Hi Paul,
I believe there are two possibilities as to how rope would dampens element
vibration. One is that it may add enough mass to lower the resonant
frequency of the assembly to a value which is not going to cause fatigue.
The second is that it may add enough internal friction to the assembly to
cause any vibrations to rapidly decay.
Regarding rope, a few of my older Hygain (pre-MFJ) monobanders used a soft
nylon rope with many small strands which made the ends easy to fray to slip
the end caps over. I use nylon clothes line rope as a replacement which is
very similar. The original old style plastic end caps seemed to generally
hold up pretty good - I do not know what they were made of. The caps that
MFJ shipped last time I bought replacement hardware IMHO are junk - they
appear to be made of very low density PE which split easily and fall off
easily. I do not use them, but instead found some nice quality resilient
nylon caps from McMaster Carr which work very well - part number 9753K43.
There are a number of other popular recommendations that have already been
made in this thread.
Hope this info is helpful & good luck on your project.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Paul N1BUG
Sent: Monday, August 29, 2022 6:25 AM
To: towertalk@contesting.com
Subject: [TowerTalk] which rope for element anti-vibration
I'm trying to get a better sense of how the rope in elements to stop
vibration thing works. I've read that it works because as the element swings
in one direction, the rope slams against the opposite side, providing a
counter-force. What confuses me is that I don't understand how the rope is
free to move around. Nylon or polypropylene seem to be recommended but those
ropes come coiled or folded and they have a memory effect, so they don't lay
flat. When put inside an element, they are going to be pressing against it
in multiple places and directions. It seems like that would limit the rope's
ability to move to do its job.
What am I missing? I have seen braided rope with extremely fine strands that
is soft and doesn't have the memory effect. Is that what I should be using?
My 6 meter yagi was having a problem. The element tips were oscillating at
about a ~200 Hz rate, and the tips were moving at least two inches!
It took four trips up the tower to rig and get it down. It will take another
four climbs to put it back up, and more if it still has a problem and needs
to come down again. I'd like to try to get this right on the first try to
avoid all that extra climbing. The four foot center section of each element
is .750" OD, with .625" tips. Any practical tips or experiences with similar
elements would be appreciated.
Paul N1BUG
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