Dealing with improperly designed things is always quite entertaining!
I appreciate all the efforts put forth to do this with antennas their
designers did not understand, because they were office dudes, not
mechanical engineers that climbed towers and had to deal with what they
had actually designed....
I went and spent a bunch of time to go study "Vortex Shedding" , maybe
~15-20 years ago, as I saw it going on everywhere, on all towers, with
almost every existing commercially built antenna.....
When, I finally understood how it worked, it was a no brainer to figure
out how to try to defeat it! That needs to be done in the engineering
office, by someone that understands it!
What is going on is that each size and shape of each antenna member is
going to experience "Vortex Shedding" in the wind speed range physics
decides it will do that with its shape, at the wind speed it will do
that! What is gong on is that wind flow over each section remains
connected on one side of it, and cavitates and becomes disconnected from
it on the other side, this reverses at the necessary low wind speeds to
become reversed from one side of the member to the other side of the
member, after the first displacement movement....so each piece of an
antenna wants to do this at just the right wind speeds each size of
tubing wants to do that by itself!
Configuring these things to not do that is possible....
------------------------------
Message: 4
Date: Fri, 16 Jun 2017 21:22:58 -0400
From: Steve Maki<lists@oakcom.org>
To: towertalk<towertalk@contesting.com>
Subject: Re: [TowerTalk] Antenna & Tower Wind Load Ratings
Message-ID:<4da959b2-e771-8b41-12e9-e86a3b29293e@oakcom.org>
Content-Type: text/plain; charset=utf-8; format=flowed
On 6/16/2017 10:53 AM, Jim Thomson wrote:
Vortex shedding is well known. Eles vibrate up + down like crazy, like 6
Inches in total,
in just a light breeze. Ask anybody who own a 204BA or any wilson product.
Those swedged eles are a pita..and so is
having to put rope inside the eles..which is still in the current Hy-gain
204-BA manual.
While rope in the elements is not what I'd call an elegant solution; it
works, and works well in almost all cases to completely cure breeze
flutter without having to toss an existing antenna in the trash and
start from scratch.
-Steve K8LX
------------------------------
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