Don:
Odd 1/4 wave multiples force equal currents in the antennas, which
helps preserve the desired phasing and reduce pattern degradation.
This is true whether you use 75 ohm for matching or have a 50 ohm
system with a Stackmatch. A good reference is Llewellen in the ARRL
Antenna book regarding feeding arrays of verticals. In a yagi stack,
the problem is generally not as severe as in his examples given the
increased (in terms of wavelength) spacings and therefore reduced
mutual coupling effects. Another school of thought is equal multiples
of 1/2 wave, which repeats the antenna's impedence and eliminates
transformtion effects. An antenna with a relatively flat impedence
bandwidth would probably make for a more forgiving system whichever
method you use.
I never found cutting coax to an electrical length to be unmanageable.
This isn't rocket science and the tolerances required for an
effective system aren't that tight.
Greg
na8v/4
You wrote:
To: <towertalk@contesting.com>
Date: Wed, 22 Jul 1998 16:11:04 -0600 (MDT)
From: Don Moman <ve6jy@freenet.edmonton.ab.ca>
Subject: [TowerTalk] Another Stacking question
I see comments on two methods of connecting antennas in a stack.
Most frequently, using equal lengths of cable from all antennas is
mentioned. The other way mentioned is using odd multiples of 1/4 wave
lengths of 50 ohm.
(a lot snipped)
. I am willing to believe both methods are fine, and perhaps the
equal length approach is simpler (no math) and that is why it is
suggested
more frequently. Is one method better than the other? and why?
(snip)
Thanks, 73
Don
VE6JY
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