From: dnichols@d-and-d.com (DoN. Nichols)
Subject: Re: Ribbon cable ?
Organization: D and D Data, Vienna VA
Distribution: rec
Date: Sun, 10 Jan 1993 03:40:58 GMT

In article <PAISLEY.93Jan8102544@mars.asc.slb.com> paisley@asc.slb.com (Gary Paisley) writes:
>
>	More than a few months ago in this news group, a poster
>mentioned He was going to wire his studio using ribbon cable. 
>
>	I have the opportunity to do the same, but I was
>wondering about the results.
>
>	Seems like the stuff would have lower capacitance for
>making RCA connections than single conductor shielded cable, and
>thus better high frequency characteristics, but what is the downside ?
>(More noise ?)

	Well, it acts like a transmission line, so it should be driven and
terminated with sources/loads of its characteristic impedance.  How much of
a problem this would be at audio frequencies I'm not sure.

>	I also have a sample of 26 conductor with a foil shield
>around the ribbon. How would this work as a 13 pair balanced cable ?
>Would Adjacent channel cross talk be a problem here ?

	Well, I've never used this cable for audio purposes, but for digital
use, standard practice is to ground every other line to act as a shield
between active conductors.  for your use, I would think that you could
ground the first pin, use the next two as a ballanced pair, ground the next,
use the next two ... and ground the last, so for N circuits, you would need
(3*N)+1 conductors total.

	You would perhaps be a little better off with differential pairs
using the twisted-pair ribbon cables, but I have not seen shielded versions
of them yet.  (The twisted pair stops the twist about once every foot or 18"
and runs straight for about two-three inches so an IDC-style connector can be
crimped on, rather than having to solder all the individual wires.)  It
would be nice if every other time the twist stopped 180 deg. out of phase
with the start, but then it wouldn't work for the connectors that it was
intended for. You *should not* ground every third wire in this case, and the
main question is whether the 2" out of 12" running parallel will accumulate
to enough crosstalk to be a problem.  That depends on your running length,
maximum frequency, impedance, and required S/N ratio.

	I believe that I have seen makers offer zipper-sealed shielding for
existing ribbon cable, so that could perhaps be combined with the
twisted-pair cable for your needs.  The shielding jackets also add a *lot*
of abrasion resistance to the cable, and a lot of mass.

	I have also seen ribbon coax cable, which is *quite* expensive, and
the connectors designed for use with them are a little more difficult to
utilize.

	There is at least one maker who offers woven ribbon cable, which is
made up with conductors of your choice (coax, shielded twisted pair, power,
control, whatever) with an insulator woven back and forth across the cable
to bind everything into a ribbon shape.  This might be useful when you need
to run a mix of types of wire to multiple locations, but I have no idea what
the set-up charge is for a run.  They try to make it sound affordable, but
that is in publications aimed at volume manufacturers.

	Good Luck, and please post your results to the net.
		DoN.

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