[TowerTalk] tri banders vs mono banders

[Jay Terleski]

Bruce Makas wrote:
> 
> Has anyone ever done any analysis of stacked tribanders (KT34XA's) vs the
> performance of similar long boom mono banders? Contrary to some of the
> opinions I read recently, I would think that a stack of 3  would be a great
> deal simpler than 3 stacks of 3. Even if the tri banders are mechanically
> more complex?
> 
> M2 suggests a stacking spacing of 38 to 42 feet so that would be 150/110/70
> or so but Mike also says that computer modeling of the KT34XA/KT36XA is
> very difficult.
> 
> Any thoughts on this?
> 
> Bruce, K1MY
> 


Stacking Tri-banders makes good sense if you want to improve say a one
or two tower station.
You benefit in several ways

1 Being able to fill in the angles by switching, combining, and skewing
them (advanced).
2 Beam in two directions at the same time if desired.
3 Least important of the above,  Almost 3 db gain
4 Elimination of Rain or Snow static by switching to the lower beam
5 Ease of installation and maintenance vs mono banders.

#3 is least important of the top 3 because you can obtain more effective
gain (10-20db) just by filling in a null if the signal is propagating at
the null angle.

To find the best effective stacking distance do the math yourself by
taking the effective boom length of the antenna in wavelengths and take
the square root of it.  This is the optimum stacking distance of your
beams in Wavelength.

So in case of a Tri-bander, figure the effective boom length on 20m,
15m, and 10m  By using those elements only from reflector to last
director.  You can then find the compromise distance that is suitable
for that tri-bander.

I would always model it at the proposed installation heights to do a
final verification.
In the case of a complex tri-bander, just make a simple model of it for
each band. The traps or linear loading can be dealt with easier than.

Some manufactures will give out the model too.

I hope this helps someone.

Jay, WX0B

-- 
Jay Terleski
WX0B - Array Solutions
www.arraysolutions.com

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