[SCCC] Stacking Tribander on 54' crank up?

[Glenn Rattmann]

Tim,
I applaud your enthusiasm and energy on this upgrade!

I don't have a lot of specifics to add... your intended antenna 
hardware looks good to me.  On the question of whether an extra 
tribander at 37ft will help, it may depend somewhat on whether you 
are in a DX contest, or in a domestic contest.  The club member who 
has direct experience with this is Dave, K6LL over in Yuma.  I 
believe he has a small tribander down low on his 50ft tower, and a 
KT-34XA and 40m beam on top.  Perhaps he can comment on how he used this combo.

I'd guess the diversity gained (two separate directions) and less 
need for rotating would be helpful.  But at only 17ft spacing I 
wouldn't expect any significant stacking gain (when both are pointed 
at the same target).  There may be a bit of stacking gain on 10m, but 
that may not be fully realized due to the fact that the antennas are 
different design and boom length.  So, being able to point different 
directions, with quick switching, is probably the main advantage 
gained.  To take advantage of the system you will want a stacking 
switch (U-L-B) that lets you pick either antenna, or the pair 
together (splittiing power in two directions, or one).  Because it 
has to work on 3 bands, it will have to be one of the broadband-type 
switchers, like Array Solutions stack-match.  No doubt, there will be 
some interaction between these two tribanders and your patterns could 
be affected somewhat.  Modelling might identify some potential 
serious interactions-- but in general, I'd guess you could live with it.

You didn't mention SO2R.  K6LL and others have done this with one 
tower and tribanders, but it's not trivial.  Of course, you would use 
passband filters on the radios.  But, you should probably do some 
serious calculations to determine if unwanted signal levels are still 
too high for the receiver inputs, even with the presence of the 
filters.  I recommend the W2VJN book on this subject, before you 
start running a kW in SO2R with multiband antennas only 17ft apart.

At my station I'm fortunate to have a lower 20m beam, and a lower 15m 
beam (60 and 90ft), which I can rotate independently from the upper 
ones.  In domestic contests I typically park them pointing to Ohio, 
while the very high 20/15 pair are aimed at north.  This is helpful 
in working some of the rare multipliers up that way, and in picking 
up some of the weaker W7 callers.  I have diversity switching, U-L-B, 
to take advantage of any particular situation.

In DX contests I rotate these antennas as needed, to work the two 
best (azimuth) openings at the time.  I very seldom employ stacking 
gain (both antennas pointing to the same target) in DX contests, but 
most often just split power or go to one antenna.  I might use 
stacking gain to help work the VU in a ten-minute opening, but after 
that is accomplished I usually swing antennas to separate directions 
again.  No doubt, the switching is helpful, and often saves rotation 
time.  Does it make 10% improvement in score?  There's really no way 
to know, but probably not that much.  Just a guess.

When 10/15m improve, I'd guess the fixed low tribander might be 
pretty useful in domestic contests.  If you are able to run with it, 
and then rotate your higher one north, it will help you (assumes you 
have the switch).  Of course, your 40m beam would then be pointed 
north a lot of the time, so you will still have to rotate your main 
mast to bring the 40m beam toward the east coast, when you do switch 
bands.  But hey, this keeps you awake! ;-)

--Glenn K6NA
PS  The LM-354HD is a really great tower.  Congrats on a good choice!

At 05:43 PM 4/7/2010, you wrote:
>Hi all, I am in the process of budgeting and planning for a LM 354HD 54'
>Crankup tower. It's going in my back yard in place of my current 29' of Rohn
>25G. I cannot at this time see having two towers installed as my property is
>not very big (75X100' lot).
>
>Equipment on the tower will be:
>
>24' 4130 Chromolly mast 2" OD x .250" walls
>M2 Orion Rotator
>TB-2 thrust bearing
>Force 12 C31XR 0.5' above TB-2
>Cushcraft A3WS w/30m 7.5' above TB-2
>Cushcraft XM240 17' above TB-2
>80m shortended Double bazooka on pulley mounted off top section of tower @
>54'
>
>With the above in mind, I was considering placing a second tribander at 37'
>fixed on the north-east (stateside contest running). The tower manufacturer
>is willing to weld an adapter to allow for this.
>
>My question is... is this worth the expense and extra work? Can I get away
>with running a TH7DXX (have one on hand) at 37' to run the east coast while
>running the C31XR at Japan? Am I dreaming here with two different tribanders
>spread only 17' in height? Will it honestly make a difference in my contest
>scores (CQP, NAQP, NA Sprint, Sweepstakes)?
>
>Thanks for your thoughts,
>
>Tim, N6WIN.
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