Posted by Tomi Engdahl (126.96.36.199) on April 16, 2002 at 17:38:03:
In Reply to: How to send signal over AC Power line? posted by The Thinker on April 16, 2002 at 10:56:09:
: If somebody knows if it is possible to transmit a digital signal over a AC power line (to drive a dimmer for example), I would appriciate any information.
Powerline Carrier (PLC) is a communication technique that uses the existing power wiring (120 Volts, 240, etc) to carry information. It is kind of "wireless" means of communication, because PLC technology can supersede the installation of dedicated wiring in some applications. Various applications use PLC technology from power company equipment controlling to computer networking.
Typical frequency ranges used in powerline communication is from 30 Khz to 150 Khz. In the A-band, the carrier signal can be from 9KHz to 95KHz where electricity suppliers and their licensees are permitted to communicate. Powerlines can also be used for other applications, The C-band is for consumer use with an access protocol. This band goes from 125KHz to 140KHz. Between the A-band and C-band is the B-band, used for consumer use without an access protocol so this band has some freedom of communication. Devices can interfere with one another and baby alarms use this band. Above 150KHz, communication is prohibited in Europe. But in USA those higher frequencies are usable. Popular "wireless" intercom systems for exmaple operate at around 150kHz..500 Khz frequency range.
Three different techniques can be used for mains power line communications. With a PLL (Phase Looked Loop), the transmission could be performed with Amplitude Shift Keying, Frequency Shift Keying or Phase Shift keying.
A second technique is based upon Spread Spectrum with a correlator.
The third technique incorporates a DSP working in a narrow band and using dual carrier frequency operation mode with impulse noise cancellation and an adaptive distortion correction mechanism.
The powerline enviroment is hard enviroment for any communication. For example vacuum cleaners, hand-held drilling machines etcetera which use univeral series wound motors generate a lot of impulse noise to power line. TV-sets are a very common source of distortion. Light dimmers are also a source of mains noise. Switch mode power supplies use high frequency components, and usually a lot of tonal noise is generated. Everything can change over the frequency range, both the attenuation, phase response and noise level.
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