Alan,
Think also in terms of magnetic fields, or "area loops".
The area defined by the small loop between signal lines and
ground lines now have rather opaque metal plates over them.
Starting around 10KHz the conductive "shield" kills all
the magnetic fields coming out. Which were probably more
significant than the E-Field contributions.
- Robert -
On Thu, 15 Sep 2005 16:22:31 +0100
"Hudson, Alan" <[email protected]> wrote:
> G'Day!
>
> Came across an oddity today which has failed to stimulate
> any memories (from
> about the time the old King died!) of basic
> electromagnetic theory. A
> well-known computer Company supplies what it calls
> "shielded ribbon cables".
> When we examine one of these we find it's essentially a
> metallic braid
> sleeve around a standard ribbon cable. The braid isn't
> connected to anything
> (not even a drain wire at the connector ends).
>
> So what level of shielding is this going to give - if
> any?
>
> I could imagine signal lines being capacitively coupled
> to the braid and
> then capacitively coupled to any 0V lines in the ribbon.
> But I can also
> imagine signal lines being capacitively coupled to other
> signal lines.
> Similarly with external signals hitting the braid - they
> could go to either
> the signal or 0V lines - yes/no?
>
> I know I should know the answer to this, but obviously,
> today at least, if I
> had a brain I'd be dangerous!
>
> :-)
>
> Regards,
>
> Alan
> --
> Principal Engineer,
> BAE Systems Limited,
> UK
-
2005 IEEE Symposium on Product Safety Engineering
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