[UK-CONTEST] 28Mhz propagation

[Clive Whelan]

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