Most yagi installations @ HF have the attachment of the beam to the mast at
approximately the middle - or - center of gravity along the boom.
When you get up to the VHF and UHF stuff you see end mounting of yagis as it
is physically feasible with such little tiny weights involved.
My Question to the unwashed masses of towertalkians:
Somewhere down the road I plan on a stack of beams for 10 meters....the
sunspots are rumoured to be coming back, and ten will be a DX band again for
a lil while.
I am considering using 4 element yagis on about a 15 foot boom.....why not
make that boom 17 feet long, extending it behind the reflector and mounting
the boom to the tower face fixed at EU (of course)......with a Philystran
truss to a turnbuckle running up from the 2nd director end of the boom?
By making the tower be "behind" the reflector it (I think) will have a
negligible effect on the antenna's pattern....whenever I do the side mount on
the leg/face of the tower it ends up near an element and although it is not re
sonant I think the tower MUST do some degrading of the beam's pattern.
How about it, you yagi sages....at 10 meters these antennas will weigh in at
about 20 lbs. (including the coaxial feed line)....I am not worried about
upsetting the "balance" of the physical load on the Rohn 55 they are mounting
to...if they were bigger beams at a higher frequency I could see being
worried but these are overgrown TV antennas.
(They also won't make climbing up the tower as awkward at their
heights....ever had your climbing belt catch on a gamma match?)
How bout it?
AND, the very top antenna of the stack will be mounted in traditional (center
of gravity/boom) fashion, at the top of the Christmas Tree...above another
yagi for another band.
DOES THE FACT THAT THE OTHER ANTENNAS BELOW IT ARE NOT "directly" BELOW CAUSE
ANY POTENTIAL QFU? (Seem that when you use swinging gate side mounts and
ringrotors you are never directly underneath the top beam, anyhow.
Pretty good question, huh!
What do you think.....LB are you out there?
Jim, K4OJ
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