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Author Topic: Antenna in the Wind  (Read 2433 times)
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W1QWT
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« on: October 27, 2006, 08:33:42 AM »

I think this qualifies as a tech question since it is about antennas.
I have never had a yagi until now. I have a 3 element six meter beam and above that a 5 element 2 meter beam and above that a 6 element 432 MHZ yagi. All horizontally polarized. These are all on a guyed 35 foot mast.
We are supposed to have a big wind blowing here along the coast this weekend and I got to thinking about them 'Blowin in the Wind'.
IS it best to point a yagi array into the wind, let the wind blow broadside to the array, or don't worry about it.
I was trying to figure out which orientation would have the least wind load.
Figured those of you who have had yagis for years would have a handle on this.

Regards
Q, W1QWT
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WA1GFZ
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« Reply #1 on: October 27, 2006, 09:49:31 AM »

I think facing the wind would the least resistance.
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K1JJ
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« Reply #2 on: October 27, 2006, 11:53:35 AM »

Hi Q,

Well much has to do with the size and length of the elements as compared to the boom. In some cases, the boom can be MUCH longer and heavier than the eles. Or, like a 2 el 40M full-size or 2 el 75M full-size, an occassional design may have the boom of less wind resitance than the eles. The only way to really find out is to let it swing in the wind and see how it "weather-vanes". But this is impractical. 

In your case as described, I would agree with Frank and point the array elements into the wind.

At one time I had a broken rotator on my 30' boom 7el 6M Yagi and got to watch it swing like a weather vane for a few months. It always sat with the elements broadside to the wind.

Now some think that becuz the eles all line up in the horiz plane that the wind sees JUST one element in effective wind loading. This is not entirely true since the wind can come from many different vertical directions in gusts, so at times you may have the acummulative effect of many elements in wind loading.

In Pacific coast Calif and Scotland, the guys lose Yagi antennas to broken booms because of severe updrafts that want to flip the antenna over. Just imagine a big Yagi that is overhead trussed for gravity with no under-trussing in a situation like this.  This happens to guys on cliffs that have severe wind shear from updrafts on the hills, etc.

But generally, the rule is that whenever there is a Nor'easter coming, face your Yagi into the wind like a ship... Grin

T
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flintstone mop
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« Reply #3 on: October 27, 2006, 12:23:42 PM »

WOW!
I hope your guying system is up to the wind and the load of those Yagis. I realize these are not 40M Yagis but there is a lot of windloading on that mast. Time for a 60 foot tower.......................hi
Fred
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n3lrx
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« Reply #4 on: October 28, 2006, 02:34:40 PM »

Although you lived your life like an antenna in the wind
your balun burned out long before your signal ever did..

Sorry,
Elton John's Candle in the wind came to mind! Cheesy
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W1QWT
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« Reply #5 on: October 29, 2006, 01:03:59 AM »

Quote
Although you lived your life like an antenna in the wind
your balun burned out long before your signal ever did..
I'm Irish, I got no balun!

Well I just got home from a wedding I went to up in Jackson N.H.(North of N. Conway)
Man what a ride, 3.5 hours back to Scituate MA.!
First thing I did was to check the array and I must report that it is 'ok
fine business'. As some of you mentioned I pointed it into the wind direction.
I heard we had 60 MPH gusts here. I know we lost electricity cause all the digital
cocks were blinking.

Well the antenna array is still up.

Regards
Q, W1QWT
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K1JJ
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« Reply #6 on: October 29, 2006, 10:18:03 AM »

Glad everything is intact.

Yes, the wind was brutal here too. I'd guess it was 60 mph and even stronger than a few days ago.

Two of my new 6M Yagis at the top got spun 90 degrees... looks like they need a few more U-bolts clamping to the tower leg. It's interesting how the wind gusts in narrow vertical bands. Evidently there was a strong gust between 160'-180' -  while the other stuff was untouched.

T

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flintstone mop
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« Reply #7 on: October 29, 2006, 11:57:41 AM »

OK FB
I did the K1JJ thing on my Yagi Aerial and there was less rockin and rollin of the elements pointing directly into the wind. We had some huge gusts here yesterday, musta been around 60mph. Today we're still gusting up to the 40 mph mark.
G'day
Fred
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WU2D
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« Reply #8 on: October 29, 2006, 10:30:46 PM »

Crash at 2:00PM today - I lost the 20 foot mast on the roof which supported the house portion of my inverted L- it landed safely in the garden without destroying my roof. Must have been one hell of a gust. I had just been up there removing the 6M beam two weeks ago and I checked the guys. That system has been up there for 15 years with no issues. But the system was not good enough for this storm. The aluminum guy wires could not take it.

The inverted L is destroyed as well from the trees. I did manage to get a 100 ft longwire thrown up into a tree, so I am not completely off the air.

Looks like antenna work ahead next weekend - if the weather will settle down!

Mike WU2D
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K1JJ
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« Reply #9 on: October 29, 2006, 10:47:57 PM »

Wow, that's quite a shake down.  It's actually good now instead of in Jan.

I've been wondering what would happen if we got 1/2" of ice and the wind blows like that. It's been a few years since we've had that combination.

I can always tell unusual WX by taking a walk in the woods and looking for limbs on the beverages. It's a cleanout out there too. I cringe to think what I'll find tmw when I take a walk...  Yaz and I'll carry out some patch wire, the torch and solder knowing the score.

T
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flintstone mop
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« Reply #10 on: December 15, 2006, 05:30:24 PM »

Sorry to bring this to the top of the list again BUT I made a discovery with my Cushcraft A3S Yagi blowing in the 40mph wind.
I / We thought pointing the Yagi INTO the wind would give the aerial a better ride. My discovery was the opposite effect! I pointed the antenna broadside to the wind ( Wind blowing out of the West, I pointed antenna to the NORTH) there was a lot less rockin and rollin of the elements and less motion from the boom and yankin on the poor rotor.
G'day
Fred
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K1JJ
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« Reply #11 on: December 15, 2006, 07:11:50 PM »

Hi Fred,

Interesting.

Back a few posts I mentioned that some Yagis with short, thinner  booms will have less wind resistance with the boom sitting broadside.

To take an extreme example... a Yagi that had 36' long elements and a tiny 2' boom would have less resistance with the boom broadside. But if that same boom were increased to 30' and made fat, it's the opposite.

Two ways to find out are to use "YagiStress" software and model it, or let the Yagi swing free in the wind and watch.  I suppose the manufacturer can tell you too.

I notice here that MOST Yagis like to face the wind, but a few are the opposite. My 40M Yagi with a short 28' boom and 75' long elements would probably ride best with the boom broadside to the wind, like yours. Sometime I'll let it free and see.

73,
T
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Yaz's dream sailing adventure:
http://www.youtube.com/watch?v=Dc8GI6RR_f0
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