rickman wrote in :

Why would the wind tend to twist the ladder? Is your antenna highly
asymmetrical? I would be more concerned by the bending forces which can
be very high if the antenna is a considerable distance from the highest
guying point.

Even if the antenna were not symetrical, that bending would cause enough
assymetry to be bad. The only thin tall antenna mast I ever put up long term
was a receiving dipole for VHF, based on a thin angle-section scrap peice
from a a very long discarded shop front sign. It was as thin as a reed, and I
figured out that if I guyed it such that the flex above was countered by the
bowing below, then few gusts would ever cause it much risk. It twisted a lot,
but very gracefully, and despoite storm force widns it stood for fifteen
years until it rotted where it stood. The wind never harmed it, but
corrosion eventually did.

On 10/9/2014 3:50 PM, Lostgallifreyan wrote:
rickman wrote in :

Why would the wind tend to twist the ladder? Is your antenna highly
asymmetrical? I would be more concerned by the bending forces which can
be very high if the antenna is a considerable distance from the highest
guying point.

Even if the antenna were not symetrical, that bending would cause enough
assymetry to be bad. The only thin tall antenna mast I ever put up long term
was a receiving dipole for VHF, based on a thin angle-section scrap peice
from a a very long discarded shop front sign. It was as thin as a reed, and I
figured out that if I guyed it such that the flex above was countered by the
bowing below, then few gusts would ever cause it much risk. It twisted a lot,
but very gracefully, and despoite storm force widns it stood for fifteen
years until it rotted where it stood. The wind never harmed it, but
corrosion eventually did.

I think you are getting confused. If the wind makes the antenna bend,
any asymmetry would be along the direction the wind is blowing and so
have no torsional force.

Or are you saying the antenna would bow of it's own weight? That is a
flimsy antenna. I think if you put this on top of a ladder you don't
need to worry about the ladder being the first thing to go.

--

Rick

rickman wrote in :

I think you are getting confused. If the wind makes the antenna bend,
any asymmetry would be along the direction the wind is blowing and so
have no torsional force.


Want to bet? It will oscillate, displacing energy into any possible
motion that is not directly restrained. I ought to know, I sat watching it
often wnough.

rickman wrote in :

Or are you saying the antenna would bow of it's own weight? That is a
flimsy antenna.

Yes. It was flimsy, but so is a reed, and those evolved to live with the
wind. Watch the way grass moves. Those things don't even have guy ropes, my
antenna mast did, so if anything it got an 'unfair' advantage... Obviously
this method won't work for a heavy antenna, but something with little weight,
little displacement off its vertical axis, and little wind resistance
compared to its mast, will work. Just pick a material that is never bent
beyond its fatigue point. Like I said, FIFTEEN YEARS. Storm force winds too.
If I hadn't seen it and done it, I wouldn't be saying it.

I can add a small remembered detail about the point where I added the guy
lines. When I first placed the mast vertical, just to see it that way, I
noticed one major node that tended to stay still, roughly two-thirds up it. I
decided that if I guyed the mast not exactly at that point, but slightly
offset from it, it should damp resonaces in a similar way to the placement
used to damp a guitar string. That way I get the best placement, combined
with enough damping to prevent the oscillations building up to a critical
level. It worked. My neighbours became convinced at around year five, but I
managed to calm their anxieties beforehand.