I would use a mast calculator to see if you want to spend your money on 3/8
wall 4130. While you are calculating you should also look at a 3" x 1/4"
wall mast.
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Mast inquiries
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Tue, 12 May 2015 14:22:58 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On the HRO Web site:
*Detailed Product Description*
US Tower offers three different types of masts. The M-5, 10, 15 and 20 masts
have .120" wall thickness. The M-15R and 20R have steel pipe inserts in the
lower half of the mast which provides extra strength where most needed
without adding unnecessary weight in the top portion. The M-15R and 20R have
a thickness of .250".
On the UST web site there is also listed CM alloy tube that is 2 inch OD and
0.375 wall thickness.
Can someone please give me an explanation of the comment above regarding the
extra strength where needed in the lower half of the mast? Does this assume
the lower part of the mast is still above the thrust bearing? I can see how
the leverage of the part of the mast above the top bearing would try to fold
the mast at the upper bearing. I see how lateral force on the part of the
mast above the thrust bearing is distributed to the rotator acording to the
comparative lever arm lengths: 1. rotator to thrust bearing distance and 2.
thrust bearing to the antenna's center of lateral resistance ( like CG but
for aerodynamics.) If their statement is true in the case where the
reinforced part of the mast is below the thrust bearing then I need it
explained to me.
Also, while on this topic, how does the reinforced-at-the-bottom mast
compare to the CM tube with .250 wall.
Any thoughts on the efficacy of upgrading to the .375 wall CM tubing? Is it
overkill and a waste of $ or just slightly belt and suspemnders and worth
considering? My application is a SteppIR DB42 with 80m and 6m accessories
plus a NN4ZZ TiltPlate atop a Tashjian HD LM354 turned by a Kurt Andress
PropPitch motor with the antenna height above ground of 94 ft or so due to
mounting the Tash Tower on a 40 ft steel structure. I intend to only have
the mast a couple feet or so above the top of the tower unless I use the
.375 wall CM tube for the mast. Note: the tower site is more or less at
heart of tornado alley a few miles from locations that repetitively are in
the news for tornado damage.
Thanks for your consideration.
Patrick NJ5G
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