Topband: On Long- and Short-Paths

[Nm7m at aol.com]

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     In ionospheric radio, propagation paths are based on the
spherical trigonometry of great-circles.  For programs like IONCAP
and the like, such great-circles are defined geometrically as the
intersection of a plane with the spherical earth, the plane
passing through the terminii, A and B, on its surface and the
center of the earth.  Great circles through A and B have two
segments, a short one and a long one, and the segments of the
great-circle ionospheric path across the earth are termed short-
and long-path, or SP and LP, resp.

     Any other paths between A and B that are determined by the
intersection of a plane through A and B (but not the center of the
eaerth) are termed "non-great circle" (NGC) paths.  Those NGC
paths will be shorter and longer, respectively, than the long and
short segments of the true great-circle through A and B.

     In practical terms, paths of a NGC nature may result from
ionospheric skewing between A and B and should be identified as
such, to avoid confusion with the ionospheric conditions along the
more rigorously defined paths.

Bob, NM7M