In a message dated 98-03-22 19:15:37 EST, KB9RPM@centuryinter.net writes:
> I currently have a Rohn 25 that is 85' high.It has Rohn guy
> brackets with guy wires every 20'(4 guys at each point)I am going to
> put up 3 new antennas that will have a combined windload of about 20
> square ft.
Really? Since the tower is rated for 15.3 sq.ft at 70 MPH, I think you'd
be foolish to pursue this.
Since the number of guys and spacing is not what the factory recommends,
I'll assume you don't have a Rohn book. Please get one. They are five bucks
from TOWER TECH.
What other non-manufacturer things have you done? What size of guy wires
are you using? What grade are the cables?
What county are you in? I'll look up the windspeed for your county.
>The mast pipe for these will be about 18' out of the tower.
What kind of mast are you going to use, hmm?
>My guy anchors are 38',48',38' and 46' from the tower.My lot size only
> allows these distances.My question is:Would it be safe to add 2 more
> sections of Rohn 25 with 1 more set of guywires at the top of the tower
> to maintain having them every 20'.
Good question. Please get a PE (Professional Engineer) involved. With
those steep guy angles, the forces on the guys and anchors are MUCH larger
than a typical installation. That still doesn't change the fact that the tower
is significantly overloaded.
Don't get me wrong. The Rohn specs are only ONE scenario. Yes, your tower
can be engineered to be safe and reliable for it's rating loading but unless
you are qualified to do the engineering calculations to ensure that everything
is within specs, DO NOT go any farther without professional help. Check the
ARRL web page for a VCE (Volunterr Civil Engineer) in your area.
73 and GL, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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