At 06:32 AM 9/28/98 -0600, T A RUSSELL wrote:
...
>>3) If stacking tri-banders, I will have to live with a height
>>separation
>>that is not optimal for all three bands. Does anyone believe that
>>this is a
>>major problem? Has anyone modeled a two stack of small tri-banders,
>>and
>>convinced themselves that the separation issue has a major or minor
>>effect.
>>Remember, I am selecting the stack in part because of the extra db of
>>gain -
>>if I am going to burn that db because of non-optimal separation, it
>>would
>>matter. Has anyone stacking tri-banders on a crank-up played games
>>with
>>lowering the tower to get better separation on 10 or 15 meters -
>>modeling
>>the net effect of the lower height vs better separation?
>>
> Your best solution here is to model it, or find someone
> who already has done so. (Ask N6BT)
See my article in July-August 96 NCJ for a first attempt at modeling a C-3
stack. My results tended to indicate that a spacing of about 28 feet gave
a decent compromise between gain on 20 and degradation of F/B ratio on 15.
The 10-meter case is pretty far outside the normal stacking range anyway
(almost a full wave).
I also recently looked at a 3-high stack of C-3s with the antennas only
about 20 feet apart, thinking that I might get better performance on 15 and
10, then "cut out" the middle one on 20. Trouble is that you can
disconnect the feedline but all those resonant or near-resonant elements
are still there, so the 20-meter performance looks terrible.
My current plan, for whatever it's worth, is to install a C-4XL at 97 feet
-- building it now -- and stack a C-3 at 69. Since the 10-20 meter
sections are identical, that should give me good 10-40 meter performance.
I know Tom'll say I need a third C-3 down at 35 feet or so, but one thing
at a time!
73, Pete Smith N4ZR
In wild, wonderful, only middlin' rare WEST Virginia
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