At last! Something to attract me back on to the radio. Over the past two days I have been able to work into southern Africa via Trans Equatorial Propagation (TEP). Great to see TEP again. I am still puzzled as to why this is possible but I am happy enough to work it.
I have had a few good contacts over the past six weeks, but mostly on 432MHz and above. 6m has seemed pretty mediocre as is often the case at this time of year. I even took some time off to visit EA6 ...
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| GM4FVM looking thoughtful but thirsty in Cala En Bosc (JM19) in Menorca |
Although tropo conditions looked very good, I did not take a radio to Menorca. At one time I took a radio wherever I went, but these days I have too much other stuff to carry.
Anyway, after returning to IO85, on 20 September at 18:56 I worked ZS6OB and ZS6NK. On 21 September at 17:27 I contacted V51WW, having missed him the previous day at around the same time.
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| 50MHz contacts at GM4FVM on 20 and 21 September 2025 |
The best DX was to ZS6OB in KG44 at 9513km and even V51WW is 8505km from here.
Now, these contacts are not unusual. Between them, I have worked these three stations 12 times. All of these contacts were after April 2023. Before that I had become accustomed to watching other stations working TEP which never came far enough north for me to reach it. Particularly galling was reading reports of stations elsewhere in the United Kingdom working into southern Africa, the Indian Ocean and South America when nothing had been heard here from those areas.
I have mentioned all this ad nauseam on this site (search for TEP is you don't believe me) but I feel obliged to go at it at great length again today.
So - first part to the puzzle, is the appearance of TEP here since 2023 due to the proximity of the solar maximum? Will TEP disappear again as solar conditions worsen? Or, another possibility, is the fact that more stations are looking for DX on 50MHz simply making this possible? Does gathering together on a single FT8 frequency make a difference?
My ARRL Handbook states that TEP "supports propagation between 5000 and 8000km", but these contacts are further than that. It also states that "stations attempting TE contacts must be nearly equidistant from the geomagnetic equator", providing a handy chart which shows a northern limit of TEP passing through southern England. I am about 600km north of this Northern Limit of TEP.
So the second puzzle is how this happens this far north. The simple answer is "Sporadic E linking into TEP", which would extend the range by one Es hop. One would guess that if there was any Es around I would hear stations within one hop as well as the TEP stations. However, on neither date did I hear any other stations on Es. Maybe the one hop took me to the middle of the Mediterranean Sea where there might not be any stations (though the paths seem to pass near to 9H1 and EA6 after passing over most of Europe). Nor did any stations in those areas seem to be working TEP at the same time. So some other explanation is needed here.
I suspect, with no particular empirical evidence, that the explanation for this is that these were indeed Es linking to TEP paths. However, the link may have occurred at a height above ground level which prevented local stations being involved near the link site. While others call anything occurring above ground level "chordal hop", that is a term I would not apply here. I suspect a good many multi-hop Es contacts involve a path which does not come down to ground level, and TEP may do the same. If you look at the diagrams in books you often find a plot of ionospheric propagation which is not refracted to ground level as ionisation at the time is not strong enough. Also, minor variations in Es layer could result in a refracted signal not reaching ground level. These effects could happen on both the Es and the TEP parts of the path, meaning that no station on the ground below the link would hear the signals.
The third puzzle is the time of year and time of day when I could expect to hear TEP. TEP is reported to be "equinoctal". Whilst the solar Autumnal Equinox is on 21 September and the Vernal one is on 21 March (give or take a day or two for leap years etc), it is the geomagnetic equinox which matters here. This varies with the position on the geomagnetic equator but should still be at the same date each year for any particular path. My other contacts with these stations range for the ZS stations from April, June, September (2), October (2) and November (2). For V51WW the dates are one each in June, July, August and September. These dates do not seem to fit easily int0 the idea of a group around the geomagnetic equinox at any point. My ARRL Handbook states 5 to 10pm, though there is a well known early afternoon peak too. For these stations my contacts are at the following hours of 11 (2), 12 (2), 14, 15 (2), 17 (3) and 18 (2).
Into this well mixed data group goes the further variable of Es linking. If there is Es linking then there has to be Es around at the time. For the recent contact no Es was observed at the time. A popular band conditions site showed "6m Es - Band Closed". September is a very poor months for Es at GM4FVM.
Basically the text books say that we get Es in the Summer, and TEP in the Spring and Autumn, making linking of the two a bit improbable. Nevertheless, I have the QSOs in the log to show it seems to be happening.
Thus to explain what I see I suspect a combination of weak Es and weak TEP linking well above ground level at some point along the path, possibly over southern Europe. Ironically, if either Es or TEP had been stronger it might never have happened and stations within the "Northern Limit of TEP" would have had a chance instead while I would have had a good path into Italy.
Well, that is what I think. As for definitive evidence of this - I only have the contacts in my log to suggest it. Nevertheless it has happened 12 times so far and I am happy to accept the QSOs.
I look forward to more of this over the coming months, but we just do not know for sure. What about some to South America.
73 Jim
GM4FVM
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