In my previous post on the subject I failed to mention that the element tip
failures did have the ropes inside. When the first failures occurred the
repair included adding ropes to the elements. The ropes did improve the
vibration problem but more failures occurred after the ropes were installed,
but more infrequently. At the suggestion of Dick Weber, K5IU the tip weights
were added and all failures ceased. My tower is probably a worst case
situation in that it is almost 200ft tall and is guyed with Phillystran. Wind
exposure is as bad as it gets in this part of the country and we have seen
winds over 90mph in spite of the 70mph in the zone chart. Goes to show the
need to use the new EIA standards that take wind exposure and height into
consideration.
On a subject related to the vibration discussion, many of my element tip
failures occurred near the end of the second tubing section where the swage
ended. It appeared that the swaging process may have work hardened the
material to excessive brittleness and actually lead to the failure. None of my
homebrew beams, 2 full size 3-el 40m and a full size 3-el 80m use swaged
elements. These three antennas were designed using stress software and have
been up for over 10 years with no element failures at all, including the above
mentioned 90 mph winds. Needless to say, I am a believer in the stress
modelling software and a non-believer in swaged elements!
Many thanks to the Texas Towers customers for your continued support through
the year. We greatly appreciate your business and look forward to serving you
in 1999 and beyond!
73 de Gerald Williamson, K5GW
Owner/General Manager, Texas Towers
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