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[TowerTalk] re Balun for vertical

To: towertalk@contesting.com
Subject: [TowerTalk] re Balun for vertical
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Date: Sat, 07 Oct 2006 18:57:08 +0000
List-post: <mailto:towertalk@contesting.com>
I had a huge coax choke at the feedpoint of my 160 m. inverted L (see 
http://www.qrz.com/K5UJ for a photo).  It was made with 100 feet of 213 
wound on a 20 gal. garbage can, which had around a 16 or 18 inch diameter.   
The choke gave a lot of inductive reactance (if my calculation was correct) 
for common mode rf on 160.   The downside was that it also lengthened the 
feedline by 100 feet and that together with the feed out from the shack, 
added up to a surprising amount of loss, even on 160--probably not enough to 
be noticed but more than I expected.  I view antennas, feeds, transmatches 
etc. as a system.  A little loss here; a little loss there, and pretty soon 
you're into some big losses, hi hi (to corrupt what some congressman once 
said about money).   Anyway, with 101 radials on the ground, I eventually 
found that the amount of return rf current on the outside of the coax was 
insignificant, removed the choke and never noticed a problem with it gone.  
so what's the point--the point is that if you have enough radials, the 
distribution of return rf is so extensive, there isn't going to be much on 
the coax shield and you can probably do without the choke.  How many radials 
I don't know.  probably more than 20 but less than 100.

Rob / K5UJ

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