Foundations Of Amateur Radio

Foundations of Amateur Radio After recently talking about noise, today I want to discuss gain, specifically antenna gain. When you say that your antenna has 18 dBi gain, what does that mean? This entire discussion starts with an isotropic radiator or antenna. It's often described as the perfect antenna, but rarely is there any description on how that actually works, so I'd like to start there. Before we dig in too much, it's worth remembering that an isotropic antenna is a thought experiment, it cannot physically exist, but it's a useful tool for comparing antennas. Antennas have a physical size. There's often a direct relationship between the size of the antenna and the frequencies for which it works best. A lower frequency means a longer wavelength and corresponding large antenna to handle that radio frequency. In contrast, an isotropic antenna is infinitesimally small and responds equally well for all frequencies. Similarly, unlike an actual antenna, an isotropic antenna is symmetric in all directions

Foundations of Amateur Radio Today I'd like to talk about noise, but before I do, I need to cover some ground. Recently I explored the idea that, on their own, neither antenna, nor coax, made a big difference in the potential for a contact when compared to the impact of path loss between two stations. I went on to point out that you'd be unlikely to even notice the difference in normal communications. Only when you're working at the margins, when the signal is barely detectable, would adding a single dB here or there make any potential difference. In saying that, I skipped over one detail, noise. Noise is by definition an unwanted signal that arrives together with a wanted signal at the receiver. In HF communications, noise comes from many sources, the galaxy, our atmosphere, and man-made noise from things like electrical switches, motors, alternator circuits, inverters and computers. The example I used was my 10 dBm beacon being reported by an Antarctic station. My signal report was about 5 dB above the

Foundations of Amateur Radio Recently I explained some of the reasons why I've shifted to using dBm to discuss power. You might recall that 1 Watt is defined as 1,000 mW and that's represented by 30 dBm. 10 Watts is 40 dBm, 400 Watts, the maximum power output in Australia is 56 dBm and 1,500 Watts, the maximum in the USA, is just under 62 dBm. My favourite power level, 5 Watts, is 37 dBm. I mentioned that using dBm allows us to create a continuous scale between the transmitted power and the received signal. On HF, an S9 report is defined as -73 dBm. Between each S-point lies 6 dB, so an S8 signal is -79 dBm, S7 is -85 dBm and so-on to S0, which is -127 dBm. Said differently, to increase the received signal by one S-point you need to quadruple the power output. Now, let's consider a contact with a 100 Watt station, 50 dBm. Let's imagine that the receiver reports an S8 signal. That means that between a transmitter output of 50 dBm and the received signal at -79 dBm, there's a loss of 129 dB. If we dial the p

Foundations of Amateur Radio The other day I went looking for a software defined radio or SDR for HF. This happened because all such devices on my desk are rated at higher frequencies and I've still not managed to fix the broken SMA board connector on the transverter I purchased over a year and a half ago. In case you're wondering, the design has two SMA connectors attached at either end of a printed circuit board, also known as a PCB. The board slides into a metal case and both connectors are tightened to either side of the case, which causes the problem when the circuit board is slightly shorter than the case and the nuts pull the connector apart, causing the device to fail. Replacing the SMA board connectors would be relatively simple, but they appear hard to come by and the micro SMA connectors that a friend purchased to help, changed the task into finding adaptors, which I've not managed to solve yet. I'm detailing this all for a purpose, trust me. Anyway, the hunt for an SDR for HF lead me to a pro

Foundations of Amateur Radio If you've been following my amateur radio journey, you'll have likely noticed that I've been straying from the fold. The words I use for power have been changing. I've reduced references to Watt and increased use of the term decibel. Initially this was incidental, recently it's been more of a deliberate decision and I'd like to explain how this came to be. It starts with representing really big and really small numbers. Let's start big. On 14 September, 2015 the first direct observation of gravitational waves was made when a pair of black holes with a combined estimated weight of 65 solar masses merged. The signal was named GW150914, combining "Gravitational Wave" and the observation date to immortalise the event. Following the collision, it was estimated that the radiated energy from the resulting gravitational waves was 50 times the combined power output of all the light from all the stars in the observable universe. As a number in Watts, that's 36 followed by 48 zeros. If

