Message-ID: <001601c30a5d$414ff020$6507a8c0@Main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Date: Thu, 24 Apr 2003 13:19:15 +0100
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Subject: LF: Propagation 3000kms and 5000kms
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Hi Jim Congratulations on the new Russian station. This is a virtually
"all-land" path so is slightly more difficult.

On the propagation front yes you are right there is a considerable
difference between paths of 2000-3000 kms and paths of over 4000kms at night
after geomagnetic activity. The effect can be seen by noting the difference
between Brains night-time received strength for DCF39 ( at 1950 kms) and
Steve's W3EEE at over 5000kms. On the 23rd Brians plot's show night-time
levels also at my "benchmark" average, which is surprisingly good
considering the geomagnetic conditions we have had recently. If you look at
the real-time plots on Steve's site the levels are very poor and 20dB or
more below the best seen in January.

I beleive the the difference is accounted for by the path geometry. It is
possible that the major signal path up to 3000kms on current nights is a one
hop path. Even there 3000kms is stretching it a bit. The difference is that
the two hop path must ,of course, make two journeys through the absorbing
D-layer (the result of precipitated 'hot' electrons associated with the
geomagnetic events) and as a result be significantly attenuated. When these
hot eletrons decay away, you will find that the trans-Atlantic path improves
but there could be a deterioration in the 3000kms paths !! I believe this
could be due to destructive interference between the two hop and one hop
paths over that distance. I saw this quite a lot on plots of SXV and for a
long time did not understand why the path was not better ( it was cut up
with deep frequenct fading ) when the path to CFH was good.

I believe Brian's T/A success is due to the slightly more southerly path
which is nearly all over water, and the use of 60sec mode which seems to get
over even under poor conditions at the 1W ERP power level. His routes in
other directions are by no means as good. Jose-Manuel EA1PX gets much better
signals from and into Europe firing across Biscay, that Brian whose paths
cross Northern Spain and the Pyrenees (on some paths possibly also the Alps
as well !)

Fascinating stuff this LF.....now where are all the South American and Cuban
stations ??

Cheers de Alan G3NYK
alan.melia@btinternet.com
http://www.alan.melia.btinternet.co.uk/index.htm#propagation