[TowerTalk] Antenna & Tower Wind Load Ratings

[Jim Thomson]

Date: Fri, 16 Jun 2017 13:01:10 -0500
From: Patrick Greenlee <patrick_g at windstream.net>
To: towertalk at 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