Message-ID: <001e01c2d112$5603c7a0$6507a8c0@Main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "LF-Group" <rsgb_lf_group@blacksheep.org>
Date: Mon, 10 Feb 2003 14:40:16 -0000
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Subject: LF: re "strange" Propagation
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Hi all, Tom and Rich mentioned deep fading on relatively short path signals.
This is I believe due to multipath destructive interference. The recent
series of geomagnetic disturbances have caused a "precipitation" of high
energy electrons to be injected into the D-layer. I believe that one and two
hop signals or even ground wave and first hop are arriving at the Rx at
nearly the same strength leading to very deep fades depending upon the phase
difference.

You can see the effect on the plots of the path from DCF39 to CT1DRP on my
Propagation reports (see web site URL below). Overnight levels have been
very poor (the first stage is increased absorption) we are probably moving
into the second phase of recovery which is characterised by deep and often
rapid fading. Over the next few nights the length of time between fades
should increase, and in the final stage of the "return to normal" there may
be some advantageous constructive interference peaks.
Finally if there are no more geomagnetic disturbances the propagation will
settle and change only slowly over the night-time period. this period of
disruption began around 27th January, and is characterised by rises in the
Kp index to 5 and 6. It will normally take from 10 to 14 days after the
event for conditions to return to "normal".

Treat with some skepticism the 6dB jump in daytime on the plot DCF39 of the
9th Jan. we are investigating that.

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