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?".
Antenna testing in the field.
Foundations of Amateur Radio
Antenna testing in the field.
If you've been around amateur radio for any time at all, you'll know that we spend an awful lot of time talking about antennas. How they work, where to get them, how to build them, how strong they are, how cheap they are, how effective, how resonant, you name it, we have a discussion about it.
It might not be immediately obvious why this is the case. An antenna is an antenna, right?
Well ... no.
Just like the infinite variety of cars on the road, the unending choice of mobile phones, ways to cook an egg and clothes to wear to avoid getting wet, antennas are designed and built for a specific purpose. I've talked at length about these variations, but in summary we can alter the dimensions to alter characteristics like frequency responsiveness, gain, weight, cost and a myriad of other parameters.
If we take a step back and look at two antennas, let's say a vertical and a horizontal dipole, we immediately see that the antennas are physically different, even if they're intended for exactly the same frequency range. Leaving cost and construction aside, how do you compare these two antennas in a meaningful way?
In the past I've suggested that you use a coax switch, a device that allows you to switch between two connectors and feed one or the other into your radio.
If you do this, you can select first one antenna, then the other and listen to their differences. If the difference is large enough, you'll be able to hear and some of the time it's absolutely obvious how they differ. You might find that a station on the other side of the planet is much stronger on one antenna than on the other, or that the noise level on one is much higher than the other. Based on the one measurement you might come to the conclusion that one antenna is "better" than the other.
If you did come to this conclusion, I can almost guarantee that you're wrong.
Why can I say this?
Because one of the aspects of the better antenna is dependent on something that you cannot control, the ionosphere, and it is changing all the time.
I have previously suggested that you listen to your antenna over the length of a day and notice how things change, but that is both time consuming and not very repeatable, nor does it give you anything but a fuzzy warm feeling, rather than an at least passing scientific comparison.
A much more effective way is to set up your station, configure it to monitor WSPR, or Weak Signal Propagation Reporter transmissions using one antenna, for say a week, then doing it again with the other antenna.
If you do this for long enough you can gather actual meaningful data to determine how your antenna performs during different conditions. You can use that knowledge to make more reliable choices when you're attempting to make contact with a rare station, or when it's 2 o'clock in the morning and you're trying to get another multiplier for the current contest.
You don't even have to do anything different and spend little or no money on the testing and data gathering.
You can do this with your normal radio and your computer running WSJT-X, or with a single board computer like a raspberry pi and an external DVB-T tuner, a so-called RTL-SDR dongle, or with an all-in-one ready-made piece of hardware that integrates all of this into a single circuit board.
If you want to get really fancy, you can even use automatic antenna switching to change antennas multiple times an hour and see in real-time what is going on.
You also don't have to wait until you have two antennas to compare. You can do this on a field day when you get together with friends who bring their own contraptions to the party.
If there's any doubt in your mind, you can start with a piece of wire sticking out the back of a dongle. I know, I'm looking at one right now. I've been receiving stations across the planet.
The making of a Crystal Radio
Foundations of Amateur Radio
Recently I made a commitment to building a crystal radio. That started a fevered discussion with several people who provided many helpful suggestions. This is the first time I'm building a crystal radio and to make things interesting I'm selecting my own components, and circuit diagram. What could possibly go wrong?
Crystal radios have been around for a while. Around 1894 Indian physicist Jagadish Chandra Bose was the first to use a crystal as a radio wave detector, using galena detectors to receive microwaves. He patented this in 1901. The advice I was given sometimes feels like it harks back to 1894, with suggestions of using cats whiskers, razor blades, and any number of other techniques that create the various components to make a so-called simple crystal radio.
At the other end of the scale there were suggestions to go to the local electronics store and buy a kit.
The first suggestions, rebuilding historic radios from parts made of unobtanium would mean many hours of yak shaving, just to get to the point of getting the components, rather than actually building the radio.
I realise that part of the experience is the journey and I'm sure that if my current project gets me hooked I'll look into it, but I really don't want to become that amateur who has a collection of home-brew crystal radios across the ages. Besides, I'm having a look at using my crystal radio as a front end to my software, so I want to keep sight of the radio part of what I'm doing, rather than the building part.
Before you get all hot and bothered, remember, amateur radio is a hobby that means different things to different people and for me I'm currently playing with software and I'm attempting to learn about the electronics principles that form the basis of our hobby.
