In a message dated 99-07-25 09:06:39 EDT, wa4dou@excite.com writes:
> 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.
> 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.
> 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?
Sounds reasonable to me. I assume that you're looking in the Rohn
catalog at drawings A871302R1 and A871266R1.
What you're really looking for is the distance from the top housebracket
to the top of the tower. That's the amount of naked exposed tower that's
allowed to be above the housebracket.
BTW, Wilson County is an 80 MPH windspeed zone and you're within 100
miles of hurricane oceanline so you might want to design everything for 90
MPH wind survival or higher. Your proposed installation is pretty modest so
you don't have much reason to worry. Thirty feet of free-standing 25G will
also handle your installation @ 80 MPH so having a housebracket is the
(recommended) belt-and-suspenders approach.
> Or is there some practical
> data to be found somewhere other than the Rohn catalog?
No more practical data is available. All of the housebracketed and
self-supporting specs for 25G, 45G, 55G and SSV/RTP are in a handy little
Rohn pamphlet titled "Manufacturer's Technical Information for Bracketed or
Self Supporting Towers". It's available for an SASE from Champion Radio
Products (Box 2034, El Macero, CA, 95618).
Cheers, Steve K7LXC
Champion Radio Products
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