[SI-LIST] : Question about Thin Flexible Coaxial cable

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From: Jerry Martinson ([email protected])
Date: Fri Nov 10 2000 - 15:25:05 PST


I need to skew some clocks on a board to correct a minor clock skew
issue with a prototype that I have. Actually this situation comes up a
lot in the lab where you want to skew a clock or a net a nanosecond or
so to verify that some intermittent error is or isn't from a setup/hold
violation on a
certain bus, etc... To me the obvious choice (assuming no roboclock) to
skew things around a bit in the lab is to use a small length coaxial
cable cut to the appropriate length. The problem is that most coax
(even RG174) is pretty hard to work with because it is so thick and has
this gnarly braided shield that is a real pain to solder with. Despite
the best efforts
of tinning the shield, half the time these little braided strands fall
off and do interesting things between the pins of fine pitch PQFP's.
All I need is a small length of cable so I don't really care about
having really good cable but it is nice to have the beneficial
properties of using coax rather
than a unshielded wire.

I used to work for a company that had a huge spool of this wonderful
micro coax wire that was perfect for the job. It had blue (Teflon?)
insulation and had a foil shield with a wire running with the shield
that could be easily soldered to the closest ground. It has a very
elastic di-electric.
The cable was very flexible and maybe 2mm in diameter. It was nominally
50 ohms and maintained pretty good SI for TTL at lengths of up to 2m
before the signal distorted significantly. It was great for debugging
all sorts of nasty problems because it was so easy to work with that it
would only take 1
minute to change the length of the cable on a prototype. I wish I would
have written down the manufacturer of that cable before I left that
company because now I'm trying to find a coax company that carries this
stuff. I've searched the catalogs (Belden etc...) but I couldn't find
anything that matched this description.

Does anybody know where I could find this micro coaxial cable that I'm
describing is or does anybody have any other suggestions for doing some
lab skewing?


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