In a message dated 99-11-03 16:20:28 EST, k4wa@nuc.net writes:
> I've just acquired enough Rohn 25G to consider putting up a 75' (or so)
> guyed tower. While waiting for my Rohn catalog (it's on its way - ed) to
get here, I downloaded
> some information off the Rohn site. Ideally, I'd like to put up a 40-2CD,
> but I'm not sure it makes sense here just nine miles from the Gulf of
> Mexico. Looking at Rohn's 110 mph guy and load specs (though surely the
> beam wouldn't survive that wind), I saw two numbers for load at top,
"round"
> or "flat." Call me stupid, but what does "round" and "flat" refer to?
> Which category does the 40-2CD fall into? It makes a difference, since the
> antenna is rated at 6.38 sq.. ft.
This is a topic that still doesn't have a single, standardized answer.
The purist engineering-types want to use a standardized "projected area" for
antenna windload and tower capacity. While I agree with them, unfortunately
almost no manufacturer uses this in their sales literature.
If you *really* want to be conservative with your tower loading, use the
6.38 sq.ft. against the flat figure. You might want to calculate the actual
projected windload by finding the total square footage of the boom and
elements and use it against the flat figure. Personally I'm still using the
round figure as an approximation since antennas are round cylindrical objects.
> And am I being optimistic thinking a
> 40-2CD will work in a hurricane-prone area (even though we were lucky this
> year), or am I throwing my money to the wind?
It'll WORK just fine. Whether or not it'll survive is another question.
CC doesn't list a wind survivability figure in their catalog so I'm going to
guess that it's +/- 80 MPH. The new XM240 is rated at 90+ MPH and it is
mechanically MUCH stronger.
Yes - I would put it up and use it. Replacing it in case of hurricane
damage is the purpose of insurance. It's been pointed out before that the
antenna might survive the wind but the *real* damage is done by other objects
that are flying through the air.
>
> Also, my used tower sections come in two sizes; I have five 10' sections,
> and three 7' sections. Is there any magic in how I stack these differing
> sizes, i.e., 10 footers first, then sevens, or does it not matter?
Nope. As long as the guys are in the right places on the tower, it
don't make no never mind.
>
> My first effort to install a "real" tower, as opposed to an old, small
> crank-up, so I apologize for my lack of experience.
>
No problemo, Senor. We've all been there. And that's why there is a
TowerTalk - so people can get answers to their questions that ultimately
result in a safe, reliable and fun tower and antenna installation.
There's no such thing as a dumb question so don't be shy.
Cheers, Steve K7LXC
Champion Radio Products
http://www.championradio.com
Tower Tech
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