On Sun, 22 Mar 1998 20:49:33 +0000 Andrew Williamson
<andrew@gi0nwg.demon.co.uk> writes:
>
>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,
I cant name one person who knows it all....welcome to the mix.
>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 :-(
He is plenty loud here at all times! Do you know the ground conductivity?
>
>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?
The BW should be excellent at the 90 degree point but feeding could be a
problem. I would be interested in the replies you receive for feed
methods. With such a wide face I wonder if the standard Gamma/Omega match
would work. The d1/d2 ratios with say a 1" diameter rod would be extreme.
>Would this type of system be effective?
I vote a big YES once the feed is resolved.
>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 ;-)
It should be a fairly simple installation time wise...then give it a
workout. If the feeling is not good then go back to the original. Oft
times gut feel from many years of operating from the same QTH is worth
more than all the theories.
Performing before and after FS tests may also be useful; just try and
duplicate the test setup as close as possible.
GL Carl KM1H
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