Topband: Another small item or two

[Robert Brown]

Friends in Radio Land -

In his recent posting, Tom, W8JI, brought up new points in the power
coupling discussion: the alignment of "random ions" and the correctness 
of power coupling calculations.,

For the first point, in an earlier QEX publication, I have tried to make
the point that positive ions are not entirely random in their motions. In
the lower ionosphere where they are literally surrounded by millions of
neutral particles, being of the same mass as collision partners, they are
dragged along with the atmospheric motions of the neutrals by virtue of
their high, mutual collision rate.  Electrons in the ionospheric layers 
we depend on for low-band propagation tag along because of Coulomb
attraction.  So there are meteoroligical factors in low-band propagation;
we just need to find them!

At high altitudes which control HF propagation, positive ions are bound
to geomagnetic field lines, like beads on a wire, because of their low
collision frequency with neutrals up there and electrons are controlled
by electric fields of magnetospheric origin.  So "moving" chaos changes to
order (of atmospheric and geomagnetic origin) with altitude.

As for the "correctness" of power coupling calculations, that depends on a
correct understanding of the application of Maxwell's Equations to the
problem, not making errors in the algebra of vector analysis and testing a
calculation against a known principle.  It is not all that hard but takes
a lot of time as writing code for polarization problems can be complex. 

Tom, W8JI, raised the "random ion" issue when he questioned the reality of
sharp variations in power coupling at low latitudes.  In that regard,
there are other "sharp variations" in ionospheric experience, the "spitze"
or discontinuity in ray paths discussed at the end of the chapter on
"Oblique Propagation" in Davies' book, "Ionospheric Radio".  So all
ionospheric propagation is not "smooth", we never see "the warts" with our 
simple set-ups.

73,

Bob, NM7M