[TowerTalk] Experience with MA550 tower

[Ed]

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Subject: 

Re: [TowerTalk] Experience with MA550 tower


From: 

"larryjspammenot at teleport.com <mailto:larryjspammenot%40teleport.com> "
<larryj at teleport.com <mailto:larryj%40teleport.com> >


Date: 

Wed, 7 May 2008 23:01:12 -0400 (EDT)


 

 

					

 


I have a 3-section Wilson MT-61B crankup tubular tower, which is not
installed 
- it's just lying on the ground as I don't have any particular plans for it 
right now. I just looked through the manual for it, and then went out and 
actually looked at it - it doesn't appear to have any kind of steel pins 
anywhere, just the single raising cable. I also had the 40-foot tall
2-section 
version of the same Wilson tubular tower about 16-17 years ago, same thing.
I 
did have it braced against the house with a bracket, and it worked out well 
with a 2-element tribander quad on it. If I remember correctly, Wilson also 
made a 77-foot, 4-section version of this tubular tower.
 
 
I also have the RB-61B Rotor Base/Raising Fixture manual for this MT-61B
Tower 
(but not the actual fixture), and the manual for the companion GK-61B Guy
Kit. 
Looking through the TT archives and following the related discussions, it
seems 
that the US Towers MA-550 is the modern replacement for the Wilson MT-61B.
The 
top section of the MA-550 is a square tube, while the Wilson top section was

round, and maybe a few other design changes. I believe I saw info about
people 
ordering the MA-550 series raising fixture, rotor base, etc. from UST to use

with their older Wilson MT-61B.
 
The GK-61B Guying Kit manual specifies four guy wires going to the top of
the 
tubular tower. The pictorial on the front page shows the tower being used
with 
the RB-61B Rotor Base/Raising fixture, out in the clear, away from any 
buildings. 
 
A couple of notes that make me hesitant to try to guy any of these tubular 
towers though - these notes are from the GK-61B guying kit manual (dated 
06/01/80):
 
"NOTE: With this Guy Kit properly installed the tower is capable of
supporting 
a 20 sq. ft. antenna at 80 mph."
"Do not over tighten guy cables. Leave enough slack so tower top can move
about 
1 ft. from vertical."
 
It sounds to me like the single set of guys are just loosely attached, and
will 
hopefully keep the tower from falling over if the wind blows TOO hard! It 
doesn't look like a very encouraging, stable way to support an antenna. This
is 
one of those situations where I don't know if I'd really want to "Do what
the 
manufacturer suggests", by guying a lightweight tower like these. 
 
If Wilson was still in the tower manufacturing business, I have doubts that 
they'd still be offering this guying kit. If I wanted a guyed tower, I think

I'd find a way to go with Rohn 45, or similar.
 
LJ
I have an MT-61 tower - on the ground, not installed yet - and received a
copy of the manual from a helpful member of this list.  It is rated for a 10
sq ft antenna wind load at 53 feet but only for 50 mph wind speed.  I
attempted to calculate what it could handle at 70 mph for the same torque at
the ground that would be produced by a 10 sq ft antenna with 50 mph wind.
It looks like even a small antenna (3.5 sq ft) would have to be lowered to
about 45 feet to keep the torque under the same level as the 10 sq ft
antenna at 53 feet with 50 mph wind speed.
 
I would be happy to send the spreadsheet to anyone with the proper
qualifications in structural engineering to review it.
 
Mine does have the brackets for the pin on the top of the first section but
the pin assembly did not come with it.
 
Ed
WB6YTE