[TowerTalk] For Chrome Moly and tower/wind load experts out there - Mountain top tower installation

[john at kk9a.com]

I doubt there's much difference in strength between the 2dia x 1/4 wall and 
the 2.5dia x 1/8 wall mast, however you can calculate this yourself using 
any mast software.  K7LXC sells a product for this and there are also a few 
free programs on the internet.    If a reasonable sized mast does not 
provide the strength that you need,  you could always use a tower ring 
rotator and mount one of the antennas directly on the tower or use a single 
beam that will cover all of the bands that you desire.

I'm not sure what protection adding a lightning rod on top of your tower 
will provide as all of the energy will still go through your tower will be 
induced into anything nearby.

John KK9A



To: towertalk at contesting.com
Subject: [TowerTalk] For Chrome Moly and tower/wind load experts out there - 
Mountain top tower installation
From: <Date: Sat, 15 Aug 2009 10:20:11 -0500

<snip>

HERE is the question: I have both 2.0" and 2.5" Chrome Moly Mast tubing
available, each about 18' long.  The 2.0" Mast pipe (I have learned that the
word "tube" is the preferred term by experts, instead of "pipe") has a wall
thickness of 1/4", and the 2.5" mast tube has a smaller 0.12" wall 
thickness. I
suppose there is a book with a formula for yield strength of tubes of 
different
inside and outside radii, made of the same material, its probably an 
undergrad
ME question, but I was hoping some of you out there might know off hand the
answer to this question:

Which is better/stronger/wiser to use for ice/wind strength on a mountain 
top
tower, and why?

a. The 2.0" OD  0.25" wall thickness Chrome Moly 4130N tube, weighing 100 
lbs
for 18'
b. The 2.5" OD  0.120" wall thickness Chome Moly 4130N tube, weighing 75 lbs
for 18'

And a second question: would it be wise to put a little 4' or 5' lightning 
rod
above the mast pipe to attract electrons, and if so, is there a cheap/easy 
way
to affix the lightning rod to the top of the mast, and what should it be 
made
of...I am thinking of a sacraficial metal element that might offer 
protection,
etc. and would be very hard to see ("invisible") so as not to exceed zoning
height requirements.

Thanks to all... 73 Ted N9NB   trappaport at austin dot rr dot com