[TowerTalk] Re: Dipoles or G5RV

[David Jordan]

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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