On Tue, 8 Jan 2008 20:26:03 -0500, "AI4QJ" wrote:


"Richard Clark" wrote in message
.. .

Now, if you want to discard EZNEC (which for some odd reason you seem
to approach method of moments with a sneer), conventional methods
would still bear out the same results.

The NEC program is just a computer model,

Hi Dan,

"Just a" is a familiar dismissal for almost anything offered. Without
corroborating evidence for the fear that is associated with its usage;
then such an expression is a totem or religious chant to chase away
spirits.

"Computer model"s are as useful as they are predictive. EZNEC
conforms to NEC which in turn conforms to field tests. The chain of
evidence is quite strong and I have yet to hear of any real-life
design that has defied NEC analysis.

for discussion purposes only. I
think there are far too many variables in real life for the program to take
into account. It may be valuable but I am not yet convinced it is
infallible.

"Infallible" is a feeble demand to the gods for proof of their
existence. I very seriously doubt you have ever encountered anything
infallible in your life, so why start now? This desire for guarantee
is usually a crutch for the turmoil of nervous youth.

A computer model is explicitly not "real life" except to the extent by
which it is included as a parameter. You don't name anything in
particular that troubles you about "real life," so you don't appear to
be looking for assurance, just negation.

NEC has certainly responded to "real life" through the iterations of
its successive designs (something that Roy may have more to say).
There are explicit allowances for Ohmic loss of the conductor, and
dielectric loss of insulation. Also added is the issue of the
proximity of earth, and NEC offers similar parameter controls for
describing it. In fact, you (or anyone) is probably far more ignorant
of the characteristics of the earth in their "real life" than would be
the problem of NEC to successfully model it.

As to this last statement, the problem with modeling is far more
operator error borne than computer borne. If you have any suspicions,
gripes, grief, or indecision, it can frequently be laid at the feet of
the designer. That is why I use the designer's own designs to split
open their logic to reveal the corruption. If the model lacks
interior fidelity, it is not the fault of NEC.

Any review of EZNEC's help files will quickly reveal there are many
trip points that can result in low accuracy, or outright errors. These
can be investigated by simply asking for the model and examining it
yourself. I revealed a couple from Cecil's offering: a strongly earth
associated design modeled against a perfect earth; remote stimulus. I
explicitly described changes of one or two parameters (expressly
demanded by Cecil) and revealed that Traveling Wave antennas have
Standing Waves upon them. This is hardly a monumental observation -
except when it upsets the horse cart of celebrity.

If you want to remain unconvinced, that is a rather passive activity
of low participation and little information. I would suspect that of
the 6 billion inhabitants of earth, there are 6 billion like you, but
they don't write here. Their motivations lie elsewhere where they
participate in activities to their interests.

What was my main point, and how is yours conflict with it?

You were arguing about an SWR on a NEC model being 8:1, due, I have heard,
to an erroneous assumption of Zo.

Well, with nothing more substantial than that, this is not a
particularly condemning point. You should note that you are trapped
by your own passivity into accepting other people's "word for it."
This is an odd position to be in when you are writing in a community
of Modelers who exchange designs for review and can either confirm or
deny claims against rather more substantial evidence than what was
overheard.

No problem with me. But when you made an
assertion that I thought could not be measured easily, I hesitated to take
it true using faith based science. As you can see, the NEC model falls apart
by making one simple erroneous assumption. Or was it? You can argue about
that. That is the problem with these models, nobody is so intelligent that
they are free of errors and no model is infallible either.

You would stand to learn far more by examining the model yourself than
have me swear on my credentials. You could stand to learn far more by
asking for data instead of pondering the emotional chemistry of
writing to a newsgroup, or second guessing how a model might fail.

Those that stand to lose the most in celebrity, rarely offer
correlating data or respond in true faith to enquiry for details. This
is, after all, the point of the exchange of correspondence where
celebrities post merely to pronounce their claims a spark of invention
to be validated here. That just isn't the way it works here, or in
"real life" either.

73's
Richard Clark, KB7QHC