N4AF has his antennas in the middle of a BIG, FLAT, slightly soggy
meadow, water table no lower than maybe 5 feet, about 30 feet MSL, to
north through east sloping very gradually to Pamlico Sound, about a
mile away. No hills, no mountains, no nuthin, except trees harvested
every 15 years or so.
Think the nulls on a horizontal pattern out there are completely
predictable.
Further, one CAN model close clutter like buildings using TA. Enough
to see if height really helps much or is just wasted dough producing
the same result.
The thing about modeling is that AT LEAST it gives us some input about
things that are otherwise plain old guesswork.
This is a free country. Anybody who wants can spend their money based
on their personal hunches. Far be it from me to discourage it.
But a lot of these folks posting are suspicious of hunches and want
something to sift through possible consequences. Debunk modeling all
you want, but what is offered in its place?
----- Original Message -----
From: "Tom Rauch" <w8ji@akorn.net>
To: "Pete Smith" <n4zr@contesting.com>
Cc: <towertalk@contesting.com>
Sent: Sunday, February 03, 2002 7:45 PM
Subject: RE: [TowerTalk] Antenna Heights and EZNEC
> 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
W8JI@contesting.com
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