On 10/23/13 1:38 PM, Larry Loen wrote:
I agree with you, but to play devil's advocate a bit, maybe you plan for
something that basically doesn't survive.
Yes, that's actually *my* preferred approach. Determine what the
acceptable failures are, and design with that in mind.
Suppose you have a TV push up mast style design that is guyed decently.
You put a two element quad on it or a small Yagi and only go up 43 feet.
KY6R proved that even living in a big bowl in California, you can make
Honor Roll with such a setup. They key is a very light windload. You
don't go all out. Say, a quad or a two element monobander.
And if that lightweight mast and antenna DOES come crashing down into
your backyard.. there's no significant damage.
I think that's really the key: Most hams don't have a 24/7 availability
requirement (compared to, say, FAA control towers or public safety).
They can tolerate substantial failures, whether by the antenna elements
breaking off, the tower bending, lightning evaporating the feedline, or
whatever.
So, maybe you just make sure it can't fall on anything interesting and
build simple??
Me, I'd go for the big tower with the (engineered) deeper hole. But, if
you have the space and you don't have to worry about it falling on
someone, maybe you plan for something inexpensive that you can simply
replace. It would also be collapsible in the event of a hurricane as
well. The big worry would be unplanned storms or maybe being out of
town when the hurricane blows in quickly.
Rapid stow is, I think, more of a peace of mind, than a valid mitigation
of the risk. As you note, what if the tower is extended, and you can't
retract under load.
here's an example: If had a neighbor putting up one of those 150 foot
telescoping contraptions and she claimed that in the event of a high
wind, she'd retract it to 30 feet, so it couldn't fall on my house,
mitigating the risk of her 150 foot tower coming through my roof.
I'd want to see an awful lot of analysis and testing showing that he
could retract it fast enough, under all conditions. It would be likely
cheaper to drill a 50 foot deep pier and put a cellphone tower in his
backyard, engineered to withstand the highest wind speed continuously.
The extending mast, though potentially does have aesthetic advantages.
So it might be worth it for my neighbor to spend the extra time and
money and complexity.
But "I'll crank it down if the wind comes up" scenario is pretty much
the same as "I'll disconnect the feed lines when I hear thunder". They
protect against some fraction of the failures, but not all.
Maybe the take home is that it's more "reduce the chance of breaking
equipment" than "safety of life and property"
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