Subj: Power Line Communications Capabilities
Date: 8/30/00 8:06:55 PM Pacific Daylight Time

Many large electric utilities have private communications networks
independent of local and regional telephone companies. These systems
normally consist of separate copper or fiber-optic cabling ran adjacent to
the power-lines but not using the power-line system per se.

High-tension power cable can transmit both voice and data, but most other
electric power cable is inadequate for all but very low bandwidths.
Technologies such as Ultra Narrow Bandwidth (UNB) Power Line Carrier (PLC)
offer long range transmission but have exceedingly narrow bandwidth. Other
techniques offer higher bandwidth but are very limited in range.

In summary, power line communications is more a dream than a reality. The
systems just aren't very adaptable to frequencies much above 60 Hz or below
50 Hz. Frequencies above 60 Hz are quickly attenuated by the cable
characteristics, overwhelmed by power line noise, and ultimately absorbed by
the nearest transformer. Frequencies below 50 Hz carry comparatively little
information and must be kept at low amplitudes to prevent phase imbalances
and transformer overheating.


The Promise of Communicating over Power Lines