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[TowerTalk] Inverted L, Sloper or Shunt Feed?

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Subject: [TowerTalk] Inverted L, Sloper or Shunt Feed?
From: (Bill Coleman)
Date: Sun May 11 00:46:38 2003
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 

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:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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