The only place Ive found tuned elevated radials being discussed so much is
on ham forums.
A bit over 20 years ago I installed a slanted wire 1/4 wave vertical for 160
coming off the top guy wire of a 160' tower and about 10' out.
Started with 4 radials of roughly 130', trimmed the radiator for best match
with zero reactance and measured the 2:1 bandwidth. Added 4 more radials and
the BW narrowed, added 8 more and it narrowed a bit more. Added another 16
and no change in BW so I assume the sweet spot is somewhere in the 20's at
this location and the radials starting at 12' and slowly sloping to 20' and
then thru tree branches. Just the way they were placed likely precludes any
chance of resonance. That antenna worked so well I added another, and used
nothing but coax phasing lines to switch directions or fire a figure 8
broadside. Cheap, simple and effective unless you like throwing away money
for a mailorder solution.
YMMV depending on ground effects and surrounding objects. OTOH I believe
people spend way too much time analyzing and relying on some questionable
answers and too little time doing some basic construction work and testing.
Carl
KM1H
----- Original Message -----
From: "Grant Saviers" <grants2@pacbell.net>
To: "Dennis W0JX" <w0jx@yahoo.com>
Cc: <topband@contesting.com>
Sent: Thursday, December 13, 2012 5:27 PM
Subject: Re: Topband: Elevated Radials Questions
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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