[TowerTalk] Stacked tri-banders and 40m dipole - which antenna where?

[Dan Levin]

I am in the process of getting things nailed down for the upcoming contest
season.  I plan to concentrate on two domestic contests (CQP and SS), and I
am in Northern California.

My main antenna system will be a 2 stack of 4 element 20' boom tri-banders,
and a shorty forty rotatable dipole.  Not much, I realize, compared to the
big guns, but all my suburban lot can cope with.

I've got a 70' crank-up tower, with 15' of good mast sticking out the top.
The top of the 3rd section is at 54', and the top of the 2nd section is at
38'.  I need to arrange the two tri-banders and the dipole on this tower for
maximum effect.  Yes, I will model it with YTAD, but the tri-banders are of
a fairly odd design, and I can't model them accurately with available tools
(NEC or MININEC) (they are dual driven element antennas with a whacky
capacitive coupling feed system.  W4RNL has looked at them, and pretty much
shrugged about the odds of modeling them).  So in addition to the YTAD
models, I am soliciting opinions from those of you with more experience than
I.

The two options seem to be:

1) Put the upper tri-bander at the top of the mast (85').  Put the lower
tri-bander at the top of the 3rd section (56', allowing for the side-mount).
Put the dipole near the bottom of the mast, probably at around 76'.

2) Put the dipole at the top of the mast (85').  Put the upper tri-bander on
the mast somewhere towards the bottom, probably at 72' (that's about as low
as I can go, what with the thrust bearing and all).  Put the lower
tri-bander at the top of the 2nd section, at 40' (again, allowing for the
side-mount).

The good news on option 1 is that I get the upper tri-bander as high as
possible (85'), and I get pretty good separation between the stacked beams
(29' or so).  The bad news is that my main 40 meter antenna is 9' lower than
it could be, at about 76'.

The good news on option 2 is that my 40 meter antenna is as high as possible
(85').  The bad news is that I've now got 32' separation on the stack (bad
because I expect and hope that 10 will be the big band this fall), and the
lower antenna is at 40' instead of 56'.

I'd appreciate your thoughts, particularly on the questions of which option
would be best, and whether having the 40 meter dipole in the middle of the
stack will cause a problem.

Thanks much,

            ***dan, N6BZA


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