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NewSci: Net Noise Threat to Emergency Radio

Marcus Didius Falco (
Mon, 24 Jan 2005 19:48:15 -0500

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From: Paul Saffo <>
Date: Mon, 24 Jan 2005 06:20:04 -0800
To: Dave Farber <>
Subject: NewSci: Net Noise Threat to Emergency Radio

Internet noise threatens emergency radio

New Scientist Print Edition
Barry Fox

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 UK branch.

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

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 Graph). 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.

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's 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

Some technical fixes may be in the works though (see "Aiming high").
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.

Aiming high

Corridor Systems of Santa Rosa, California, thinks it has hit on a way
to set up an interference-free power-line internet service. It plans
to use overhead power lines to carry data at frequencies between 800
megahertz and 10 gigahertz, way above the amateur radio and
conventional power-line communications band and, which it will send in
an outer power conductor.

Thanks to the "surface wave" effect, in which signals launched
straight down a cable tend to stay inside the cable, near the surface,
Corridor's system will not generate radio waves that might interfere
with mobile phones at these frequencies. For the final link into
subscribers' homes they will use very low-power radio transmitters,
like those used for Wi-Fi hotspots, which will be fixed to the nearest
power cable.

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