At 07:39 PM 6/15/2005, WarrenWolff@aol.com wrote:
>When checking out which antenna will survive the harshest
>of threats, pay all the attention to the experienced fellows
>on here----not the manufacturer.
>
>Years ago, I had some fancy UHF antennas put on top of
>100 meter towers in Kuwait. Only rare, really rare, times would any ice at
>all show up there, but the wind blows. These antennas were
>rated at 100 mph by the US manufacturer. After just a few months,
>we found a piece of aluminum element on the ground - - - more to
>follow in days.
>
>The Minister of Defense requested/demanded that I produce test
>sheets from the manufacturer to verify that I/we had not short
>changed them! Well, they did NOT have any. They had put these,
>the ruggedized versions, together by the seat of their britches.
This is, in general, true of all things sold into the amateur/consumer
market. The price isn't high enough to pay for real testing, even of a
preproduction prototype. I cringe to contemplate what it would cost to do
wind survival testing for a HF antenna. Even doing it the "cheap way":
bolting it on the back of a flatbed truck and driving into the wind at a
sufficiently high speed.
The only practical alternative is to see design calculations that shows
that if manufactured properly, it will stand up. And then, you have to have
sufficient "visibility" into the manufacturing process to tell if it is
doing what's expected. On commercial construction projects, for instance,
they require certified welders, and sometimes require X-ray inspection of
critical welds, as well as test coupons. Likewise, that's why they take
samples of the concrete from the truck for testing.
Most manufacturing tests for consumer equipment is more in the nature of a
functional test, rather than a performance test. That is, does it light up
when you apply power? Do some of the buttons work? And if they do a
performance test, it's unlikely they'd supply the test results (or even the
test procedure, for that matter) to the eventual purchaser. For most
manufacturing companies it would be a trade secret anyway.
So this is why it's wretchedly expensive to buy things for airplanes and
spacecraft. Those buyers tend to be a bit more demanding and less trusting.
They want to see "physical artifacts" of the manufacturing and test
processes: documentation of processes; documentation of test results; etc.
>
>Bottom line; I had to replace/rebuild them at my cost. Manufacturer
>would not stand behind them according to my Purchasing Dept. I
>had to pop for $1000 per antenna times two per tower times 10
>towers. My company? Lockheed Aircraft Service Co; the supplier?
>Phelps-Dodge, if I recall correctly. My chief engineer has passed
>on or I would ask him. Probably a mute point now; Saddam stole
>the whole system.
>
>Good luck in your survey, Warren; W5KKW
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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