Date: Fri, 16 Jun 2017 13:01:10 -0500
From: Patrick Greenlee <patrick_g@windstream.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Antenna & Tower Wind Load Ratings
<A common, easily applied, and often quite effective effective solution
to vortex shedding that is causing element oscillation is a spiral wrap
of a string around the element that is oscillating. The technique from
which this strategy has been borrowed is in common use to protect such
items as smoke stacks and other tall cylindrical structures, albeit not
with string or small cord. Modern automobiles often come with radio
antennas with a spiral wrap.
Patrick NJ5G
## I have seen that spiral wrap trick used on 80m hb 4 square arrays, where
the entire vertical was made from 4 inch al irrigation pipe. Better, but
still
osc a bit. One fellow in W6 land was telling me he also tried using expanding
foam
inside his hb tapered, free-standing 40M vertical. Now that did kill the
vortex shedding dead
in its tracks.
## the f12 eles typ start at .375 inch tips, then increase in .125 increments.
IE typ f12
20m ele uses 7 different sizes..from .375 up to 1.125. Zero vortex shedding,
problem solved,
no rope required.
## An overhead truss line on 40 and 80m eles will generally reduce vortex
shedding to nothing...
when combined with several ele tapers, esp on the last 18-25 foot of each
tip.
Jim VE7RF
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