Posted: Fri Jan 07, 2005 5:58 pm Post subject: Antenna on winds
Hi all,
I´ve been always supposing that when wind is strong you should head the rear part of your yagi to the wind direction. But recently on a ham forum, someone have said that this could be not a good idea. Most of the guys on the forum have replied to this guy telling he´s completely wrong on his coment but would like to know what´s your opinion about this and why. 73!
Fernando 30AT239
30at239@dxhunters.com
Please read your message again because I dont know if you wrote it on purpose or maybe you just misunderstood directions, anyway, what I´ve always belived is that while strong winds, you should point the driven element of your antenna towards the wind so that the antenna opposes minimum resistance against the wind.
On the other hand, if you direct your antenna 90 degrees against the wind, what you are doing is showing the boom to the wind with the effect of possibly damaging the rotor´s bearins as well as finding the boom in two pieces after the storm.
I have always pointed my yagis towards the wind during storms, if you do that, you will realize how better the elements and boom react and behave.
Both of you are right. And this what I´m supposed to do under heavy winds. It looks simple if you use your common sense. Thanks anyway, cuñao and Juan. 73
30AT239 Fernando
30at239@dxhunters.com
Regarding this old subject, I found out this tip on the web. As far as I read, Carlos and Juan were right. Here you have:
____________________________________________________________
Parking Your Yagi
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.
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