[TowerTalk] Several questions :-)

[Dan Levin]

Just hoping that the assembled brain-trust can clarify a couple of things.

All of the below pertains to my planned installation of 10, 15, 20 and 40
meter coverage on a heavy duty 70 foot crank up with a heavy duty mast
sticking 15' out on top.  All references to Force 12 antennas are for
example only (although I am leaning that way :-).

1) A well designed small tri-bander (e.g. C3) has about 4.4 db of gain on
each band (yes, I know, plus or minus a bit).  A well designed large
tri-bander (e.g. C31-XR) has about 6 db of gain (ditto).  In return for that
1.5 db, you pay about 2x the dollars, and have about 2x the boom length.
But a two stack of small tri-banders, again say two C3's, has about 7 db of
gain - at least according to the F12 brochure.  In my case, this argues
strongly for the stack - I would get a smaller footprint (shorter booms),
the ability to "spray" in two directions, and more gain than I would get
with the larger antenna.  Am I missing something here?  Are there any
significant reasons why I would not want to stack two small tri-banders,
rather than having one large one?

2) If I am going to stack, then the two antennas will not be perfectly
aligned.  One will be on the mast centered in the tower, and the other will
be on either a TIC or a side-mount - in either case offset horizontally from
the top antenna by at least a foot or two (maybe three).  Does this cause
any major problems?  Are there any solutions?

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?

4) If you have your way, with all of your experience and hindsight, what
would you suggest that I put up?  My options (realistically, as I see them)
are:

1) One large tri-bander, either with 40 meters built-in (C4 of some type or
C-36XR), or with a 2 element 40 meter shorty above it.  Tri-bander alone at
~80 feet, or tri-bander at 72' and 40 at 82'.

2) A two stack of small tri-banders, with a 2 element 40 above the top one.
Tri-banders at say 42' and 72', 40 at 80 feet.

3) Two large dual band antennas - perhaps a 20/40 at 72' and a 10/15 at 82'.
It looks like I could use the EF-240/320 (4 on 20, 2 on 40) and the Magnum
415/410 (4 on 10 and 4 on 15).

All suggestions appreciated.

            ***dan
            Dan Levin, N6BZA



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