Air-safety watch on mains data

A faster generation of devices that turn household mains wiring into network links has hit the market, despite fears they may be a danger to aircraft.

The devices use a low-power high-frequency signal that is filtered off from the low-frequency mains AC. The problem is that the wire acts as an aerial and can interfere with radio reception.

In fact, the technology is in many cases a wireless link in disguise. Household wiring consists of a set of loops, typically two per floor: one driving the pocket sockets and the other the lighting.

Peter Huddlestone of power-over-mains specialist Devolo confirmed that the connection between loops is wireless. ‘The wires have to run close to each other for at least a metre for it to work,’ he said.

Interference expert Jonathan Stott, of the BBC’s R&D Laboratory, suspects radio plays a part even on a direct link, with RF being transmitted at one end and absorbed at the other.

The devices satisfy EC interference regulations and vendors say they can get round problems with amateur, commercial and BBC broadcasts. However, Stott says EC rules ignore the possible effect of thousands of them in cities – and he fears passing aircraft may be vulnerable because there are no buildings in the way to block the signal.

The Civil Aviation Authority, which is responsible for air safety, said in a statement it was ‘fully aware of mains data devices’ and was monitoring the situation closely. It added: ‘We will not be taking a position on it until there is something more tangible to assess.’

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