[TowerTalk] Rohn 25G - Exposure B - 90 MPH - 70' - JK Mid Tri

[w4nf at comcast.net]

Hello and HNY,

 

I haven't posted here since I put my first tower up in 1999 that is still
doing fine.  I am considering a second tower of Rohn 25G at 70' with a
single JK Mid Tri.  Looking at the Rohn Spec sheets, I am interpreting that
I am in an Exposure B area - Characterized by urban/suburban areas, wooded
lots, or terrain with many closely spaced obstructions (like houses) that
slow wind down.

 

The JK Mid Tri has the following specs:

 

JK Mid-Tri

 

Approx wt. = 98 lbs

Wind Area "C" = 10.6 Sq. Ft

                  "G" = 19.06 Sq. Ft

Projected Area = 16.0 Sq. Ft

Max Wind Speed = 100 Mph

 

The Rohn 25G 70' specs shows a 19.4 Sq Ft Allowable Projected Area.

 

A google AI search on the JK specs had the following:

 

*	Wind Area "C" refers to the antenna's wind area calculation based on
the older EIA/TIA-222-C standard (or similar older standards like UBC-97).
This standard uses the "fastest-mile" wind speed to calculate wind pressure,
which is an average speed over a distance of one mile.
*	Wind Area "G" refers to the antenna's wind area calculation based on
the newer, more conservative TIA-222-G standard. This standard uses the
3-second gust wind speed, which is a measurement of the peak instantaneous
wind speed, resulting in a higher (and generally considered more accurate
and safer) calculated wind area for the same antenna.

Should I be using the JK Wind Area or Projected Area to determine if the 25G
is sufficient to support this antenna at 70'.

 

Thanks for any assistance and HNY,

 

Jack W4NF