Foundations of Amateur Radio Between decibels and milliwatts ... As you might recall, I've been working towards using a cheap $20 RTL-SDR dongle to measure the second and third harmonic of a handheld radio in an attempt to discover how realistic that is as a solution when compared to using professional equipment like a Hewlett Packard 8920A RF Communications Test Set. I spent quite some time discussing how to protect the receiver against the transmitter output and described a methodology to calculate just how much attenuation might be needed and what level of power handling. With that information in-hand, for reference, I used two 30 dB attenuators, one capable of handling 10 Watts and one capable of handling 2 Watts. In case you're wondering, it's not the dummy load with variable attenuation that I was discussing recently. I ended up using a simple command-line tool, rtl-power, something which I've discussed before. You can use it to measure power output between a set of frequencies. In my case I measure

Foundations of Amateur Radio Over the weekend a friend of mine convinced me to help plant some trees. Mind you, I was told that this was going to be a blue tree painting day. The Blue Tree Project is now a global awareness campaign that paints dead trees blue to spread the message that "it's OK to not be OK", and help break down the stigma that's still largely attached to mental health. In the process, I learnt that my physical stamina is not what it once was and my current appetite for bending over and shovelling dirt is, let's call it, muted. After the digging and the sausage sizzle under the branches of an actual blue tree, there was some opportunity for playing radio, something I haven't done in much too long. I wasn't sure when I last got into the fresh air to actually listen, but I must confess, the coax cable that I picked up out of my shed had been hanging there for several years. The location where we planned to play was in a rural setting, right next to a dam, which surprisingly actually had wat

Foundations of Amateur Radio Before we start I should give you fair warning. There are many moving parts in what I'm about to discuss and there's lots of numbers coming. Don't stress too much about the exact numbers. In essence, what I'm attempting is to explore how we can reduce the power output from a transmitter in such a way that it doesn't blow up a receiver whilst making sure that the signal is strong enough that we can actually measure it. With that in mind, recently I discussed the idea of adding a series of attenuators to a transmitter to reduce the power output by a known amount so you could connect it to a receiver and use that to measure output power at various frequencies. One hurdle to overcome is the need to handle enough power in order to stop magic smoke from escaping. None of my attenuators are capable of handling more than 1 or 2 Watts of power, so I cannot use any of them as the first in line. As it happens, a good friend of mine, Glynn VK6PAW, dropped off a device that allows you to di

Foundations of Amateur Radio Recently I had the opportunity to use a piece of professional equipment to measure the so-called unwanted or spurious emissions that a transceiver might produce. In describing this I finished off with the idea that you could use a $20 RTL-SDR dongle to do these measurements in your own shack. I did point out that you should use enough attenuation to prevent the white smoke from escaping from your dongle, but it left a question, how much attenuation is enough? An RTL-SDR dongle is a USB powered device originally designed to act as a Digital TV and FM radio receiver. It's normally fitted with an antenna plugged into a socket on the side. I'll refer to it more generically as a receiver because much of what we're about to explore is applicable for other devices too. Using your transceiver, or transmitter, as a signal source isn't the same as tuning to a broadcast station, unless you move it some distance away, as-in meters or even kilometres away, depending on how much power you're

Foundations of Amateur Radio At a recent local HAMfest we set-up a table to measure second and third harmonic emissions from any handheld radio that came our way. The process was fun and we learnt lots and in due course we plan to publish a report on our findings. When we received a handheld, we would disconnect the antenna, and replace it with a short length of coax and connect it to a spectrum analyser. We would then trigger the Push To Talk, or PTT button and measure several things. We'd record the actual frequency and how many Watts that the transmitter was producing and then record the power level in dBm for the base frequency, double that frequency and triple that frequency. In other words, we'd record the base, second and third harmonics. This resulted in a list of numbers. Frequency and power in Watts are obvious, but the three dBm numbers caused confusion for many visitors. The most perplexing appeared to be that we were producing negative dBm numbers, and truth be told, some positive ones as well

