In a message dated 97-05-14 12:25:42 EDT, elewis@dsp.com (Edward Lewis)
writes:
> I put up a Rohn 25G free standing at 32feet. I have been using 5 feet
> of mast with a cushcraft A3S which places my antenna at about 35 feet
> after I deduct the amount of mast which is in the tower.
First of all, Contra Costa county is only a 70 MPH wind speed zone which
is the lowest rating given by the TIA-222. Don't I remember some big winds
this winter or fall there? Anyway, 70 MPH is the MINIMUM.
Thirty feet of freestanding 25G is rated at 3.6 sq.ft. Your A3 plus mast
is over 5 sq.ft. You're overloaded, dude, by about 40%.
> Are Rohn
> specs for wind load based on the height of the tower or the actual
> height of the antenna, and is the wind load of the mast factored in
> by Rohn or is this something I need to consider.
I haven't found out from Rohn engineering how they consider ham tower
loads with masts yet. 45G and 55G is designed for commercial antenna and
mount headloads which can be bigger loads but don't use any masts sticking
up. When I find out, I'll let everyone know.
The mast needs to be added in as part of the tower load. A 10 foot mast
of 2 inch OD material is about 1.1 sq.ft.
>The reason I am
> asking these questions is that I would like to use a 10 foot mast
> pipe which would place my antenna at 40 feet and give me room to
> install an A3WS below the A3S. Also would 7 feet be enough seperation
> between the 2 antennas. 73 Ed
Please do not add any more load or bending moment to your overloaded
tower. You need to guy it in order to implement your proposed system.
A discussion of suitable mast material as well as proper stacking
distance can be addressed when the present problem is resolved.
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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