Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.dcom.modems
Subject: Re: rs232 over power lines (and hayes 2400)
Message-ID: <17745@glacier.STANFORD.EDU>
Date: 28 Sep 88 03:08:55 GMT
References: <2148@stpstn.UUCP>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 17


     Power line modems are not at all uncommon.  They generally use an
FM carrier in the 100KHz range and are typically just frequency-shift
keying devices.  Range usually includes everybody on the same power
transformer.  Interference from various sources, including power-line
intercoms, power-line based control systems such as the BSR units, control
signals sent by power companies, antique jukebox remotes, master clock systems,
music distribution systems, and other various arcane devices, is possible.
There's no frequency coordination for signals via the power line.  So
products of this type tend to not work right in some installations, which makes
the technology unpopular.

     Incidentally, it's quite proper to speak of a power line modem as a
"modem".  Most modems are telephone-line oriented, but there are also RF
modems for radio links, for example.  

					John Nagle