As I said, the other end of the scale was to get a kit and build that. It has its appeal, but there's little in the way of learning and the construction part of things is pretty much putting together a kit which is something I first did when I constructed an LC meter kit a while ago. So that too doesn't really appeal to me.
Now comes the bit where I tell you what I've done to date.
On the physical side of things, nothing. On the thinking and learning and planning side, lots.
Here's where I'm at.
My current understanding of a crystal radio is that you need to detect the AM wave form of an RF frequency and pipe that into something that makes noise. Traditionally this is done with a crystal earpiece, but I saw someone use powered computer speakers with a built in amplifier, so I'm going to start with that as my first noise maker.
I should also mention that the crystal earpiece was a source of confusion. I thought that the crystal in crystal radio was referring to that one. It's not.
So, back to where I'm at. What do I need?
To start off, I cannot just connect an antenna to a speaker, since it will attempt to make sound for every known frequency, well, at least the ones that the antenna can handle that fit within the response envelope of the speaker and its amplifier. If you want to know what that sounds like, put your finger on the input plug to some powered speakers. Don't turn up the volume too loud, you'll regret it.
So step one is to make a way to only let specific frequencies through. I've previously discussed this. You might know it as a band-pass filter. You can make one using a capacitor and an inductor. If you make the capacitor variable, you can change what frequency passes. This is helpful because you don't want to be decoding more than one radio station at a time.
There are plenty of designs for crystal radios that offer hand wound inductors and home brew capacitors, but I'm not doing this to learn how to build those, I'm doing this because I want to learn how it works. I want to use readily available components from my local electronic
An ionospheric monitoring service at home
Foundations of Amateur Radio
One of the more fundamental aspects of long distance radio communication is the impact of the ionosphere. Depending on how excited the Sun is, what time of day it is and what frequency you're using at the time will determine if the signal you're trying to hear from the other side of the planet makes it to you or is on its way to a radio amateur on Proxima B who is likely to hear this podcast in just over 4 years from now.
In other words, the ionosphere can act like a mirror to radio waves, or it can be all but invisible.
As luck would have it, this changes all the time. Much like waiting for the local weather bureau for the forecast for tomorrow's field-day, there are several services that provide ionospheric predictions. The Australian Space Weather Service, SWS, is one of those. You might have previously known it as the Ionospheric Prediction Service, but Space is much more buzz-word compliant, so SWS is the go.
If you're not a radio amateur, space weather can impact stuff here on Earth, like the ability to communicate, transfer energy across the electricity grid, use navigation systems and other life-essentials. The SWS offers alerts for aviation and several other non-amateur services.
If you're interested in HF communications, the SWS offers HF prediction tools that allow you to check what frequencies to use to communicate with particular locations using visualisations like the Hourly Area Prediction map.
If you're more of the Do-It-Yourself kind of person, you might be pleasantly surprised that you can have your very own ionospheric monitoring station at home. Not only that, it's probably already in place, configured and ready to go.
If you're using WSJT-X to monitor WSPR transmissions, then you'll have noticed that the screen shows all the stations you've been able to decode and you can scroll back as far as you like to the time when you launched WSJT-X.
If you want to do some analysis on that, copy and paste is an option, but it turns out that there's a handy little document being stored on your computer called ALL_WSPR.TXT that contains the very same data going back to when you installed and launched the first time.
This information represents what stations you heard, at what time and with what level of signal to noise at your shack, not some fancy station in the middle of nowhere with specialist hardware, your actual station, the one you use to talk to your friends, with your antenna, your power supply, the whole thing.
For my own entertainment I've been working on a way to visualise this. I created a map that shows the location every station I've logged, 30,000 of these reports in the past four months. It's interesting to see that I can hear most of the globe from my shack. Notably absent is South America but that is likely a combination of band selection and local noise.
In the meantime I've gone down another rabbit hole in figuring out if I can use an image file to visualise all this without needing fancy software, unless you consider a web-browser and bash fancy.
The idea being that a simple script could take the output from your station and convert that into a map you can see on your browser. In case you're wondering, I'm thinking that a style-sheet attached to a Scalable Vector Graphic or SVG might be just the ticket to showing just how many times I've heard a particular grid-square.
If you have ideas on what else you might do with this data, get in touch.
I'm Onno VK6FLAB
csdr will rock your world ...
