[UK-CONTEST] 28Mhz propagation

[Doug Roberts]

Hi Clive,

There's an article on the ARRL website about unusual propagation - seems 
somewhat allied to your experience!

http://www.arrl.org/news/stories/2004/12/10/2/?nc=1

73,
Doug G0WMW


Clive Whelan wrote:

>If you have a low boredom threshold, you might wish to hit delete now!
>
>I remember operating the ARRl 10m contest in 2001, and being very struck by
>a phenomenon, which I believe I have again experienced today, albeit at a
>different end of the day.
>
>Please note in the subsequent text that I am using essentially
>omni-directional antennas, of zero or very low gain.
>
>
>
>
>In 2001, I was quite serious about the event-which I am not this weekend-,
>and was on the band around dawn, and surprised to hear it already jumping
>with S9+ Russian stations( nothing much closer I seem to recall). I was most
>frustrated that I simply couldn't raise any of these guys despite calling my
>head off. When I say S9+ I do mean S9+, like loud. After a little while
>perhaps 30 minutes up pops A61AJ, who was running the UAs at quite a rate. I
>gave a call more in hope than anything, and after perhaps two calls he
>replied. A minute later I worked Bob P3F, but still none of the Russians
>replied to me. I could see from Geoclock that there was a grey-line running
>down into A61, and not a million miles from 5B4. However A61AJ was clearly
>not beaming my way, so something wasn't quite right. I cursed and blasphemed
>about one way propagation, in which I didn't really believe, but then
>hearing IS believing in our game! I drew back the shack curtains, and noted
>that it was still not really light ( looking North). Continuing to call and
>watch the sky, it was patently clear that I didn't raise the first Russian,
>until it was quite light outside. None of this made much sense to me,
>because although I could, in some sense explain the grey line path from A61
>to me as being skewed in some way, why couldn't I raise the Russians? After
>all, we all know-don't we!-that the point of ionospheric refraction is
>pretty much at the centre of the path, probably about 1000kM for the UAs,
>and it would have been well light there, even when it was still dark here,
>and should have supported propagation. I came to the logical conclusion,
>that I could work to the South East along the grey line, but there was some
>kind of barrier, perpendicular to this line, which prevented me working the
>Russians. Furthermore it seemed that this was a phenomenon occurring right
>at the home end of the path, after the ray had been refracted at mid path,
>and was then perhaps grazing a lower layer ( E?, F1?) close to the home end
>of the path. However, I had, and still have not an explanation for the
>apparent one way phenomenon. It was later suggested to me that while the
>band was pretty quiet at the G end, there would have been lots of QRM in say
>UA3. However, it really didn't sound like that, and I certainly would have
>expected to work one of the Russians with all the calling I was doing.
>
>So fast forward to this year.
>
>Preamble: Heard GM4AFF and a French station via MS mode in the morning and
>realised that it is almost the peak of the Geminids shower.
>
>
>I worked some East Eu in the late morning, and then ZF2NT opened the band up
>to the West at about 1240z. A few other Caribbean stations, as well as YV4A
>also found their way into the log. However it was a bit slow, and so I
>decided to go and eat at around 1300z, not getting back to the shack until
>about 1530, when I heard two verrrry weak W4s ( one being NE4AA), just too
>weak even to think about calling. Quite a swag of South Americans got into
>the log, the last one being at 1605z, when I noticed that it was already
>getting rather grey and gloomy outside. I worked F5IN, not thinking much
>about it, but then worked four HA stations in a row, having heard nothing
>from them before. I thought this a little strange, called up Geoclock, to
>see that they were right along the grey-line. The HAs disappeared, but were
>replaced about 15 minutes later, by about six YU stations and a 9A, further
>along the grey-line. By now it is 1706z, and exactly one hour since I worked
>the last SA station. I looked out of the window, and noticed that it was now
>completely dark outside. I stuck it for another 15 minutes, but heard
>absolutely nothing at all. I did a couple of chores, and made a phone call
>assuming that band was closed; WRONG! Returning at 1802z, the band is now
>open again to SA, and I work quite a few without much difficulty. However,
>signals now fade down, and  I have worked everything I can hear. However, I
>stick with it, but a little after 1900z, I hear no more, and looking at the
>grey-line, I can see that it is now almost at the midpoint of the path to
>PY/LU, and with a flux of only 85, it is hardly surprising that the band has
>closed to my modest antenna and medium power ( 400w!).  But wait a minute
>what's this, TK5KP at S9, ditto DL1IAO; then they are gone; then they are
>back! I manage to work both, but it was as struggle. This did not sound like
>MS propagation, but think it might well have been. Now, at 1910z the band is
>well gone, and although I check after 30 and 60 minutes, I hear nothing
>further.
>
>
>So it seems( prima facie) that this is another case of failure to cross the
>grey line barrier at an angle approaching 90 degrees. I have no evidence of
>a one way path on this occasion, but it could be of course that the South
>Americans were hearing Eu at this time, but unable to raise us, at least
>those of us with puny antennas.
>
>
>Now I am more than a mite puzzled about all of this, since I have never read
>of the grey line being a hindrance rather than a help. However it does seem
>to me that, towards the MUF at least, that it is difficult for RF to
>propagate perpendicularly to the grey-line, perhaps with loss of
>reciprocity. It goes without saying that if anyone else ahs experience of or
>information about this phenomenon, I would please to get it.
>
>Perhaps this should really be on a propagation reflector, but contesters are
>imp particularly well placed, and qualified to investigate such matters.
>However if you don't think so, sorry for the bandwidth.
>
>
>73
>
>
>
>Clive
>GW3NJW
>
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