A very interesting explanation of 6m propagation by VP8DBL


Being a northern European type who is used to only to hearing white noise this cycle, I felt that I had spectacular propagation from in the Falklands. What made it all the better was that it was totally unexpected! I really thought that I would hear little from the islands because of its remote location and southerly latitude. How wrong can one be? So what was happening? I will be not be tempted to generalize too much from a short visit, but my considered opinion is that VP8 is a magic spot for 6m!

Cross section of Transequitorial Propagtion (thanks: ARRL)Cross section of Transequitorial Propagation (thanks: ARRL)

Let's take a look at some propagation basics. The mode of propagation I experienced for most of my north-south QSO's was undoubtedly classic Transequitorial Propagation or Spread-F. This mode of propagation supports long distance QSO's between stations that are equidistant on either side of the geomagnetic equator. Note the word 'geomagnetic'. This is important as the physical and geomagnetic equators are not aligned in most parts of the world. The way it works is that 6m signals are refracted twice over the geomagnetic equator at angles that normally would be insufficient to bring the signals back to earth.

TEP takes place between stations equidistant across the geomagnetic equator (thanks: ARRL)TEP takes place between stations equidistant across the geomagnetic equator (thanks: ARRL)

Another important point, but a pretty obvious one from all our 6m experiences, is that the 'equidistant stations on either side of the equator' can be significantly shifted east or west of each other by thousands of miles. We have all seen this with the openings between Argentina and Europe over many years. 

The key point to notice on the plots of the earth's magnetic inclination is that it takes a nosedive southwards over South America and the deviation peaks over the VP8 group of countries. Perhaps I should have noticed this before! 

Plot of Magnetic Inclination (Thanks: NOAA)Plot of Magnetic Inclination (Thanks: NOAA)

Looking at the graphs indicates that the Falkland Islands lies at approximately -47o south of the Geomagnetic equator while Malta and Greece, who came up first each day, are located around +45o. So the Falklands and the southern Mediterranean are located equidistant either side optimally placed for TEP propagation. Who would ever have thought this, certainly not me. I would hazard a hypothesis that this explains the incredible propagation between VP8 and the Mediterranean areas experienced every day during my visit. VP8 really is a magic spot! This might also explain my empirical opinion that TEP signals have always been stronger from South America that South Africa. Have other North Europeans noticed this as well? And it probably explains why Peter, PY5CC does so well on 6m.

MUF : MARCH 15z SSN=140 (thanks: G0AEV)MUF : March 15:00z SSN=140 (thanks: G0AEV)

At the UKSMG's AGM in February, we heard an excellent talk from Steve, G0AEV focusing on the possibilities of 6m propagation this cycle. The graph on the right shows a forecast plot of the MUF Europe in March with an SSN of 140. Although my activity from VP8 was in April rather than March and the SSN was lower, it does show graphically the propagation that possibilities are focused on the area around the Falkland Islands.

A possible explanation for the propagation - nope!A possible explanation for the propagation - nope!

However neat, the TEP model outlined above does not explain some of the other QSO's that I had. For example, I was hearing South Africa on a direct short path, turning the antenna north lost the signals. Also, at the height of the TEP on Sunday morning, when I was receiving Africa, Europe and the Caribbean simultaneously on 110, I was called by several LU's and PY5CC. To the 'keen ears of a 6m DXer'  :>) these signals sounded different to the others, in that they were hollow and there were significant echoes. I was beaming east at the time and when I turned the antenna west the signals disappeared. Turning it back east again brought them back up. As I suspected I was receiving these on classic backscatter from a ionization cloud somewhere to the east. It must have well south as well because I also worked ZD9BV, again on a direct short path. I assume that his signal was transiting the cloud? So was the propagation I experienced a mixture of TEP and and an ionization cloud in the South Atlantic. Put it this way, it certainly was NOT just a cloud in the south Atlantic alone or TEP alone as I was beaming great circle alignments except for the backscatter QSO's. It was a combination of both. From what I remember, South African stations were hearing Europe strongly but were not receiving the Caribbean stations I was hearing. This helps confirm my opinion that the QSO's above the equator were via TEP and those below via F2 direct.

I postulated from all this that I would not be able to work South America on the short path. Wrong! On Monday I worked LU7FA in FF96 only hearing him pointing the antenna in that direction! Later I also heard Peter, PY5CC calling CQ, again on short path! This really is a magic band sometimes.

The only disappointment I had was that I did not experience any long path openings while in VP8 (don't forget that the nearest country to south of VP8 past Puntas Arenas is New Zealand!) even though Australia, Argentina and Brazil were experiencing it. These long-path openings were over Europe so I am sure I would have heard something if there had have been any. I would hazard a guess, that remains to be proven, that if we had a really serious 6m operator over the last few years on VP8 his/her country score would have been as high as PY5CCs!