[TowerTalk] Stacked Yagis

[K4RO Kirk Pickering]

Just another data point...

I live on a sharp ridge, with steep slopes downward to
the southeast and west.  For a satellite's eye view, have 
a look at:   http://www.k4ro.net/tcg/image/k4ro_elev2.gif.
You can't really see the slope from this image.  A larger
scale 3-D surface model is in the works.  Stay tuned.

I'm talking limited experience with stacked 5-banders (20m-10m) 
at 60' & 100' (a pair of Mosley PRO-57A's - 3 elements per band 
except 12m--2el) on a 24 foot boom.  Using latest version of 
the WX0B stack match, with 1/2" Andrews 50-ohm to the stackbox, 
and fresh RG-213 feeders cut to within 1/8" from the same spool
to the antennas.  The stack box and antennas appear to be working 
(as they say on Star Trek) "within normal operating parameters."

My experience has been that a single antenna (including the single
low antenna) usually beats the stack on any band in most directions.  
It seems neither EZNEC nor TA accurately predict what I observe on 
the bands in this fairly irregular terrain.

My tower is visible from 2 to 3 miles away in certain directions,
(E SE and W) and I'm convinced that the height and terrain play 
a bigger role than NEC or YT are telling me.  I think part of
this might be due to the 2-D profile slice reflection analysis 
versus an integrated 2.5 dimensional surface reflection analysis. 

Fortunately, the reason I put up 2 yagis was to beam 2 directions
at once, and I rarely run the "stack" in the same direction.  I find 
the independently rotatable combination to work very well for contesting.
If I'm focusing on just one area, I almost always use the high antenna.

One last observation I'll contribute is that the higher antenna is almost 
always superior to the lower antenna.  There have been exceptions, but 
usually the stack provides less QSB during those exceptions.  Many of 
the locals I've talked with have reported similar findings, regardless 
of their terrain.  

More grist for the mill.  Grind away, and thanks for contributing
your observations.

-Kirk  K4RO

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