--------------------------------------------------
From: "Robert Harmon" <k6uj@pacbell.net>
Sent: Wednesday, September 29, 2010 3:11 PM
To: "Jim Thomson" <jim.thom@telus.net>
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Motorized UST tower... very smooth and dead
> The HDX-689 is rated for 60 sq ft not 50 sq ft.
>
> It has twice the capacity of the HDX-589.
>
> Bob
> K6UJ
>
>
### I have both stress analysis spec sheets, which depict abt 8 x wind
load ratings Which
one do you want ?
## In a 70 mph wind, they rate it at 62.5 sq ft IF the ant eles/boom are
>2" OD
and 50 sq ft is els, etc. are 2" or less in OD. Both those are based on
PROJECTED AREA
OF A CYLINDER ! They rate the flat eq at 38.5 sq ft. [ effective
projected area of a cylinder, factoring
in the drag coef ].
## be careful here. F-12 /M2 etc rate their ants in the flat eq of a
cylinder IE: effective area.
F-12 calculates the projected area of all the ele's, adds em up , then
multiplies by .67
## The point here is..... don't assume you can put up 50 sq ft of F-12
ants, you cant. I'd use the
38.5 sq ft flat rating of the HDX-689. Rohn rates their towers in EPA
[effective projected area/flat area eq], which
is a smart move.
## In the past, ant makers quote effective area, cuz it makes for smaller
numbers. Tower makers will quote
projected area's, cuz they end up being bigger numbers. Both methods are
legit, just don't mix them up.
On some yagi's, the quoted sq footage is way out to lunch. Most of the yagi
mech stress programs will
give you the effective area of all the els...and also the boom.
Jim VE7RF
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