Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!hsi!stpstn!lerman
From: lerman@stpstn.UUCP (Ken Lerman)
Newsgroups: comp.unix.sysv386
Subject: Re: Wiring terminals 300 ft. from the computer
Message-ID: <5619@stpstn.UUCP>
Date: 28 Sep 90 11:31:10 GMT
References: <11774@bsu-cs.bsu.edu- <1990Sep19.083601.21364@pilikia.pegasus.com> <1142@atti07.ATT.COM> <1990Sep25.052558.11002@chinet.chi.il.us> <3927@segue.segue.com>
Reply-To: lerman@stpstn.UUCP (Ken Lerman)
Organization: The Stepstone Corporation, Sandy Hook, CT 06482
Lines: 17

[...]
->Not exactly nothing.  Try this experiment at home, hook up about 200-300 
->feet of twisted pair to the RD and TD pins of your favorite 9600 baud 
->terminal.  Leave the far end disconnected (this is the trick).  Now type 
->something on the keyboard.  The last time I tried this the unterminated 
->cable run magically echo-ed every character as if it was really attached 
->to a host port.  Can you say "inductive coupling"?  
->-- 
->bruce@segue.com, ism.isc.com!segue!bruce, aero.org!segue!bruce

Or, more likely, capacitive coupling.  Inductive coupling would
require that there be a current path back from each wire.  Of course,
that current path could be capacitive and you could have a combination
of inductive and capacitive coupling, but in this case, I would expect
capacitive coupling to be the "culprit".

Ken