[CQ-Contest] Grey zone absorption?
clive at gw3njw.fsworld.co.uk
Sat Dec 22 20:54:00 EST 2001
This post to uk-contest produced a very small response. Anyone
here have a slant?
This is a tad off topic, but I know of no better source than
contesters to discuss.
Over many years, substantially in contests, it has been
noticeable on 21 and 28 ( particularly) that it is difficult to
raise even quite loud stations when firing out of the twilight
zone. This happens often, even when the other station doesn't
reply to anyone else.
This phenomenon was particularly noticeable in last weekend's
ARRL 10m contest.
In particular I hit the shack with toast and coffee in hand
about 06:30. Quite a few strong East Eu sigs already racking up
the QSOs, but could not raise any of them ( 400 watts, vertical
antenna). Then I heard A61AJ and raised him (06:53) without too
much trouble ( why the difference?), followed by P3F(06:55) when
the Russians were still not workable. I managed the first
Russian at about 07:00, but it was not until after 08:00 that
the rate picked up at all.
Then at 10:27 I was called by K1KI a big gun, but quite weak,
and clearly he was still in his own twilight zone. Shortly after
a weakish K3ZO ( what's going on!) got into the log through the
now rock crushing QRM from Eu.
Later still as dusk came to GW , it became more difficult to
raise US and Caribbean stations.
In a recent sked with Ed who operated as FM/G3SQX, he told me
that he experienced the same thing. In his case the contest
started at 20:00 local which is dusk in FM, but less so in the
in the USA. He experienced the same difficulty raising US
stations in this situation, and made very few QSOs before going
to bed. Later on in daylight he had no difficulty at all in
generating pile ups even with 100 watts and a vertical.
So the question is , why is the rx/tx path apparently not
reciprocal in such situations, and further why is the
transmitting station disadvantaged . Is there perhaps absorption
in (one of?) the lower layers of the ionosphere, which affects
both signals but perhaps not enough to sink the *received
signal* below the receiver noise floor.. Conversely is there
perhaps greater absorption of signals travelling upwards rather
than downwards through the F ( or others) layers in twilight.
Perhaps this is a well known scientific phenomenon, but
certainly not to me! Your perspective is solicited.
gw3njw at gw7x.org
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