Jim;
I've learned quite a bit from you, and have a question about what you
are saying here.
On Jul 7, 2005, at 8:48 AM, Jim Brown wrote:
To gain the benefits of the twisting, use one pair (orange and
orange/white, for example) to connect pin 2, with orange to pin 2 and
orange/white to pin 5. Likewise, green to pin 3, green/white to pin
5. The
overall shield should go to the DB9 shell on each end, not to pin 5.
If you are using UN-shielded twisted pair, connect the return of
each pair
to the DB9 shell, NOT to pin 5. This puts a "band-aid" on pin 1
problems
on each end.
We have gone out of our way in the RS-232 cables to avoid ground
loops by not connecting the DE9 shell at one end (or in the case of
the KIO2 cable, both). I have also seen this technique described
(reference Bob Heil's web page), indicating that it is best to leave
the computer end of the shield unconnected. So my question is why the
suggestion to connect both ends here? Why doesn't this create the
very ground loop problem we are trying to avoid?
Thanks. My engineering career has taught me that grounding, like RF,
is magical - I continue to learn things about it that change my way
of thinking.
- Jack Brindle, W6FB
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