Hi all,
I've been following the elevated radial discussion with great interest
and have learnt a LOT. Thanks guys.
Now I have a few questions regarding shunt-feeding a grounded tower with
elevated radials attached. I don't really know much about topband
antennas, hence the following questions.
I don't know if this is feasible, but I'll try to explain it anyway.
At Robert GI0KOW's QTH at present is an Inverted-L running up the side
of a tower, spaced about 3-4 feet from the face of the tower. It has
about 16 random length buried radials attached (50-250ft). It works
after a fashion, but not as well as we'd like. Especially not in
contests :-(
So, will this work. First we'll remove the Inverted-L. The tower is a
fixed unguyed grounded tower 90ft high, starting at 7ft wide at the base
and tapering to about 18 inches at the top. On top of the tower is a
4el 20M yagi on a 40ft boom at 90ft and shortly a Force12 Magnum 340
will be placed at 100 ft (if it ever arrives!!). From ON4UN's book I
estimate the tower to be about 100-110 electrical degrees long with
these antennas on top. As it is over 90 degrees long, would it be
feasible to place an elevated radial system (4 or 8 radials) 10-20
degrees up the tower and shunt feed against them? This way, I guess I'd
be feeding into a resonant 90 deg vertical? I guess the radials would
have to be bonded electrically to the face of the tower which would
still be some 6ft wide at this height? As the radial attachment point
is about 6ft wide, how does this affect the performance of the radials?
Would this type of system be effective?
I don't want to get into the elevated/non-elevated radial debate but how
effective, in real terms, would this be? If it'll save days of back-
breaking radial laying and is within a couple of dB of a decent ground
system (32-64 radials in my book), I'd be more than happy with the
compromise ;-)
As a final query to the knowledgable. Would there be any benefit
extending the elevated radials from 1/4 WL to 3/4 WL? This (I guess) in
theory should show a similar match at the feedpoint, but should (again
guessing) help the overall system performance? True or false?
Any help is appreciated and will help GI0KOW's signal in the contests.
And you just KNOW you need him for a multiplier ;-)
TIA and VY 73,
Andrew Williamson GI0NWG / AC6WI
Homepage = http://www.gi0nwg.demon.co.uk/
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|