Jeff wrote:
If you understand what I wrote above, you'll see my point was about
local conductivity and how it affects the radiation pattern after being
launched from an antenna, rather than the variability along a signal
path, although I did mention for completeness that models can now take
such variability into account.


Spike

I think it is your choice of words that is causing the confusion. It is
not normally the practice to consider the ground conductivity over the
entire transmission path when considering the radiation pattern of an
antenna. It is usual to have a 'local' radiation pattern and then
consider what happens on the path as a separate (path loss) issue.

Obviously with a sky wave path the intervening ground has no effect, but
with a ground wave signal it can have a huge effect, particularly is
there is water in the path. The ground causes the lower portion of the
wave to be retarded so you can think of the wave-front as starting to
slope, the degree of additional slope along the path depends on the
ground properties (conductivity and permittivity) at any point. The wave
will propagate like this until the 'slope**' becomes too great an angle
for the wave to propagate.


**apologies to Jeremy Clarkson


Jeff, Spike's too far down the hole he's dug to climb out now without
losing face, so I fear your assistance will be rejected.

--
STC // M0TEY // twitter.com/ukradioamateur