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[TowerTalk] Antenna Heights and EZNEC

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Subject: [TowerTalk] Antenna Heights and EZNEC
From: (Tom Rauch)
Date: Sun, 3 Feb 2002 19:45:16 -0500
> I think you are.  The US Government spent a lot of money doing tests
> to verify that NEC-2 and 4 represented good approximations of the real
> world. The situations in which this approximation breaks down are 
> mostly pretty well understood and documented (intersecting conductors
> of greatly different diameters, etc.).  

As I recall, Roy Lewallen said he could find little if any verification 
of ground influences on low frequencies.
> I am fully prepared to believe that your 160m case (you believe the
> effects of ground are not accurately modeled, right?) is an additional
> such instance.  But in the vast majority of cases, I think it's been
> proven that the models can indeed be trusted.

I think they can to, as long as we remember what models are. 

My point is this:

If we can not relay on measurements because of slopes in terrain, 
wires, houses, powerlines, etc..... tell me how we rely on the 
model without it allowing for all those things?

Do you really think NEC models can predict the effective height of 
and antenna over earth within five feet? I don't.

I don't believe it is possible because none of us have homogeneous 
earth below the antenna, as NEC models assume it is, let alone 
have areas free of things like wiring, fences, and so on.

Now granted it is the best thing going for us, but predicting null 
patterns at four wavelengths height or null angles within a few 
degrees elevation? I wouldn't bet on it. Not unless you live in the 
middle of many wavelengths of empty flat metal sheeting.
73, Tom W8JI 

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