[TowerTalk] aluminum mast vs. tramming

[Earl Morse]

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

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Message: 1
Date: Sat, 12 Mar 2016 17:18:45 -0800
From: "Steve K7AWB" <k7awbgoog at gmail.com>
To: <towertalk at contesting.com>
Subject: [TowerTalk] aluminum mast vs. tramming
Message-ID: <A8E7D6EF95034756B3E40592E3F3895E at 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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