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Author Topic: Rohn Rooftop Tripods  (Read 577 times)
KB0ETC
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Posts: 248




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« on: August 02, 2003, 09:47:23 PM »

Anyone have any experience with rooftop tripods, especially the Rohn 10' model.

I can't find any specifications anywhere on it, even Rohn's site.  They are inexpensive, but need to know if they will support my antenna system.

So I would have a 10' tripod on the roof of the house, and probably a chrome moly 15' mast.

Antennas: 6 band quad, 3.1 sq ft wind load.  Diamond X-500HNA 17' repeater antenna, Diamond discone, and obviously a rotator - perhaps a HAM IV.  I would like to be able to add a 6m, 2m, and 70cm directional antennas too someday.

Are these things as strong as a 10' tower section.  They seem to have climbing braces that bolt onto the side.

How hard is it to keep the roof sealed after you seal the lag bolts that are screwed into the roof trusses?

Do you need to guy the tripod?  Debating if a full-blown tower project is in the budget.  Would love to have one, but can't find any used ones is the area and for a good price.

Thanks for any information and your experience with the tripods.

73's
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N6AJR
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Posts: 9888




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« Reply #1 on: August 03, 2003, 02:29:42 AM »

wow, that is a load.  I would not use the tower for any thing bigger than a small tri bander, slightly above the top of the tripod.  

This is a tripod not a tower section. you need to mount it to the roof structure ( rafters with lag bolts) seal it with goo,  and probably guy it too. You are looking at a huge wind load with all that on there and probably a lot of interference between them.

 spread it out, either use a "real" tower or a couple 3 push up poles and spread it out a bit ( ground mounted and gyued and possibly attched to the edge of the roof too.)

 hope this helps, its what I would do
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KT8K
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Posts: 1490




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« Reply #2 on: August 04, 2003, 12:39:44 PM »

I never use the lag bolts.  I drill through the trusses and put in high strength aircraft bolts (sometimes need to slightly enlarge the holes in the tripod feet) with large fender washers on both sides and 3/4" x 10" x 4' plywood strips across the trusses in the attic.  Then I liberally cover the tripod feet with roofing tar and clamp a run of at least #6 copper to the tripod length, running to a buried 8' ground rod as near as possible.

That said, you should check with Rohn about the load-bearing capacity of their tripod.  It sounds like you want to put an awful lot on it, and the wind is going to pull on that thing like a mack truck.  

I usually use only a 5' tripod anyway - they are easier to work on, and the 5 foot difference doesn't hurt my signal much at all.  That way I feel safer without guying them.  With a heavy load like you are describing, you would almost certainly have to guy it, but I would consult Rohn first.  The telescoping masts might be a better idea, if you can't actually put up a tower.
Good luck de kt8k - Tim
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WB2WIK
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Posts: 20542




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« Reply #3 on: August 04, 2003, 01:37:58 PM »

I prefer the Glen Martin Engineering model RT-936 (or even the RT-832) to the Rohn tripod.  Reasons:

-They're all aluminum construction, with a well-trussed design that is very strong but quite lightweight.

-These are four-legged designs, not tripods.

-They spread the applied load over a greater portion of the roof.

-Either of these models is fully climbable (use a climbing belt for safety!).

-These products have a rotor shelf bracket included by design, and heavy-duty thrust bearings are available that take all the weight off the rotor and transfer it to the tower, making the rotor's job easier and making rotor installation and maintenance a cinch.

-I've used them numerous times with zero problems, including some loads that are actually larger than the one you describe.

-They come complete with excellent installation instructions, including complete, detailed instructions regarding reinforcing the roof and precisely how to affix the roof tower to the roof for minimum damage and maximum strength.

-After several years, they tend to still look brand new, as the aluminum never degrades.  (They also come with all stainless steel assembly hardware, which remains shiny forever.)

-And, they require no guying at all.  There would be no reason to guy one of these.

WB2WIK/6

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W4CYM
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Posts: 5




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« Reply #4 on: May 04, 2006, 08:45:48 PM »

Well, you guys have got me headed the right direction it appears. It's a decently small discone antenna made by MFJ. It's pretty light so I'm wondering if the rooftop tower is a bit of overkill. But then again, I've never done this before so it may be the perfect solution.
Thanks for the info!
-Ed W4CYM
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