Ya'll have me wondering about my 40M tower plan. Last fall I took delivery
of two M2 40M4LLDD Yagis. This antenna has 4 elements on a 42 foot boom,
but a surprisingly sparse 13 square feet windload rating. They will be
mounted at 100 and 200 feet on a 190 foot Rohn 55G tower. The top antenna
will be rotated by an Orion 2800 that was purchased at the same time. The
lower will be rotated by a TIC Ring.
This tower was supposed to be going up this spring but unexpected surgery
has delayed the project for a year.
After hearing about all of the mast slipping problems I decided to take the
Orion out of its box and have a look. According to the instructions, the
"positioner" has been recently improved and strengthened. Since I do not
have an older unit, I have no way of knowing what is improved or how much
stronger it is. Here are some specs:
wind area 35 sq ft
start torque 4200 in lb
rotating torque 3200 in lb
braking torque 17000 in lbs
vert load cap 1800 lbs
I took a photo of the mast clamp halves (see below). Interestingly, there
is a hole in each that is sized to take a 1/4 inch bolt. This could
certainly be used to pin the mast but leaves doubt about the strength to
hold it.
http://www.dutson.net/Transfer/HamRadio/Orion2800Clampds.JPG
73, Keith NM5G
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of K7LXC@aol.com
Sent: Sunday, April 22, 2007 12:04 PM
To: towertalk@contesting.com; alwilliams@olywa.net
Subject: Re: [TowerTalk] Mast slipping
In a message dated 4/22/2007 8:43:23 A.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
> About a year ago I had a conversation with the m2 people about their
rotator
clamp slipping on my Monstr's mast. What follows is my memory of the
conversation:
> 1. It is better to have the clamp slip than to harm the rotator. (Note:
the
wind banging repeatedly on the gearing can weaken the gears?)
> 2. The specified braking torque has not been measured (or calculated?).
> 3. Pinning voids the warranty. I would assume that using a
> different
mfrs
clamp would also void the warranty.
> 4. They recommended a clamp bolt tightening sequence that should be
followed. Unfortunately I wasn't able to get a firm answer on what torque
to tighten the nuts to. The sequence to follow is:
> a) bolt the rotator to the mounting plate but leave the bolt/nuts
> not
tightened
b) with the bolts to holding the rotator to the mounting plate loose,
tighten the bolt/nut pair of the clamp that is nearest the bottom.
c) tighten the next (middle) bolt/nut pair of the clamp
d) tighten the top bolt/nut pair of the clamp
e) repeat steps b,c,d several times
f) now lastly, tighten the bolt/nuts of step a
> I did get an answer of 40 ft/lbs from the m2 person but I think that
> was
just pulled out of the air.
Very interesting but not useful. It doesn't do anything about the
significant design flaws of the Orion mast clamp that ARE the problems.
None of the above will keep the mast from slipping.
Cheers,
Steve K7LXC
TOWER TECH
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http://www.aol.com.
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