[TowerTalk] Fw: stacking yagis - benefits?

[John Langdon]

questions concerning operating when multiple yagis are connected
>in parallel.
>
>1.  If a yagi at 40' and a yagi at 70' are simultaneously driven, is the
>power being fed to each yagi reduced by one half?
If they are identical yagis and fed by feed lines of equal electrical
length, and properly matched, then half the power will be dissipated in each
antenna.  This may or may not be half of what is dissipated in each when fed
separately.
Then the radiation at the >major elevation angle is also reduced by one
half?
>2.   Radiation at the 40' and 70' elevation angles, when simultaneously fed
>will be less at each of those >angles than if only one yagi is fed?  This
is because the radiation from
the >other elevation angle is not enough to make up for the one half power
lost
>at the other radiation angle?
>
>3.  Radiation at angles between  the 3 db down angle  of the 40' &  and the
>3db down angle of the 70' elevation angles will be increased up to a
maximum >of 3db? if both yagis are fed over that of either
>yagi if only one is fed?
It depends on so many factors that a good modeling session is the best
answer, but in general, NO.  It is dependant upon operating frequency, the
ground conductivity of the soil, the terrain surrounding the site, and other
factors.  To name one perhaps counterintuitive example, at long spacing
between the antennas relative to the operating frequency, the pattern "blows
up" and produces higher angle lobes than either antenna alone.
Take a look at N6BV's articles in the ARRL Antenna Book and the Antenna
Compendiums.  If you go to Visilia this year, look for WX0B who will be
giving a presentation on just this subject.
73 John N5CQ







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