At 07:05 PM 10/15/2006, Mark Beckwith wrote:
> >> I plan to install a wind speed meter
> >> and diligently crank down the tower
> >> every time the wind exceeds 50mph.
>
> > I would recommend the opposite approach:
> > Keep it cranked down and only crank up
> > when actually on the air.
>
>I second that - with just a minor change your plan will go from one that is
>more risky than safe into one that's more safe than risky. W6AQ has a
>crankup with a lot of really big antennas on it, but it's only extended when
>needed, and spends the majority of it's time nested. Never a problem in
>many years of service.
Indeed. And, for that matter, if there were an honest-to-god life or
death emergency during a howling storm, you might leave the tower up
because the communications is more valuable than the potential damage
from a failure. But, it would depend on the consequences of a
failure. A slightly bent tower that requires an expensive crane to
get it down is a lot different than collapsed tower with an antennan
element impaling one of the kids sheltering from the storm in the
preschool next door.
The practical problem is that most towers, while they give "stay
below this and no damage occurs" numbers, tend not to have
documentation that gives "here's our guarantee of how it will fail
when you exceed that limit". So that leaves it up to you to decide
how you want to deal with "over margin" events. Developing the "fail
soft" sorts of numbers, or, for that matter, designing something that
fails in a predictable manner, is MUCH harder engineering than just
determining a "will not fail below" limit, where you can just be real
conservative, and be guaranteed right (albeit with heavy and/or
expensive overdesign).
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