Foundations of Amateur Radio
When you start playing with software defined radio, you're likely to begin your journey using something with a display that shows you a lovely waterfall, gives you a way to pick out a frequency, decode it and play it over your speakers all over the house. Likely your first effort involves a local FM radio station. These graphical tools come in many and varied forms available on pretty much anything with a display. Tools like SDR#, cuSDR, fldigi and WSJT-X.
That can be immensely satisfying as an experience.
Underneath the graphics is software that is essentially translating an antenna voltage to a sound, in much the same way as that happens in an analogue radio. There are the parts that get the signal, then they get translated and filtered, translated some more, decoded, and eventually you have sound coming from your speakers.
During the week I caught up with a fellow amateur who pointed me at the work of Andras HA7ILM who for a number of years has been quietly beavering away making various tools in the SDR landscape.
One of those tools has the innocuous name of "csdr", a command-line software defined radio digital signal processor. It started life on November 1st, 2014 and has had many updates and community changes since.
This tool has no graphics, no user interface, nothing visible that you can toggle with a mouse and yet it's one of the coolest tools I've seen in a long time and from a learning perspective, it's everything you might hope for and then some.
Before I explain how it works, I need to tell you about pipes. They're much like water pipes in your home, but in computing they're a tool that allow you to connect two programs together so you can exchange data between them.
One of the ways that you can think of a computer is a tool that transforms one type of information into another. This transformation can be trivial, like say adding up numbers, or it can be complex, like filtering out unwanted information.
The idea is that you take a stream of data and use a pipe to send it to a program that transforms it in some way, then use another pipe into another program and so on, until the original stream of numbers has become what you need them to be, creating a transformation pipeline with a string of programs that sequentially each do a little thing to the data.
That stream of data could be numbers that represent the voltage of the signal at your antenna and the final output could be sound coming from your speaker.
If you were to take that example, you could use one tool that knows how to measure voltage, pipe that to a tool that knows how to convert that into FM and pipe that to a tool that knows how to play audio on your speaker.
Converting something to FM is, in and of itself, a series of steps. It involves taking the raw numbers, extracting the part of the samples that are the station you want to hear, decoding those and converting that into something that is ready to be played on your speakers.
This process is fundamentally different from using a so-called monolithic tool that does everything behind the scenes. The person writing the software has decided what to do, how to do it, in what order and in what way. If you want to do something that the author hadn't thought of, like say listening to a new type of broadcast, you'll be waiting until they update the software.
In another way, this is the difference between making a cake from raw ingredients and buying it up the road at the shops
One final part of the puzzle.
There's nothing preventing you from piping the output of your program to another copy of the same program.
So, if you had a tool that knows how to do the maths behind filters, AM and FM decoding, translating Lower Side Band into Upper Side Band and vice-versa, band filtering, etc., you'd be able to set up individual steps that translate a signal, one step at a
New day, new mode ... SSTV
Foundations of Amateur Radio
In 1958 The Kentucky Engineer published an award winning student article by Copthorne "Coppie" MacDonald. He described a Slow-Scan T.V. System for Image Transmission. If you get the opportunity, have a look for the link on his archived home-page which you can find from the Wikipedia SSTV page.
The purpose of this narrow band television idea was to be able to send images using cheaper equipment and less bandwidth than normal television. The idea caught on and it's still in use today.
In 1959 the idea of slow scan tv was used by the Luna 3 mission to transmit images from the far side of the moon. The NASA Apollo program also used SSTV to transmit images from Apollo 7, 8, 9 and from the Apollo 11 Lunar Module.
In 1968 SSTV became a legal mode for radio amateurs in the United States.
The International Space Station regularly uses SSTV to send images to radio amateurs across the globe.
The version of SSTV in use by radio amateurs today is different from the earlier grainy black and white images coming from the moon and if you're expecting a moving image, something that TV implies, you're going to be disappointed, since the popular SSTV modes send images one at a time, taking up to a minute or so to send. With a frame-rate of one frame per minute, watching anything other than grass grow is going to be a challenge.
That said, SSTV is a lovely and relatively simple way of sending images across the air.
In my quest for new adventures I like to play with things I know nothing about. I suspect that it's ingrained but it does keep me off the street. The other day I received an email from a local amateur, Adrian VK6XAM, who sent a message describing a new SSTV repeater he'd set-up for testing purposes. It's a local 2m repeater that waits for an activation tone, then it expects you to transmit an SSTV image and it will replay the image back to you. If you've familiar with a parrot repeater, this is a similar thing, just for SSTV rather than audio. The repeater is running on solar power and with the 100% duty cycle of SSTV, it's only available during daylight hours.
