Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!gem.mps.ohio-state.edu!usc!trwind!johng
From: johng@trwind.UUCP (John Greene)
Newsgroups: comp.dcom.lans
Subject: Re: Req For Info - Ethernet Electrical Rules/Specs
Message-ID: <580@trwind.UUCP>
Date: 5 Oct 89 20:26:44 GMT
References: <188.2526de30@acci.com>
Reply-To: johng@trwind.UUCP (John Greene)
Organization: TRW Information Networks Div
Lines: 24

In article <188.2526de30@acci.com> ta2@acci.com writes:
>
>1) Why can't you use 75ohm cable for thin ethernet?

You would be creating an impedance mis-match with the Thin Ethernet transceiver.
This will cause relections on the cable (transmission line) and distort the 
signal.  The problem may not be noticed with a small number of nodes and short
cable lengths but as the number of nodes increase and the length of cable 
increases, so will the trouble.
>
>2) Is is legal to run a pigtail of two or three feet from the
>   base of the BNC T to the Ethernet card?

This is a definite no-no.  Not only would you be radiating all over the place
(an FCC taboo) but you would cause an even more severe mis-match than if you
used a 75 ohm cable.  The impedance of the pigtail will depend on the thickness
of the conductors and the distance between them.  The cards would probably not
work with a pigtail an inch long let alone two or three feet.
>
-- 
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