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[TowerTalk] Optimum Stacking Distance

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Subject: [TowerTalk] Optimum Stacking Distance
From: (Bill Tippett)
Date: Sat, 28 Jul 2001 13:17:29 +0100

"What happens if the elements are several feet in from the ends?
Do we still use the boomlength as expressed in wavelengths, or do we use the
actual length between the elements?"

Hi Bob et al!

        Boomlength is distance between reflector and the last director.  WX0B's
SQRT [boomlength] is only an approximation and you should model it exactly
as others have suggested.  My 10M antennas are .791 wl long, WX0B's model 
suggests .889 wl spacing, but EZNEC said 1.007 for maximum gain.  If you 
really want to do things right, use YO7 which will let you optimize much
more rapidly and flexibly than EZNEC.  K6STI is still in business and can
be contacted at  I put my KLM's up with stock dimensions since 
I was in a hurry, but later retuned them for ~1 dB more gain, ~8 dB more F/B
and better bandwidth over 28.0-28.8. 

        I believe better RX patterns are more important than small improvements
in gain, so I optimized with higher weighting to F/B.  I also discovered that
better F/B can be obtained with wider separations.  You can see this in YO7
as you optimize with different stack separations.  I verified the F/B using 
another RX antenna ~500' away from the stack.

        Another point...YO7 would allow you to mount the elements at the
ends of your boom and take full advantage of the boom length you have.  It's
a waste to not use every available inch of boom you have since the wind
loading, weight, etc are essentially the same.  If you have several stacks,
the cost of YO7 would be well repaid IMHO.

        I'm very happy with my stack holds alltime USA SOSB10 records
for both CQ WW's, both CQ WPX's, ARRL DX SSB and ARRL 10 CW (missed ARRL DX CW
by 0.21% last year and it appears I missed it for 2001 also...connector failure
during the middle of EU run!)

                                                73,  Bill  W4ZV

P.S.  This is not a paid YO7 commercial...I just happen to be a big fan of it
because it has worked so well for me!

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