Technicalities aside, I couldn't resist.
So, I fired up QSSTV, a piece of Linux software that among other things knows how to receive and send SSTV images. After turning on my radio, tuning to the correct frequency, I received my first ever SSTV picture.
On a bright red background a yellow symbol appeared. At first I thought it was a hammer and sickle, but on closer inspection it was a micrometer and caliper, which absolutely tickled my fancy, having just taken delivery of some precision measuring tools - a Mitutoyo Test Indicator and a few other bits and pieces for another project I'm working on.
Had to learn how to drive QSSTV, make a template so you can overlay text on an image, learn what a signal report should look like, then when I figured all that out I triumphantly hit send and it made all the right noises, but nothing was happening.
More time looking at the inter-web taught me that if I want to use the rear connection on my FT-857d to send audio using FM, as opposed to SSB which is what most digital modes need, you need to set the radio to PSK mode and magically it starts to work.
My first ever SSTV image was sent an hour and a half after receiving my first image and the repeater dutifully sent it back. Then I got a picture from Keith VK6WK.
Of course the paint isn't even dry on any of this, so there's plenty more to learn, but the process is not too complex.
I will note a few things.
I had already set-up digital modes, that is, my radio was talking to my computer via CAT, that's Computer Assisted Tuning, essentially a serial connection that controls the radio and the audio was already being sent and received from the rear connector of my radio.
Getting SSTV running was really an extension on those activities, so if you're
Simplicity among the complexity ...
Foundations of Amateur Radio
My radio shack consists of two radios, identical, well, in as much as that they're the same model, a Yaesu FT-857d. Their memories are different, their microphones are different, but both of them are connected via a coaxial switch to the same VHF and UHF antenna. One of them is also connected to a HF antenna.
Let's call these two radios alpha and bravo.
Alpha is used to host F-troop and play on the local repeater. Bravo is used to do HF stuff. It's also connected to a computer via a serial cable, called a CAT cable, Computer Assisted Tuning, but really, a way to control the radio remotely.
The audio output on the rear of the radio is also connected to the computer.
These two connections are combined to provide me with access to digital modes like PSK31, WSPR and SSTV, though I haven't actually yet made that work. The computer itself is running Linux and depending on what I'm doing on the radio some or other software, often it's fldigi, a cross-platform tool that knows about many different digital modes.
The computer is also connected to the Internet via Wi-Fi, and is used to see what various reporting websites have to say about my station, things like propagation, the DX cluster, an electronic way of seeing what other stations can hear, then there's solar radiation information and other neat tools.
This shack is pretty typical in my circle of friends. I'm lucky enough to have a dedicated table with my shack on it, for others they're lucky to have a shelf in a cupboard, or at the other end of the spectrum, a whole room or building dedicated to the task.
The level of complexity associated with this set-up is not extreme, let's call it in the middle of the range of things you can add to the system to add complexity.
In case you're wondering, you might consider automatic antenna switching, band switches, band filters, amplifiers, more radios, audio switching, automatic voice keyers. If you look at the world of Software Defined Radio, the hardware might include many of those things and then add a computer that's actually doing all the signal processing, making life even more complex.
At the other end of the complexity scale there's a crystal radio.
As I've been growing into this field of amateur radio it's becoming increasingly clear that we as a community, by enlarge, are heading towards maximum complexity.
There's nothing wrong with that as such, but as a QRP, or low-power operator, I often set-up my radio in a temporary setting like a car or a camp site. Complexity in the field is not to be sneezed at and I've lost count of the number of times where complexity has caused me to go off-air.
It occurred to me that it would be helpful to investigate a little bit more just what's possible at the other end of the scale, at the simple end of complexity if you like.
So, I'm intending, before the year is out, supplies permitting, to build a crystal radio from scratch. I realise that I have absolutely no idea what I'm getting myself into, no doubt there will be more complexity that I'm anticipating, but I'm getting myself ready to build something to be able to look at it and say to myself, look, this is how simple you can get with radio.
I'm currently too chicken to commit to making the simplest - legal - transmitter, but if you have suggestions, I'll look into it.
Just so you know, simplicity is an option.
I'm Onno VK6FLAB