Tramming is more of an issue when you have a large moment arm, the distance
from the top guy to the point that the tram line is attached.
On my 100' Rohn 45 the top guys are at 90' with 10' of tower sticking up above
that and another 10 feet of mast above that. I trammed up the top antenna, a
KT34XA, at just above the top of the tower. Then jacked the mast into place,
set the rotator, and trammed up the 2 element 40M beam in place. This left a
minimal of moment arm above top guys and a back guy was not used.
The higher you mount the tram line, the greater the bending PSI of the mast at
the top of the tower. In my case it is a Moly4180 mast and is very strong
>100k? PSI and in excess of 150lb. I probably could have mounted the tram line
at 10 feet above the top of the tower and not had a problem.
I agree that back guying the mast is a lot less of an issue and wouldn't even
consider dropping a guy, especially after they have all been tensioned and the
tower pulled plumb.
Earl
N8SS
----------------------------------------------------------------------
Message: 1
Date: Sat, 12 Mar 2016 17:18:45 -0800
From: "Steve K7AWB" <k7awbgoog@gmail.com>
To: <towertalk@contesting.com>
Subject: [TowerTalk] aluminum mast vs. tramming
Message-ID: <A8E7D6EF95034756B3E40592E3F3895E@Ham2>
Content-Type: text/plain; charset="utf-8"
I have an aluminum mast (which is 2? OD and 0.25? wall and about 11 feet) out
of the flat top of the Rohn 25. Already I have a M2 17-element 2-meter yagi at
the top of the mast. Below that antenna, and right above the flat top plate of
the tower, I want to put my Force 12 5BA 5-band, 15 element yagi.
With my other tower, 90 feet of Rohn 45, we put up a 6-element Force 12 Mag 620
the first time by simply dropping each of guys and reconnecting once the
antenna was above each guy point. The second time we put it up, after balun
replacement, we used a friend?s tram line and back-stay ? of course the mast
was 2? OD and 0.25? wall and heavy!
I don?t think I want to chance the Rohn 25 at 102 feet with that drop-the-guy
process.
So the question is : will a tram line work or will I bend the mast? Even using
a back-stay might cause undue pressure and bend the expensive mast. And a bent
mast does not rotate nicely.
Steve K7AWB
Nine Mile Falls, WA
DN17es
------------------------------
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