Bill:
You might want to try a shunt wire for 160M on another tower face, but
space it more than a just few inches from the tower. I'd suggest a couple
of feet. Most shunt wire designs I've read here on TT and elsewhere usually
have the wires off the tower by a considerable distance.
I shunt feed my Trylon 64-footer on 160M with two parallel wires about
two feet off the tower face plus a series (gamma) cap. The wires tap the
tower at about 53 feet up. I had fed the tower from the same face with a
second pair of wires less than a foot off the face, but it was very
narrow-banded.
On 80M I use a half-sloper wire connected to the tower at about the
fifty foot level. It's very broad-banded, with the 2:1 SWR points below 3.5
and at about 3.9 MHz. This sloper works better (higher sigs on TX and RX)
than the shunt feed on 80 did.
I have seven #18 radials around the tower. Five are about 100 feet
long and two are about 35 feet or so. BUt my lightning ground is 135 feet
of #2 solid tinned copper on twleve ground rods buried two feet down. I
think that helps.
73 de
Gene Smar AD3F
-----Original Message-----
From: Bill Coleman <aa4lr@arrl.net>
To: towertalk@contesting.com <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Sunday, May 11, 2003 12:55 AM
Subject: [TowerTalk] Inverted L, Sloper or Shunt Feed?
>
>Now that it is summer, I need to make some improvements to my station on
>the low bands - particularly 160m and 80m.
>
>Right now, I've got a 15m tower with an A3S on top. I have a shunt feed
>made of two #14 wires spaced 10" apart that goes from the base to the 12m
>level at a spacing of roughly 5". I have 13 60 foot (.22 wl on 80m)
>radials installed, and feed it with an omega match on 80m.
>
>So far, the shunt works, although not noticably different than my low 80m
>doublet at 10m. I plan to add 12 more radials, but I don't know if that
>will improve the antenna that much.
>
>For 160m I've considered putting up an inverted L, which I can run to the
>12m level and then down into the front yard. The advantage is that I can
>share the radial field of the shunt. The inverted L would run on the
>opposite side of the tower from the shunt, but would be only 1/2m from
>the tower.
>
>I'm worried that the 160m inverted L may seriously detune the 80m shunt.
>
>Another idea is to put a 1/4 wave sloper at the 12m level. I already have
>a 40m 1/4 wave sloper at the 11m level.
>
>Another ham had suggested I just put in a matching network to run the
>shunt feed on 160m. I've experimented with a few different capacitor
>values in the omega match, but I haven't been able to achieve at matched
>condition.
>
>One limitation I have is that the tower is the highest support on my
>property, so just about any antenna has to be mounted to the tower, or be
>substantially lower.
>
>Anyone had any good advise, suggestions? Will the Inverted L work, should
>I try a sloper, or how to I figure the matching network for the shunt?
>
>
>
>Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
>Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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