Several net control stations on ECARS use NVIS antennas....they lay a
reflector on the ground under their NVIS antennas and don't sweat the
earth losses...
HAVE FUN,
dave
WA3GIN
=======================================
n4kg@juno.com wrote:
> N4KG comment below.
>
> On Wed, 31 Jan 2001 "Al Williams" <alwilliams@olywa.net> writes:
> >
> >
> > > > NVIS has shown up in several posts. I'm a big fan of acronyms
> > but I can't figure this one out. What is it?
> > > >
> > > > Ken AB5A
> > > >
> > NEAR VERTICAL INCIDENT SKYWAVE
> > As the excellent article on p39 of Jan 1995 QST reports, NVIS
> > propagation
> > is
> > basically straight up radiation without any skip regions i.e.
> > continuos
> > coverage out to about 400 miles.
> >
> > I just modeled an 80m wire dipole over perfect ground. The EZNEC
> > elevation pattern showed virtually no difference in gain at all
> > elevation angles for
> > heights of 16,24, and 33 feet. The gain for height of 63 feet was
> > down a db or so from elevation angle of 90 deg(straight up) to 60 deg
> > where the gain converged with the lower heights.
> >
> > PS Another helpful article in QST "Why an Antenna Radiates" , Nov
> > 1992 p59
> >
> > k7puc
> >
>
> The unanswered question here is:
>
> How well does the 'effective ground' approach 'perfect ground'?
>
> A metal roof may actually come fairly close.
> Over 'perfect ground', dipoles lower than 1/4WL
> show some gain over a 1/4 WL high dipole.
>
> REAL ground is quite lossy and I suspect
> a 1/4 WL high dipole would be a better NVIS
> antenna than a lower one due to near field losses.
>
> Remember that most modeling programs do NOT
> model real earth losses well. Anyone with NEC2
> want to confirm this?
>
> de Tom N4KG
>
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