R: [TowerTalk] COUNTERPOISE for Dipoles

[Maurizio Panicara]

In case of horizontally polarized electrical dipoles (here intended as
opposed to the magnetical ones), the maximum straight up field occur when
the height is 1/4 wavelenght from ground. At such height the dipole gain is
approximately 6 dBd at 90° elevation and lowering its height from ground, as
you indicated, only produces a gain decrease, even with the straight up
radiation.
Althought is not so easy to rise a 160m half wave dipole some quarter
wavelenght from ground (and other solutions like NVIS could be more easily
applicable for short range contacts) there's no chance any of those very
close to ground antennas (magnetical radiators included) can produce the
same 6 dBd gain at 90° elevations.

73
Mauri I4JMY

----- Original Message -----
From: Bruce <wd4ngb@qsl.net>
To: <W8JI@contesting.com>; <TOWERTALK@contesting.com>
Sent: Friday, August 11, 2000 5:46 PM
Subject: Re: [TowerTalk] COUNTERPOISE for Dipoles



>
> If you want to see the NVIS concept  really work,  install a second 40 or
80m
> dipole at 1/8 to 1/16 wave above ground. After this talk to some one
within
> 300 miles on the high one, then the low one. The low one will blow the
high
> one away. The higher antenna is trying to put the signal towards the
horizon,
> while the low one is using the earth under it as a reflector, and beaming
it up
> for a great cloud warmer. Not intended for DX, but Great for close in
work.
>
> In the desert, since the dry sand is a insulator for RF, the antennas are
often
> buried in the sand since RF ground is several feet lower.
>
> Many books, both civilian and military, have been written on the NVIS
> ( Near Vertical Incidence Skywave) concept. The best, and easiest  to
> understand and NOT Classified is, "Near Vertical Incidence Skywave
> Communications" It is written by LTC Fiedler and Maj. Farmer. It is
> published by Worldradio Books.
>
>                             73/DX, Bruce
>
> >
> > It amazes me people use horizontal full-wave loops near ground in
> > an effort to get NVIS gain, when the difference to a dipole is almost
> > zero dB...yet ignore ground losses (which if removed can add a few
> > dB to the signal).
> >
> > This enhancement occurs most profoundly with antennas mounted
> > near earth, but also occurs in diminishing amounts as height
> > increases to large fractions of a wavelength.
> >
> > I've never seen real world measurements of the change, but I can
> > readily see the change in A-B tests of dipoles 1/4 wl high at any
> > distance..not just in close.
> >
> >
> > 73, Tom W8JI
> > w8ji@contesting.com



--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com