Networking over AC power lines has long been a tempting target, especially for homes and small businesses. After all, the average home has up to 50 outlets, each a potential network port. And even the most unimproved office space has AC wiring.
Various companies have talked about introducing power-line networking, but no one has yet come to market with a viable product. The reason is simple: Power lines make networking over telephone lines look like a walk in the park. Phone lines are hard enough, but at least you have a twisted-pair with a characteristic impedance and a standardized set of signals and voltages.
Power lines introduce many unknowns, starting with different kinds of wiring, grounding, circuit breakers and branch circuits. Then you have an incredible variety of loads on the line. Some, like heating elements, are purely resistive and come darn close to being a short circuit across the line, drawing tens of amps or more in an electrically heated home. The controls that turn some of the simpler heating elements on and off, as in a toaster oven, switch the full load, complete with sparks and resulting pulses on the line.
Then there are motors. The smooth-running, quiet ones are induction motors, but the miles of wire inside them and their soft iron cores resemble a sponge that wants to soak up data signals, or so soften them that it becomes next to impossible to tell a 1 from a 0. The noisy universal motors in blenders, vacuum cleaners and hair dryers have brushes that spark and commutators that produce lots of high-frequency noise, up into the range easily picked up by AM radios.
You may be surprised to learn that computer power supplies can also wreak havoc on power lines. Their filters that squelch line noise can obliterate data signals, while the high-speed switching components in the power supply generate a healthy amount of electrical noise. Light dimmers are another common source of switching noise.
Finally, your wiring is a natural antenna for local radio stations, passing vehicles with transmitters and even the electromagnetic pulses from distant lightning. Why would anyone think that they could run 10M-bps Ethernet through this mess?
Into the fray comes Intellon, with 10 years' experience producing power-line control chips for industry. Control chips get the signal through, but at speeds too low for networking. However, Intellon has introduced PowerPacket, which piggybacks up to 84 low-power radio frequency carriers (the FCC would frown on excessive emissions) onto your power line, between 3.5MHz and 16MHz. In tests, Intellon's boards move raw packets at a zippy 11M bps. With impairments—30-db attenuation, resistive loads, a hair dryer and a dimmer-powered halogen light—the rate never dropped below 7M bps.
The demonstration boards are full-size ISA boards, crammed with chips and doubtless expensive. Intellon says that it'll have a much smaller version, built around a custom chip, available for commercial products late this year. If they work and they're inexpensive, they could revolutionize connectivity and redefine Internet devices. I can hardly wait.
Bill Machrone is vice president of technology for Ziff-Davis. He can be reached at firstname.lastname@example.org.