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Re: [TowerTalk] [Bulk] 160m Shunt Feed

To: Kelley <>
Subject: Re: [TowerTalk] [Bulk] 160m Shunt Feed
From: Bill Coleman <>
Date: Sat, 30 Apr 2011 19:22:13 -0400
List-post: <">>
On Dec 11, 2010, at 6:57 PM, Kelley wrote:

> Multitudes of web pages show, well, multitudes of setups for shunt feeding a 
> tower. Many appear to use a couple of variable capacitors in order to adjust 
> for lowest SWR. Having a limited junk box, what kind of parts should I be 
> looking for to build a generic matching network? 

It really depends on the shunt-feeding arrangement. Some can get by with a 
single shunt capacitor, others use an omega match, still others use L or T 

It really all hinges on the complex impedance that shows up at the feedpoint.

I have a short tower that I have shunt-fed for 160 and 80m. It works pretty 
well. Just about any installation is unique though -- how tall is the tower, 
how big are the antennas at the top, how high and how far away is the shunt 
wire(s), etc. K9AY suggested I run a shunt wire as high as I could, and then 
measure the impedance at the base and build a matching network to suit. And 
that's what I did, basically.

You can read the entire article on my blog here:

I didn't have any sophisticated equipment to measure the impedance, so I 
designed an L-network through trial and error.

If you want to run more than 100 watts or so, you are likely to need pretty 
beefy components in the matching network. Capacitors with 1-4 kV ratings 
recommended. Coils (if you need them) would be very large. 

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


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