Wow! Talk about long delayed echoes...I posted that question on
Oct 11 2000 ( http://lists.contesting.com/_towertalk/200010/msg00195.html )
Being in a hurry to get my antennas back up for the CQWW SSB, I made
an educated guess (after talking to Mike Stahl now at M2) that the
phasing mark from the 1980 vintage balun would match the 1999 vintage.
It did and the antenna worked fine in the stack. I did check performance
before the contest using another Yagi mounted 500' away just to satisfy
That check bought up another interesting result which I'll share.
The F/B of a single KLM 610 in the stack was much greater (~10 dB more) than
predicted for a single antenna in free space. I mentioned this to K6STI
and he checked it out in AO. The passive (undriven) presence of the other
two antennas made the active one perform better even though the vertical
stacking distance was 35' (~1 wavelength) between antennas!
I recently did another YO7 run for K4XS using my dimensions (which
were optimized for a 35' stacking distance) but using Bill's stacking
distance of 27'. Here are the results:
Freq 28.0 28.4 28.8
at 27' spacing:
Gain 12.87 13.17 13.46 (Free space gain of stacked pair...not a single)
F/B 18.04 18.58 24.61 (Model uses 180o weighted-average backside F/B)
SWR 1.18 1.16 1.28
at 35' spacing:
Gain 13.40 13.73 13.91
F/B 26.68 28.01 29.79
SWR 1.25 1.19 1.24
The moral to this story is...if you plan to stack antennas, you
would be well advised to invest $100 in YO7 and model them for the exact
stacking distance you plan to use. IMHO interactions between stacked
antennas are so complex that it requires custom modeling to do it right.
YO7 is without doubt the most powerful and easiest-to-use antenna modeling
program I have ever seen. I have no interest in it except as a very
satisfied user. Brian K6STI is still in business and can be reached at
firstname.lastname@example.org Thought this might be of interest to those of you who
may be considering stacking, and it should be of interest to all as
we consider the interactions of guy wires, other antennas, etc on our
73, Bill W4ZV
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