Every year, the Geminid meteor shower peaks around the 14th of December and many VHF radio amateurs make contacts by bouncing signals off the meteor trails left behind. The maximum distance tends to be similar to Sporadic-E i.e. in the region of 2300 kms.
During this years Geminids, Stamen LZ1KU announced a suprise reception on 144 MHz of Jon OY9JD on the Faroe Islands, a distance of 3075 kms!
A composite of the screenshot from LZ1KU is shown below...
As can be seen, the mode used was MSK144 and there is one decode from OY9JD.
On an online forum later, OY9JD did confirm that he was on air at that time...
According to info provided by SO3Z, Jon OY9JD is using an ICOM IC970 with 500W into an 8 el Yagi 3m long. LZ1KU is using an array of 4 x 12 elements and 1.7kW.
Even though there was no two way contact on this occasion, it is still an impressive distance for 144 MHz. Remember that 3075 kms is roughly the distance across the North Atlantic between Ireland and Newfoundland.
In fact, 3075 kms to the west from OY9JD actually reaches the remote areas of Labrador in NE Canada.
Mode of Propagation??? (Updated)...
(Theory 1) Double Hop Meteor Scatter... Most meteor trails capable of supporting propagation of 144 MHz signals last for a fraction of a second at best with the occasional one lasting several seconds.
Was it a case that that on this particular occasion, two meteor trails were in just the right spot happened at the same time?
In other words, the MSK144 signal from OY9JD was reflected off the ionised trail of one meteor, then hit off another trail several hundred kms later and then was picked up in Bulgaria.
As you might imagine, this isn't that common as it requires there to be two meteor trails to be just in the right place and at just the right time.
(Theory 2) Tropo Assist?... As for did tropo play a part in the path? The conditions looked pretty poor as can be seen from the image below.
It seems unlikely that any sort of tropo ducting played any part in this reception report.
Theory 3... Refection from the International Space Station??? It would seem as if the International Space Station (ISS) was above the horizon at the same time.
In response to my original theory that it was double hop meteor scatter, Alejandro LU8YD from Argentina writes...
"My opinion is that the QSO analysis is not correct. You have to check the location of the ISS space station at the time of the QSO and you will see that it was crossing the path between stations LZ and OY. In my opinion it is a QSO by Spacecraft scatter and not by meteor scatter. Reflections of amateur radio signals by the ISS as a passive reflector has occurred before. Despite this, it must be considered an extraordinary QSO and achievement by LZ1KU and OY9JD for which I congratulate them.
Please send my regards and congratulations to Stamen and Jon
Kind regards Alejandro LU8YD"
After receiving Alejandro's message, I checked out the position of the ISS on the morning of the 14th of December.
The beam heading from the Faroe Islands to Bulgaria is 147 degrees. The time stamp on the MSK144 signal was 11:03 UTC.
It's not a perfect match but the ISS was certainly in the same general area of sky at the time. The ISS reached a maximum elevation of 10 degrees during that pass and it was probably around 4-5 degrees at 11:03 UTC.
This is the view of the pass from Bulgaria...
From the Bulgarian perspective with a higher pass, the time and beam heading seem closer aligned. The Faroe Islands are on a beam heading of 327 degrees from Bulgaria.
Considering the size of the ISS and the size of the reflective surface, it has to considered a strong contender for the reception report.
However, I still have some questions. What about doppler shift? Would the doppler shift have moved the signals outside the receive passband of the receiver? What impact does doppler have on a MSK144 signal and the ability to decode it?
Conclusion (Updated)... My original thinking was that it was probably double hop meteor scatter. After all, there must be occasions when two meteors trails just happen to line up in the correct position at the same time.
The fact that the International Space Station was in the same area of sky at the same time must make this the most likely reason although in retrospect, I don't think we can be absolutely certain but it does seem likely.
I'd be inclined to say 90:10 in favour of refection off the ISS as opposed to double hop MS but others may have different opinions.
North Atlantic on 144 MHz??? ... Here is an intriguing thought: If the signal at 144 MHz can get 3075 kms from the Faroe Islands to Bulgaria was via double hop meteor scatter then why not across the North Atlantic from Ireland/UK to Newfoundland?
Very nice account, John.
ReplyDeleteAs with all things digital, what was once considered impossible, or not even considered at all, is often realised now as quite possible.
I'm sure what you muse about in relation to transatlantic possibilities can occur in reality. But I am not sure the chances of it occurring to enable a two-way QSO are very high, not least because it's unlikely many would be trying on the US side (notorious for lack of effort on 2m transatlantic tropo attempts, for example).
2m MS is already hard, with very strong signals from any given station often never appearing again, or not for a very long time. But someone may be lucky, one day!
Two hop meteor scatter on 144MHz is very statistically unlikely and indeed the probability is so low that for the time it takes for a MSK144 burst to be properly decoded, ie overlap for >200ms, I would I would completely reject this explanation.
ReplyDeleteThe tropo plus MS is interesting as I have had over 50 QSOs >3,000Km this way on 144MHz. However Hepburn and F5LEN maps show that the tropo path path from OY to OZ and beyond was not really there.
On the low probability side is also ionospheric refraction coupled with MS, such as occurs during the summer sporadic e season, coupled with MS. It is not uncommon to hear occasional bursts from stations 3000+Km away.
Unfortunately ISS reflection as you have accurately described is the probable answer. The absolute proof of this comes from looking at the absolute frequency of both stations and the Doppler shift caused by the relative motion of ISS. In some versions of my 3000+ Km Contacts on 144MHz talk I describe this process.
John G4SWX
Enjoyed this interesting discussion with images.
ReplyDelete--From Athens, Ga (USA). KN4IJM
You can add information about setup of both stations:
ReplyDeleteOY9JD = ic970, 500W, 8 el yagi 3m long ; LZ1KU = 4x12el 1,7kW
73!
de SO3Z
1,7KW by VHF?! Time to cook Turkey on air, directory, LOL! 😊
ReplyDeleteHi John,
ReplyDeleteI enjoy reading your blog.
There are several reports of passive, ISS reflection on 144MHz now.
https://www.youtube.com/watch?v=Vii8DmG3ftc&ab_channel=Tim%2a%2a%2a%2a
Verifed, multi-hop (Chordal) MS however, seems to be much rarer.... Even though it is "unlikely", with so many stations continuously monitoring/reporting it seems that it *never* happens.
Would love to see some reports of it if you come across any.
Tim G4LOH