing your transmitter frequency whilst listening on the same frequency, helpful when you're trying to break through a DX pile-up. Y is for Yagi, or Yagi-Uda antenna, the most popular directional antenna invented in 1926 by Shintaro Uda at the Tohoku Imperial University in Japan and popularised to the English speaking world by his boss Hidetsugu Yagi. Z is for Zulu, the last word in the phonetic alphabet that every amateur should know and use. 73 is for best regards. Saying goodbye is hard to do, this says so without fanfare and clears your station from the air. I'm Onno VK6FLAB
Do you really know when the best time is to go on air?
5:02Foundations of Amateur Radio Getting on air and making noise is a phrase that you've likely heard me repeat often, actually, this will be the 24th time or so. It's an attempt at encouraging you to actually transmit and use the radio spectrum that is available to you. It's a nicer way of saying: Use it or lose it! One of the more frustrating aspects of our hobby is finding other people to interact with. At the beginning of your hobby you have access to all these magic radio frequencies with no idea on how to use them. Often a new amateur will turn on their radio, call CQ a couple of times to see if there's anyone out there, hear nothing and give up. As you get more experience you'll discover that radio frequencies change over time and that some work better at certain times of the day. This is reinforced by others who will talk to you about propagation, the solar cycle and how the ionosphere and its various so-called layers will change and what you can achieve throughout the day, the year and the long term cycle. Armed with all this knowledge you are likely to get to a point where you make noise on a certain band depending on the time of day. For example, experienced amateurs will avoid the 10m band at night because it's a so-called day-time band, in other words, their perception is that you cannot make contact on the 10m band after sunset and for the same reason, it's not suitable for early morning contacts. What if we could test that perception and see if it's true or not? Turns out that we have a perfect dataset to discover what actually happens. If I look at the 10m band WSPR or Weak Signal Propagation Reporter data for the past year, a year that had me using a beacon pretty much 24 hours a day, you'd expect that you could see just which times worked and which ones didn't. Turns out that regardless of time of day, my beacon was heard across every hour of the day. Of course the numbers aren't uniform across the day. The peak is at noon local time, the trough is at 5 am local time, 10% of reports are at noon, about 1.5% at 5 am. In other words, the worst time of day for my beacon to be reported is 5 am in the morning and it's not zero. Interestingly the same isn't true for the signal to noise ratio, a measure of just how weak or strong a signal is in comparison to the local noise at the receiver. If you account for differences in transmitter power, meaning that a stronger transmitter is measured in the same way as a weaker one, the 10m band has the best signal to noise ratio at my location at 9 pm local time and the worst at 4 pm local time. Given that I'm only using the 10m band with my beacon I also looked at the local OF78 grid square across all bands. It shows that reports are not directly related to when the average signal to noise is best. It seems to me that people are transmitting when they think it works best, not when it actually works best and I'll mention that the definition of "best" depends on each user. Note that I haven't yet sat down to discover if there are automatic transmitter and receiver pairs that have been reporting 24/7 across a year on the same band to determine if there is more to learn about the relationship between how often something is reported and what the signal report was at the time. I can say that it's likely that your favourite band is more popular when others think it's popular, not when the conditions are better. Consider for example that there are no local reports on the 12m band at 10am, but there are at 9am and 11am, so, was the band magically unusable the whole year at that time, or did people just not use it? The same is true for 160m. No reports at all before 5pm or after 3am, despite the bands around it having contacts throughout the day. I will point out some things I've ignored. For example, what is a useful contact? Is it measured by distance, by quantity, by uniqueness? Is this choice the same for each band? Is it reasonable to compare a whole year, or should it be by some other time period, like month, season or lunar month? What is the signal to noise ratio for a band that's considered closed? I'm mentioning this because each of those will directly affect what it looks like when you create a chart and it's likely to change what works best for you. So, next time you get on air, try a band that shouldn't work according to your knowledge and see what happens. Perhaps you'll get lucky, make a contact and discover something unexpected. I'm Onno VK6FLAB
The evolution of software in radio ...
