Friends in Radio Land-
In a recent posting Tom, KN4LF, said "medium frequency path
skewing is that the transmitted RF signal will "always" seek to
propagate along the path with least absorption, which always means
via a dark path." I wish to take exception to that remark as it
implies that a non-existant "variation principle" applies to radio
propagation.
Radio propagation involves the advance of wavefronts radiated into
the ionosphere from an antenna. The waves from the entenna are
very wide in their extent and re-radiated (i.e., refracted or
skewed) and absorbed according to the dynamics of ionospheric
electrons encountered along their path. While the dynamics of the
electrons, driven in their motion by the wave, may be derived from
Newton's Laws of Motion or some equivalwent formulation using a
"variation principle" (Hamilton's or Lagrange's Equations), there
is no variation principle that applies to the advance of the broad
wavefront like that which applies to the motion of point particles
(electrons) along the path.
Lacking a variation principle, it cannot be said that waves always
seek to propagate along the path with least absorption, i.e. an
extremum (maximum or minimum) relative to small variations from
the actual path. In short, the signal strength at B depends on
the path from A to B and may be more or less than the strength at
C, for the path from A to C.
In simple terms, it cannot be said that the signal from A to B
will always seek to be propagated along the path with least
absorption. Such a principle does not exist for analysis of
wavefront propagation.
73,
Bob, NM7M
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