To: | towertalk@contesting.com |
---|---|
Subject: | Re: [TowerTalk] High VSWR |
From: | Grant Saviers <grants2@pacbell.net> |
Date: | Mon, 2 Sep 2019 21:39:11 -0700 |
List-post: | <mailto:towertalk@contesting.com> |
I understand the objectives and mechanics of wind torque balancing of a
beam. Leeson explains how to do this with round elements so it works at
all wind angles. (Physical Design of Yagi Antennas, chapter 6)
However, I don't understand why a counter-weight balanced beam is a benefit other than when tramming the beam and for on the tower work. Could some one explain the dynamic mechanical principles of counter-weighting? It seems to me that increasing the rotational inertia of the beam is a bad idea as it increases the dynamic start-stop load on the rotator. Then a radial top bearing takes care of most of the center of mass offset moment of an unbalanced boom and the rotator can handle whatever is left. When the wind blows the bending moments on radial bearing and rotator will be many times whatever the imbalance mechanical mass moment exerts. And anything that brings the resonances of the boom on both sides of the mast closer together increases the chances of resonant coupling from vortex shedding. Resonances are a very complex parameter to calculate but the reasoning applies. Grant KZ1W _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk |
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