5:54Foundations of Amateur Radio The amateur community is nothing if not entertaining. Look at any discussion about a mode like FT8 and you'll discover people who describe it as the dehumanising end of the hobby. In the same thread you'll find an amateur who's been licensed longer than I have been alive who welcomes it using words like revitalising, more active, and the like. If you're not familiar, FT8 is one of many weak signal digital modes that gained popularity over the past years during the most recent solar minimum when long distance HF propagation was challenging. That example discussion was about the visible end of a mode like FT8, but there's an often overlooked all but invisible aspect of these modes that is much more significant, namely the popularisation of signal processing in software. In many ways amateur radio is more about receiving than transmitting. This might not be obvious, but what's the point of transmitting if you cannot receive? Using software to do the listening makes for an interesting evolution that might be hard to grasp if I start digging into the fundamental algorithms that make this happen, instead let me describe a process that is easier to explain. Imagine that there's a piece of software that knows how to decode digital signals. As the user of that decoding software, or decoder, you send audio into one end and callsigns and grid-squares come out the other end. How it does this isn't important right now. We measure the quality of this decoder by how many times it correctly does this, in other words, how many times a correct callsign and grid-square comes out. The decoder can be improved by changing the way that the decoding process works. If the number of correct callsign and grid-squares that come out increases, the quality of the decoder is improved. Now imagine that the decoder spits out the callsign 7N5EC with the grid-square OF78. This particular combination emerged as a WSPR decode on the 10th of December 2022. It was reported by AA7NM as a 100 Watt signal, 14,882 km away on the 40m band. The signal report was -30 dB. If you know where OF78 is, you'll immediately spot a potential problem, if not, I'll help you out, OF78 is located near Perth in Western Australia. It's unlikely that a transmitted callsign in that part of the world starts with anything other than VK6. Mind you, a weather balloon with an odd callsign could theoretically be overhead in that location, but I've not yet heard of a 100 Watt transmitter on 7 MHz that someone hung from a weather balloon. Another problem is that 7N5EC is a callsign that appears to be Japanese. It starts with 7N which is part of the Japanese callsign block, but the next symbol is the number 5 and at least according to the research I was able to do is not actually a currently valid callsign. The prefix 7N4 is allocated to the Kanto region on Honshu island, the largest island in Japan. 7N5 doesn't seem to be valid as a prefix. Ironically, that callsign will now exist on the Internet as soon as this article is published, but that's a whole other problem. Either way, the chances of the combination of the callsign 7N5EC with the grid-square OF78 is unlikely to be correct. It gets even less likely if you consider that the callsign was reported only once in fifteen years and over 500 million WSPR decodes, I checked. That means that if you updated the software to ignore that particular decode, you'd have improved the decoder by removing an incorrect combination. You could keep doing this by checking callsigns against grid-squares and against allocated callsigns and you'd have made a higher quality decoder. Before you start arguing that this isn't fair, it's exactly the same process as the super check partial list does for people operating in a contest. The idea being that if you only recognise known contesting callsigns, you've got a better chance of making contact. Think of it as a way of filtering out potentially incorrect callsigns. It still leaves the operator having the option to ignore the suggested callsigns and listen to what's actually coming in. I realise that this is not how you would realistically improve a digital signal processing decoder, but it's an example of how changing the software can change the quality of a decoder and that was the point of this example. In reality you'd attempt to discover how this decode happened and what caused it to be wrong. If you want to consider a more signal centric example, consider a decoder that starts with a first attempt at making a decode. With a single decode, it can then remove that known signal from the original audio and start another decoding cycle. You can repeat this as many times as you want until you end up with gibberish. Essentially this is an example of how a modern decoder can improve its performance. This is why signal processing in software is so powerful and important and why FT8 and the rest of the digital firmament are here to stay. I should point out for those wondering, FT8 and WSPR are examples of simple messages, but there's nothing stopping us from using digital messages like this to exchange little bits of audio, or video, or something else. It's how mobile phones work today and at some point amateur radio is going to extend the envelope and come up with the next thing, it always has. So, FT8, it's changing amateur radio, but not because we're glued to a screen having our computer talk to another one, but because it represents digital signal processing in software and it's just the beginning. I'm Onno VK6FLAB
Path loss and very small numbers ...
