Topband: beverage antennas
Mon, 23 Aug 1999 16:16:20 -0600
Content-Type: text/plain; charset=us-ascii
X-Sponsor: W4AN, KM3T, N5KO & AD1C
> If you are talking about an identical wire laying on the ground
> under the Beverage, a counterpoise is the absolutely worst thing
> you can do. The Beverage depends on a lossy ground under the
> wire. ( not under the ends though ) It is a "traveling wave"
> antenna and depends on the ground loss to tilt the angle.
Perhaps my comments and suggestions based upon my experience did not
come across clear.
#1, the counterpoise wire is installed ONLY where the Beverage
conductor must cross a gully, ravine, small canyon or whatever you want to
call it, and the span would be a 1/4 wavelength or more long and 1/8
wavelength or more above ground for that span. Its purpose is to maintain
the integrity of the parallel transmission line such that the portion of
the antenna that is high above ground for a short distance will act like a
simple long wire antenna.
#2, it is not an identical wire. I suggested using galvanized steel
wire which has a lower velocity factor than the copper or copper weld wire
conductors normally used for the Beverage wire. It is the difference of
velocity factor of the parallel conductors (Beverage wire and earth) that
causes the tilt of the wave angle. Granted, the VF of the galvanized steel
wire is not as slow as the VF of the earth, but it is not detrimental to
the performance of the antenna.
This application corrects the directional performance of Beverage
antennas that must cross over irregular terrain where the space between the
Beverage wire and the earth becomes great enough to allow the Beverage wire
to act like a long wire antenna.
I first noticed this phenomena when certain Beverage antennas in a
multiple antenna field were not performing as they should; ie. they were
not discriminating against signals from the sides. Ten antennas were
performing correctly but two were not. All the antennas were identically
constructed, so what was the difference?
The common denominator for both the non-performers Vs. the ten
performers was that they spanned gullies of the dimensions mentioned
above. Installation of grounded spans of a single galvanized steel
counterpoise wire underneath each antenna at the problem locations totally
cured the pattern distortion. Both antennas then performed as well as the
ten which were contructed over even terrain.
I sincerely hope that this more in depth explanation will assist you
and others. 73 de Milt, N5IA
FAQ on WWW: http://www.contesting.com/topband.html
Administrative requests: topband-REQUEST@contesting.com