Chuck Dietz (KE5FI) wrote:
>
> > > My 40-2 CD is 12 feet above TH-7 and both work great. Just put the
> > > cushcraft boom supports downward instead of above the boom.
>
> > Watch out...W6QHS (now W6NL) says not to do this, even though he once
> > advocated it.
> >
> > Instead, beef up the boom...
> -snip-
>
> Why not? Logically, the supports would seem to work about as well under
> the beam as over.
>
negative!
try this thought experiment. take two beams, one with supports up
and one with them down. add extra weight at the end of each boom
(ala ice). now, as long as there is no side force (ala wind) the
supports are the same and both hold the boom up. now give each one
a push sidewise.
1. with the boom brace on top the side force deflects the boom to
the side which causes the boom brace to pull up and back toward the
normal boom position so the boom naturally comes back to where it
belongs.
2. with the boom brace below the side force deflects the boom to the
side, but now the boom brace is pushing to the same side and pulling
down, exactly the wrong response which adds more bending forceto the
boom and will not help it back to its normal position. kind of like
standing a cone on its tip, it falls over once its given a little
push.
--
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net or robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html
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