I haven’t been an amateur radio operator for a long time, but I’ve already discovered that one of the pleasures of the hobby is that there is always some new rabbit hole available when you feel like falling into one.
My latest rabbit hole has been digital radio.
It started innocently enough. I wanted to experiment with some weak-signal digital modes, learn a bit more about HF propagation, and get the Yaesu FTdx10 talking properly to the various bits of software on my M1 MacBook Air.
A few weeks later I was watching five watts of RF from a dipole hanging in a maple tree being reported from Australia, installing propagation-prediction software descended from programs written when computers ate punch cards, talking to stations using text modes at signals buried in the noise, and developing opinions about USB audio levels that no reasonable person should possess.
So, yes. That escalated quickly.
First, make the computer talk to the radio
My station is fairly modest.
The radio is a Yaesu FTdx10. My main computer is an M1 MacBook Air named Timnit. For antennas, I have been using resonant wire dipoles rather than anything exotic.
That sounds simple.
It isn’t.
Modern digital amateur radio has several separate things that all need to work at once. The computer has to control the radio frequency and mode. Something has to key the transmitter. Audio has to get from the computer to the radio at the correct level. Received audio has to travel in the other direction. And, ideally, two different programs shouldn’t simultaneously decide that they own the CAT interface.
My setup gradually evolved around FLrig as the intermediary between the radio and applications such as fldigi. WSJT-X handles modes such as FT8 and WSPR, while JS8Call handles JS8. I have also experimented with fldigi modes including Olivia, and eventually wandered into Winlink, ARDOP and VARA HF.
There was quite a lot of:
“Why isn’t this transmitting?”
followed by:
“Oh.”
One particularly fine episode involved troubleshooting what seemed like a complete absence of RF from ARDOP, only to discover that the external RF monitor I was using to check for RF was switched off.
DOH.
Once you sort that out, though, digital radio becomes enormously interesting.
WSPR: the gateway drug
WSPR stands for Weak Signal Propagation Reporter.
It isn’t really a conversational mode. A WSPR transmission contains little more than a callsign, grid square and transmitter power. The transmission takes nearly two minutes and occupies only a few hertz of bandwidth.
The clever bit is that receivers running WSPR software all over the world decode these tiny signals and upload their reports to a central database.
You transmit.
Then you look at a map.
And that is where the trouble begins.
My first serious experiments were on 20 metres, transmitting only 5 W into a dipole.
The antenna wasn’t on a tower. It wasn’t even particularly high.
It was suspended from the maple tree in our backyard, roughly in an inverted-V arrangement, with the apex about five metres above ground and the ends perhaps two metres up.
And people started hearing me.
First around North America.
Then Europe.
Then farther.
Germany.
Austria.
The Canary Islands.
South Africa.
Australia.
At one point, VK5ARG in South Australia reported my five-watt WSPR transmission from approximately 16,500 km away.
Another Australian station, VK5EI, was a little farther still.
Let that sink in for a moment.
Five watts.
A piece of wire hanging from a tree in Kitchener.
Australia.
That works out to roughly 3,300 km per watt, although of course kilometres-per-watt isn’t actually how propagation works. It is nevertheless a deeply satisfying number.
On another evening, VK5ARG was hearing me at around -6 or -7 dB signal-to-noise ratio.
At that point the appropriate technical diagnosis was essentially:
“Yeah. The radio is working.”
Watching the ionosphere move
What made WSPR really fascinating wasn’t simply collecting distant spots.
It was watching them change.
On a good evening, I could watch my signal being reported simultaneously across North America, Europe, South America and Australia. Then, perhaps half an hour later, the Australians would disappear. Europe would begin to fade. Strong reports would remain from Texas, Florida or the western United States.
The RF map was rearranging itself in front of me.
That was when propagation stopped being an abstract collection of terms such as MUF, F2 layer, grey line and skip distance.
You can read about those things.
It is quite another experience to watch them happen.
WSPR also taught me very quickly that a band isn’t simply “open” or “closed.”
Open to where?
For whom?
At what angle?
In which direction?
A path can disappear in one direction while remaining excellent in another. A receiver might hear very little, while stations thousands of kilometres away still hear your transmitter perfectly well.
The ionosphere apparently has no interest in making things tidy for beginners.
Then I borrowed a 17-metre dipole
Naturally, having established that the 20-metre antenna worked, the obvious response was to hang another wire in the tree.
I borrowed and lofted a 17-metre dipole and put 5 W of WSPR into it on 18.1061 MHz.
On the first serious run, the signal reached Europe, North America, the Canary Islands…
…and Australia.
VK5ARG again.
About 16,519 km away at -20 dB.
That answered the question of whether the 17-metre dipole worked.
The more interesting thing was what happened afterwards. That extraordinary long-path opening disappeared fairly quickly, while reports across North America and the Atlantic remained strong.
For a brief period, apparently, the propagation geometry had aligned just right.
WSPR caught it.
Without WSPR, I would probably never have known it existed.
FT8: signals you can barely hear, everywhere
FT8 is related to WSPR in spirit but designed for making contacts rather than simply reporting propagation.
On 20 metres, FT8 activity centres around 14.074 MHz.
The exchanges are highly structured and very short: callsigns, grid squares, signal reports and acknowledgements. It isn’t exactly sparkling conversation.
But that isn’t really the point.
FT8 is astonishing at recovering signals well below the noise floor.
Watching the WSJT-X decode window fill with stations that I could barely — or couldn’t — hear by ear was another one of those small amateur-radio revelations.
Oddly, WSPR also gave me a useful lesson about interpreting FT8 activity. There were occasions when WSPR showed that my signal was travelling extremely well while the FT8 receive window looked rather sparse.
