While living in the Seattle area, I had an A3 at 50-feet on Rohn 25, with 2
house brackets. I had about 30 feet of tower above the top bracket.
I never had a problem and we did have a few stiff breezes in that area in
the winter. Breezes that took trees down.
FWIW,
73, K7JJ
Dave Earnest
k7jj@home.com
http://www.members.home.net/k7jj
----- Original Message -----
From: Bill Coleman AA4LR <aa4lr@radio.org>
To: <wa4dou@excite.com>; <towertalk@contesting.com>
Sent: Monday, July 26, 1999 12:55 PM
Subject: Re: [TowerTalk] Housebracketed Rohn 25G
>
> On 7/25/99 9:05, wa4dou@excite.com at wa4dou@excite.com wrote:
>
> > Am building a housebracketed Rohn 25G for my 6 meter yagi.
> >It will only be 31 ft. high. The yagi will be a couple feet higher. My
> >bracket is at 10-11 ft. off the ground. Windloading will be about 2.5 sq.
> >ft. I'm guessing it should be safe at 80-90 mph.
>
> I'm no mechanical engineer, but memory serves that Rohn 25 should be
> practically self-supporting up to 40 feet (with no antenna). 2.5 square
> feet isn't a really large antenna.
>
> > Anyone noticed that Rohn never specifies these towers below 40 feet,
and
> >they always call for 2 housebrackets. The tower above the top bracket is
> >either 10 ft.higher, 14 ft. higher, 24 ft. higher or 34 ft. higher, as
the
> >tower approaches 100 ft.
>
> I've scrutinized these drawings myself. You'll notice really quick how
> the allowable antenna area diminishes with the height of tower above the
> bracket.
>
> > Am i correct in my assessment that below 40 ft. one must draw
conclusions
> >based on inferred info found in the data mentioned above and in the
> >freestanding data and interpolation of same?
>
> Rohn always shows two brackets, but the brackets are always more than 10
> feet apart. Given the rigidity of one section of tower, I doubt that a
> second bracket in a 11 foot span is going to do much. So one bracket is
> probably all that's needed.
>
> The main question is how safe is the 31 foot installation with 2.5 sq
> feet of antenna? Steve's already given you the wind speeds for your area.
>
> I'd approach it like this. Think of this short-bracketed installation as
> something between a free-standing 31 foot tower and a free-standing 20
> foot tower (minus the 11 feet below the bracket).
>
> I don't have a catalog, but it seems like Rohn 25 ought to be able to
> hold 2.5 sq feet of antenna in a free-standing 20 foot height at an
> appreciable wind speed. Your installation would be somewhat less than
> that.
>
>
>
> Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@radio.org
> Quote: "Boot, you transistorized tormentor! Boot!"
> -- Archibald Asparagus, VeggieTales
>
>
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