In a message dated 3/27/2001 05:03:20 Eastern Standard Time,
clive@gm3poi.prestel.co.uk writes:
> Force 12s Tapering may have solved low wind speed resonances, However I have
> a broken shortest 10m Director on a C31XR-H which was rated at 135mph. That
> broke at the junction of the 5/8"and 1/2" tube at wind speeds of 80-85mph.
> At the time I stood under the tower and could hear the another (probably
> 10m ) also in mechanical resonance so this problem still exists. It has
just
> shifted higher in wind speed. F12 don't suggest rope mainly because of ice
> loading. However I will have to do something to upgrade my C31 otherwise I
> can expect it to break again.
It is very difficult to predict mechanical resonances on system like antennas
on the mast, on the tower and rest of the decoration. What might work on mock
up and appear to be safe and free of resonances and vibration, when mounted
on real tower, mast, guying, etc. might happily resonate and vibrate to death
(breakage).
Rope helps to dampen oscillations, it is like hand being there to grab the
element and calm it down. Can't see what sealed rope inside the element have
to do with ice loading.
After having even Telrex elements falling off, no elements without rope here.
Yuri, K3BU
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