Don,
You are muddying the waters without providing a basis for
your disbelief. That takes us into "Black Magic" explainations.
What exactly don't you believe about ground reflection effects?
Antenna radiation patterns over a smooth reflecting surface
and well defined.
Tom N4KG
On Sat, 02 Feb 2002 Don Havlicek <n8de@thepoint.net> writes:
>
> Pete,
> Perhaps my use of the word 'excessive' wasn't quite correct for the
> situation described, but the results of modelling are still
> IDEALIZED.
>
> You say you don't agree .. but then you talk about a 'smooth and
> predictable change in the radiation pattern' ... this is IDEALIZED
> ..
>
> As I said:
>
> This is one of the reasons that we must NOT trust the software to
> give
> EXACT answers, but rather to give 'idealized' situational results of
> the
> MATHEMATICS involved [not shouting ... just emphasis].
>
> Don - N8DE
>
>
>
> Pete Smith wrote:
> >
> > At 08:54 AM 2/2/02 -0500, Don Havlicek wrote:
> > >>
> > >> A lot higher than 4-6 wavelengths. I ran a 10m yagi in EZNEC
> at 200 feet
> > >> above ground, and both the deep nulls and reflection gain were
> still fully
> > >> evident.
> > >
> > >Obviously, the mathematical functions utilized within the
> modelling
> > >program do NOT vary when the height above ground [or HAAT] is
> > >'excessive'.
> > >
> > >This is one of the reasons that we must NOT trust the software to
> give
> > >EXACT answers, but rather to give 'idealized' situational results
> of the
> > >MATHEMATICS involved [not shouting ... just emphasis].
> >
> > Sorry, but I don't agree. This modeling software (NEC-2) would be
> of no
> > use at all if it hadn't been extensively verified against the
> real-world
> > situations that it was developed to model. There are known
> limitations of
> > this representation of real antennas, but a yagi 4-6 wavelengths
> above
> > ground at 28 MHz isn't one of them, and certainly isn't
> "excessive."
> > Varying the height of the model yagi above ground, from less than
> 1
> > wavelength to more than 6, shows a smooth and predictable change
> in the
> > radiation pattern that is entirely consistent with experimental
> data
> >
> > 73, Pete N4ZR
>
>
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