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 鈥減ower-line telecoms鈥� 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 (快猫短视频, 30 May 1998, p 4).
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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. 鈥淚n some cases of power-line interference you are hearing more noise than short-wave radio signal,鈥� 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 拢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.
