Wherein we all might tempest-up in spite of ourselves?
Cheers,
RAH
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http://www.newscientist.com/article.ns?id=dn6866&print=true
New Scientist
Internet noise threatens emergency radio
10:31 14 January 2005
Exclusive from New Scientist Print Edition
Barry Fox
Enlarge image
Short-wave interference
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.
Unshielded cables
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.
Unhappy coincidence
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.
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R. A. Hettinga