Isn't it interesting that ARRL accepts GAP advertising.
It used to be that claims had to be proven before ads
were accepted. I guess that's true no longer.
I was satisfied with the performance of my Titan (as is)
in Nevada. I guess that's the crux of the issue.
Soil Conductivity can be improved by "salting" the earth
with GEM, coke breeze or MgSO4 (epsom salt). I wonder
if that would work as good as the radial field Phil suggests.
73,
Bob AA0CY
----------
From: Phil Clements[SMTP:philk5pc@tyler.net]
Sent: Sunday, October 10, 1999 8:21 PM
To: Jim Reid; Bob Wanderer; Dinsterdog@aol.com; 'Tower Reflector'
Subject: Re: [TowerTalk] GAP Titan
> Anyway, it appears from the Gov's experience, that radials
> under 1/2 wave vertical antennas, with the lower end near
> ground, can result in a much higher efficiency radiating
> system as judged from field strength measurements
> way out in the Western Pacific.
Alas, Jim..I had no idea so many folks had drunk the Kool Aid
at the Gap booth!
When I started this thread, I ASSuMEd that the majority of TT
subscribers have educated themselves with the fine literature
available on the subject from ARRL and other sources. I got
some really remarkable replys from the ignorant and/or
brain washed, and the knowledgable just stood silently by
until your post.
One fellow even stated that the Gap antennas are not a vertical
per se....I doubt if even the Gap advertizing goes this far!
You and WWV are absolutely right, a half-wave vertical dipole
requires even a better ground screen directly under the antenna
and better soil conductivity in the Fresnal zone to realize any
improvement over a quarter-wave vertical.
The reason for the variation in performance with vertical antennas
with little or no ground screen is the soil in the area for several
wave lengths around the antenna. It is impractical in most cases
to do anything about improving the the Fresnal zone other than
moving to Dallas or Des Moines or an island surrounded by
salt water. You can definately improve the soil under a vertical
antenna by installing radials or a ground screen. This is what
got the wive's tale of "verticals radiate equally poorly in all
directions" started....with no or few radials, you are loosing
energy into the lossy earth, big time!
"C.J. Michaels, W7XC (SK) calculated the depth of penetration
of RF current in ground of different properties. He defined the
depth of penetration as the depth at which the current density
is 37% of what it is at the surface. Under those conditions, for
80 meters, a depth of penetration of an amazing 1.5 meters
has been calculated for VERY good ground. For very poor
ground (desert and beach, etc.) the depth reaches 12 meters!"
(Quote from ON4UN's "Low band DXing")
All vertical antennas mounted near or on the ground including
the Gap will warm the worms and dissipate power into the lossy
earth unless the RF is reflected up by a proper ground screen.
I think what some of the "Gappers" do not understand is that
the so called radials or ground screen do not connect physically
to the antenna. One chap wrote that the worst thing you can do
with a Gap is to put radials under it.
The radials or screen are constructed in a pattern, and just lay
there on the ground, doing their thing. It is just like bringing in
a new load of soil from the midwest! How long, how many, or
how deep this radial system should be is very simple. Run as
many radials as you can, as long as you can; you can bury them
a few inches or just staple them into a scalped lawn and let them
bury themselves.
You doubting Thomases out there need only a field strength meter
placed several wavelengths away from the antenna as you add
wire under it. You can watch the needle climb as the RF quits
going into the ground and into the air!
Rebuttles are encouraged, but please use your own test results
or literature other than Gap brochures to make your case.
(((73)))
Phil, K5PC
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