[TowerTalk] Single Tram Line
k7lxc at aol.com
k7lxc at aol.com
Sun Aug 26 11:32:11 EDT 2018
> I have a 4 el 20 meter HyGain yagi, that I am going to tram to a 60 foot Rohn 25.I bought 3/16 inch stranded stainless and will attach it to my garden tractorI have a 2 inch diameter 1/4" wall aluminum mast on the towerNow my question.The tower is guyed in two locations.Being the antenna only weighs 50 lbs, how important is it to back guy the mast ????
The two factors to consider are the tension on the tram line and the height of the tram connection point (TCP) on the mast. At one foot, the tension factor will be a multiplier of 1. At 2 feet, the factor is 2, that is twice the bending moment and so forth.
I might try having the tram connection 2-3 feet and then put some tension on it. Slowly increase the tension and after each adjustment, look at the mast from the side to see if you can see any deflection. Some deflection is okay but obviously you don't want to over do it.
Your choices are either use a small distance up the mast for your TCP to get the antenna to the top of the tower and then heft the antenna to the mast manually. (An alternative is to hang the antenna from the tower once it reaches the top and then re-rig your haul line higher on the mast so your ground crew can pull it up into place and there's only a vertical pull on the mast.) The second way is to position the TCP high enough on the mast so that the antenna arrives at the top ready to be bolted to the mast. This is where you have more bending moment and may require back-guying.
Just proceed carefully and you should keep yourself out of trouble. You could always start out with the back-guying but of course it takes longer and you may not need it if you follow the aforementioned steps. And BTW a 50 pound antenna weight is not insignificant. Just ask the climber at the top of the tower as he's trying to heft the antenna into place!
Cheers & GL,
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