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Re: [TowerTalk] Stacking KLM KT34's

To: "David Hachadorian" <>,"Towertalk Reflector" <>
Subject: Re: [TowerTalk] Stacking KLM KT34's
From: "Jim Lux" <>
Date: Sun, 14 Nov 2004 13:57:11 -0800
List-post: <>
----- Original Message -----
From: "David Hachadorian" <>
> ----- Original Message -----
> From: "Courtney Judd K4WI" <>
> To: "TowerTalk" <>
> Sent: Sunday, November 14, 2004 9:22 AM
> Subject: [TowerTalk] Stacking KLM KT34's
> > I would be extremely interested in finding out the details pro/con on
> > stacking KLM tribanders. I have a new KT36XA and two
> like new KT34A's that I
> > am thinking about stacking together. I have the
> tower, coax and StackMatch
> > already in place. Thinking about 100, 70, and 40 feet
> with the two bottom
> > ones on swing arms. Anyone did/doing anything like
> this? Thanks and 73's
> Sounds like it should work fb. Since the XA's driven
> els will be behind the 34As' by about 74 inches, make
> the coax to the XA about 49 inches shorter than the
> cables going to the 34's (using .66vf coax). That
> should bring it into phase on all 3 bands. Watch the
> balun polarities.

I wouldn't assume that the phase center (which is what you're trying to
adjust for here) of the antenna is co-located with the driven element,
particularly in a directive beam, where there's a fair amount of mutual
coupling among elements.
I didn't have any real good 3 element models handy as I write this, but, for
instance, a 2 element model from K6STI for 20m has the two elements 2 meters
apart. The driven element is 1 meter from the center of the model (.114
wavelengths back), and the far field phase (with reference to the 0,0,0
point)  is 136 degrees (=0.38 wavelengths).

The moral of the story is that you should ask the mfr (or do a quick model)
to get a handle on where the apparent phase center of the antenna is.  Of
course, it might not make all that much difference in practice. The value in
having the various antennas with switching to combine them in various ways
is that you can change the vertical pattern among various possibilities.
What, exactly, the vertical pattern happens to be probably isn't as
important as the fact that it's different.

Jim, W6RMK


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