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From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.dcom.lans
Subject: Re: Why Ethernet-over-twisted-pair, anyway?
Message-ID: <2230037@hprnd.HP.COM>
Date: 1 Dec 89 17:40:18 GMT
References: <4645@blake.acs.washington.edu>
Organization: HP Roseville Networks Division
Lines: 32

johnl@n3dmc.UU.NET (John Limpert) writes:
> 
> Is anyone besides me concerned about the RFI/EMI vulnerabilities
> of twisted pair?  I see enough problems with non-existent or poor
> shielding in current business/consumer electronics equipment.
> Is your LAN going to collapse every time someone keys up their
> radio?  Is your LAN going to blanket the area with RF garbage?
> 
> -- 
> John A. Limpert			I'm the NRA!
> Internet: johnl@n3dmc.UU.NET	UUCP: uunet!n3dmc!johnl
> ----------
When we initially looked at 10 Mbits on twisted pair, this was
one of our first concerns.  The 10BASE-T committee looked at
susceptability including noise measurements on inplace wiring
in actual buildings.  We also looked at susceptability to 
crosstalk from other services on twisted pair.  RFI and the
ability to meet requirements of FCC, VDE, and others was 
investigated, as was interference with other services on 
twisted pair.

So my answer is: Given good design practice, a 10BASE-T LAN will
not "collapse every time someone keys up their radio" and will
not "blanket the area with RF garbage."  Twisted pair is a balanced
media and performs fairly well as far as RFI/EMI.  It is limited
in length due to attenuation and crosstalk.

Given poor design practice, anything can emit.  I had a 1200 baud
modem at home which interfered with my 2m (~144 MHz) handitalkie
if it was plugged in, transmitting or not.

Pat Thaler