Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!ginosko!usc!trwind!johng
From: johng@trwind.UUCP (John Greene)
Newsgroups: comp.dcom.lans
Subject: Re: Grounding Ethernet coax lines.
Message-ID: <586@trwind.UUCP>
Date: 11 Oct 89 16:00:35 GMT
References: <3824.25292578@zeus.unl.edu> <2128@avsd.UUCP> <27682@amdcad.AMD.COM> <2140@avsd.UUCP>
Reply-To: johng@trwind.UUCP (John Greene)
Organization: TRW Information Networks Div
Lines: 21


For those of you that are still interested, the IEEE 802.3 specification 
addresses this subject.  It states that for thick Ethernet, the shield should
be 'earth' grounded at exactly one point.  Connectors should be insulated to
prevent accidental grounding at more than one point.  It also says that this
only applies to cable contained within a building.  Outsides runs are beyond
the scope of the specification and need "special" consideration.  All 
transceivers are to be AC grounded to the shield in such a way that it has a
high impedance at 60 hertz (> 250 k-ohm) and not greater than 15 ohms between
3 MHz and 30MHz.

One small point on the 75-ohm cable subject: most transceivers that I have 
seen "sink" current from the cable rather than "source" current into the
cable.  But hey, what's a little minus sign amongst friends? ;-)


-- 
John E. Greene    "People are just like frankfurters....You have to decide
                   if you're going to be a hot dog or just another wiener" DLR
TRW Information Networks Division 23800 Hawthorne Blvd, Torrance CA 90505
ARPA: johng@trwind.ind.TRW.COM  USENET: ..trwrb!trwind!johng