[TowerTalk] Wind Antenna Damage

Phil Snyder n9lah at comcast.net
Sun Apr 20 16:58:51 EDT 2014

I have a stack on my tower that consists of, from bottom to top, an 
XR-5, EF-606, 2M9SSB, 424B and a dual band vertical at the top. I have 
always been of the opinion that I want the antennas to face into the 
wind. With the short elements on the U/VHF antennas, I figured there is 
less windload/resistance from the elements then there would be with all 
those long booms being broad side to the wind. I would be glad to take 
suggestions on a better scheme, but no one has suggested differently yet.

  Phil Snyder
*Get the new WUST award from the Metro DX Club

/*On 4/20/2014 1:53 PM, Dan Hearn wrote:
> Recently I lost a 6l 20 yagi in a windstorm when my power went off and I
> could not rotate it into the wind.
>    Some time ago I wrote a short note to post on our www.sdxa.org web page
> under articals which explains how to minimize this problem. Here it is.
> Parking Your Yagi – by Dan, N5AR <http://www.sdxa.org/?p=16>
> Does it make a difference which way your yagi is pointed during a
> windstorm? Of course it does. There are different opinions on this subject.
> Here is mine.
> You must first decide what you are trying to protect, your tower, your
> yagi, or your rotator. Minimum tower wind loading occurs when the yagi
> presents the least area to the wind. This will usually be at some angle
> other than boom end or element end into the wind. Several articles have
> been written about how to calculate the optimum angle using trigonometry.
> Yagis seldom have equal spacing between the elements and the directors are
> always shorter than the reflector so a yagi oriented as above will see
> quite a bit of element and boom flexing as well as intermittent torque
> loading on the rotator.
> Yagis are typically clamped to the mast at their center of gravity (balance
> point). Since the directors weigh less than the reflector, this is not the
> center point of the boom. If the boom is positioned broadside to the wind,
> the yagi will swing left and right as the wind varies, causing variable
> wind loading forces on the rotator gears and brake if it has one. This can
> be taken care of by adding additional wind loading on the short side of the
> boom. This can be a plate or extra boom material. This technique has been
> the subject of a paper by Dick Weber, K5IU.
> I prefer to point the end of the boom into the wind. The elements are the
> same length left and right so there is no variable torque on the rotator
> and the boom during wind surges. The majority of the wind loading is then
> on the elements. The wind here is usually from the southwest so I leave my
> beams pointed that direction unless unusual conditions prevail. If someone
> has a better solution, I would like to hear about it.
> 73, Dan, N5AR

Phil Snyder
*Get the new WUST award from the Metro DX Club

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