The Curious Case of K6MCS.

A little while ago, my blogger friend Bas, PE4BAS, wrote on the somewhat unexpected spot of his WSPR signal by, in particular, a VE6 station.

The explanation could be geomagnetic enhancement - a proposition superficially supported by the coincidental increase in the Kp index at the time of those spots.  Other explanations are, of course, always possible, but are always tough to prove, one way or the other.

Last evening, with quite a lot of family stuff to attend to, I started WSPR on both RX and TX.  With initially fairly quiet geomagnetic conditions, the cut-off of DX spots being received from the US occurred very sharply, and in good agreement with the local ionosphere at about 1000km up losing sight of the sun at around 20:00UT.

I appreciate these kinds of 'research' posts can be a bit long and perhaps dull.  But because the data becomes harder to extract over time, and because many will rightly want to scrutinise and question it, it's important to present as much evidence as possible.

This is how ionospheric sunset looked here, as revealed by spots of my WSPR transmissions dropping off a cliff:

So far, so predictable.  Looking at the receive side here, and apart from the odd nearby European station, the cliff edge in TX was repeated in that all I could hear from 19:30UT were ground waves from very nearby, UK stations. 

This is an extract of how the spots being received by me looked:

If you read that table properly, you will have noticed something very odd.  K6MCS, way out in California, suddenly appears at 22:04UT, his 5 Watts being heard a further two times over the next half an hour or so.  The initial SNR is quite strong, at -18dB.

This needs some explanation, because the propagation afforded by the ionosphere had clearly shut down two hours previously, and then remained firmly shut to all other DX.

What happened to allow a signal from 8130km to make it to the UK?  Did anybody else hear it?

This is what K6MCS was hearing (30 minute window) at 22:11UT (the terminator is correct for the time of the spot in this graphic):

Checking who K6MCS heard over the past 24 hours at 10:07UT this morning, it's clear that my hearing him was unique on the night side.

If we now look at the Kiruna magnetogram, it's evident that the Z (vertical) component at the time was deepening a southerly variation, indicating a geomagnetic disturbance:

Image courtesy IRF Kiruna.

This is how the aurora forecast expected things to look at the time:

Image NOAA/SWPC.

The disturbance was moderate, rising to a Kp of 4 for an hour or two.

This is the great circle path between us, but there is no certainty that this was the actual (or only) path of the signal, of course:

Then, at 23:00UT, and again at 23:30UT, I heard KJ6WSM at -23dB from a 2W signal.  Again, I was the only station on the night side to hear him (the only other station to hear him in 24 hours to 10UT today was a G4 station last hearing him at 18:34UT, when the sun was still illuminating the ionosphere locally).

The only other extraordinary signal heard (twice) during the night was from the extreme-northerly station of VY0ERC, 3 hours after K6MCS, which looked like this:

This was also quite an unusual event, in that, apart from two spots from OH-land at 22:40UT, I was the only dark side station to hear VY0ERC (the terminator should be ignored in this graphic, as it was depicted at the time of consulting the database, not the time of the spots):

From all the above, and coupled to earlier research that unambiguously showed geomagnetic enhancements to propagation occurs at 14MHz, it's clear that this, fairly minor and short-lived disturbance also caused a slight enhancement.

The VY0ERC spots seem to be linked to the onset phase of a further, sharp southerly swing in the Z component, though no DX spots were heard during the period of most southerly swing, lasting just over an hour.

The odd thing is, of course, that I was only one of a large number of WSPR receiving stations on the dark side receiving the K6 and KJ6 stations.  What was it about their location that selected them from all the others across the US?  Even more remarkable is this graphic, revealing the two Californian stations are only 13km apart!

Image: Google Earth.

Most texts I've read assert that auroral absorption is very high at HF, more so at the lower end.  This gives rise to the usual expectation that geomagnetic disturbances cause poor propagation conditions.

This latest result shows that this expectation is not always correct, and indeed can sometimes be the opposite of what is to be expected.  After all, without last night's rise in Kp to 4, it is almost certain that those stations would not have been heard here.


Looking at the other, direct path possibility - the so-called 'long path' - I can't see any obvious way in which that could have been responsible.  Skewed paths, which are quite common, are also worth considering, but difficult to determine without expensive software or access to other data that I don't have.

The singular reception spots probably arise, again, from a very quiet RF location with a good, clear environment.  But there must be a lot of other WSPR receivers in equally quiet, and probably even quieter locations, especially in sparsely-populated high latitude regions like Scandinavia.  Development always threatens this, sadly, with a very large PV 'farm' due for construction near this QTH soon, and various other things that constantly raise the HF noise floor.

The whole event does, also, remind us that listening for WSPR signals is very important.  Transmitting only is rather anti-social for a mode that depends on someone hearing you.  WSPRlite is a wonderful development, but does threaten to be a disrupter when a significant imbalance between TX and RX comes to exist.


If you have any ideas, criticisms or observations, do post a comment!