Sunday, January 1, 2023

Auroral Zone Case Study

I haven't had much time for radio these days.  At this latitude, the return of the sunspots put the kibosh on my 160m dxing and with 322 (mixed, current) DXCC entities confirmed there haven't been any workable new ones available for me.  My Station 2021 project has been languishing and even my existing station has fallen into disrepair.  My rotator quit working in 2021 and this spring I accidentally overdrove my amp and blew something.  Life was busy but sooner or later something would come along that motivated me to get back on the air.  I still followed the DX news and was keeping an eye out for any new ones coming along.  I followed (and donated to) the 3Y0J expedition to Bouvet Island, still on track for the end of January 2023, and also took note of the one-man operation heading for Crozet Island.  When Thierry F6CUK arrived on Crozet and began operating as FT8WW over the Christmas holidays I knew that it was time to get it together.

When swapping out a couple of boards in the amplifier didn't solve the problem I determined it had to be an issue with my homebrew T/R switch and attenuator.  After removing it and putting it on the bench I found that a 50 ohm resistor in the attenuator had failed.  Stands to reason that accidentally pumping 100 watts into a 30 watt resistor too often would eventually lead to problems!  I was already planning to replace one resistor in there to adjust for my new 10-watt IC-705 but I didn't have any spare non-inductive 50 ohm resistors.  Nothing in the junk box either but I did find an old splitter/combiner set that each had a 25 ohm resistor so I put them in series and voila- problem solved.  Fortunately, the antenna with the broken rotator is pointed North over the pole so I didn't have to climb the tower in the dark and 40 below, at least not until the Bouvet activation later this month. 

Once all that and all the other minor repairs and software upgrades were done it was time make a contact!  Well, that part was not going to be so easy.  FT8WW was
so far only using a low wire antenna .  The active solar conditions would make signals very weak as the path between here (at 68 degrees North) and Crozet (nearly antipodal from here) travels straight over the North pole (which means passing through the aurora TWICE) and then all the way down the other side of the world.  At least we marginally shared a grey line between midnight zulu and 0200z.  That would be the best time to try.

The entire eastern hemisphere is straight over the pole from here and Crozet is no exception.

Conditions were lousy all week.  The elevated X-ray Flux attenuates signals like crazy up here!

I was in the shack every evening watching for him.  He was operating mostly FT8 digital mode and alternating between the 30m band and the 20m band.  FT8 is great for making contact with weak signals but it is strongly affected by the multipathing and phase shifting from the aurora.  The sun was spitting out B and C-class solar flares every few hours.  The aurora was blazing overhead and the absorption was extremely high.  Most of the time I could only decode a few of the hundreds of other stations calling FT8WW.  You could even see on the waterfall display how the geomagnetic activity messed with the signals.  Instead of straight lines on the scope they would often "bend" in the middle like digital macaroni.  Occasionally I would see a weak trace on the scope that I assumed was FT8WW but the horrible conditions prevented successful decoding.  I could see the KL7 stations in Alaska calling and giving him good signal reports but even stations only a few hundred miles south of here have a path to Crozet that manages to skirt the edge of the auroral oval and follows the grey line perfectly.

Nevertheless, I persevered. Finally, on New Year's Eve, FT8WW was on 30m around 0100z and as I watched the signals all started to get a bit stronger.  Then I finally got ONE decode of FT8WW, only -18dB.  Three minutes later I got another decode, this time -15dB.  I started calling him.  4 periods (2 minutes) later he decoded again, this time I got both of his streams (he was using MSHV and running two carriers).  Then nothing again for another 5 minutes.  I could SEE his transmissions on the display but they just weren't decoding.  Finally, I got another decode and it was the one I wanted to see. He was answering me!  I acknowledged my report (sent RR73) and right away received an RR73 from him.  Done and done.  And that was it!  I didn't get any more decodes after that.  I only received a total of 7 transmissions from him and between calling and answering I transmitted 13 times over six minutes.  

So what actually happened in that very short time span?  Here is what I think was going on.  The first thing was the auroral oval.  Here is the NOAA Ovation forecast for that period around 0100z:

You can see that there is a gap in the oval around solar noon.  I was just inside the gap which probably helped to get his signal down to me.  The path between us (marked in red) also crossed a slightly narrower auroral band on the other side of the pole.

Shooting through the gap helped but the real answer was the solar wind.  Like earthly wind, it "blows" fast or slow depending on the level of solar activity.  The stronger the solar wind the worse the space weather is for HF radio in the polar regions.  And again like the earthly wind, it also has "gusts" but these variations aren't changes in the speed.  They are changes in the magnetic polarity.  In the Northern auroral zone, the more negative the magnetic polarity the stronger the geomagnetic badness is.  Here is the NOAA real-time solar wind plot for the time of my contact:

You can see right at the time I started getting a few decodes from FT8WW, the magnetic polarity (Bz) of the solar wind peaked in the positive direction which momentarily eased the distortion from the electromagnetism.  This effect is especially pronounced on the lower HF bands.  Our contact was on the 30m band which tends to share characteristics of both the lower and higher bands.

#323 finally in the log!

As an aside, for those radio Luddites out there, CW transmissions are also affected by the geomagnetic field here in the same way.  For anything faster than about 15 words-per-minute, the multipath distortion makes CW sound like a weak RTTY signal.  The differences between dots and dashes is virtually indistinguishable.  Think about that the next time you're in the ARRL CW Sweepstakes looking for that NT multiplier but blasting away with the keyer set at 30wpm!

Next up at the end of January is a two-fer: Bouvet Island and Burundi, both of which I have been waiting for a chance at for a long time!  The last attempt at both of those did not end well but I have a feeling that 2023 is going to be the year they finally make it into the log.  Fingers crossed!

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