[UK-CONTEST] 28MHz Propagation

[Steve Reed]

       Longish: probably skippable before you get to the end...

      <snip>
From:	Mike Farmer [SMTP:G3VAO at hortonbc.demon.co.uk]

 2004 - 65 QSOs (Both days and all between 07:30 and 16:00) - 1st G
<snip>

Oops: your 2004 "result" may be a bit premature Mike!  After a couple of HP 
entries I decided to do low power phone again this year -

Station: G0AEV
Class: SO SSB LP
SSB QSOs: 183
SSB Mults: 48
Claimed Score: 17,568

I'm not sure what I dare say regarding ARRL 10m propagation.  I thought it 
was great!  The reason I work this contest every year (18th consecutive 
entry if I count right) is for the challenging mix of propagation modes and 
changes in propagation that nicely compensate for the strategy restrictions 
of a single band contest. Unlike other contests with single band entry 
classes, participants in this test can't desert an unproductive 10m for 
lower frequencies.  They have to make best of "difficult" (but dare I say 
it, more interesting) propagation. Its much more fun in such circumstances 
when you know there are other people out there trying to make contact and 
that they haven't all cleared off to where the rate is highest!

OK, the F-layer wasn't up to much this time - especially when compared with 
CQWW SSB (35z+131c worked on 10m: difficult to believe it was only 6 weeks 
ago).  As noted by others, best band-opening directions (often scatter 
paths) swung all over the place and a fair bit of concentration was needed 
to make the best of it.  Best DX here was two VK3's in a row on Saturday 
morning.  Most anoying DX: VQ9 someone-or-other working a list.  MS was 
reasonable (but then this contest was built around the Geminids shower to 
ensure there would always be some propagation), as was troposcatter 
(although the high pressure was wasted: too few Gs on) and Es (limited but 
very useful) - and, incidentally, none of these "VHF" modes stop operating 
when the sun goes down.....

Phone band propagation was notably poorer than on CW.  At "dead" times I 
sometimes monitored the CW portion of the band (at 0.5 MHz lower in 
frequency its a good early warning for phone users).  At 17.20 ish on 
Sunday the W's came back in on CW for perhaps the weekend's best 
propagation to the States (I heard Florida/Texas/Louisiana, all direct path 
not scatter).  I guess many Europeans had switched off by then.  The 
propagation only just made it up to 28.5 and as stateside were working each 
other with strong(er) signals making oneself heard was a struggle.  I only 
made one QSO (W5PR was the man with the good ears).  Then between 20.00 and 
21.30 there was a splendid Es opening to I and 9A, but I think I had the 
band to myself.  I worked a small number of startled Italians: a couple of 
them came back later in the opening to give me additional 59+ signal 
reports.  No one heard on CW at all.  It beats me: this is supposed to be 
the premier 28 MHz contest and here's 28 MHz operating in an expected 
manner yet most entrants had gone to sleep already!

Propagation theory: you may want to switch off now

I don't really believe in one-way propagation although I have an open mind 
on the subject - many people think it exists.  In the cases I've looked at 
there are satisfactory alternative explanations involving noise/QRM levels 
or the fact that the station who can't hear you has his attention on 
stronger signals from another direction.  Very difficult to prove one way 
or the other.  Some stations really are deaf: PY5YA gets this year's prize 
for apparent deafness - I couldn't get any response from him until he was a 
true S9 signal with me, yet I worked other Brazilians whose signals barely 
registered.  Perhaps he has a very noisy QTH.

As for "grey-line", I prefer the term "dusk/dawn propagation" in this 
context.  This is because grey-line propagation is strictly an LF- effect 
controlled by D-layer absorption and as the D-layer is effectively 
transparent at 28 MHz, whatever is happening at dusk/dawn on 10m, it can't 
be grey-line "as defined".  Dusk-dawn phenomena at 28 MHz relate to changes 
in layer ionisation, altitude and attitude, and combinations of these are 
responsible for the in-and-out nature of band openings, especially those 
commonly seen at the end of the day.  The times when the band "dies" and 
then comes back to "life" (often with quite different skip lengths) do not 
correlate well with the time of dusk (as seen at hop mid-path points and at 
F-layer heights, of course).  This is because the F2 layer (unlike the 
D-layer) retains ionisation after solar illumination ceases and because 
recombination only happens relatively slowly - there are no sudden layer 
changes when illumination goes.  At this time of the year, highest critical 
frequencies occur at, or close to, local noon and generally recombination 
rates will increasingly exceed ionisation rates as the afternoon and 
evening progress.  At some point the ionisation will be insufficient to 
support propagation (MUF drops below 28 MHz) but on poor days this happens 
well before sunset while on good days the band will stay open well after 
sunset.  The interesting part is at near-MUF when small fluctuations in 
layer morphology can bring a dead band back to life again.  When such 
effects occur exactly at sunset it is tempting to see a cause and effect, 
but I believe this is illusory.

Steve, G0AEV