K7LXC@aol.com wrote:
> So the newly revised Hy-Gain figures are for ROUND MEMBER PROJECTED
> AREAS?
Yes! To clarify, we know that the Hygain antennas are made with round
members.Hygain has provided the projected areas so they can be directly applied
to
the Rohn EIA tower plans or any other specification.
> And while the antenna figures changed (increased), their application to
> RMPA comparisons did not change?
The antenna figures changed due to 1) new method for finding the max area, and
2)
removing the application of a shape factor by the antenna Mfgr.Need
clarification
of RMPA?
> Aren't all ham antennas (approximately)
> calculated for round members? What method do you use in YagiStress?
Ugh! Ok, Steve, I'll try a really short answer here. I want to get past the
current turmoil before participating in another one. I've got to finish
designing
and build a couple of antennas, instead of talking about them. HI!All ham
antennas
are round membered structures, except for the few who use rectangular tubing
(mostly for little antenna booms).
In MY OPINION, most antenna builders have applied a drag reduction factor to
account for the round members. Some were using my software and some weren't.
So, I
know what some were doing at some point in time. I also don't know what most
were
doing at a different point in time. Why is this important? Because, unless we
can
find out which shape reducion factors each one was using, we don't how to answer
the first question in a meaningful manner. This is because the different spec's
use different factors.
The current discussion about a new standard, which you "made me" think about
(HI!)
proposes that no shape reduction should be made by the antenna guys, so the area
can be applied to any chosen application spec.
> What method do you use in YagiStress?
YS uses the older EIA-222-C method to determine antenna loads. This method used
a
.66 shape factor for round sections and .004V^2 to determine effective wind
pressure.
I have many reasons for using this approach with the software (mostly good
reasons
IMHO!). Some of them open up the discussion I am trying to avoid right now. The
projected areas can be easily obtained from the YS values, just mulitply the YS
area by 1.5 to get the projected area. It also gives the two antenna areas at 0
&
90 Deg, and provides antenna torque for 0 thru 90 deg azimuth. When the industry
figures out it should agree on a standard, the software change will be
fruitfull.
73, Kurt
>
>
> Cheers, Steve K7LXC
>
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