Re: [SI-LIST] : What's your favourite Screwy SI Concept?

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From: Doug McKean (dmckean@corp.auspex.com)
Date: Fri Jan 14 2000 - 13:07:04 PST


Lee Ritchey wrote:
>
> Why do people insist on making right angle bends a major
> villian in SI and EMI without some real proof that it is true?

I am asking for data. My previous posts ask if
right angle bends do or do not cause an increase
in "crosstalk". The specific article you mention
does not address "crosstalk".

I am not insisting on anything. The thread is in
the spirit of discussing certain issues within SI
objectively.

Hopefully, this will continue without people becoming
overly emotional. In a professional forum, we have no
use for that type of behavior.

* If there is data that right angle bends do cause an
  increase in crosstalk, then please provide it for us.

* If there is data that right angle bends do NOT cause an
  increase in crosstalk, then please provide it for us.

I have read articles that address EMI and impedance.
But I have not seen real data showing if "crosstalk"
is or is not increased. The only thing I've seen so
far is a simulation by Dr. Bracken of Ansoft that
"suggests" a 0.1 volt level of crosstalk for each
1 volt of signal. That's terribly high.

If it is true that reality follows the simulation, then
someone, I would assume, must have seen it by now. I
can create a hypothetical discussion wherein the geometry
of right angle turns within a bus structure almost demand
crosstalk to follow Dr. Bracken's simulation. But, my own
thinking would be that it's low. And, that's simply hypothesis.

Unfortunately it happens that topics within engineering
are at times forced into the genre of legality. That is,
if one is "accused" of something, the "burden of proof"
is upon the accuser. Otherwise, all is well a good.

Not so all the time in engineering.

One may have to provide proof for NOT doing something just
as one may have to provide proof for doing something.
Simply demanding proof for following a certain practice
probably ignores one whole half of the field of engineering.

If someone is not using a rule simply because there's
no "proof" FOR it's use, I would then ask for data
concerning it's "non-use". Otherwise, it's non-use
simply falls under the heading of "using or not using
some practice without supporting data". - Doug McKean

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