Wiring terminals 300 ft. from the computer

[Bruce Adler]

In article <1990Sep25.052558.11002 at chinet.chi.il.us> floydd at chinet.chi.il.us (Floyd Davidson) writes:
>Pray tell what does using twisted pair wire do on an unbalanced
>circuit?  Nothing.  Twisted pair will do wonders for common mode
>rejection on balance telephone lines, maybe on RS-422, but nothing
>for RS-232.

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 at segue.com, ism.isc.com!segue!bruce, aero.org!segue!bruce