After the tsunami hit Sri Lanka on 26 December, Victor Goonetilleke, head of the island's amateur radio society, delivered a short-wave radio set and two 12-volt car batteries to the prime minister's emergency headquarters in Colombo. At the same time, three of his friends drove through the devastation to Hambantota, on the hard-hit south-east coast, where they set up another battery-powered short-wave radio.
For two days, while the military struggled to restore electricity supplies and phone lines, the prime minister was able to use the short-wave link to talk to staff on the ground.
Short-wave signals from Sri Lanka, the Andaman Islands and mainland India also helped to spread news of the disaster around the world. The same happened after the 9/11 attacks and last year's hurricanes in the Caribbean. When phones and mains electricity are down, making the internet unusable, short-wave radio enthusiasts are able to maintain emergency communications.
But not, perhaps, for much longer. Plans to deliver broadband internet signals to homes and businesses down mains electricity cables, rather than telephone lines, could cause interference that will drown out the faint signals from distant short-wave transmitters.
Power companies in the US and Europe are pressing ahead with the technology, with the aim of setting up in competition to existing phone-based services. The downside is that the packets of internet data pulsing down unshielded mains cables makes the cables behave like aerials that send short-wave interference beaming out over a wide area.
Unless interference of this kind is tightly controlled, it could spell the end for emergency short-wave communications. "A few extra decibels of interference from future networks and I would not have been able to hear the news from amateurs in Sri Lanka, India and the Andaman Islands," says Hilary Claytonsmith of the International Amateur Radio Union's UKbranch.
The threat began when the US government gave the go-ahead to broadband over power line (BPL) technology in October. And the European Commission (EC) is close to approving its own version, called power-line communications (PLC). The names are different but the technology is the same: broadband data is sent into people's homes as a high-frequency signal piggybacked on the 50 or 60-hertz mains supply.
Because the mains is a noisy environment with ever-changing patterns of interference from sockets, switches, control circuits and electric motors in appliances, the power-line data must be spread over many high-frequency carrier signals if it is to be delivered at the 5 to 10 megabits per second that these services are aiming for.
The carrier frequencies used range up to 30 megahertz - which by unhappy coincidence is the radio band that travels best around the world. It is used for amateur radio, short-wave broadcasting (such as the BBC World Service and Deutsche Welle) and includes several dedicated emergency frequencies (see graphic). Because these frequencies bounce off the ionosphere, they carry long distances, which makes them ideal for long-range intercontinental broadcasting.
When the US Federal Communications Commission (FCC) gave the go-ahead to BPL, it ruled that at frequencies up to 80 megahertz service providers must use filters on their household equipment. These could be set by a service engineer to chop out any internet transmission frequencies shown to be causing interference to any short-wave radio receivers nearby. The EC and the European Committee for Electrotechnical Standardisation (CENELEC) are trying to set similar filtering rules.
Deciding on importance
But radio amateurs fear that the rules will allow the filtering to be lifted if it is having a serious effect on internet access speeds. The EC says it wants firm rules that balance "technical, social and economic" factors against the "importance" of services which suffer interference. But who is to decide what is more important, and on what grounds, the radio amateurs ask.
Michael Copps, the one FCC commissioner who opposed BPL, believes the organisation has made a rod for its own back. It is going to have to "work hard to monitor, investigate and take quick action" over any power-line internet interference to radio amateurs and others, he says.
Some technical fixes may be in the works though. The BBC, for instance, is developing a PLC modem that makes use of the fact that the short-wave frequencies for broadcast radio change throughout the day, as ionospheric conditions dictate. The BBC modem detects which frequency bands are in use at any one time - and filters them out. Such technology is not part of any PLC or BPL system currently in trials, however.