[TowerTalk] Wind Noise

[Michael Tope]

I don't doubt that putting the rope on the outside is more effective, 
but I have just never seen or heard of anyone doing that with a Yagi. 
What diameter rope would be sufficient. What would be the pitch of the 
turns (I am picturing a helical wrap). Any downsides?

73, Mike W4EF...................

On 3/15/2021 8:08 PM, Al Kozakiewicz wrote:
> Around the outside is considerably easier as well. The antenna was assembled on the ground and hoisted into place with me alone on a bucket lift. Getting to the element ends would require either a lot of acrobatics standing on the roof, or spending another $400 to rent the lift again. That was the single most expensive element of the tower construction last fall even though everything was purchased new except for the rotor and C3.
>
> The elements are tapered so I can't use that formula.  The longest are 1.000 down to 0.375. When I first heard the noise I thought it was construction equipment working up the road, but there is nothing going on up there. 4-500hz sounds about right. In the winter especially, we get  40 mph winds from the west whenever a nor'easter passes by.
>
> Thanks!
>
> Al
> AB2ZY
>
> -----Original Message-----
> From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of Lux, Jim
> Sent: Monday, March 15, 2021 8:52 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Wind Noise
>
> On 3/15/21 4:54 PM, Al Kozakiewicz wrote:
>> I appreciate all the suggestions.
>>
>> I don’t think isolating the tower from the house is possible. Yes, I can slip some rubber or other material between the bracket and the house, but I probably over-engineered the anchors. They consist of threaded rod passed through the header in the gable end of the house along with two of the roof trusses. It is rigidly fixed with nuts and washers on each side of every member the rods pass through. The bracket is bolted to the rods.
> In general, you're better off preventing the oscillation in the first place than trying to isolate it once it's there.
>
>
>> Rope through the elements sounds like the way to go.
> Rope around the elements (on the outside) is far more effective at
> killing the vibration.  Inside just damps it, but the forces are still
> driving it and the mass just changes the resonant frequency. Around the
> outside stops the oscillation.
>
>
> Do you have an estimate of the vibration frequency? That can help you
> figure out what is vibrating.
>
>
> F (Hz) = 3.26 * V(mi/hr) / d (inches)
>
> For instance, a 1" diameter tube in a 10 mi/hr wind will shed vortices
> at about 33 Hz
>
> Typically, aeolian vibrations are most noticeable in mild winds (10
> mi/hr) - when the speed gets up higher, you often have turbulence or
> gustyness so it can't excite the "resonator" as well.
>
> However, anyone who's been in a high wind (>40 mi/hr) can tell stories
> about wires and cables singing (or screaming), during the gusts too..
>
>
> 0.25" at 40 mi/hr is 521 Hz - and that's pretty noticeable.
>
>
>
>
>
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