Paul,
Thank you for the data and analysis. The WH2XBA/1 and WH2XBA/1 - NAA phase
and amplitude plots are fascinating. Thanks to you and Bob for providing
this valuable information (and great SNR!). The reference point on number of
hops to consider for reasonable diurnal prediction is also much appreciated.
Regarding day-to-day variations seen over the last week or so in phase and
amplitude of signals received from WH2XBA/1: if these were to be seen over a
longer period, would, in your experience, these be uncharacteristic of
day-to-day variations seen in phase and amplitude of signals received from
NAA, NWC, NPM and similar beacons at long range?
Maybe the question is premature, in that the variations seen to date could
be episodic. If they turn out to be recurrent, and if they are atypical of
stability of signals from beacons like NAA, NWC and NPM at long range, I
might be curious about the effects of polarization (and/or pattern) of
electrically-short VLF radiators. Alternatively, if signals from beacons
like NAA, NWC and NPM at long range often exhibit substantial day-to-day
variations in diurnal amplitude and phase (>10dB, >100 degrees, >4 hours
offset), I'd be interested in RX antenna polarization. Interactions in the
waveguide are sensitive to inbound polarization, and cause additional
changes in polarization, to which RX phase and amplitude are sensitive to
different degrees, depending on how polarization is post-processed. I don't
know, however, if these types of polarization effects ever culminate in
100-degree variations, for the types of equipment we've discussed. Sorry to
bring this up before any issues are identified; I just thought I'd mention
it while it was on my mind, and in case it's of interest later.
73, Jim
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Monday, March 10, 2014 3:08 PM
To: [email protected]
Subject: Re: LF: Daytime 29.499 kHz
A better signal last night from WH2XBA/1 and I was able to go back to using
10 minute averages to improve time resolution
http://abelian.org/vlf/tmp/29499_140310a.gif
120 deg phase change as usual but taking till 04:00 to complete.
S/N here was good between 04:00 and 08:00 thanks to background subsiding.
Now four days comparison with NAA
http://abelian.org/vlf/tmp/29499_140310b.gif
The first 3 nights were opera but last night was carrier until
04:00 and carrier would be sqrt(2) times stronger than opera.
Yes it is possible for winter day maximum to exceed that of summer on
certain paths. There is no simple rule to say which path.
For example DHO at 23.4kHz to Todmorden (646 km)
http://abelian.org/vlf/tmp/dho_2013a.png
http://abelian.org/vlf/tmp/dho_2012a.png
Propagation is complicated at short range because there are many modes (or
combinations of rays with different number of hops if you visualise things
that way) contributing to the total signal. When calculating signals by ray
tracing it is usually necessary to include paths with up to 12 or 15 hops at
least, in order to get a model that resembles a real diurnal.
--
Paul Nicholson
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