I've received a lot of response to my query on stacking distance for HF
tribanders. Most of it has been in two categories:
Anecdotal -- "Mine works fine at x feet" or "4/4/4/4 at 50 foot spacing
works great"
Practical -- "Guys limit your choices, and the best place to put an added
yagi is right above an intermediate guy point."
Nobody responded to my query about whether different tribanders respond
differently to different stacking distances.
Since I have model files for 2 different tribanders (my C-3 and a simplified
TH-7 model) I decided to compare them at various spacings. My very
tentative and preliminary conclusion, using EZNEC, is that the C-3 stack
produces a slightly better pattern and slightly more gain than the TH-7 at
the optimum stacking distance, but that the pattern and gain of the TH-7
stack "goes sour" less rapidly than the C-3 does as the spacing departs from
optimum. Moreover, the optimum spacing for the two antennas on a given band
is different, and the best compromise probably will be too.
It's been suggested that an extension of this work might be welcome in one
of the journals contesters read. What I have in mind is running models of
several common tribanders in 2-stacks, at various heights and stacking
distances that take into account the guy geometry of the most common guyed
towers (presumably Rohn 25 and 45)as described in Rohn's catalogue. In
other words, nothing impossible!
As the antennas, I propose (if I can get models of those I don't have) the
C-3, the TH-7, and the KT-34XA.
Sound interesting? Any suggestions for project design? Should I add the
Cushcraft A4S? Some other tribander?
If you think this is worth doing, I need a little help. Does anyone have
the following:
a. The turning radius of the TH-7 and KT34XA (to see how much leeway there
is inside the guy geometry).
b. A model of the TH-7 including the traps (the model I'm currently using
is really 3 simplified yagis, one for each band, and it's a chore to run
that way -- I also wonder about trap losses).
c. Ditto for the KT34-XA, or, failing that, a simplified model, as above).
d. Info on the offset from the adjacent tower leg of a) the Tic Ring and
b) a common side mount. I want at least to test the effect before I decide
there isn't anything significant ... (but I hope there isn't, because that
would really complicate the problem).
Thanks!
73, Pete Smith N4ZR
n4zr@ix.netcom.com
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