You also can use Yagi-Mech software from DX Engineering to check Yagi
wind and ice load stresses. It's a little confusing about how to enter
sleeved sections, but other than that it has an ok Windows GUI. It also
only does max element stress analysis - head on wind. I found weak
spots in a couple of commercial designs, not dissimilar to those
analyzed in Leeson's book (out of print but available on Amazon). Both
antennas have shown damage where the software predicted it should first
occur. Pretty good for $39, and it doesn't require much engineering
knowledge.
My A4S is on an exposed (for sure exposure D) 1550' asl ridge top which
slopes directly west to 30' asl. It is across SiVly from Leeson & line
of sight to his Santa Cruz QTH where he has had 160mph gusts. My A4S has
withstood some good blows for 7 years, probably nothing higher than
70-80mph, as a higher station near to me had 85mph gusts. So the A4S
seems like a sturdy antenna but I haven't run it through Yagi-Mech.
Another great resource is wunderground.com, a network of private weather
stations and (if available) years of archived weather data. Enter your
zip code, click on 'station select' and chose a nearby station with
similar terrain and check out the wind history. At my new QTH, the
codes require exposure B, 80mph but from the available thousand yard
away history that is way way over-engineering. That's informative when
considering max antenna load vs tower specs.
Grant KZ1W
On 3/9/2012 1:40 PM, Pete Smith N4ZR wrote:
> This is a very complicated subject for us non-engineers. One
> complication I ran into years ago was that Rohn was quoting their
> windload figures by one standard, while most antenna manufacturers were
> using quite another, which tended to understate the amount of load when
> compared to Rohn's capacity figures. The difference was enough to scare
> me off putting a third small tribander on my Rohn 25.
>
> Thee is a good article on the subject at
> <http://k7nv.com/notebook/topics/windload.html>. He, too, recommends
> the Leeson book, but if you don't have it handy this will get you started
>
> 73, Pete N4ZR
> The World Contest Station Database, updated daily at www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000 and
> arcluster.reversebeacon.net, port 7000
>
> snip
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