In message <b9.c9433c1.27f1fbaa@aol.com>, K3BU@aol.com writes
>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).
Just a thought (well, more of a query really)....
Is it somehow possible that the mechanical resonances in the elements
could feed through to the mounting bracket on the boom and cause some of
the rivet failures F12 have had with some of their antennas? For those
who don't know what I'm talking about, I'm referring to some of the
failures in the rivets that hold the element brackets to the boom. I'm
trying to figure out what caused this (so it can be prevented from
happening again) and was wondering if resonances could have been a
contributing factor (in addition to them using the wrong rivets)?
Andrew Williamson GI0NWG / AC6WI
Homepage = http://www.gi0nwg.freeserve.co.uk/
One of the ZL9CI gang
http://www.qsl.net/zl9ci/
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