> -Unless you have high confidence in the product you are buying _and_ you
> understand the your operating conditions, you need to over-rate your
components.
> That means that a $30-40 PVC thingy might not be a good idea for your
multi-KW
> transmmission line. [In a conservative system design, you might require
that
> components should survive a serious fault, like an open or shorted antenna
> connection - or at least fail safely.]
It's way extreme beyond what's needed for ham gear, but, in the spacecraft
business, the usual requirement is demonstrated capability with 4x rated
power (actually twice voltage and twice current, so you could get it with a
open/short/transmissionline at rated power). Analysis might work if testing
isn't feasible, but your analysis would need to be fairly rigorous.
>
> -Everybody uses PVC, but PVC is not known for its ability to dissipate
heat, and
> it makes pretty nasty smoke. Is there a better design? Open air? Water
cooled? :-)
PVC should work just fine, if designed appropriately.. (the IF is the
important word)
>
> -Some 3rd party should be doing destructive testing on QRO items. This
could be
> fun for the right person! Burning attic anecdotes are nice, but it's an
> inefficient way to learn about products.
Perhaps manufacturers should publish their design analysis that backs up
their rating claims? The initial thought is that you're going to be
revealing trade secrets, but, I think that none of these products have any
special magic in their design. What you're really paying for is that
someone else is scrounging up the parts, assembling it, keeping them in
stock, shipping it to you (or to HRO,AES,etc) in a nice box. This is
definitely worth something (nobody's time is really free, if nothing else.).
If someone really does have a magic design, then (theoretically) they can
patent it, and keep others from manufacturing it for 17 years (I say this
somewhat cynically... having been involved in some patent infringement
lawsuits over the years).
>
> -The line isolator product is available from at least 3 vendors at about
the
> same price. MFJ's product info says _nothing_ about power handling
ability.
> The W2DU unit (radio-ware.com) claims 10 KW PEP at 10 MHz and 2:1 VSWR.
What's a
> fella to do?
Oh yeah, theoretically, that retail price also covers some liability
insurance to cover the mfr of the device when it doesn't perform to spec,
burns down a house, and it's traced back to the device. I am fairly sure
that Chuck's insurance company would do the forensics, find that the fire
originated where that isolator was, and attempt to recover some of their
loss from the manufacturer. The net result would be unhappiness all around
(Chuck would never get the full value back, the mfr probably would have
insufficient resources anyway, and lots of people would spend lots of time
responding to paperwork of one sort or another), but, at least the mfr would
theoretically learn to be a bit more forthcoming and responsible.
But, to answer Martin's last question: What's a fella to do? A fella is to
challenge the mfrs on their specs. A lot of mfrs catering to the amateur
market seem to play a bit fast and loose with the specs , particularly when
it comes to max power ratings and antenna gains. If they can't substantiate
it, get larger organizations to stop them from advertising (i.e. do they
advertise in QST? what about the FTC?). Don't be complacent, don't assume
someone else is going to take care of it. In my mind, what separates a
real business from someone making stuff for their friends and acquaintances
is the acceptance of the responsibility that comes with selling a product to
the general public. That responsibility implies real analysis, real
testing, real disclosure, etc., and, it doesn't come cheap.
Jim, W6RMK
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