5:31Foundations of Amateur Radio Sometimes you learn mind boggling things about this hobby, often when you least expect it. Recently I discussed having my 20 mW WSPR or Weak Signal Propagation Reporter beacon heard on the other side of the planet, in Denmark, 13,612 km away. That in and of itself is pretty spectacular, but it gets better if you consider just how weak the signal was by the time it got there. In radio communications there is a concept called path loss or path attenuation. Until recently I understood this to mean the things that impede a signal getting from transmitter to receiver. That includes coax and connector losses, refraction across the ionosphere, reflection off the surface of the planet and diffraction around objects. It turns out there is another factor called "Free Space Path Loss" to consider. It's loosely defined as the loss of signal strength between two antennas. The name sort of implies that something happens to the signal in free space, which is odd if you know that in space, radio waves, regardless of frequency, travel without loss and will travel pretty much indefinitely. So what's going on? To get started, think about a dome lawn sprinkler, one of those little round discs that sits on the ground with the hose connected to the side. You turn on the tap and the water sprays in all directions. If you're really close to the sprinkler when the tap is turned on you'll get sopping wet almost immediately, since most of the water will hit you directly. This is particularly fun in the heat of summer on New Years Day in Australia, not so much in the middle of winter on the other side of the globe. If you stand a couple of meters away, you'll still get wet, eventually, but it will take much longer, because most of the water isn't hitting you. If you stand even further away and assuming the water still gets that far, it will take even longer. A small towel and a big towel will both take the same length of time to get wet if they're held at the same distance from the sprinkler, but if you wring them both out, you'll discover that the big towel captured much more water during the same time. In radio communications we can combine these two ideas, the distance and the size of the receiver, to describe free space path loss. The further away from the transmitter you are, the less signal is available to you to capture since much of the signal is not heading in your direction and the bigger your antenna, the more signal you receive. The bigger the antenna, the lower the frequency, which is why you'll discover that free space path loss is dependent on both distance and frequency. To give you an idea of scale, the free space path loss for 28 MHz over 13000 km is about 144 dB. While the name "Free Space Path Loss" implies loss of signal across the path in free space, the loss is not due to distance as such, rather it's caused by how much the signal is spread out in space. Similarly, there isn't more loss because the frequency is increased, it's that less signal is captured by the smaller size or aperture of the antenna required for a higher frequency. So perhaps a better name might be Spherical and Aperture Loss, but then everyone would have to learn how to spell that, so "Free Space Path Loss" it is. I'll point out that this is the minimum theoretical loss, in reality the loss is higher than this, since it also includes all the other parts of the path loss which are things that we can control, like coax and connector loss, and things we can improve by frequency selection, like ionospheric reflection and refraction which depend on solar conditions. The one aspect of path loss that we have no control over is the "Free Space Path Loss", so perhaps that's why we don't talk about it very much. I'll mention that in path loss calculations often antenna gain at the transmitter and receiver are used to reduce any path loss figures. If I have an antenna with 6 dB gain, then that reduces my overall path loss by 6 dB, which is why we spend so much time and effort figuring out what antenna to use when we get on air to make noise. I mentioned that the free space path loss for my beacon between Australia and Denmark was about 144 dB. This means that my 20 milliwatt signal arrived in Denmark as a -131 dBm signal. That might not mean much, but that's the equivalent of about 80 attowatts. If you're not sure how big that is, 1 milliwatt is 1 quadrillion attowatts, a 1 with 15 zeros. Said another way, 1 watt is 1000 milliwatts, 1 milliwatt is 1000 microwatts. 1 microwatt is 1000 nanowatts, 1 nanowatt is 1000 picowatts, 1 picowatt is 1000 femtowatts, 1 femtowatt is 1000 attowatts. It might come as a surprise, but these numbers are not unusual. Don't believe me? When your radio shows an S0 signal on HF, it is defined as -127 dBm, so we deal with tiny numbers like this all the time, we're just not quite aware of it on a daily basis. Remember, my numbers are theoretical only, to give you an idea of scale. In reality everything in the path between the transmitter and receiver affects what ends up at the other end and might make the difference between hearing someone, or not. I'm Onno VK6FLAB
What is the difference between handheld, mobile and a base radio?
