電力線通信：一個可行的消費者鏈接

　　電力線通信已經存在了很長一段時間，我們大多數人最先接觸到這項技術，它早期用于家用自動化和家電的遠程控制。它使用交流電源線作為電源和通信介質。

　　最初向公眾介紹了什么是現在被稱為X10協議，使用相同的導線，電源線通信的好處已經得到很好的理解，這一技術擴展用于電力公用事業，以及計算機網絡與分布式音頻流內的建筑。

　　本文著眼于電力線通信技術和工程師可以用來實現它的設備。它檢查了一些歷史和流行的協議及其優點和局限性，并討論了在決定電力線通信是否適合您的應用程序時需要注意的問題。

　　From whence it came

　　The power utilities discovered early on that in addition to delivering raw high-voltage AC power through an extensive network of cables， switches， transformers， and circuit breakers， they also needed a way of communicating. In the 1920s and 1930s， people were not as dependent on electricity as they are today， so when power went out it could routinely take days or even weeks to send crews to find and fix power faults， especially in remote areas.

　　The most basic need for remote data gathering drove the early systems. The simplest implementations use narrow band 15 to 500 KHz carrier waves for rudimentary on/off keying for long haul remote data measurements over high tension power lines. These low-frequency RF signals are capacitively coupled at relatively low amplitudes （compared to the kilovolt levels of the AC power）， and do not interfere with the 60 Hz power and timing signals used in early electric appliances. （For example， before crystals， early clocks would get their time reference from the 60 Hz power line and high frequencies did not get through the transformers that converted the high-tension voltage to standard 120 volts used today）。