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[TowerTalk] how vertical is vertical

To: <>
Subject: [TowerTalk] how vertical is vertical
From: (Michael Tope)
Date: Wed Mar 5 01:54:56 2003
This discussion reminds me of an antenna I worked on for the
air force about 10 years ago. We were having trouble meeting
a specification for the elevation pattern. I suggested we ask the
customer if our results were "good enough". Management
hesitated thinking that this might sew doubt in the mind of the
customer regarding our ability to "perform" on the contract. After
a lot of hand wringing, we were finally allowed to approach the
customer and present our results. They said "okay" without
hesitation as if it didn't matter one bit :)

73 de Mike, W4EF................................

----- Original Message -----
From: "Jim Lux" <>
To: <>; <>
Cc: <>
Sent: Tuesday, March 04, 2003 8:24 PM
Subject: Re: [TowerTalk] how vertical is vertical

> ----- Original Message -----
> From: <>
> To: <>; <>
> Cc: <>
> Sent: Tuesday, March 04, 2003 6:43 PM
> Subject: Re: [TowerTalk] how vertical is vertical
> > In a message dated 3/4/2003 5:25:06 PM US Mountain Standard Time,
> > writes:
> >
> >
> > > I'd be interested to know the basis of the "verticality"
> 1
> > > part in 100 (about 1/2 degree) wouldn't appreciably change the loads
> the
> > >
> > Hi Jim;
> >
> > My EIA-222-D (yes, its old but its the most current I have here and this
> > section probably hasnt changed) says;
> >
> >
> > Section 6.1 Standard
> >
> > Section - Plumb - For guyed structures, the maximum deviation
> > the true vertical shall be one part in 400. For self-supporting
> structures,
> > the maximum deviation from true vertical shall be one part in 250.
> >
> Indeed, it looks like a standard industry spec.  But I was wondering why
> they selected that?  And, is it aimed at 50-150 foot towers or 1000 ft
> behemoths..   For all we know, the EIA standard said that because it
> like a good number" and "it was in some other spec we had that seemed to
> work". Or, they may have had some independent analysis to back it up.
> Some background.... In my job at Jet Propulsion Lab, I deal with all
> of specifications, and, in the context of the ever pressing schedule,
> sometimes specs get in because they just got copied from somewhere else,
> without any backup for why that spec existed in the first place.  The
> thing is that the original spec (7 or 8 generations back) may have been
> written as a "let's see what the prospective bidders will say" kind of
> requirement; or, perhaps, in that previous project, "cost is no object";
> maybe they wound up writing a waiver against an impossible requirement
> never went back and modified the spec).
> Therefore, when I see a specification that is cast in nice round numbers
> in 250, 1 in 400), and that appears to be reasonably achievable in a
> commercial environment (i.e. cranes, trucks, lots of people being paid to
> their job), I wonder if the spec was set as "well, it shouldn't cause any
> real cost impact to meet, and it would cost us a lot to figure out a real
> number that is looser, but still safe."  Those kinds of commercial specs
> not be appropriate for a different kind of operation (i.e. less labor,
> capital intensive) where a perfectly safe(!) installation might result,
> though it doesn't meet the commercial spec. It also properly embodies a
> conservatism.  After voting to approve that spec, you could go home and
> lose sleep worrying about whether a tower meeting the spec would fall over
> from not being plumb.
> Let's be realistic.. relatively few amateurs do all aspects of their
> to full commercial standard (Hmm.. surely you all comply with all aspects
> the 2002 NEC and the NESC, and the IEEE grounding standard, and you use
> rated transformers in your power supplies, you wouldn't think of shooting
> AWG 20 wire over a tree with a slingshot, you use only fully type accepted
> hardware,  etc.etc.etc.)..  Commercial and industry standards exist for
> reasons other than pure safety.  Commercial broadcasters, for example,
> substantially better reliability than the average amateur. Industrial
> installations often have to account for people who may not have a
> understanding, and may not appreciate, certain fundamental limitations.
> So, to come back to the original question.... Is a tower that is 1 foot
> of plumb in a 150 foot column unsafe?  Sure, it doesn't meet EIA-222, so
> it's suspect at first glance, but, is it unsafe?  I don't know that you
> could actually see it be off-vertical without an outside reference (a
> transit or plumb line), so it probably meets the "pretty enough" test.
> Again, pretty doesn't imply safe, nor does safe imply pretty.
> So, what's the origin of the original 1 in 400 spec?   (I don't actually
> expect to find out.. it's one of those things that is probably lost in the
> mists of time, or is loosely derived on some rule of thumb for eccentric
> column loading/buckling)
> _______________________________________________
> See:  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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