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.
----
Reg.

Reg Edwards wrote:
. . . Whereas Eznec always
reports the groundwave strength as being zero. . .

If you're using the strict definition of "groundwave" as being the field
at an elevation angle of zero, only EZNEC's far field analysis reports
it as zero, because (as the manual explains, and as I've explained here
several times before) the far field results are valid at a distance
beyond the point where the surface wave has decayed to essentially zero
-- a few miles at HF. And at that distance, the field at zero elevation
angle is zero if the ground conductivity is finite. If the surface wave
strength is wanted, it can easily be found using EZNEC's near field
calculation, which calculates the total field at any point in space --
including just above the ground surface.

It is of no use in the
prediction of often-used ground waves between stations.

Unless you use the near field results, which do give an accurate
indication of the field at any point in space. I assume you've just
forgotten the several times I've explained that to you. Maybe this will
be the magic time it'll sink in.

Whenever a resistive ground is involved, programs like Eznec do not
produce the true radiation pattern of an antenna. . .

For sure, the modeling of ground is the weakest point of all antenna
modeling programs including EZNEC. But the pattern is generally a good
representation of reality. Remembering, of course, that the far field
pattern is just that -- the pattern at a distant point at which the
surface wave has decayed to zero.

A graphical pattern which includes the surface wave component would be
different at every distance from the antenna up to the distance where
the surface wave has decayed to essentially zero (a few miles at HF).
The field strength at angles greater than zero would be of little
interest to amateurs doing local communication by surface wave. Those
who want to know the field strength at ground level at any distance can
easily get this information from EZNEC's near field analysis (which
reports the total field, not just the near field).

Most amateurs who are interested in local communication over a few miles
using surface waves don't need to see the overall elevation pattern, and
they can get numerical results of the surface field strength from the
near field analysis. Amateurs communicating by sky wave, by far the more
common situation, can benefit from the graphical results afforded by
EZNEC's far field elevation pattern.

Not that there is
anything incorrect with Eznec. It is just the confusing description
of what it displays.

It's interesting that in the 15 years EZNEC and its predecessor ELNEC
have been available, and the thousands of users, no more than a half
dozen people have expressed any confusion regarding its far and near
field analysis. And none of the others has required repeated
explanations. But some people are sure to have more trouble with the
concept than others.

It's explained in the EZNEC manual, and I always welcome questions and
suggestions which would help me make it more clear. I am, however,
resigned to the fact that some small number of people aren't capable of,
and some simply aren't interested in, understanding.

Because of your deep interest in surface wave propagation and field
strength prediction, and your characterization of it as "often-used",
you must do a lot of communication by this mode. What bands do you use,
and what sort of range do you reliably communicate over? How many hams
are within this radius whom you talk to?

Roy Lewallen, W7EL