[TowerTalk] Guy rope damping

Wed Apr 30 18:22:22 EDT 2008

Try a couple things like utilities do to dampen vibrations... 

Tie a fishing weight or a big nut, a couple ounces should do, on a short
rope, just a couple inches, and put it a few feet up the guy from the anchor
point... the exact weight and distance may vary the effectiveness, if you
can put it where the rope moves the most that would have the most effect.
The idea is not to attach it solidly to the guy but to let it move to absorb
the motion.

Wrap another rope in a spiral around the guy rope, if the vibration is from
air moving over the guy rope and not from the vertical vibrating this will
break up the vortices that cause the vibration.

Instead of tightly tying the 2 guys together try tying a rope or bungee cord
between them a few feet up from the anchor, again where they move the most
would be the best spot.  This may cause one to fight the other and dampen
the vibration.  Tying it too tight will just change the resonance point.

Add a piece of pipe a few feet long on the bottom of each guy.  Again the
idea is to let the pipe move around the rope to let it absorb the energy
before it gets singing... kind of a backwards version of putting ropes in
yagi elements to damp vibrations.  Make sure the ends are smooth so they
don't chew on the rope though.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of AI1P Matt Steven
> Sent: Wednesday, April 30, 2008 21:19
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Guy rope damping
> 
> I'll try to get some more info out, thanks for the ideas so far.
> 
> It's possible that the source of the resonance is the vertical itself,
> the vibrations extend to all ropes simultaneously though at different
> frequencies.  Since two of the guys sets tie into the far end of the
> garage I don't have to listen to those often.
> 
> There are 6 total guy lines.  It's guyed along three sides, with two
> levels of guys per side (low ~35' long, high ~45') and I have added a
> few "tension connections" made with short lengths of wire between the
> two guys on each side near the bottom to try to break up the resonance a
> bit, but it still comes through.  Think of a short wire hooking the two
> guys together into a tighter angle for a short run to visualize this.
> 
> The lines are as tight as I can pull them to keep a lot of downward
> pressure , I did it this way after reading about guying in an old
> Antenna Book, but that info related more to towers than verticals.  So I
> may loosen them to lower the resonant frequency to reduce annoyance but
> it will likely still vibrate some.  I would guess that such vibration
> would wear the rope out a lot faster than if it were dampened and I'd
> rather avoid that.
> 
> The vertical is a MFJ-1793 which is basically a series of aluminum tubes
> about 35' high with (in my case) four opposed 1/8" diameter aluminum
> roughly 18" spokes on the top for a capacitance hat.
> 
> The rope is nothing serious, a hardware store poly/nylon blend stranded
> type 3/16" or 1/8".  There's not a lot of wind load with this sort of
> antenna so I wanted to keep it light.
> 
> 
> Dan Kovatch wrote:
> > Matt, I don't know if this will work but it should. Somewhere on the guy
> > in at least 2 places put an insulator -just run the rope through
> > it-don't cut the rope. Wrap tape around the rope so the insulator will
> > stay in place. You want to break up the resonance of the rope so if it's
> > 30 feet put one at 11 feet and 18 feet from the top or bottom. You don't
> > mention how much rope is involved but it does seem strange to hear of it
> > vibrating. Are you sure the vertical isn't sending an ocillation into
> > the rope? I use the black covering rope here and have never had any hint
> > of ocillation or wind noise.
> >
> > Good luck
> > Dan W8CAR
> > ----- Original Message ----- From: "AI1P Matt Steven" <KD0BVK at gmail.com>
> > To: <towertalk at contesting.com>
> > Sent: Wednesday, April 30, 2008 2:05 PM
> > Subject: [TowerTalk] Guy rope damping
> >
> >
> >> Hello,
> >>
> >> I have a vertical antenna on a rooftop tripod that is guyed with
> >> stranded nylon rope.  The rope naturally gets vibrating very heavily in
> >> wind probably due to its uneven surface and it really can sing.
> >>
> >> The problem is that the house hook it ties to is anchored (necessarily)
> >> to a roof joist for support and these vibrations transfer right into my
> >> bedroom making for plenty of banshees on windy nights.
> >>
> >> What I've tried so far to dampen it:
> >>
> >> 1) Wrap the anchoring hook very thickly with electrical tape.
> little/no
> >> effect
> >>
> >> 2) Use scrap coax to absorb some of the vibration on the string as it
> >> comes in, before it touches the metal of the hook (acts as padding
> >> basically) little effect, the coax redirects some of the vibration but
> >> not enough to notice.
> >>
> >> 3) Same as 2 but running the actual tie-off to further down the roof,
> >> and just having the hook as a guide point.  Not much effect.
> >>
> >> I can't afford Phillystran or anything really nice like that, so that's
> >> out of the question, but is there any way to stay on the cheap and at
> >> least get the vibration to stop resonating in the rafters?
> >>
> >> 73s,
> >> Matt
> >> ai1p
> >> _______________________________________________
> >>
> >>
> >>
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> >
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> 
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