From: Kurt Andress <andresskurt@gmail.com>
To: towertalk@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
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