From: wood@rtsg.mot.com (Dan Wood)
Subject: Re: Beware when prewiring for telephone
Organization: Motorola Inc., Cellular Infrastructure Group
Distribution: usa
Date: Fri, 28 Aug 1992 15:03:00 GMT

   There seems to be some confusion about flat vs. twisted wiring,
and the suitable applications.  I'll try to shed some light, however
it's been a few years since I played 'sparky', so if anyone out there
has found the perfect truth, feel free to enlighten us all.

   My apologies if my diatribe bores or offends you, there is a
key with an "N" on it...

   Twisted cable is for balanced signals.  The signal has no polarity
as such, the signal is represented by the difference in voltage or
current between the conducting pair.  Induced signals appear on both
conductors, so the difference is nil, and there is no resulting
interference.  The twist in the wire is to ensure that the induced
signal affects each conductor by an equal amount (ie. one conductor
isn't always physically closer to the "inteference" source).   Examples 
are: audio speaker wiring, telephone cables, antenna twin-lead, and
twisted-pair LANs.

   Nontwisted or "flat" cable is for unbalanced signals, where one
conductor carries the signal, and another (sometimes common to
several signals and/or grounded) conductor serves as a "reference"
level, typically at 0 volts.  This reference conductor typically
carries the return current, to complete the circuit.  At the receiver,
the reference conductor is typically connected to ground.  Noise  
induced on the line are seen at the receiver only on the signal
conductor, since the reference conductor is grounded.  Thus, 
unbalanced (or "single-ended") signals are much more susceptible
to interference.  Examples are RS-232, 110V power, cable TV,
and the signals inside your computer.

   The balanced signal approach is generally considered superior.
The unbalanced approach is cheaper as it requires fewer conductors
(where more than one signal is transmitted) and simpler circuitry.

   RS-232 has somewhat undeservedly earned a bad reputation in
the computer industry.  Within it's limitations it works fine.
The designers included pulse-shaping (signal is more of a lump
than a pulse) to reduce crosstalk, and hysteresis for a small
amount of noise immunity.  Where +12V and -12V levels are used
for the 0/1 representations, it will work reliably well beyond
the 50' limit specified.  So, it will probably be OK for
moderate distances in the house.

   Did the original author say he needed an in-house network?
If so, I missed it.

   Very interesting that the DTMF tone crosstalk would dial
the other phone line: it would have to be off-hook, with the
CO in the receiving digits state, usually a narrow window.
If the crosstalk was so bad that one phone off-hook induced 
an off-hook condition onto the other line, I'm positively
intrigued.  |^)

-- 
*********************************************************************************
*	Dan Wood   Motorola Inc.	*	 Moto didn't say it,       	*
*	wood@rtsg.mot.com 		*	 and I don't recall...  	*
*********************************************************************************
From: brooksp@hpcc01.corp.hp.com (Peter Brooks)
Date: Thu, 27 Aug 1992 17:21:10 GMT
Subject: Re: wood floor or carpet?
Organization: the HP Corporate notes server