Foundations of Amateur Radio There's nothing quite as satisfying as the click of a well designed piece of equipment. It's something that tickles the brain and done well it makes the hairs stand up on the back of your neck. If time was on my side and I wasn't going somewhere else with this, I'd now regale you with research on the phenomenon, I'd explore the community of people building mechanical keyboards and those who restore equipment to their former glory, instead I'm encouraging you to dig whilst I talk about the second and third harmonics. This is about amateur radio after all. Over the years there has been a steady stream of commentary around the quality of handheld radios. Some suggest that the cheaper the radio, the worse it is. Given that these kinds of radios are often the very first purchase for an aspiring amateur it would be useful to have a go at exploring this. When a radio is designed the aim is for it to transmit exactly where it's intended to and only there. Any transmission that's not w

Foundations of Amateur Radio If you walk into your radio shack and switch on a light, the result is instantaneous, one moment it's dark, the next it's not. What if I told you that as immediate as it appears, there is actually a small delay between you closing the circuit and the light coming on. Likely the distance between your switch and your light is less than say 10 meters, so the delay is likely to be less than 33 nanoseconds, not something you'd notice unless you're out to measure it. What if your light switch is 3,200 km away? That's the length of the first transatlantic telegraph cable in 1858. Let's start with the notion that between the action of closing a switch, or applying a voltage at one end of the cable and it being seen at the other end takes time. If we ignore the wire for a moment, pretending that both ends are separated by vacuum, then the delay between the two ends is just over 10 milliseconds because that's how long it takes travelling at the speed of light. One of the effects of using

Foundations of Amateur Radio The first official telegram to pass between two continents was a letter of congratulations from Queen Victoria of the United Kingdom to President of the United States James Buchanan on 16 August 1858. The text is captured in the collection of the US Library of Congress. It's a low resolution image of a photo of a wood engraving. Based on me counting the characters, the text from the Queen to the President is about 650 characters. IEEE reports it as 98 words, where my count gives 103 words or 95 words, depending on how you count the address. Due to a misunderstanding between the operators at either end of the 3,200 km long cable, the message took 16 hours to transmit and 67 minutes to repeat back. If you use the shortest duration, the effective speed is just over one and a half Words Per Minute or WPM. That's not fast in comparison with speeds we use today. Until 2003, the ITU expected that emergency and meteorological messages should not exceed 16 WPM, that a second class operat

Foundations of Amateur Radio Morse code is a way for people to send information across long distances. The code we use today, made from dit and dah elements is nothing like the code demonstrated and attributed to Samuel Morse in 1837. Over years and with assistance from Professor of Chemistry Leonard Gail and Physicist Joseph Henry, then Professor of Literature, Samuel Morse, and mechanically minded Alfred Vail developed an electrical telegraph system that automatically moved a paper tape and used an electromagnet to pull a stylus into the paper and a spring to retract it, marking the paper with lines. The original system was only intended to transmit numbers, and combined with a dictionary, the operator could decode the message. The telegraph was able to send zig-zag and straight lines, transmitting the message "Successful experiment with telegraph September 4 1837". The system was enhanced to include letters, making it much more versatile. On the 6th of January 1838, across 4.8 km of wire, strung across a

Foundations of Amateur Radio Thanks to several high profile races we already know that sending Morse is faster than SMS. Recently I started digging into the underpinnings of Morse code to answer the question, "Can you send Morse faster than binary encoded ASCII?" Both ASCII, the American Standard Code for Information Interchange and Morse are techniques to encode information for electronic transmission. One is built for humans, the other for computers. To answer the question, which is faster, I set out to investigate. I'm using the 2009 ITU or International Telecommunications Union standard Morse for this. Morse is said to be optimised for sending messages in English. In Morse the letter "e", represented by "dit" is the quickest to send, the next is the letter "t", "dah", followed by "i", dit-dit, "a", dit-dah, "n", dah-dit, and "m", dah-dah. The underlying idea is that communication speed is increased by making the most common letter the fastest to send and so-on. Using a computer this is simple to test.

