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SWLers, listen up! DXers, get your ears on! New Scientist has the skinny:

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.

It develops that electric companies in the US have gotten, and those in Europe are about to get, permission to pursue a technology called broadband over power line (BPL), enabling them to compete with telephone companies in providing high-speed internet access to private homes. This is accomplished by having a high-frequency signal piggyback onto the normal 50 or 60 Hertz (cycles per second) current running through the lines. Electric power supply is what's called a "noisy" environment: What with all switches going on and off, machines running and stopping, and so on, there'd be a fair amount of electrical interference, which would dramatically slow the transmission of data. The solution is to have that data sent at a bunch of different frequencies.

That "solution" is exactly where the problem here lies. The cables used to carry power were designed for that 50-60 Hertz current, so they're not shielded against the high frequencies of the carrier wave carrying the internet data - and instead of acting like shields, the wires would act more like broadcasting antennas. What's more, the best frequencies for transmitting the data prove to be those up to about 30 megaHertz: Exactly the same band that is best for international radio transmissions, including national and private shortwave radio stations, ham radio, some emergency services, and a number of other applications. Which means that any shortwave radio near a power line could find that instead of producing music and news from dozens of countries around the world, it put out nothing but static.

What's more,

[u]nless 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.

Supposed protections based on the use of filters were included in the FCC's approval, but they are singularly unimpressive, not only since they require proof of interference with nearby shortwave radios - and how long do you think that will stand in the face of corporate complaints about the cost involved in dealing with the "selfish complaints" of a "tiny handful of people" - but because outgoing FCC Chairman Michael Powell has said that the FCC

must balance the benefits of BPL against the relative value of other licensed services,

which radio amateurs take, as do I, as hinting that filters will only be used if they don't significantly affect the speed of data transmission over the power lines and the shortwave spectrum be damned.

New Scientist says that

[s]ome 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.

It also seems quite inadequate since I can't see what such detection could be based on other than time of day at the receiver, even though time of day at the transmitter and the difference between the two are also relevant.

So I have a better fix: Don't do it. Drop BPL as an idea that is simply not ready for prime time and may never be.