From: John Rabson <john.rabson07@gmail.com>
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Date: Mon, 11 Dec 2017 12:07:25 +0100
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Subject: Re: VLF: Transatlantic success East to West
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With reference to the propagation charts, perhaps one of our Swedish friends could arrange to borrow the SAQ antenna system from time to time?

John F5VLF

> On 11 Dec 2017, at 11:41, Paul Nicholson <vlf0403@abelian.org> wrote:
> 
> 
> Jacek wrote:
> 
> > could you give a short explanation? i don't really understand
> > nonreciprocal propagation
> 
> I don't either, really.    The ionospheric reflection
> coefficient depends on the direction of the radio wave relative
> to the Earth's magnetic field.  The wave accelerates free
> electrons in the plasma, and they're pulled into circular or
> helical paths by the magnetic field.  This alters the phase of
> the reflection and the attenuation of the wave through energy
> loss by collisions.
> 
> The consequence is the reflection coefficient isn't a nice
> simple number, it's a 2x2 matrix with each component a
> (frequency dependent) complex number.
> 
> It's all the in Appleton-Hartree equations
> 
> https://en.wikipedia.org/wiki/Appleton%E2%80%93Hartree_equation
> 
> which are quite easy to calculate and program (easier than
> they look at first glance) but few people would admit to
> understanding them.
> 
> Spent some time with LWPC measuring the T/A path at some
> different frequencies.   The figures below are the extra loss
> on the east-to-west, compared with west-to-east.
> 
> The results don't depend much on which end points I choose,
> but are quite frequency dependent:
> 
> Midnight UTC:
> 
> 18.0 kHz:    2 dB
> 17.4 kHz:    3 dB
> 16.5 kHz:    6 dB
> 16.0 kHz:    9 dB
> 15.0 kHz:   14 dB
> 14.0 kHz:   18 dB
> 13.0 kHz:   16 dB
> 12.0 kHz:   13 dB
> 11.0 kHz:   11 dB
> 10.0 kHz:   10 dB
>  9.0 kHz:   10 dB
>  8.2 kHz:   12 dB
>  5.2 kHz:   27 dB
>  4.2 kHz:   44 dB
>  2.9 kHz:   LWPC doesn't run
> 
> Generally a lot more anisotropy as the frequency drops,
> but there's a funny peak around 14 kHz.
> 
> Midday UTC:
> 
> 18.0 kHz:   4 dB
> 17.4 kHz:   4 dB
> 16.0 kHz:   5 dB
> 15.0 kHz:   5 dB
> 14.0 kHz:   6 dB
> 13.0 kHz:   7 dB
> 12.0 kHz:   8 dB
> 11.0 kHz:   9 dB
> 10.0 kHz:  10 dB
>  9.0 kHz:  12 dB
>  8.2 kHz:  14 dB
>  5.2 kHz:  35 dB
>  4.2 kHz:  no output from LWPC
> 
> The funny peak vanishes during the day.
> 
> So, nowhere near as much anisotropy as I thought at
> 17.4 kHz.  I don't fancy our chances at the lower
> VLF bands - it might be easier to take the long path!
> 
> --
> Paul Nicholson
> --
>