To Novices -

It is use of the term "take off angle" which causes all the confusion
surrounding DX and the "best" take off angles. It is a misnomer.

The elevation angle of a radio path between two stations is purely a
geometric function of their locations on the Earth's surface and the
heights of ionospheric reflecting layers. It has nothing whatever to
do with either of the antennas or ground conditions - except that it
is the best elevation angle at which an antenna beam should be
pointing.

If, purely by coincidence, the "take off angle" indicated by Eznec
happens to be the same as the exceedingly changeable "path elevation
angle" then all is well and good.

The true "take off angle" having maximum gain (another misnomer) for
any vertical antenna is always zero degrees, ie., it corresponds to
the always existent very strong groundwave. Whereas Eznec always
reports the groundwave strength as being zero. It is of no use in the
prediction of often-used ground waves between stations.

Whenever a resistive ground is involved, programs like Eznec do not
produce the true radiation pattern of an antenna. Not that there is
anything incorrect with Eznec. It is just the confusing description
of what it displays.
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Reg.