[TowerTalk] US Tower HDX-55 and Hygain TH11DX

[David Frederick]

After being a ham for 20 years I finally have an opportunity to put up a tower and a beam.  I'm planning on putting up a US Tower HDX-555, and to put on top of the the tower a Hygain TH11DX.  I'd also like to put an OptiBeam OB4030 stacked on the tower at a future date if this is an acceptable load for the tower.  The city I live in, City of Rio Rancho in New Mexico, is in Sandoval county and the county is listed on Champion Radio Products Tech notes "County Listings of Minimum Wind Speeds" as a Minimum Wind Speed of 70 mph.


I have applied for a permit to install the tower with the city. When I applied for the permit I provided a site plan and the Structural Analysis Report from US Tower for the HDX-555  The city has now requested the tower and antenna load information for the initial install.

I need to say that I am not a degreed engineer.  I am an IT professional and have been out of school for quite a number of years, and I'm finding trying to do the load calculations a bit above my head.

I was looking at the US Tower data and see the following -
Basic Wind Velocity:    90 mph 3 second gust, 76 mph fastest mile

Ice:    None

Max. Allowable Antenna Wind Loads (lbs):    389
Max. Allowable Antenna Weight (lbs):    200
Max. Allowable Antenna Wind Area (sq. ft.):    23.4  (All round Members)
Max. Allowable Antenna Wind Area (sq. ft.):    13.4  (All Flat Members)

The TH11DX Manual says the following -
Net Weight:    88 lbs

Wind Surface Area (max):    12.5 sq. ft.
Maximum wind Load at 99 mph:    490 lbs.

So I have a few questions:
1.The tower's Max Allowable Antenna Wind Loads is389 lbs, and the antenna'sMaximum wind Load at 99 mph is 490 lbs.  Does this make the TH11DX to big to put on this tower?  I think the tower is strong enough if properly installed, but am not sure how to convert for the wind speed differences.

2. Which of the Max. Allowable Antenna Wind Area (sq. ft.) numbers do I use?  The round members or the flat members?  And are these at 76 mph?  How do I get these wind speeds to match up?

3. What documentation should I provide to the city?  Are the specs from US Tower and the specification for the TX11DX fro the manual sufficient?  Or do I need to use something like the W9JCC spreadsheet to present the numbers?

Any help is appreciated.
Dave
ARS KQ5M