[New Scientist] Power-line internet hits world radio

maxheadroom

Power-line internet hits world radio

New Scientist vol 180 issue 2424 - 06 December 2003, page 26


HOUSEHOLDS that choose to use broadband internet delivered by new systems that route data down the mains power cables may be denied access to short-wave radio broadcasts. That is the warning from broadcasting engineers in the UK who say that interference from the cables is so severe that it will block out short-wave transmissions in the homes that use the system.

Electricity utilities have long wanted to use their power cables to deliver broadband internet services. The idea is for the digital data signal to piggyback on the standard 50 or 60-hertz mains frequency. Many power companies in the US and Europe see this "power-line telecoms" as a new source of revenue.

But tests by the BBC have shown that the data transmissions, which use a frequency of a few megahertz, generate powerful harmonics at short-wave frequencies which radiate from the cables. This should not be news to the power firms. Five years ago, the utility Nortel abandoned a project in the UK to use power cables to carry telecoms signals, after this was found to cause street lamps to radiate signals that interfered with radio reception (New Scientist, 30 May 1998, p 4).

This lesson appears to have gone unheeded, because a system set up by Scottish and Southern Energy (S&SE) has run into similar problems in tests carried out in Crieff, Perthshire. BBC engineers who measured the interference created by the service were horrified by its effect on short-wave radio reception in homes. "In some cases of power-line interference you are hearing more noise than short-wave radio signal," says Andrew Oliphant, of the BBC. Though the interference only extends a metre or two from the mains cable, this is far enough to affect most radios in homes.

Nevertheless, S&SE is now offering the service in two towns Stonehaven, Kincardinshire, in Scotland and Winchester in southern England. In each town a 1-megabit-per-second broadband service will be available to around 500 homes for 30 a month. S&SE says it has had no problems with radio, but it has been looking at AM medium-wave transmissions, not short-wave radio.

Ironically, the problem comes just as leading broadcasters worldwide, including Radio France International, Deutsche Welle and the BBC World Service, have agreed a new standard called Digital Radio Mondiale, which broadcasts digital signals over short-wave frequencies. It uses built-in error-correcting codes that will allow short-wave broadcasts, which can travel thousands of kilometres round the Earth by bouncing off the upper atmosphere, to sound far better than they do at present.

The BBC fears power-line telecoms could jeopardise the whole future of short-wave radio, and is lobbying for broadcasters and power utilities to agree limits on interference levels.

Barry Fox

maxheadroom

This is the 5 year old article referred to above:

The light programme

New Scientist vol 158 issue 2136 - 30 May 1998, page 4


It was touted as the Net's future but has turned streetlights into rogue radio transmitters


ULTRAFAST Internet access via the electricity mains . . . it sounded too good to be true, and perhaps it was. Trials of the scheme in Manchester have hit an embarrassing snag. Streetlamps using the same power supply as Net surfers are acting as aerials and broadcasting downloaded data as high-frequency radio waves.

If the current technology were to be widely used, experts fear that sections of the radio spectrum could be swamped, disrupting emergency communications, annoying amateur radio buffs and interfering with the BBC World Service. Britain's Department of Trade and Industry (DTI) has stepped in to mediate between users of the affected frequencies and NOR.WEB, the company developing the system.

NOR.WEB is a joint venture between the British energy supplier United Utilities and the Canadian telecommunications equipment company Nortel. Its Digital PowerLine system transfers data between electricity substations and people's homes using a 1-megahertz carrier wave riding on top of the 50-hertz AC electricity supply (Technology, 18 January 1997, p 18). The connection from substation to the Internet is via a conventional high-bandwidth optical fibre.

The system can download data about twenty times as fast as the modems used by most domestic Net useres, and also leaves phone lines free. NOR.WEB is confident that it can bring about a revolution in Net access. The company is marketing the technology worldwide.

The Manchester trials delivered the impressive access speeds that the system had promised. But the company's engineers hadn't taken the physical characteristics of streetlights into consideration. "If you set out to design radio aerials to fit with this system, they would look like streetlamps," says Nick Long, chief engineer with Great Circle Design, a radio systems consultancy based in Wincanton, Somerset. "They are just the right vertical length of conductor." As a result, data being downloaded by users of the system are being broadcast as radio waves between 2 and 10 megahertz.

If the technology is not modified to remove this interference, says Long, some sections of the radio spectrum could become unusable. The online activities of Net surfers using the system could also, in theory, be tracked by monitoring the radio transmissions, he adds.

British users of the affected radio frequencies include the BBC, the Civil Aviation Authority and even GCHQ, the government's electronic communications nerve centre. "We are trying to gauge the level of risk," says a GCHQ spokeswoman.

Robin Page-Jones of the Radio Society of Great Britain fears that his members will be hit hardest. "It could be very difficult in the long term to control this," he says. "Regulations need to be nailed down now."

The Radiocommunications Agency at the DTI has been holding meetings with NOR.WEB and radio users to resolve the problem, but a solution has not yet been thrashed out.

Nevertheless, John Seddon, operations director for NOR.WEB, is confident that the problem can be solved. "The technology that will be deployed in volume will be at low power levels in comparison to the general radio noise that's already out there," he predicts.

Mark Ward

bminish

I was pleased to see this article in New Scientist since it raised the interference issues however I felt that for such a journal it was rather poorly researched.

Originally posted by maxheadroom

.... That is the warning from broadcasting engineers in the UK who say that interference from the cables is so severe that it will block out short-wave transmissions in the homes that use the system.

The problem is that the PLC signals are on all of the mains wiring of everyone connected to that transformer or substation, Even if they decide not to take the PLC service.

But tests by the BBC have shown that the data transmissions, which use a frequency of a few megahertz, generate powerful harmonics at short-wave frequencies which radiate from the cables.

It is not harmonics that are radiated, the fundamental operating frequencies of PLC are within the shortwave spectrum

The BBC report in question is available on line
http://www.bbc.co.uk/rd/pubs/whp/whp067.html

Though the interference only extends a metre or two from the mains cable, this is far enough to affect most radios in homes.

Unfortunately the Journalist seems to be confusing the standard field strength measurement distances with the actual distances over which the interference is a problem, distances of a few hundred m are more appropriate for the small trials in the UK. Both the Stonehave and Winchester trials are very limited in area. The Stonehave trial currently covers one Housing Estate and the Winchester trial involves currently a single transformer servicing less than 50 houses

Besides having severe interface problems PLC has very short line reach, less than 300m from the inject point and also needs a backhaul solution since PLC has neither the line reach nor the capacity to do backhaul.


You an find out more about the problems of radio interference to Amateur radio from PLC on the ARRL PLC page
http://www.arrl.org/tis/info/HTML/plc/

A few months ago the EU held a short consultation as part of the ongoing process to develop acceptable (to all parties) emission limits for PLC, unfortunately PLC is unlikely to operate effectively at the low emission limits required to protect radio users so no limits have yet been set.

My submission is here (144k PDF file)
http://www.tradcentral.com/plcsubmission.pdf

All the submissions can be read here
http://forum.europa.eu.int/Public/irc/enterprise/tcam/library?l=/emcsstandardisationsmand&vm=detailed&sb=Title

I would like to point out that EMC 'Experts' that made the academic presentation in session 3 both are in full time employment in PLC fields rather than in EMC or radio related fields.

The submissions by stakeholders (including my own submission) come from a wide range of sources and give a more complete overview of the situation in Europe.

there were also a couple of (long!) threads about this on this forum a couple of months ago

.Brendan