Broadband Over Power Lines

Broadband Over Power Lines?
PLC -- "There's trouble a comin' down the lines..."
Tom Cox ~ KT9OM

ams and other users of the HF bands in the USA have reason for worry. The Federal Communications Commission (FCC), the agency that regulates the civilian use of the RF spectrum in the US, is all aglow about allowing the power companies to connect customers to the Internet over their power lines. Power line communications (PLC), or Broadband over Power Line (BPL) -- the practice goes by either name -- uses an RF signal sent over medium- and low-voltage AC power lines to allow end users to connect to the internet. The RF signal is modulated with digital information that is converted by an interface in the home or small business into Ethernet-compatible data.

By "medium- and low voltage," the power companies mean the residential power lines that deliver AC power from the nearest substation at about 7,200 VAC, and the 220 VAC that is usually available at the service entrance to a home or small business. Unfortunately, no HF user in his right mind expects the RF energy imposed on 60-Hz power to be confined to the power company's lines.

As someone who has dealt with the local power company about line noise for years, I am not at all confident that this outfit is capable of maintaining its physical plant in the condition needed to pass data without problems. The question is this: when their own lines produce enough noise because of loose connections and other maintenance problems to interfere with data transmission, what will the utility do? Will they send out crews to re-do ground systems and repair defective equipment, or will they just turn up the power on the data signal? How much "incidental radiation" will the FCC force us to put up with so the power company can sell Internet access?

Some power line equipment in my semi-rural area was installed during the Rural Electrification Act era of the 1930s.It has been allowed to operate with minimal maintenance, except for repair of catastrophic failures and storm damage. Hams who have spent any time tracking down a source of line noise, know how far from the offending equipment such signals can travel down the lines -- miles. And, we know what havoc it plays with trying to copy weak signals from 160M through at least 6M. Now the power company is going to send HF signals down these lines deliberately?

I don't know what the FCC and people marketing this technology are smoking, but they obviously think the "incidental radiation" from this technology is just that -- "incidental." In order to send data down these lines fast enough to compete with Digital Subscriber Line (telephone) and Cable TV connections, the utilities will have to use multiple carriers, modulated independently, from just above the US AM broadcast band (1.6MHz), to just below the FM broadcast band (80MHz). Of course these signals will radiate, and of course our signals -- the ones we have a license to produce -- will enter the nearby lines and travel with the data. How will the power companies deal with that? Will glassy-eyed promotion of universal Internet access push us out of the HF spectrum? Complaints about European PLC systems abound, and Japan, according to the ARRL, has decided against the technology because of the potential noise problems.

Here are some URLs of interest to Hams who want to know more about PLC. Search in Google with "Power Line Communication" for hundreds more.

A "booster" site that promotes PLC and offers several links on the topic--none mentioning interference that I was able to find in a cursory search. This must be the site the FCC is using!

This is a good article on the interference potential of PLC. There are several other resources of interest on the ARRL site, as well as an extensive discussion with linked resources at http://www.remote.arrl.org/tis/info/HTML/plc/ -30-

BRIEF BIOGRAPHY OF THE AUTHOR
Tom Cox, KT9OM, is assistant director of the information technology department of a 10,000-student, 7,000-computer public school corporation. His most recent project is replacing the corporation's leased digital telephone lines with high-speed wireless connections. On his own time, Tom plays with antennas, reads fiction and non-fiction, and gardens or removes snow and splits firewood, depending on the season, and rides about 250 miles a summer on a bicycle.

He was born to generous and patient parents, Jim and Jeannette Cox (both deceased), in 1949, and has been a Ham since 1982. He shares his Muncie, Indiana home with his lovely and indulgent wife, Sherry, and three dogs. He shares his neighborhood with his brother, KA9PBO, with whom he plays radio and attends hamfests. Tom is an active member of the GARDS.

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