12th March 2023: As we approach the equinox, there are a lot of TEP (Trans-Equatorial Propagation) openings between the south of Europe and South America on the 50 MHz band. As were near the peak of the solar cycle and with the solar flux up around the 150 mark, this is nothing special.
What is highly unusual however was the appearance in Europe of some stations in the South Pacific during the TEP opening!
E51WL is located on North Cook Island in the South Pacific and the 50 MHz paths are shown above.
Things to note...
1) South America... There was an opening from E51WL to South America and was being reported by South American stations at around 23:00 UTC. At the same time, there was a TEP opening from South America to the south of Europe.
2) Direct SP... The map shows the paths on FT8 from E51WL to the south of Europe. The direct short paths travel far to the north.
3) Skewed Path... European stations were beaming towards South America when the path to E51WL was open. On KST Chat, SV1DH in Greece reports E51WL on a beam heading of 225 degrees, IW5DHN in the north of Italy reports 220 deg and IT9TYR in Sicily reports 240 deg. IW0FFK in Rome reports working E51WL at 235 deg but didn't have time to verify the beam heading.
While it's difficult to know the exact beam heading with a modest antenna at a frequency of 50 MHz, it still shows that the signal was coming from the direction of South America on a beam heading of about 240 degrees, not on the direct short path heading to the north-west. i.e. the path was skewed.
For the stations in the eastern half of the Mediterranean, the short path actually goes to the east while the long path would go down over Africa and cross the Antarctica to reach the Cook Islands. Regardless of long path or short path, the signal was at roughly 240 degrees and skewed.
Fiji to Europe... 3D2AG on the island of Fiji was also reported in the Iberian Peninsula and the Canary Islands.
Note the direct short paths from CT1BOH in Portugal and EA5NW in Spain go over the Arctic. In reality, it was a skewed path to the south-west.
On the map above, there are several paths to EA8... the Canary Islands. I suspect that these may have been skewed to the south as well.
As for the how???.... There is a theory that the signal can get propagated westwards between the north and south boundaries of the TEP zone. Eventually the signal escapes further west where the direct path via F2 layer propagation is more favourable.
I put together a simple diagram above which shows this concept.
In Conclusion... Skewed paths like this have been reported in the past but now with so many stations using a weak signal mode like FT8 on one frequency, these skewed paths should become a lot more obvious.
The key take away point is that for very distant paths, don't always assume a signal is on the direct short path.
It would be interesting to see more stations in the Pacific exploring these skewed paths to Europe. Obviously doing it near the equinox is important as well as the time of day... around 22:00-23:00 UTC.
It might be an idea to also try a quieter frequency than 50.313 MHz and use the appropriate time slot for transmitting.
Questions, questions, questions... I wonder if there is an equivalent but longer skewed path from Europe to the South Pacific to the east rather than the west?
Maybe 8-9pm local time for each station in the Pacific?
A skewed long path rather than a skewed short path?
Is it too early in the morning for 50 MHz signals in Europe?
Does it happen on the higher HF bands all the time but nobody notices or knows any better?
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Signal reports for E51WL and 3D2AG are shown below.
FT8 reports (15,000kms +) for E51WL...
