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From: rf@wu1.UUCP
Newsgroups: net.dcom
Subject: Re: Having trouble with a cable under a parking lot
Message-ID: <334@wu1.UUCP>
Date: Tue, 22-Jan-85 16:00:03 EST
Article-I.D.: wu1.334
Posted: Tue Jan 22 16:00:03 1985
Date-Received: Fri, 25-Jan-85 07:57:14 EST
References: <1600@fritz.UUCP>
Organization: Western Union Telegraph, Mahwah, NJ
Lines: 29
In-Reply-To: zemon's message of Wed, 16-Jan-85 162317 EST

180 Hz sawtooths are common noises when three-phase power is involved.  The
coupling between the noise source and your cable could be converting it from
a screwy triple sine wave to a sawtooth - especially if there are some
rectifiers around.

Some rules of cable installation:

  - *Never ground both ends of a shield!*  Ground potential very likely
    differs at the opposite ends.  Ground one end only.

  - Make sure the ground you use is a good one -- if possible, check to
    see that it is actually earth (cold water pipes are good).  You
    sometimes can use building green-wire ground - but check for ground
    currents first.

  - *Never use electrical neutral for grounding!*  This one can literally
    kill you -- be careful.

  - Never ground either side of a pair.  Keep your pairs isolated - that's
    what line drivers are for.

  - Don't use RS-232 between buildings - it is possible to damage your
    computers if there are substantial ground currents.


Uucp: 	  {decvax,ihnp4}!philabs!wu1!rf		Randolph Fritz
Easylink: 62905318				Western Union Telegraph
phone:	  1-201-529-6238			90 McKee Dr.
	  1-201-529-6221			Mahwah, NJ 07430