Hi Everyone,
Seems time for me to open my big mouth and get into a bunch of trouble
again!
The "What small Tribander..." electrical discussion has wandered to
"flexible" vs "Brute Force" and "Ice" mechanical questions about how
antennas handle various load cases.
Don't even go there, if you aren't prepared to pursue the answers on
your own!
Software is available to model these questions and provide the answers.
The empirical/anecdotal experiences of subscribers will help you guess
at the answers.
If you have the same conditions of someone who has had a Brand X antenna
survive the same condx, then buy what he has!
The antenna manufacturers generally don't provide enough accurate
information to allow you to make these decisions. Many of them are using
antique & obsolete methods of determining simple antenna properties,
such as "Effective Area."
Everyone challenges the electrical performance claims, so they work on
addressing these issues.
Since, nobody challenges the the mechanical values, they do nothing and
everybody goes on happily accepting the nonsense. There are some
commercial builders who claim 100 Mph survival, when it is actually less
than 70 Mph! Of course, you guys have to wait to hear from someone who
has suffered a failure to think it might not be so good. Then, try and
guess what it all; really means!
If you are prepared to ask the question, be prepared to answer it for
yourself, you'll not get it from the antenna suppliers!
The simple, answers to the recent questions are:
Small flexible elements are better in warm, dry climates. The elements
flex and unload themselves during high windloads.
In the Ice Kingdom, the larger elements do better, because they need the
greater section moments to carry the ice loads. During high ice loading,
the ice weight overshadows the wind loads.
Don't say that one fellow "brute forced it" when you don't understand
the problem!
Hamdoom has firmly entrenched in it's mind that small flexible elements
are "weak." This fairy tale has been fed by several, notable "experts"
who have claimed the same.
Strength and stiffness are two different things! They happen to be
related, but are not the same.
Most people rate the strength of an element by its sag. A drooping
element is "weak" by conventional wisdom.
I can show you a 10 Mph element, that is constructed with .001 In thick
wall material that doesn't sag very much, and makes everyone think is
must be strong, because it doesn't sag very much!
Another element, good to 100 Mph will sag, "Too Much," to be acceptable
to the masses.
Again, the software is available, make up your own mind about how to
make a decision.
Designing by conjecture is really fun, because you can get away with
anything!
73, Kurt
--
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress
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