[TowerTalk] Modeling and measurement

[L. B. Cebik]

Mention in the discussion has been made to what modeling patterns show,
but all references have been to what we call the far-field pattern, which
NEC literature calls the RP0 output, defined as "The space-wave field
computed in spherical coordinates."

It seems to me that for the types of test under discussion, a more
applicable output is the RP1 output, defined in NEC literature as "The
total ground wave, including surface wave, computed in a cylindical
coordinate system."

The latter radiation pattern has not been readily available in the most
used software for modeling, but is available in NEC-Win Pro and in GNEC
(NEC-2 and NEC-4 products of Nittany-Scientific).  Even there, it is
available only in tabular form.  However, the next year or so may well
see some graphical adaptations of this output for easier interpretation.
(As an incidental, I expect to see over the same period the introduction
of good graphical outputs for near field analysis as well.)

Although the RP1 output may give some better correlations to test results
than RP0, terrain and reflective/re-radiating "clutter" will remain
problems.  Synthsizing some objects (also expected to become easier
within the next 12 months) may help reduce part of the problem, but the
flat terrain presumed by both NEC cores will leave large portions of the
problem unresolved--unless I can figure out how to synthsize hills.

I have seen some work-arounds available by the use of multiple software
packages, but so far, these are applicable (aspparently) only to the usual
RP0 type (space-wave) outputs.

Hope this is useful to the modeling side of the group of questions under
discussion.

-73-

LB, W4RNL





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