Here's the nighttime signal along the 88 degree bearing to Amberg,

 http://abelian.org/vlf/tmp/171017d.gif

Quite the opposite to what signal reports suggest?

The daytime signal on 88 deg isn't significantly different to
307 deg (not much anisotropy apparent at these short ranges).

I don't put much faith in this model but it serves to illustrate
the complicated way that signals can vary as a function of
range.  A major difficulty at short ranges is the ground wave
calculation, knowing how much power couples into the ground wave,
and the average ground conductivity and permittivity.

The precise ups and downs depend critically on the amplitude
and phase of ground and several sky waves.   At best it is in
the right ballpark in terms of typical average field strengths.

(I take some comfort that LWPC doesn't do any better.)

But at least we can see that it's plausible to blame propagation for
the different performance of signals at Stefan's two frequencies.

--
Paul Nicholson
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