[TowerTalk] properly feeding a tribander stack

Dave D'Epagnier DAVED@ctilidar.com
Mon, 18 Oct 1999 08:11:10 -0600


Pete, generally the reason why some people use odd number of quarter
waves in feed line length is to reduce unwanted current from flowing on
the outside of an unbalanced transmission line (coax) when feeding a
balance antenna (yagi, dipole). If the non antenna end of the feed line
has it's coax shield grounded, then the impedance of the line looking
from the antenna back down the outside of the line will be high. This
discourages current from flowing on the outside of the coax.

A good balun will achieve the same result and can also work on more than
one band. I can't see any advantage to using quarter wave line if a good
balun is used. 


Dave
K0QE

	----------
	From:  Pete Smith [SMTP:n4zr@contesting.com]
	Sent:  Saturday, October 16, 1999 8:18 PM
	To:  towertalk@contesting.com
	Subject:  [TowerTalk] properly feeding a tribander stack


	I have been operating all along on the premise that in feeding a
stack it
	is sufficient to have equal feedline lengths from a common
feedpoint such
	as a stackmatch, in order to feed the driven elements in phase.
Now a
	local has said that the feedlines should not only be equal in
length but
	also an odd number of quarter waves in length.  I vaguely recall
a
	discussion of stacking several years ago on Towertalk in which
one of the
	established experts said that it was necessary to do this to
force equal
	currents in the driven elements, for the best possible pattern.

	Obviously, having to switch feedlines in order to meet this
criterion would
	significantly complicate a typical tribander stack.  Does anyone
know:

	1.  Is this true, even in the abstract?

	2.  If it is, quantitatively, how significant is it?

	73, Pete Smith N4ZR
	n4zr@contesting.com 

	Sometimes a tower is just a tower

	--
	FAQ on WWW:
http://www.contesting.com/towertalkfaq.html
	Submissions:              towertalk@contesting.com
	Administrative requests:  towertalk-REQUEST@contesting.com
	Problems:                 owner-towertalk@contesting.com
	Search:
http://www.contesting.com/km9p/search.htm

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm