Hi Both interesting obseravtions. The waterfall is difficult to understnd
because they are very non linear (a signal can go from T to dog-boning with
an increse of about 3dB.
Extrapolting down as I have no data from so long a wavelength, it would seem
to be the same effect at sunset that we see at 20-24kHz and 136kHz. Both the
absorption (amplitude of the skywave) and the phases are changing as the
D-Layer decays. The response depends on your location. It may be interesting
to do a quick rough estimate of the groundwave-skywave path difference at
the two ranges you quote. You can see the noise increase as the D-layer
decays on the waterfall.
At LF and to a great extent at 24kHz the setting sun produces a highly
absorbing region at the botton of the D (45-50km) just before it sets. So if
goundwave and skywave are in phase the signal drops, but if the are out of
phase it rises, but not as much as it rises when in true darkness. I am not
sure if this is right at such relatively short ranges. Does that fit the
observations?
Alan G3NYK
----- Original Message -----
From: "Jacek Lipkowski" <[email protected]>
To: <[email protected]>
Sent: Monday, January 17, 2011 11:00 PM
Subject: Re: VLF: 8970.02 (propagation effects)
> On Mon, 17 Jan 2011, Markus Vester wrote:
>
> > Between 12 and 18 UT today, again Ossi's fieldstrength has gradually
> > decreased on Stefan's grabber in Heidelberg (about 400 km), while it has
> > increased for Lubos, Gerhard's and myself (all ~ 200 km). It looks like
> > it may have been increasing also for Jacek (~ 700 km) but I'm not quite
> > sure about the time scale of his screenshot.
>
> attached is another screenshot, with the timescale visible. the time is in
> UTC+1. you can just see the trace around 14:40 UTC, then it gets stronger,
> then the QRM gets stronger, then at around 17:20 UTC the signal is covered
> by the noise.
>
> regarding OE3HGB tests from january 15 - Gerhard turned off the tx around
> 14:40 UTC for a while, after that i couldn't receive anything.
>
> > This seems to confirm that a) VLF interference fringes are fairly
> > reproducible from one day to another, and b) they vary with range in a
> > non monotonuous way, but do not depend on direction or absolute
> > positions.
>
> probably the high interference times coincide with long distance
> propagation, bringing in more atmospheric noise. so the best period for me
> is just before that, when the path is good for 700km (in case of OE5ODL),
> but still not good enough for much larger distances. probbaly there is an
> explanation using some eartg-ionosphere waveguide model and changing
> ionosphere height during the day.
>
> VY 73
>
> Jacek / SQ5BPF
>
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