[TowerTalk] Antenna & Tower Wind Load Ratings

[Jim Thomson]

Date: Sat, 17 Jun 2017 23:10:47 -0700
From: Kurt Andress <andresskurt at gmail.com>
To: jim.thom at telus.net
Cc: towertalk at contesting.com
Subject: [TowerTalk] Antenna & Tower Wind Load Ratings

>Jim,
>I'm so glad to hear you know everything and have it all under control!
>This means this reflector does not, and never has ever really needed me!
>I will silently back out of here, I obviously made a really big mistake 
>by making my posts here, and will leave it all to you, to go out there 
>and make everything right in the World for those that need that.

>73, Kurt, K7NV


##  Kurt,  Im not trying to be a smart ass or anything.   Im still  slogging through
the 222-G, trying to understand it all...then..trying to compare 222-G  to everything 
before it..including the UBC specs.   Thats a tough slog.   I have been building yagis
since 1972, so I have been around the block a few times, including installing  5 towers
for myself..and aprx 6 more for other folks.  I experienced ice...once.  .4 inch thick.

##  I understand your points completely, but how is any yagi manufacturer supposed to
know what exact application his yagis  will be used in ?   Toss in heights ranging from
say  40-200 ft, then  exposure specs  B-C-D.  Then topographic categories 1-2-3-4-5. 
Then from fastest mile wind speed..with one type of gusts....to the 3 sec gust method. 
Then   return periods called  class 1, with its 25 year return period,  Class 2 is 50 years,
class 3 is the dreaded 100 year return. Each return period has its own importance factor.
Ice used to be two types,  glazed and rime.   Now its Glazed only, no more Rime ice. Then
the  25-50-100 year return stats for ice.   Then  3 x site classifications  1-2-3 based on 
importance... knock over a few bales of hay,  or kill  your neighbours by their pool. 
Then Seismic loads....and seismic loading + Ice.   Then 6 types of soil.  

##  On your excellent website,  under ..windloads, it compares the various specs..except
222-G.    Correct me if Im wrong but the basic YS software uses  222-C.   The Pro version
of YS does all the other specs..except 222-G ? 

Under your notes section ..under windloads  http://k7nv.com/notebook/topics/windload.html
I found the following  below.....which is my whole point.  How the heck is any yagi manufacturer 
supposed to spec anything.   Each yagi  would have to have  dozens and dozens of various combos
of specs.  That will confuse joe ham..esp when  he then trys to compare  several brands of say a 40M yagi. 
And no software exists to depict eles inclined to the wind...aka tips bending, shedding wind..and reducing the
load on the yagi..and tower..and mast.   By how much, who knows ?     I suspect a bunch. 

Jim   VE7RF


There is a fundamental problem with trying to use either the later EIA or UBC spec (or similar others) for general consumption antenna design. Both of them require a specific antenna height and/or a siting factor to develop their loads. I doubt that antenna manufacturers are going to design all of their antennas for every conceivable height and/or exposure with each spec.  If there is already some confusion about what to do with existing antenna figures, adding 20 more figures per antenna is not likely to make things easier.

EIA-222-C using its zones and wind speeds, while not the most current approach, is easy to use and provides reasonable results. It is actually quite conservative for many of the UBC scenarios.