I'm not sure if these antennas are already installed or if this is just in
the planning stages. If you're planning, I'd just purchase two C-4XL's or
two C-3's and add a 40m beam. You also need to be sure that your spacing
distance is adequate for the bands of interest. WX0B has some information
on stacking dissimilar yagis with an oscilloscope on his site.
http://www.arraysolutions.com/Products/dissimilarants.htm
73,
John
From: "Keith Dutson" <kdutson@sbcglobal.net>
Date: Tue, 10 May 2005 16:41:14 -0500
List-post: <mailto:towertalk@contesting.com>
I need some help with phasing two antennas in a stack. The antennas are
Force12 C-3 and C-4XL. The C-4XL is essentially a C-3 with 2-el added for
40M. Since element spacing and feed method (current balun) is the same for
both on 20M, I think I only need to compensate for the difference in
distance of the balun to center of tower between the two antennas. This
distance is 15 inches for the C-3 and 98 inches for the C-4XL. All coax is
Belden 9913F7 which has a velocity factor of 84%.
My first thought was to just make the coax from the C-4XL 83 inches longer,
but now I am not sure. Maybe I need to multiply this by 84%? Then last
night I was reading the ARRL antenna book about phasing different antennas
and got totally confused. Apparently I need to model the two antennas to
find the difference in phase angle in degrees, then add the appropriate
amount of coax to offset the difference. Needless to say, I do not have the
models or experience to do this.
I would appreciate any help in understanding how to properly phase these two
antennas.
73, Keith NM5G
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