On May 9, 2009, at 5:56 PM, RICHARD SOLOMON wrote:
>
> I have a chance to get a Rohn 25 Fold-Over Tower, looks to be about
> 50'.
>
> I would be putting a couple of VHF & UHF Verticals on it. Can I get
> away
>
> with not guying it ?
Absolutely NOT!
Rohn (ca. 1987) allowed ordinary Rohn 25 to go to 40 feet unguyed only
if the antenna load was under 1.5 square feet and the wind speed 70
mph or less, with no ice.
For 90 mph, Rohn drops the max unguyed height to 30 feet. Again, with
no ice. I'm certain their specs haven't gotten less stringent in the
intervening 20 years, and the tilt-over assembly certainly doesn't
help; if nothing else, the added weight is additional downward
compression on the leeward leg(s). Also, there have been revisions to
the EIA wind speed specs and maps. Check your county's rating.
> It will be next to the house and somewhat protected
It really needs to be guyed or house-bracketed right below the hinge.
I decided figuring out a way to house-bracket it without interfering
with either the counter-balance or the beams when the top half of the
tower was horizontal was beyond my pay grade so I always stuck with
the 4-way guying specs from Rohn.
I have found that a real good rule of thumb is assume you're going to
have to guy it at the point where you're nervous putting the next
section up without temporary guys. For Rohn 25, that's 30 feet or
less in my book.
Bud, W2RU
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