that separation comes about from the spacing of guy wires on the rohn towers
they are on. it also happens to work out reasonably well with the elevation
pattern software since that many antennas fairly well covers the whole range
of take off angles from new england to most of the world.

all my yagis are completely grounded designs anyway, so there is no need to
further ground them when not in use. when there is rain or snow static the
top one often becomes too noisy to use while lower ones are just fine...
another good reason to rotate the bottom antennas (except on 40m where it
won't turn under the guy wires).



"art" wrote in message
ps.com...
David that is quite an array of antennas. Two questions come to mind.
Why the separation of a half versus 0.6 of a wave length?
and 2 do you ground the top antenna when it is not in use or let it
float?
I have heard that the top array can remove static noise to advantage
and I was wondering how that would compare to an elevated mast that
would provide a cone of protection and thus allow use of the top array
regardless of conditions.
Regards
Art

art wrote:
David, are you saying that your three-some stack is made out of tri
banders of the same design such that a lobe null can be filled? I
believe that is exactly the coverage the poster is looking for, he
wants to be around to hear when the tree falls
Art

Dave wrote:
"Cecil Moore" wrote in message
t...
CW wrote:
I've been wondering for some time now why amateur operators don't
build
their Yagi antenna's
so they can be raised and lowered about 10ft in addition to being
rotated.

Many do, using motor driven towers. In addition to lowering
their arrays when a storm hits, some raise and lower their
towers during marginal conditions to maximize signal strength.
--

its really only practical on crank up type towers, for those with guyed
towers its usually not possible.

10' change on 20m would likely not be very useful though. my hf stacks
for
10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with
those
height changes (which i can select instantly so i can make direct
comparisons without worrying about fading) there is often little
difference
between antennas... though sometims there is a lot of difference. This
highlights the fact that often the signals arrive with a wide range of
angles, though at some times they must be in a relatively narrow range.
so
having multiple antennas at different heights that can be selected in
various combinations is a handy thing to do.