> 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,
Steve K7LXC
TOWER TECH
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