5:48Foundations of Amateur Radio If you've ever been in the market for a new radio, and truth be told, who isn't, you'll find yourself faced with a bewildering array of options varying from obvious to obscure and everything in between. At the obvious end of the scale are things like price, bands and transmit power and at the other end are things like Narrow Spaced Dynamic Range, which you'll find explained by Rob NC0B on his sherweng.com website where he's been publishing receiver test data for many decades. One of the more subtle options you'll need to consider are handheld, mobile or base radio. This is harder than you might think, since radios are increasing in functionality every time you wake up and if you look long enough, you'll discover that they're getting smaller at the same rate. Once upon a time you could just look at the size of a radio and define it as belonging in one or other category, but that's no longer a useful distinction. For example, my PlutoSDR is a tiny device, fits in my pocket, but there's no way I'd consider it a handheld, or even a mobile radio. You might think that a bigger box has more stuff inside, costs more and performs better. For example, the Drake R-4C receiver and companion T-4XC transmitter require external power and were once rated by the ARRL as very good. In reality the Drake R-4C performed terribly in a CW contest, incidentally, that was what caused Rob to start testing radios in 1976. That receiver and transmitter manage to cover 80m, 40m, 20m, 15m and 10m and together weigh in at 14.3 kg. They're considered a base radio. The Yaesu FT-817, runs on batteries, weighs in at just over a kilogram and can be carried with a shoulder strap. It comes as a single device and covers many more bands than the Drake transmitter and receiver do, it would be considered a mobile or even portable radio. Obviously it would be hard to jam a Drake into your car or strap it to your belt, but does that mean that you cannot use an FT-817 as the base radio in your shack? In case you're curious, the slightly beefier brother to the FT-817, the mobile FT-857d, is sitting on my desk as my current base radio. Has been for years. So why do manufacturers continue to make this distinction between handheld, mobile and base radio? One look at the nearest radio catalogue will tell you that it's not based on either performance or price, not even close. You can buy a handheld with more functionality for the same price as a mobile radio and that same is true when you compare a mobile radio to a base radio. Radios vary in price from $20 to $20,000. A cynical person would suggest that pricing is based around extracting the most money from your pocket, but a more charitable explanation might be that physical size dictates things like the number of buttons you can fit on a radio, how many connectors can be accessed before the radio flies off the desk from the weight of the coax hanging off the box, how big is the display and other such limitations. I'm not being glib when I use the word charitable, since much of modern transceiver design revolves around software which can pretty much fit in any box. Using external computers, neither buttons nor a display are needed, leaving external connectors, which if we're being really honest could all fit in a box that would fit in your pocket. At this point you might wonder if handheld, mobile or base has any meaning at all. As I said, in most cases it doesn't. There's really only one place left where this matters, and that's when you have access to strictly limited space and power if you need to put the radio in your pocket or cram it into your car. For your home shack, the distinction is unhelpful for most, if not all, amateurs. Don't believe me? The Yaesu FT-710 currently ranks fourth on Rob's Sherwood Engineering Receiver Test Data List. It's a quarter the size of the top radio and it's sold as a "Base/Portable Transceiver". Yaesu calls it "Compact". It might not fit in the dashboard of my car, but it will fit on the folding table we use during field days. That isn't an exception either. The Elecraft KX3 is the smallest radio on the first page of Rob's Receiver Test Data list. It fits in your pocket. Before you start collecting statistics for each radio, I should point out that the more you know about this hobby, the harder this process becomes, so be careful. That said, if you have a massive list of anything to choose from, a new amateur radio, pet food, car, what to have for dinner, whatever, here's a process that will guarantee a result. It works by eliminating one item at a time until you're left with your preference. To start, grab the first two items on your list and pick the best one between the two. Ignore everything else, just those two items. You're going to fret about the definition of "best", but don't worry, since every time you do this, you'll have a different idea. All you're doing is saying, all things being equal, between these two options, which one do I prefer. No need to describe why, just pick one. In picking one, you've removed one option from the list. Now, compare the winner to the next item on the list, again, ignore everything else and pick one and remove the other. Keep doing this until you run out of items. You'll end up with the single option that wins, for whatever reason, from the entire list. Now, about that radio. All I need is the next paid project. I'm Onno VK6FLAB