cable ratings Re: [TowerTalk] Using Belden 9913 on a crankup?

[Jim Lux]

----- Original Message -----
From: "Tom Rauch" <w8ji at contesting.com>
To: "Jim Lux" <jimlux at earthlink.net>; "Bill VanAlstyne"
<w5wvo at cybermesa.net>; <towertalk at contesting.com>; "Ed Kucharski"
<k3dne at adelphia.net>
Sent: Wednesday, April 28, 2004 2:06 AM
Subject: Re: cable ratings Re: [TowerTalk] Using Belden 9913 on a crankup?


> > The rating process probably isn't all that obscure.. it's
> probably laid out
> > in all it's glory in MIL-STD-C17 (I think..)
>
> My points are:
>
> 1.) I doubt you'll find small manufacturers with private
> label cables using the same test methods or standards as
> larger manufacturers.

Not always true. Small mfrs, if they're interested in selling to people who
care about specs and things certificates of compliance (which means people
buying coax for a business), tend to test and rate according to the
standard.  If you were in the coax manufacturing business, the few bucks to
get a copy of the MIL-STD, which defines what all the RG numbers are, for
one thing, would be money well invested.

I've bought, in both personal and professional settings, lots of components
and things from small suppliers, and they've generally had no problem with
understanding and meeting industry standard specs (which, in the case of
coax, would be the relevant MIL-STD).  Oddly, the big problem is with
consumer equipment from mass market outlets (the old "peak music power"
thing).  About a year ago, I wanted to buy foam rubber for bedding, and only
had the requirements for the stuff as originally mfrd in Australia. The
local supplier, though, was able to convert the Australian (and European)
rating system and standards to those used in the US to find the appropriate
material. I have no doubt that the stuff I bought probably meets the specs
for the US standard.
>
> 2.) Comparing one unknown rating method to another unknown
> method by a retailer who shops for small manufacturers to
> supply custom cables isn't a reliable way to make a choice.

My point is that the unknown rating method isn't really unknown, at least to
people who make and sell coax, and shouldn't be to people who buy coax.
Sure, the guy selling reel ends out of the back of a truck may not be aware
of it, nor might the casual ham who buys 100 ft/yr.

This discussion, though, has prompted me to go get the spec and work through
just how those ratings are derived.

>
> 3.) Insisting worse possible case tests set absolute ratings
> in our applications is silly. It just shows how we don't
> understand the ratings.

I agree.  Most hams can take advantage of the healthy margin available from
our expected environments and usage to the rated "must meet" specifications.
Actually, so can most people in most applications, with some awareness of
the consequences.  RG-8/RG-213 type coax is commonly used for HV DC power
cables in laboratory applications at tens of kV, but, presumably, the
experimenter is aware of the actual performance, in their situation, and is
willing to take the consequences if it suddenly fails.  On the other hand,
you'll not find a manufacturer selling that same coax for that application,
if for no other reason than they probably don't control for the ragged edge
of HV breakdown.


Jim, W6RMK