[TowerTalk] Antenna Windload Ratings & Tower Windload ratings

[Jim Thomson]

From: Kurt Andress <andresskurt at gmail.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Antenna Windload Ratings & Tower Windload ratings

<All of your antenna builders have absolutely no idea of what those 
<standards are! Few, if any of them, have mechanical engineers capable of 
<understanding those requirements....they are amateurs building what they 
<think you will decide you will buy....that is marketing, not engineering!

<And on top of that, few of the antenna suppliers and tower designers 
<actually define the antenna area measurements their products 
<service...... are they projected areas, or are they effective areas? 
<These are all defined in the EIA/TIA 222 spec....I know what they are 
<for each tower builder, because I have been into their detailed design 
<analyses. They are usually citing antenna projected areas! What are your 
<antenna builders citing? Rohn engineers are very clear about what they 
<are citing!
<I have lots  of analyses of commercially built amateur antennas, made 
<from their own manuals, most all of them are simply WRONG, and not the 
<least bit useful for deciding what can be put on a current 
<professionally designed tower!
<73, Kurt, K7NV

##  Hy gain + mfj,  M2, Mosely, F12  STILL use the 222-C spec.  
IE: projected area  X  .67  = effective area.    When  f12 sez an ant is
6.7 square feet, its actually  10 sq ft of projected area.   UST uses projected area,as does
all  other tower makers.     I mentioned this several times before in past posts.  Hams end up 
overloading their towers  cuz they are using 222-C effective area instead of projected area. 

##  IE:  tower rated for say  ..... 30 sq ft of  projected area.     Joe ham stuffs  30 sq ft of effective
area yagis on  said tower.   Joe hams  30 sq ft of ants  is actually  45 sq ft of projected area. Tower is
now overloaded  by  50%.  

##  Optibeam  +  JK antennas  both use projected area.   JK antennas uses the basic formulae 
of  wind velocity...IE:  max sustained gust in mph,  squared....   X  .0256 .... X projected area X .8  

##  DXE, with its ..yagi mechanical software calls that..... No wind spec.   Thats supposed to be what
you would get in a wind tunnel. 

##  DXEs  yagi mechanical software lists  several wind specs on its drop down boxes.   Other than
no wind spec, and the  222-C  spec, every other spec requires a height to be entered.  How the heck is
an ant maker to know what height  joe ham will install his yagi at ?

##  DXEs...yagi mechanical currently provides a choice of.....

-No wind spec
-EIA-222-C
-EIA-222-F
-UBC-97 Exposure B    
-UBC-97 Exposure C
=UBC-97 Exposure D

##  Pick one !   The no wind spec basic  formulae IMO, is plenty good enough...its more stringent
than the old  222-C spec.   Then I can add my own safety factor.  

###  222-F  comes out identical to the UBC-97  Exposure C   for a height of 100 ft.  

##  a generic  20M Reflector, using the various above 6 x standards..and all at 100 ft...  comes out to...
-100 mph
-107.5 mph
-78.7 mph
-94.3 mph
-78.5 mph
-72.3 mph  

##  The only way I can see the above 20M REF  being rated at less than the ...no wind spec, is to
make that the ..basic wind speed, then build in a huge gust factor..that varies by height and some ones 
version of a gust.

Jim   VE7RF