Foundations of Amateur Radio If you've ever looked at Morse Code, you might be forgiven if you conclude that it appears to be a less than ideal way of getting information from point A to point B. The idea is simple, based on a set of rules, you translate characters, one at a time, into a series of dits and dahs, each spaced apart according to the separation between each element, each character and each word. The other day I came across a statement that asserted that you could send Morse faster than binary encoded ASCII letters. If you're not sure what that means, there are many different ways to encode information. In Morse, the letter "e" is the first character, represented by "dit", the letter "t" is the second character, represented by "dah". In ASCII, the American Standard Code for Information Interchange, the letter "e" is the 69th character, represented by 100 0101. The letter "t" is number 84 on the list, represented by 101 0100. A couple of things to observe. The order of the characters between Mor

Foundations of Amateur Radio Have you ever made an international contact using amateur radio and used that towards tracking an award like for example the DXCC? If you're not familiar, it's an award for amateurs who make contact with at least 100 "distinct geographic and political entities". In 1935 the American Radio Relay League, or ARRL published an article by Clinton B. DeSoto, W1CBD, titled: "How to Count Countries Worked: A New DX Scoring System". In the article he asks: "Are Tasmania and Australia separate countries?" In case you're wondering, Tasmania has, at least in legal terms, been part of Australia since Federation in 1901. Not to be confused with New Zealand, a separate country over 4,000 kilometres to the east of Australia, Tasmania is the island at the south eastern tip of Australia. It was previously called the Colony of Tasmania, between 1856 and 1901 and before that it was called Van Diemen's Land between 1642 and 1856. Before then it was inhabited by the palawa people who lived there for

Foundations of Amateur Radio In the earlier days of my career I worked in a computing centre at a university surrounded by people with different interests and experiences in computing. There were programmers, hardware engineers, technicians, sales people, administrators, educators, support staff, statisticians and even a librarian. There wasn't a lot of socialising or foosball, but every now and then we'd bump into each other in the lunchroom and talk about things that were not work related. During such conversations I learnt that people had all manner of interests outside their work, they were volunteer firefighters, or building their house, or active in the girl guides and any number of other unrelated pursuits and skills. That same is true for the people inside the hobby of amateur radio. I've met people who were submariners, tow-truck drivers, accountants, paramedics, radio astronomers, telco and broadcast engineers, doctors, IT people, lots of IT people, and plenty of other professions. As you might

Foundations of Amateur Radio The other weekend there was an amateur radio contest on. Not surprising if you realise that's true for most weekends. For a change, I knew about this contest before it started, because I missed out a year ago, so I did the smart thing to add it to my diary with an alert a month out. In this particular contest there's points to be made by being a so-called roving station, that is, one that moves around during the contest and in the past that's how I've participated and had lots of fun. So the die was cast and a plan was concocted. Being a rover meant that I would be outfitting my car with my radio. It's been out of the car for several years, taken out when we had the transmission replaced, and never actually returned. I started making lists of everything I'd need, including learning that you can use a bench top power supply to charge a 12V battery if your trusty charger has let the smoke out. I went hunting for the cable that connects the front of the radio to the back and reali

Foundations of Amateur Radio During the week, prompted by a protest on popular social media site Reddit, I rediscovered that there are other places to spend time. It sounds absurd now, but until then much of my social interaction with the world was via a single online presence. This didn't happen overnight. Over the years more and more of my time was spent on Reddit engaging with other humans around topics of my interest, amateur radio being one of them. As you might know, I'm the host of a weekly net, F-troop. It's an on-air radio discussion for new and returning amateurs that's been running since 2011 and you can join in every Saturday for an hour at midnight UTC. In addition to the net, there's an online component. It captures items of interest shared during the on-air conversation. It's intended to stop the need to read out web addresses on-air, create a historic record of the things we talk about and allow people who are not yet amateurs to explore the kinds of things that capture our interest. Since