[TowerTalk] How critical is the 120 degree ...

[kq2m at kq2m.com]

Hi Jari,

I agree that, as a goal, you should always follow the manufacturers 
instructions.  However, in some installations that may not be possible 
due to topography and other reasons.

Both my towers, 100'  and 130' of Rohn 45, went up in 1998.  The 100' is 
guyed with 1/4" EHS @ 30', 60' and 90'.
The 130' tower is guyed with 1/4" EHS @ 40', 80, and 120'.
Both towers use pier pins and a base plate that can swivel to release 
tension.

The Rohn 100' has one short Guy @ 62' from the tower base with two 
others > 75'.
The Rohn 130' has one long Guy @ 170' from the tower base with two 
others ~ 96'.

The Rohn 100' has guys spaced 110 degrees, 120 and 130 degrees.
The Rohn 130' has guys spaced 110 degrees, 120 and 130 degrees.

The towers have survived direct hits from 3 tornadoes (EF0 and EF1), 2 
Hurricanes - one with winds gusting > 110 mph and numerous T-storms, 
Macrobursts and Microbursts with winds approaching 120 mph, as well as 
countless ice storms and some with with heavy winds.

The Rohn 100' short guy @ 62' from the tower base prevents rotation via 
a side mount at lower heights.  It would have been ideal to have the guy 
80' from the base.

The Rohn 130' guys @ 96' prevent rotation from a side mount at 80' - it 
would have been best to have the guys 100' from the base.  The third guy 
is 170' from the base - far longer than ideal.

Both towers have been up continuously for the past 23 years without any 
structural issues becoming evident.

I hope that this information is helpful to you.

73

Bob, KQ2M


On 2021-07-27 05:31, Keith Dutson wrote:
> To be safe, do not rely on opinions.  Get your advice from either the
> manufacturer or a registered professional.
> 73 Keith NM5G
>     On Tuesday, July 27, 2021, 02:49:25 AM CDT, Jari Jussila
> <jari.jussila at oh2bu.pp.fi> wrote:
> 
>  Hi ...
> 
> I'm sure these topics have been discussed earlier, but could not find
> any thread ..... Sri ...
> 
> We are at our club erecting two towers. A rotating steel tower being 31
> m high and a aluminium telescope mast 18+18 m = 32 meters.
> 
> 
> A) How critical is the rule that guy wires should be "exactly" 120
> degrees apart?
> A professional guide says, that the anchor point can be 50 mm from that
> 120 degree (119,9-120,1 degree) but some say, that a maximum of two
> degrees is OK. That meaning 118-122 degree.
> 
> What's the tower community advise?
> 
> 
> B) The steel tower height is 31 m - it's a rotating tower - but the
> upper bearing is at 23 m ( leaving 8 meters for the antennas) and the
> lower bearing at 11 meters.
> 
> Whats the advise of anchor point distance? Some say, that the 60 %
> (distance for  the tower) should be calculating from the total height
> (31 x 0,6 = 18,6 meters).
> Some say, it should be calculating from  the upper bearing (23 m x 0,6 
> =
> 12.8 m)
> 
> Whats your opinion?
> 
> Jari, OH2BU
> For OH3AC Club Station
> 
>