Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!dogie.macc.wisc.edu!decwrl!vixie!avsd!childers
From: childers@avsd.UUCP (Richard Childers)
Newsgroups: comp.dcom.lans
Subject: Re: Grounding Ethernet coax lines.
Message-ID: <2140@avsd.UUCP>
Date: 10 Oct 89 22:55:47 GMT
References: <3824.25292578@zeus.unl.edu> <2128@avsd.UUCP> <27682@amdcad.AMD.COM>
Reply-To: childers@avsd.UUCP (Richard Childers)
Organization: Metaprogrammers International
Lines: 71

rpw3@amdcad.UUCP (Rob Warnock) writes:

>Wrong. A given Ethernet (thick or thin) *must* be grounded *EXACTLY ONCE*,
>no more, no less.  To do other wise can *increase* your noise problems or
>even -- are you ready for this? -- melt your cable!

Hmm. The thin ethernet cables I'm familiar with all have two ends. Neither
end is distinguished from the other. Both have the coaxial braid firmly
attached ( grounded ) to the connector ... I don't see how you could only
ground it ONCE. It has to be connected to two devices.

>Remember, the original question was talking about between buildings. I have
>seen situations where there are MANY [is >10 many enough?] volts difference
>between two adjacent buildings, and if you ground an Ethernet at both ends
>you have just attempted to short out that potential difference.

I can see how that might be a problem, but that would seem to require that
the equipment be grounded, separately. ( In any case, I don't think ethernet
belongs between buildings, I think that's a job for fiber optic. )

>... "As designed" there is *NO* ground! Which is correct!

Here's my understanding of [thin] ethernet :


	------------------------------------------------------------	[1]
	============================================================	[2]
	------------------------------------------------------------	[1]

	[1]	coaxial cable, external braid, reference voltage
	[2]	coaxial cable, shielded inner conductor

... where the data is conveyed via [1], and said data is kept from being
radiated by [2], which is grounded.

[1] connects to the transceiver. [2] connects to the transceiver, perhaps the
case, but the transceiver, nonetheless.

This is a complementary situation to that found in RS232, where

	1	is frame ground, and
	7	is signal ground

... and while you may or may not need [1], it being optional, [7] is mandatory,
as There Can Be No Signal Without (some sort of) Ground.

>| It wouldn't hurt to go find a book on antenna theory and / or ground loops,
>| if you're interested in getting into ham radio or are really dedicated to
>| network management, as I have heard ethernet being explained successfully
>| as an insulated antenna ...

>Sounds like you need such a book, yourself.   ;-}

I have a lot of things to read. _The C Language_ is at the top of the queue,
right now ... I haven't seen anything addressing the needs of networking
support personnel, though. Any suggestions ?

>Sorry to be so harse, but you gave some really bad advice there...

Fair enough. But I'd really like to know what I'm not understanding.

>Rob Warnock
>Systems Architecture Consultant

-- richard

-- 
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