[Towertalk] ma550

[Bob Nielsen]

On Thu, May 02, 2002 at 01:25:30PM -0400, K7LXC@aol.com wrote:
> In a message dated 5/2/02 9:24:00 AM Pacific Daylight Time, ve7yc@shaw.ca 
> writes:
> 
> > Now this 
> >  is the 55 foot US Tower that I wouldn't put up over 40 feet. The joints 
> >  between sections has about a 1/4 inch slop.Or  1/2 inch total.This let the 
> >  top section wave around like a tree branch. any one have this trouble or 
> as 
> >  is it just my luck again??
> 
>     They're all like that. If the tolerances were any closer, you'd have 
> trouble getting it up and down. 
> 
>     This is an engineered structure and does a great job for what it is - a 
> bunch of pipes stuck together. Yes - it moves in the wind but it's designed 
> for that. Don't worry about it.

When I lived in So. Calif., we had a club where I worked that put up a
MA-40 on top of one of the buildings (actually on the landing of a
roofhouse with the MA-40 secured to the building at about 10 feet).  It
did move in the wind, but not excessively.  However, after several
years there was a permanent bow in the top section and it would no
longer retract.  It wasn't very noticeable but in order to service the
antennas we had to unbolt it from the base, walk it across the landing
and lay it against the roof.  It took about 15 people to do the job.

The antenna was a TH6DXX, which I think is around 8-9 sq. ft., while
the MA-40 is rated for 10 square feet at 50 mph wind.  There was a 2
meter Ringo Ranger at the top of the mast, as well.  I don't know what
the wind speed reached (the L.A. county rating is 70 mph), but there
were some pretty heavy windstorms at times in that area (western San
Fernando valley) and the beam was > 100 feet above ground, so the tower
was probably at least living up to its rating.

Of course with these towers one must use the lower mast fitting on the
rotator (Ham-II or III, I recall), so the rating there was exceeded
somewhat.  There were no problems with the rotator until the 1994
earthquake when the casting on the mast fitting cracked (the building
itself was severely damaged and was later torn down).  Of course none
of this stuff is rated for earthquake survival.

Bob, N7XY