[TowerTalk] Max Unguyed Rohn 25 height to support dipole end

[Michael Tope]

----- Original Message ----- 
From: "KDM" <KDM at ctcn.net>

> Gents,
>
> I have a pile of Rohn 25 that I'd like to use to support the ends of a 160
> mtr dipole.
>
> No other load other than the tower itself.
>
> The center is supported by a TriEx freestanding tower.
>
> What's the max height I can realistically go unguyed since I don't have 
> room
> for guys?
>


I suggest that you taper the mast. I would go with ~20 ft of freestanding
R25 (2 straight sections and 1 short top section) and then stick a 20'ft
piece of 2" schedule 40 aluminum water pipe out the top with a 12' piece
of 1 1/2" O.D. x 1/4 wall aluminum tubing inserted in the bottom 12' of the
schedule 40 as a stiffener. I have a similar setup at my QTH (except that I
have the reinforced 20' aluminum mast sitting above 4 sections of R25 with
a heavy duty house bracket at about the 20' level). Per my calcs the
aformentioned setup should take 90 MPH winds  with ~1.5 sq ft of wind
load at the top (equivalent of about 50 lbs of sideload). Also remember, if
you use a pulley at the top, you can always reduce the tension on the dipole
ends if it gets windy. You could also put a backstay on the mast the way
powerpoles are backguyed at an "end of the line" pole (imagine 1/2 of a yagi
boomtruss with the boom pointed straight up in the air and the truss strut
offset from the ground by about 8').

*
**
* *
*  *
*   *
*    *
* ***  <- horizontal backguy strut here
*     *
*     *
*     *

The 40' powerpole in front of my house is backguyed in this way with only 4
or 5 feet of offset between the backguy and the centerline of the pole.

73, Mike W4EF................................