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Re: [TowerTalk] Fwd: Fwd: effect of two wire antennas end to end

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Fwd: Fwd: effect of two wire antennas end to end
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Wed, 25 Feb 2015 16:51:03 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On Wed,2/25/2015 4:30 PM, Hans Hammarquist via TowerTalk wrote:
if you try to put a common mode choke at the antenna I can imagine difficulties 
with overheating etc as the voltage is high.

Huh? A proper common mode choke can handle legal limit at the feedpoint of centerfed dipole fed with coax. Study k9yc.com/RFI-Ham.pdf

I allow the unbalance current through the feeder and I stop it after the tuner.

That setup WILL have interaction between feedlines, and the feedlines will pick up RF noise that they will couple to the antenna.

A well design (unlike mine) Windom, or Off-Center-Fed antenna has a resistive 200 - 
400 ohm impedance at the feeding point allowing for a balun at the feeding point and 
a reasonable SWR in a coax feeder. I will not recommend what type of balun to use 
but imagine that the "right' balun reduces any common mode current outside the 
coax.

There's FAR too much imagination (as in Alice in Wonderland) in that paragraph. The word "balun" is far too vague, because it is used as if it were some magic box that solves all problems, and has no limitations. I believe in calling a spade a spade. An ordinary transformer, wound on a low loss ferrite toroid, and with sufficient insulation between the windings and the core, could isolate the line from the antenna, thus reducing the common mode current. That transformer will kill common mode current on the feedline ONLY if it is at the antenna.

I have not problem with overheating maybe my 100 W is one reason.

It certainly is. Try running an amp.

73, Jim K9YC
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