Message-ID: <00a601c0769f$d99d0d80$0748073e@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
Subject: LF: Rapid fading and QRS
Date: Thu, 4 Jan 2001 21:55:18 -0000
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Hi Jim, first is you scan through my graphs for one night when CFH went off
you will find a plot of the noise on that channel. The noise is fairly
consistent, with
the RX settings I am using the noise at 2300z measures usually about 12dBu
droping to 6 or sometimes 4 dBu in the morning period just after dawn. I
have a complete plot for one night, but it may not have been loaded (see
15th Dec). But this is measured in a 300Hz bandwidth. Now remember that my
measurements are made with a detector time-constant of 3 seconds and I take
6 samples with the ADC at 10 sec intervals and only plot the lowest one.
This is to avoid the effects of static 'crashes'.

As to the periods of the fading. A careful look at my plots shows a number
of different periods. Some of the rapid fade periods are as little as 5 to
10 minute cycles, but they do tend to be of relatively shallow amplitude.
One of my hypotheses was that the difference on the plots from different
sites was due to the same 'fourier elements' of the plot were summed with
different phase relationships at different sites. The other fortunate point
is that the rapid fades do not occur in general when conditions are good or
improving. I believe that these conditions are when the propagation is just
beginning to recover from the after-effects of a particle injection from a
CME or Coronal hole event. The 'after-effects' last well beyond the time
that the geomagnetic indexes (Ap and Kp) return to the 'quiet' state.
Conditions are usually better a couple of days of so later, provided there
is
no further disturbance. The fast fades cease and just a couple of much
slower period fades remain, it is these effects I believe that can push the
signal from CFH up over 40dBu for a period of about 30 mins. I think from
the results I have studied that on the best nights the period of the highest
peaks might be of the order of about 30 minutes. As we move further away
from a disturbed period the deep fades disappear, and there can be a fairly
constant strength for the whole of the main part of the night (see 11th
Dec), sometime only varying by say 6dB.  These night do not show the highest
peaks but have the longest consistently high signal.... maybe a good night
for MS1000 or 10 sec dots !! I also think, although we have no measurements
to prove it yet, that the signals get better as we move west and weaker as
we move east  (as might be expected) Riks plots do maybe suggest that anyone
seriously considering tackling the path should try to get some kind of a
'handle' on expected levels of CFH at their location, if they want to
utilise the effect of the constructive interference on multipath
propagation.

Rik's plots make a fascinating gallery. I have not managed to print them yet
in a sensible format so that I can compare them at leisure. I rated the 18th
a 'moderately disturbed' night, because there were lots of components to the
profile. It would have been nice for me to have been able to take plots on
succeeding nights to see the progress of the 'event' to its conclusion. It
would have been interesting if we could have managed to get a plot from
Brian, but I understand his aerials suffered in the gales.
Thanks to all who took part.....we must do it again sometime !! Hopefully
CFH will come back before too long so that I can continue my studies. I am a
bit ambivalent about the timing .....I would like to be able to get some
plots before and after the 12/14 weekend, but I am aware that the appearance
of CFH again will make Jack and John's job a lot more onerous. Alas, I have
no influence on the Canadian Navy.

Good Luck all.

Cheers de Alan G3NYK  JO02PB
Alan.Melia@btinternet.com