During an extensive Sporadic-E opening in Australia on the 15th of December 2020, WSPR signals from John VK2IJM and David VK2DVM in Sydney were heard by Peter VK6KXW near Perth in Western Australia.
Timestamp UTC Call MHz SNR Drift Grid Pwr Reporter RGrid km az Mode
2020-12-15 10:36 VK2DVM 144.490519 -25 0 QF56og 10 VK6KXW OF87jr 3199 263 2
2020-12-15 10:16 VK2IJM 144.490507 -8 0 QF56ni 10 VK6KXW OF87jr 3192 263 2
2020-12-15 10:36 VK2DVM 144.490519 -25 0 QF56og 10 VK6KXW OF87jr 3199 263 2
2020-12-15 10:16 VK2IJM 144.490507 -8 0 QF56ni 10 VK6KXW OF87jr 3192 263 2
The path was in the region of 3200 kms which is way beyond the usual 2300km or so one hop distance from Sporadic-E. It seems likely that on this occasion, the most likely propagation mode was double hop Sporadic-E which is very rare at 144 MHz.
It looks as if just one WSPR transmission from each of the VK2 stations was decoded at 10:16 and 10:36 UTC. This was about an hour after sunset in Sydney which is 11 hours ahead of UTC.
It's also worth pointing out that the reports from the WSPRnet website say that the VK2 stations were running just 10 watts.
Tropo?... As the path cross the Great Australian Bight, it's always worth checking to see if that was a factor.
The forecast was for some weak tropo across the Bight but nothing special and it doesn't seem to extend inland.
VK6CPU in Perth was also heard by VK5AYD in Adelaide at around the same time over a distance of 2149 kms which was likely to be via Sporadic-E.
Timestamp UTC Call MHz SNR Drift Grid Pwr Reporter RGrid km az Mode
2020-12-15 10:56 VK6CPU 144.490510 -24 3 OF78wb 5 VK5AYD PF97ja 2149 99 2
It would seem as if double hop Sporadic-E was the most likely mode of propagation.
Update: Just to clarify that when I say double hop Sporadic-E, I am referring to two areas of ionisation that are capable of supporting 144 MHz propagation. The signal may well be chordal i.e. Ground to cloud to cloud to ground ... as opposed to reflecting off the ground at some mid way point.
Links...
1) More info about long distance openings on 144 MHz can be seen on my 144 Page... https://ei7gl.blogspot.com/p/144-mhz.html
5 comments:
Interesting stuff. Can reflections off space hardware be ruled out? The ISS was responsible for the first, unsuccessful claim of a transatlantic crossing at 144MHz. Don't have time to check where the ISS was on the day, but in any case, there is plenty of other stuff to potentially provide specular reflections as well.
I think that there is a very simple explanation for this.
Most amateurs think of VHF sporadic-e as reflection from a relatively small area of the ionosphere as is probably the case at lower HF frequencies. This very simple explanation evades much of the complexity of ionospheric physics.
Nearly all forms of ionospheric reflection occur as a result of refraction in the ionosphere, the magnitude of this refraction with distance dependant upon the refractive index profile.
As the refractive index profile intensifies so the maximum frequency that will gain enough refraction to bring it back to ground increases.
Most of the time the area of the ionosphere that will refract 144MHz signals so that they return to the ground at a distance is relatively small. The advent of Live MuF maps has shown that occasionally the area of the ionosphere that will reflect VHF signals below 144MHz can spread over 1000+Km.
In these circumstances refraction either at two points or continuously over 1000+Km will bring signals back to the ground at points further distant than the 'normally assumed' 2300Km maximum for single hop sporadic e.
More rigorous analysis of European sporadic e data by Joachim Kraft, DL8HCZ and published in Dubus describes these contacts of which there are several every year as chordal.
It has been observed for many years that the distance of signals returning to the ground(QRB) is highest at the start and at the end of 144MHz sporadic e events. This fits exactly with the explanation that refraction is occurring along a path within the ionosphere whereby the length of path required to return a signal to the ground reduces with increasing ionisation. In simplistic 'amateur terms' as the MuF increases the hop distance reduces although the height of the e-layer refraction is also an issue.
In over 50 years of extreme DXing on 144MHz I have never seen a proven case of 2-hop sporadic e. The geometry and critical angles are very extreme as is the reflection loss from, at best a calm sea reflection. I consider that chordal or double refraction is a far better explanation of many 144MHz contacts claimed as 2-hop.
John G4SWX
To John G4SWX: I think it depends on the exact definition of what 'double hop' means. I would count chordal as double hop as there are two regions of ionisation where the Sp-E MUF is around 144 MHz. I'll update the post to make that clearer.
To John MW1CFN (Photon): I don't think the ISS or any satellite was responsible in this case. There were two reception reports and both were 20 minutes apart. In addition, WSPR transmissions last for two minutes and there is the whole doppler thing as well. I think double hop / chordal hop is the most likely explanation.
Hi all,
I was just reading your comments on our unusual VK opening and as one of the operators involved I though I would share some comments. Around this time of the year, the sun is almost directly overhead in VK and it's not unusual to get single hop sporadic E contacts for about 3 weeks either side of the solstice. The vhf WSPR community is also quite large in VK and we have a Facebook chat page to provide alerts to other operators when conditions start to peak. On this occasion, we saw a very intense double hop (chordal) path develop on 6m with signals well over S9 from VK2 to VK6, with VK5 in the middle being jumped over for most of the opening, which lasted for over an hour. At the peak of the opening, VK2KRR near Wagga was hearing FM broadcast stations in Kalgoorlie WA @ ~2800km and we communicated to other users on the chat page to move to 2m. It's possible that these types of openings are a bit more common than we realise, but the numbers of operators in WA is very sparse and the odds are a bit like playing lotto.
This fits with 3260 KM 144.100 ssb between ZL2WHO/ ZL2OK to VK5BC/p Was back around 2016 from memory. 73 Mark.
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