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@gmail.com>
> To: <towertalk@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
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|