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Author Topic: Rohn 25g  (Read 5078 times)
KM5PS
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« on: August 26, 2014, 10:55:26 AM »

Will a rohn 25g 100' guyed tower support a 2 ele 40 and 2 th5 tribanders or other tribanders
1 tribander on top and other tribander mounted fixed below somewhere, or maybe 3 tribanders.  1 on top with the 40 2 ele and other two mounted on tower fixed east and west.
Trying to decide on using a 25g or 45g.  I know 45g wud work but cost wud be around 5 to 6 thousand for 45g and hardware. 
2nd option wud be 1 40  2 ele yagi and 1 tribander on a 25g tower.  Thanks for any input or thoufhts.

John
Km5ps
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W8JX
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« Reply #1 on: August 27, 2014, 08:08:17 AM »

Will a rohn 25g 100' guyed tower support a 2 ele 40 and 2 th5 tribanders or other tribanders
1 tribander on top and other tribander mounted fixed below somewhere, or maybe 3 tribanders.  1 on top with the 40 2 ele and other two mounted on tower fixed east and west.
Trying to decide on using a 25g or 45g.  I know 45g wud work but cost wud be around 5 to 6 thousand for 45g and hardware. 
2nd option wud be 1 40  2 ele yagi and 1 tribander on a 25g tower.  Thanks for any input or thoufhts.

John
Km5ps

Its not just wind load and guying it for that load but also the twisting torque together with guy loads and tower/antenna weight that can cause it to screw in and collapse. You want Rohn 45 minimum here.  100 ft with one nice tribander would be okay on 25g but that and a 40m beam is pushing it.  Sure you could add torque straps but not a real fix. If you really want all the hardware at 100 feet get 45g. Now two antennas at 60ft of 25g should be okay with proper guying.  I knew a guy that went to 130 feet with old Rohn 20 that I helped erect but it just had a repeater antenna and no torque load and we use a tensionometer to set guy loads too.
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W9FIB
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« Reply #2 on: August 27, 2014, 09:34:59 AM »

The Rohn website has lots of information. I doubt even Rohn could design a system with that much wind load and torque for 25.

I personally would never put that large a load at that height. 25 is just not built for it. If your going to put up a big gun system, you really need a big gun tower. 25 is more for the little pistol systems.
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KM5PS
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« Reply #3 on: September 01, 2014, 06:46:46 AM »

Thanks for the advice.  I think that I am going to try to put up 2 tribander's boom length of 24' and a rotatable dipole for 40 meters above the top tribander.  1 tribander and the top and another one 30 feet below that mounted to  the tower and the 40 mtr dipole about 6 feet above the top tribander.  But that may still be too much torque for the the tower.

Thanks again
John
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W8JX
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« Reply #4 on: September 01, 2014, 07:31:21 AM »

Thanks for the advice.  I think that I am going to try to put up 2 tribander's boom length of 24' and a rotatable dipole for 40 meters above the top tribander.  1 tribander and the top and another one 30 feet below that mounted to  the tower and the 40 mtr dipole about 6 feet above the top tribander.  But that may still be too much torque for the the tower.

Thanks again
John
[/quote/]

It is at 100 feet. Unlike vhf/uhf you do not gain that much above a certain height.  60 gives you a 1/2 wave on 40 and 1 wave length or more above ground on 20 and above and it will play well.
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K8KAS
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« Reply #5 on: September 04, 2014, 01:45:18 PM »

I had a 2 El 40 and a Th6  on 68 foot of 25G with a set of guys at 45 feet . It was good until one of the guys broke during a squall
and it made a big bang and all was lost.. Why do you need 100 feet of tower, I never went higher that 65 feet from then on and worked everything I could hear all over the world one or two calls..1500 watts helped...73 Denny K8KAS
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WB2WIK
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« Reply #6 on: September 04, 2014, 02:37:41 PM »

For that kind of load I'd go with 45G.
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KL7CW
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« Reply #7 on: September 09, 2014, 09:47:22 AM »

It is much easier to climb and work on 45 G tower, especially if you have large (size 12) winter boots.  Also mounting a rotator inside 25G can present some challenges.  I would go with the 45 G if you can afford it, or simply downsize your project.  My towers are 25G, but my antennas are much smaller.  Your proposed antennas will present much torque and huge wind and other forces to the rotator, thrust bearing, tower, and any mast which extends much above the top of the tower.  I would design all components with a considerable safety margin, especially in windy or areas with ice loading.  Rotators and masts rated at over twice any expected load would not at all be overkill for large high antennas.  If you opt for the large antennas, get some professional design and installation help. I am not trying to discourage you from putting up a large high antenna, but am just suggesting that it will be expensive, but money well spent to do it right. I have seen rotators the size of a 2 drawer file cabinet torn apart by long boom LPA antennas whipping in the wind.  My recollection was that the rotator was rated for at least several times the wind load presented.  Perhaps you do not have winds like we do up here in Alaska.
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K1ZJH
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« Reply #8 on: September 10, 2014, 08:27:09 AM »

You can use torque arms on the 25G at the guy points. Those will stiffen the rotational torque that the tower can withstand.

But, if I had the choice, Rohn 45 would be a no brainer.

W8JI made a comment once that he consider Rohn 25 to be expendable for his antenna projects. Most of us have thin pockets and going the cheaper route may not be cost effective in the long run. It looks like you are planning a sizable and costly array, I would not go cheap on the support structure.

Pete
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KM5PS
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« Reply #9 on: September 12, 2014, 06:04:36 PM »

I would like to thank everyone for there comments.  I will consider it all before putting up the tower.  My plan now may be to just put the two tribanders on 1 tower and the forty on a tower by itself.  Not for sure yet if the forty will be a 2 element or just a rotatable dipole.  Thanks again.  Does anyone know of any Rohn 45g tower for sale close to Harrison, Ar?  Have found plenty, if I want to drive 8-12 yrs one way to pick some up.  Shipping is very high, even though I work for a freight company.  Thanks again.


John
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