Editing Power-line communication (section)

== Basics ==

Power-line [[communications system]]s operate by adding a modulated carrier signal to the wiring system. Different types of power-line communications use different frequency bands. Since the power distribution system was originally intended for transmission of [[AC power]] at typical frequencies of 50 or 60 [[Hz]], power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power-line communications.

The main issue determining the frequencies of power-line communication is laws to limit interference with radio services. Many nations regulate unshielded wired emissions as if they were radio transmitters. These jurisdictions usually require unlicensed uses to be below 500&nbsp;kHz or in unlicensed radio bands. Some jurisdictions (such as the EU), regulate wire-line transmissions further. The U.S. is a notable exception, permitting limited-power wide-band signals to be injected into unshielded wiring, as long as the wiring is not designed to propagate radio waves in free space.

[[Data signaling rate|Data rates]] and distance limits vary widely over many power-line communication standards. Low-frequency (about 100–200&nbsp;kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a [[local area network]] operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.