QRSS revisited

For the last couple of months, I’ve not done much in the way of traditional radio, largely down to the fact that I’ve been really busy at work. I’ve had lots to do and I’ve spent a month working away from home either on training courses or in meetings preparing for a very large project.

My Hans Summers Ultimate 3S transmitter has been running continually on 10m for a couple of years and earlier this month I decided to shift it around for a while and so it ran for a week on 20m and then a week on 17m while I was working away from home. At time of writing, it’s transmitting on 80m as there have been a few signals European transmissions received in North America recently and I thought it would be interesting to see if my 200mW QRSS signal would make the trip across the pond.

Here’s a reminder what QRSS actually is.

Imagine Morse code sent very slowly, so slowly that one simple ‘dit’ takes six seconds to send and a ‘dah’ takes eighteen seconds. Imagine also that it’s transmitted using audio frequency shift keying (AFSK) with just 4Hz differentiating the two tones and what you’ve got is QRSS. If you were to listen to it, you’d struggle to hear the difference between the two tones and that’s if you could even hear the signal because they’re transmitted with very low power, typically under 200mW.

Unlike WSPR which is automatically decoded and the callsign of the sender is uploaded to a central site, QRSS is decoded by eye and signals are so weak that it can take many repetitions stacked on top of each other to be able to see who is transmitting. There are very few stations in the world who transmit QRSS or run grabbers to receive QRSS signals.

I’ve been running my grabber again and have received some nice signals from Vernon, VE1VDM on 20m. Here’s a typical ten minute transmission from Vern.

Single QRSS frame from VE1VDM
Single QRSS frame from VE1VDM

If you click the image above, you’ll get a larger version where you can see the bare trace of a signal on the screen. Looking at the scale on the right hand side, the noise is at around -38dB and the signal is a fraction above that at about -36dB. If you were to tune your radio to the same frequency I’m monitoring on 20m, you wouldn’t hear anything because it’s that weak. FT8 can decode signals that are at -26dB and WSPR is good for about -30dB so using QRSS you can get decodes of signals significantly weaker than FT8 or WSPR.

“Ahah”, I hear you say. “But you can’t actually decode anything from the image above”. Of course, you’re correct and this is where stacking comes into play. Vernon’s signal was visible on my grabber between 11:00z and 17:50z on the 27th March 2019. QRSS operators normally transmit the same thing over and over again in ten minute frames allowing for stacking, that is combining multiple images on top of each other to build up an overall picture. If I combine the forty one frames captured on Wednesday, this is what I get.

VE1VDM stacked on 27th March 2019
VE1VDM stacked on 27th March 2019

This is literally Morse code painted on screen by the transmitted audio tones (AFSK). In order to read it you look at the top half of each character and you’ll see the code. This will make it easier.

VE1VDM drawn in QRSS

As you can tell, QRSS isn’t for the impatient. I’ve gone for weeks and weeks without anyone spotting my 10m QRSS transmitter but all of a sudden it can appear out of the noise for a few minutes if the band opens briefly. Over the last year or so, there have been quite a few spots of QRSS beacons on 10m that are purely down to meteor scatter. QRSS is also really good for aircraft scatter on 30m and there have been some fascinating studies written about aircraft scatter. By knowing the route and speed of an aircraft, the transmitting station can be located within a few miles due to the scatter on the received signal.

Frequency stability on both QRSS transmitters and receivers is absolutely vital to get a good clean signal. The difference between the two lines on the picture above is just 4Hz and the overall bandwidth on the image is just over 200Hz. If the transmitter or the receiver were to drift just one or two Hz the the signal would be nowhere near as clean as can be seen in this example from the day before. Vernon hadn’t quite got the temperature stability sorted in his transmitter and this can be seen in the approximate 2Hz variation in frequency.

Good frequency stability is the reason I installed a replacement temperature controlled crystal oscillator into my TS-590SG last year as it means my radio is absolutely bang on frequency with zero noticeable drift, even on 10m which was particularly bad before.

I really enjoy tinkering with QRSS and seeing what can be done with these incredibly weak signals. There aren’t many radio amateurs playing with it around the world so it’s very satisfying to see these signals appearing on grabbers and watching the grabbers to see where you’re being received.

If you’re interested and want to know more, our small community has an email reflector at groups.io. With just under 160 members, you can see that it’s fairly specialised.

To see some of the ‘grabber’ stations around the world, take a look at Scott’s page here which is an automatically updating list of grabbers with the current latest image. It takes more work than WSPR to find yourself but it’s worth the effort.

Updated: October 6, 2020 — 14:45

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