[TowerTalk] FW: Guy article in CQ

[Roger (K8RI)]

Dick Green WC1M wrote:
> TowerTalkians --
>
> In followup to my post about computing guy lengths over sloping terrain,
> below is an exchange with W2RU that clarifies my approach and adds important
> information. Bud's question is at the bottom, my response at the top.
>   
That makes it very difficult to follow.
> 73, Dick WC1M
>
> Hi Bud,
>
> I agree that the tension must be the same in all three directions, but not
> only in magnitude. It must also be the same for the horizontal and vertical
> vector components of the force along each guy wire. I don't believe that,
> for a given angle, simply duplicating the tension along the guy can
> reproduce the relative proportions of vertical and horizontal force of a guy
> that's at a different angle. 
>
>   
To be symmetrical the guys only need to leave the tower at the same 
angle and be under the same tension. Then the x and y vectors will be 
the same for all guys.  Length does not come into play for this 
calculation as it does in resonance.  Also symmetrical refers to only a 
tier, not that all tiers be the same.
> I think you can visualize this by picturing a tower with two guys at, say,
> 45 degrees to the tower, and a third guy at 15 degrees to the tower. That
> third guy can easily be set to the same tension as the other two, but it's
> going to have a much greater proportion of vertical (pull down) force than
> horizontal (pull out) force. I suspect there's no value of tension that
> could be used to exactly duplicated the vertical and horizontal tension
> vectors of the other two guys. 
That is correct. Hence you have to adjust the length.
OTOH when if such a situation the important part is to keep the angles 
as close as possible and let the length fall where they may.
> That proportion is a function of the angle of
> the guy to the tower.
>
> Regardless of the physics involved, one of my objectives was to follow the
> Rohn-specified layout for the tower as closely as possible, on the theory
> that the manufacturer knows best. Rohn specifies guy attachment heights and
> the distance from the tower base for the anchors, which results in a certain
> set of guy angles and horizontal/vertical vectors. 
That is on level ground so you are already not adhering to their specs.
> I wanted to get as close
> as I could to that and still allow clearance for the middle SteppIR. I had
> to push the anchors out about 5% to accommodate the middle SteppIR, but
> that's within the Rohn-specified tolerance for the distance.
IIRC the distance is there to indicate where the guy will hit at the 
given angle "on level ground", not that the length is a requirement, 
particularly on sloping ground.
>  Then the task
> was to reproduce the guy angles and forces over my sloping terrain.
>   
Just maintain the angles and tension which will mean additional guy anchors.


73

Roger (K8RI)