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Re: gEDA-user: basic anti-EMI design q

At 07:52 25-3-2006, you wrote: 
On Fri, Mar 24, 2006 at 06:03:04PM +0100, Bill Sloman wrote:
> At 12:52 24-3-2006, Karel Kulhavy wrote:
>
> >On Fri, Mar 24, 2006 at 11:04:04AM +0100, Bill Sloman wrote:
> >> At 05:21 24-3-2006, you wrote:
> >> >DJ Delorie wrote:
> >> >
> >> >>It's not the drivers that mess up, it's the octal latch.
> >> >
> >> >
> >> >if the existing latch is in the interface with ribbon cable to the
> >> >PC  - there's your problem.
> >>
> >> Have you grounded every second wire in the ribbon cable? It sounds
> >> extravagant, but if you need shielding, that's a commonly used way of
> >> getting it.
> >
> >It isn't. If it were, there would be no rule that UTP cables should be
> >put min. 20cm apart from power lines.
>
> Unshielded twisted pairs being used where and for what purpose, Karel?

Czech Republic, Ethernet.

>
> There are so many possible explanations for this requirement, in so
> many possible contexts, that it seems unlikely that this "rule"
> actually supports your claim.

What other explanation comes to your mind apart from interference
problem?

Lightning protection. As Robert Metcalf pointed out early on, the people who developed local area networks didn't have a clue about lightning protection, so that virtually every every early local area network was put out of commission by a local lightning strike early in its history. These days, the people who write the specifications for local area networks still don't have a clue about lightning protection, but they do know that lightning is a problem, so they write in all sorts of hyper-cautious rules.

Note that a classic Ethernet has galvanic isolation between the cable and the computer it is serving, and can have an extent of about 1.5 km (a mile in the U.S.A. where the used to cover an entire campus).

--
Bill Sloman, Nijmegen