[Top] [All Lists]

Re: [TowerTalk] Setback requirements (was "permit in hand")

To: bill rubin <>
Subject: Re: [TowerTalk] Setback requirements (was "permit in hand")
From: Jim Lux <>
Date: Sun, 02 Sep 2007 07:18:21 -0700
List-post: <>
bill rubin wrote:
> Perhaps this will help your case,  Rohn letter stating that tower failure is
> 1/2 to 1/3 height. see Rohn Letter on Fall Radius of a Guyed Tower at

That's an interesting letter.

Note, however, the "assuming the guys remain intact".. you'd have to 
show by analysis (or test<grin>) that the guy system's failure point is 
so much higher than the tower's, that the tower is guaranteed to 
collapse first.  That might not be a tough hurdle to bear, depending on 
the system.

And, of course, if you have a lot that is 50 feet wide (as many are), 
that would limit you to a 50 foot tower (if you take the more 
pessimistic 1/2 the height fall radius) placed precisely in the middle 
of the lot.

> Also see Gunnar Olsen Study <>
Another interesting report.  One issue that might arise in the context 
of using the Olsen analysis is that many broadcast towers have multiple 
guy anchors.  The other thing is that broadcast towers are designed, 
erected, and maintained with a lot more oversight and expense.  What if 
the city says, "fine, go ahead with your tower.. We want you to hire an 
independent engineering firm to supervise the construction. Oh, and we 
want you to develop a regular inspection and maintenance plan, and file 
annual inspection reports with a certification by a P.E. that the tower 
is still structurally sound"  This is fine for a TV station putting up a 
1000 ft tower, because they'd essentially do that anyway. Not so fine 
for a ham wanting to get a bunch of buddies over for a antenna raising 
party over Labor Day weekend.

BUT.. this, in general, is the sort of analysis that would help make the 
case in front of a planning board.  Maybe, someone could convince a 
professor with a grad student looking for a thesis topic to do a 
rigorous analysis (with experiments) of these sorts of things, with the 
product a nice consumer friendly report.  Then you could get the "Dr. 
somebody of University of XYZ has researched just the area about which 
you are concerned, and here is their summary of findings."

(Bear in mind though, that my inherent cynicism about local regulators 
is that they might just say, "we don't care, we don't like your antenna 
ideas, and we'll find anyway we can to prohibit it. By the way, have you 
surveyed your proposed construction site for Native American remains? 
Oh, and while you're at it, do you have a survey to prove it's not a 
riparian habitat? And, what about the Environmental Impact Study or the 
analysis (negative declaration) showing you don't need one.  You have, 
of course, done the required traffic pattern impact study, haven't you? 
And what about the fence to keep people outside the RF exposure limit." 
   You might laugh, but all this, and more, was faced by a local radio 
station looking to put up a 30 foot(!) high mast for a FM broadcast 
transmitter.  We're talking about something that literally looks like a 
flagpole with a funny set of rods on top on the side of a hill hundreds 
of feet from the nearest public road or building (heck, the underground 
transmitter is 700 ft away, talk about a long feedline).

Here's a picture of the entire installation, about a year later.

jim, w6rmk

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>