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Re: [TowerTalk] An alternate yagi feed method

To: towertalk@contesting.com
Subject: Re: [TowerTalk] An alternate yagi feed method
From: RCM <robrk@nidhog.net>
Date: Sun, 14 Dec 2014 22:27:49 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

On 12/14/2014 10:11 PM, Jim Thomson wrote:
After perusing through the Mosley.... tech notes, I see they use this alternate 
feed method on their
various yagis.  DE is split in the middle, and each DE ele half is insulated 
from the boom.
They  wire the center conductor of the coax to one side....and the braid to the 
other half.
They then bond the DE ele half..that has the braid, to the boom !  Then no 
requirement for a balun,
and no pesky CM current flow anywhere. Pattern is not affected.   At 1st 
glance, it appears they
have an unbalanced DE... fed with coax.  Will this actually work ?   A few 
weeks ago, I had previously
drawn the exact identical  config on paper...and wondered why it had never been 
written about in
any book.  I figured it must be fubar, but was still tempted to at least try 
it.  Apparently  Im 60 years too
late, and am just re-inventing the wheel. Is Mosley out to lunch with their 
feed system ?

To make the DE 50 ohms, Mosely resonates the DE at a lot lower freq than 
normal... to increase the feed point Z.
This of course creates XL.   The XL is tuned out with a series cap in each half 
of the DE, where the ele is split in the
middle.  Very similar concept to a .375 wave vertical, or inverted L on 160m.  
Mosley uses a short length of insulated
wire inside each ele to provide the series C.

Jim  VE7RF
_______________________________________________

My 1960 TA33, in 1980, had a broken DE insulator. Made one from a chunk of 2" plexiglas. Never could accept their feed, so tossed the ground strap and made a coax "Collins" balun.
Worked fine for 20 more years.
_______________________________________________



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