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[TowerTalk] Re:rope in elements

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Subject: [TowerTalk] Re:rope in elements
From: (alsopb)
Date: Wed, 28 Mar 2001 23:04:46 +0000
In the past the Aerospace industry and the Nuclear Navy believed they
could design to zero defects.  It wasn't until much money was spent
that the powers that be realized that a goal of zero defects was
impossible.  One could only design and produce a product that would
fail with low probability.  

How low the probability depended mostly on how much you cared to spend
to achieve it.

The original philosophy was that one determined hard and fast failure
limit. If one designed below that point, no failures would result.

Unfortunately, this completely goes against mother nature who permits
successes and failures which are distributed across a spectrum of
"design limits"

We had a particularly vexing problem with a number of units which
should not have failed under the old philosophy but did.  It wasn't
until enough data was accumulated that one could determine that they
were indeed part of a normally distributed failure profile.

Today people seem to believe (and expect) that absolute safety and
zero percent failure rates are achievable. Also products which have
vanishingly small failure rates such should be cheap.  Mother nature

73 de Brian/K3KO

Andrew Williamson wrote:
> In message <005f01c0b793$06b3dc20$0300a8c0@cruncher>, Guy Olinger, K2AV
> <> writes
> >F12 is making those antennas hand over fist.  C3SS and Z3's are the big
> >sellers. I can count the dropped piece accounts here (not to discount
> >them at all) on my fingers. F12 has what, ten thousand, twenty thousand
> >antennas out there? I have heard a lot more stories about F12 surviving
> >bad ice loads and springing back to original form.
> That's like taking a census of 100 people, getting two negative
> responses and then saying that only two people in the entire population
> has this opinion (instead of 2 per cent).
> F12 may have 10-20,000 antennas out there, but there are only 1500 or
> 1600 people on this reflector (correct?).  Of those, lets be generous
> and say a quarter have a F12 antenna (I doubt if that many have).  So,
> out of that sample of 400 F12 owners we are seeing up to 10 failures.  A
> 1:40 failure rate doesn't really inspire confidence.  And, I would say
> that the people on this reflector are probably the more competent
> antenna builders (they certainly have an above average interest if they
> are here).
> I have personally only seen four installed F12 antennas and three of
> those have had failures of one type or another.  The one that hasn't
> failed is a C3(something) at about 35ft.  The ones that have failed are
> a Magnum340, a 5BA and a C4-something.  From that, I *could* say that
> 3/4 of F12 antennas will fail, but that would be a pretty stupid
> statement as it's not true.  To get accurate results, you need a larger
> sample.
> Andrew Williamson GI0NWG / AC6WI
> Homepage =
> One of the ZL9CI gang

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