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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Communication over power lines - is it legal?
Message-ID: <1759@kitty.UUCP>
Date: Tue, 12-May-87 17:14:36 EDT
Article-I.D.: kitty.1759
Posted: Tue May 12 17:14:36 1987
Date-Received: Fri, 15-May-87 04:12:31 EDT
References: <3271@ece-csc.UUCP> <1286@ur-tut.UUCP> <1708@megaron.arizona.edu>
Organization: Recognition Research Corp., Clarence, NY
Lines: 24
Summary: RF isolation on power lines

In article <1708@megaron.arizona.edu>, wendt@arizona.edu (Alan Lee Wendt) writes:
> > >My question is this:  Does the power company get upset if you
> > >introduce a low-level (~1 volt peak-to-peak) high freq. (> 10 kHz)
> > >onto their lines (interior to your home).
> 
> I wonder if Tempest rooms (isolated computer rooms for classified stuff)
> typically include an isolation transformer to prevent transmitting
> information back from the computer along the power line?

	Not only are there isolation transformers for AC power, but each
hot and neutral leg of any AC power feed passes through some pretty hefty
"feed-through" capacitors to further attenuate any RF energy.
	Data communication lines are optically isolated whereever possible,
using simple current loop/optoisolator circuits for low-speed data lines,
with more sophisticated isolation techniques being used for circuits greater
than 19.2 kbps.  As one can intuitively imagine, the use of actual fiberoptic
data lines increases the communications security in this environment.
	ANY electrical penetration to such a secure area is isolated; this
includes such circuits as HVAC control, physical security control, etc.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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