Thanks for the comments and pointers. The land around the antenna is
mixed grass and forested islands so on the ground radials would be
partially buried and partially on the surface. Digging through the
trees and clearing the brush is not something I want to do. Also, based
on prior experience with verticals on metal roofs, I'm a real fan of
elevated radials.
I am relying on the credibility of the N6LF QEX series for how well/not
well elevated radials will work (Mar - June 2012). I realize this work
was all analysis with EZNEC PRO, but it seems to be the similar to
results of others I've read. Googling "K5IU elevated radials" I did
find the 2008 N6LF article which has the experimental data as well. His
analysis shows there isn't much difference in losses with more than 4
radials between 0.15 and 0.27 wavelengths long. I've heard conventional
wisdom is to tune radials for resonance, but the analysis for 4 or more
radials elevated > than a couple of feet seems to indicate it is a lot
of work for little benefit.
I also found the 2005 thread "tuning elevated radials" on this reflector
quite informative.
One thing that stands out is that I may be better off with more than 7
shorter than 130' radials.
Grant KZ1W
On 12/13/2012 12:06 PM, Dennis W0JX wrote:
Grant, you should consider putting in an additional 23 radials and put the
radial system on or in the ground. This will eliminate any possible detuning by
the big metal building and interaction with the RX 4 square. You said that your
vertical T will go up to 85 feet. However, by elevating the radials 10 feet,
your effective vertical distance is 75 feet which will allow you to shorten the
top hat wires a bit. As an alternate, you could put down 1/8 wavelength radials
on the ground but more of them and have a good system too.
If you must go with an elevated radial system, I recommend that you read the
articles by Dick Weber, K5IU, who strongly advocated elevated radials shorter
or longer than 1/4 wavelength. If shorter, then the radials are loaded with a
small coil. If longer, then they are tuned out with a capacitor. W5UN uses
shortened elevated radials on his 160 meter 4 square with great results. They
are about 70% of a quarter-wave in length.
73, Dennis W0JX/8
Milan OH
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