Message-ID: <000901c17436$fabf94c0$f6f57ad5@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Subject: LF: 73kHz Propagation
Date: Fri, 23 Nov 2001 14:17:05 -0000
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Hi all, I have not made any measurements on signals as low as 73kHz, but it
looks from John's results on Laurie's signal, as though the effects of the
big geomagnetic storm have not affected the lower frequency for as long as
its effects at 136. The normal final stages of the storms's effects on long
distance paths is first the show lots of very rapid fading (10 to 15 mins
peak to trough) . Over the next nights the fading period then seems to
lengthen. At 136kHz the normal pattern was often of two main peaks one about
midnight and other often better peak occuring about 60 to 90mins before dawn
in the UK. I have often seen a long dip between about 0200z and 0330z in the
137kHz path from CFH. It is a useful approximation to remember that the
shadow at 100kms altitude (Bottom of E-layer) is about about 1000 to 1200
miles further west of the shadow at ground level. The signal decays as the
sunlight ionises the region below, and the absorbtion produced wipes out the
path to the 'first reflection' point of a 2-hop path  (about 1/4 of the
transatlantic path length). In some respects I am not surprised about the
lack of other successes. I have found that conditions on 136kHz can vary
quite markedly over just 20 to 30 miles, and there were at time quite
considerable differences between the the signals I recorded, and Laurie
captured on his chart recorder. I suppose it all depends on the happy
conincidences of path-lengths and signal phases from different interfering
'rays'.

Thus the three observations from John W1TAG, seem to follow a pattern. It
goes to show you have great difficultly in predicting good nights, althouh
to be fair to the ol' rabbit's paw I did say things should be improving. The
longer wavelength at 73kHz possibly means it is not so badly affected by the
multipath fading conditions as 136kHz. and paths recover quickly. These
conditions could be an enhancement on 'normal flat conditions' as it is
possible that there was some multipath operating in Laurie and John's
favour. We have seen 6 to 10dB enhancement on 137kHz in similar conditions.
It just goes to show....never mind the theory, get on and try it !!  Dead
flat, quiet, solar conditions may not be the best, it is seeming to suggest
that the last gasp of a big geomagnetic event could just provide the boost
we need.

Well done all, keep the momentum up....we are still really just stumbling
around in the dark.

Cheers de Alan G3NYK
alan.melia@btinternet.com.