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[TowerTalk] extending tower masts

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Subject: [TowerTalk] extending tower masts
From: (Frank T. Brady)
Date: Mon, 16 Jun 1997 11:19:36 -0700
A lot of the planning that myself and others are doing with antenna systems
on a tower involve stacking low and high band yagis.  Now that I realize
this system (new) is going to be a lot closer to $10K than $5K, I want to
learn more about the effect of extending the mast to accommodate stacked arrays.

I haven't called Tri-Ex yet, but the response from US Towers was that a
written request must be submitted to their engineering department if one
wishes to have them evaluate the max wind loads and dead weights for an
installation with the mast extended more than one foot above the tower top.
This 'service' is NOT free.  Apparently, they do not have a formula or plot
to calculate the degradation of specs as the mast is extended.

Has a 'rule of thumb' evolved out of all the stacking going on out there?
As I extend the mast, is there any way to figure out what it does to my max
wind load and dead weight limits?

 Frank - W0ECS

BTW, I did get the 'missing' wind load and dead weight specs for the HDX572:
  200# dead weight and 22.8 sq feet at 70mph

The HDX572 wind load capacity is considerably more than the LM470 (7.8 sq ft
is enough to accommodate stacking an extra yagi - all other things being equal).

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