That didn’t mean the antenna had suddenly failed.
Different modes have different sensitivities, different activity levels and different operating patterns. Propagation can also be asymmetric.
The absence of FT8 decodes doesn’t necessarily mean the absence of propagation.
WSPR had given me another instrument for understanding what I was seeing.
JS8: FT8 discovers conversation
Then there is JS8.
JS8 uses a modulation technique derived from FT8, but instead of exchanging a rigid sequence of signal reports, JS8Call allows actual text communication.
That immediately appealed to me.
On 20 metres, JS8 activity is normally found around 14.078 MHz. Once I had JS8Call, FLrig and the FTdx10 behaving themselves, I began decoding stations.
Then I transmitted my own CQ.
Then somebody answered.
My early contacts included KK4QIG in Florida and AF4SH in Georgia.
They weren’t spectacular DX by WSPR standards, but they felt completely different.
There is something strangely satisfying about exchanging actual typed messages with another station using signals that may be hovering around the noise floor.
My early operating technique was not exactly flawless.
I discovered that repeatedly sending CQ and heartbeat messages is considered somewhat enthusiastic.
At various moments, I typed other people’s callsigns where my own should have gone.
I once mixed a traditional “599” report into a mode whose software was already telling me the actual signal-to-noise ratio.
In other words, I behaved exactly like someone learning a new mode.
But the contacts worked.
And each one made the underlying machinery slightly less mysterious.
Olivia and the wonderfully crowded world of fldigi
At some point I opened fldigi’s mode menu.
This was a tactical error.
There are approximately six billion digital modes in there.
PSK.
RTTY.
Olivia.
Contestia.
Thor.
DominoEX.
FSQ.
Modes apparently invented by people who believed amateur radio really needed another modulation scheme.
Obviously, I wanted to try them all.
Olivia particularly interested me because it is designed for reliable keyboard-to-keyboard communication under poor signal conditions.
Getting the transmit audio adjusted properly became another lesson in modern radio technique. The goal is not to hammer the radio until the ALC meter lights up like Christmas.
Quite the opposite.
With the FTdx10 in DATA-U mode, I eventually found settings that produced clean RF with essentially no ALC indication. The computer provides enough audio to drive the transmitter properly, and no more.
Once you begin looking at digital signals that way, “more” stops automatically meaning “better.”
Down another rabbit hole: Winlink
The next project was Winlink.
Winlink is a worldwide radio email system used extensively in emergency communications. Messages can travel through HF gateways even when conventional Internet infrastructure isn’t available.
I wanted to make it work from the Mac.
This involved MacWinlink, various helper applications, ARDOP, VARA HF running under Wine, CAT control, USB audio routing and an impressive collection of opportunities for one software component to misunderstand another.
Eventually, though, I connected through an HF RMS gateway in Georgia using VARA HF.
That was another satisfying little milestone.
The important part wasn’t sending email by radio.
Amateur radio has been doing that sort of thing for decades.
The satisfying part was understanding enough of the entire chain — computer, modem, audio, CAT, radio, propagation and remote station — to know why it worked.
And, increasingly, why it sometimes didn’t.
Propagation prediction meets propagation reality
Once I had accumulated enough WSPR observations, another question appeared:
Could I predict this?
That led me to VOACAP.
VOACAP is a descendant of ionospheric propagation models developed for professional HF communications. It can estimate the probability of communication between two locations by frequency and time of day.
Naturally, I installed the command-line version.
Naturally, it initially complained about file paths.
Naturally, some of its conventions seem designed for when computer operators carried boxes of punch cards.
Eventually I had it running.
One path I examined was from my station, VE3ZDN in grid EN93tj, to DK6UG in Germany, roughly 6,400 km away.
The predictions suggested that 17 metres should perform particularly well earlier in the evening, with 20 metres becoming the more reliable path later.
Then I could compare that prediction with actual WSPR reports.
This is where the whole experiment became much more than simply chasing DX.
I was doing a tiny version of radio science.
Make a prediction.
Transmit.
Collect observations.
Compare the result.
Change something.
Try again.
Five watts changes your sense of scale
Perhaps the biggest surprise from all this has been how little RF power is required when everything else cooperates.
Five watts is about what a USB charger might deliver.
Yet five watts of RF, applied to a resonant dipole and launched into the ionosphere at the right moment, can cross an ocean.
Several oceans, apparently.
That doesn’t mean power is irrelevant. More power gives additional link margin, and there are plenty of circumstances where it matters.
But weak-signal digital modes make something visible that ordinary voice operating can conceal:
The path itself is doing most of the work.
The antenna matters.
The noise floor matters.
Timing matters.
The ionosphere matters enormously.
And clever signal processing can extract astonishing amounts of information from almost nothing.
The real appeal
I think there’s a tendency to divide amateur radio into “traditional” and “computer” radio. I don’t find the distinction very useful.
When my five-watt WSPR transmission is decoded in Australia, I am still doing what radio amateurs have always done: putting RF into an antenna and wondering who can hear it.
The computer simply lets me see the answer.
FT8 shows me signals I would otherwise miss.
JS8 lets me turn those weak signals into a conversation.
WSPR turns thousands of receiving stations into a gigantic propagation experiment.
VOACAP lets me test theory against observation.
Winlink adds practical communications capability.
And somewhere underneath all the software, USB cables and TCP ports is still the same wonderfully improbable phenomenon that has fascinated radio operators for more than a century:
I put a small alternating current into a wire in my backyard.
A fraction of a second later, some of that energy is on the other side of the planet.
Then somebody’s computer says:
“I heard you.”
That still seems like magic.
I hope it always does.
And, of course, I have barely scratched the surface.
There are still all those other modes in the fldigi menu.
This may have been a mistake.
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