Mysterious source jams satellite communications
Pastor Dale Morgan
Mysterious source jams satellite communications*
11:45 26 January 2007
David Shiga and AFP
Paris-based satellite company Eutelsat is investigating "unidentified
interference" with its satellite broadcast services that temporarily
knocked out several television and radio stations. The company declined
to say whether it thought the interference was accidental or deliberate.
The problem began Tuesday afternoon, blocking several European, Middle
East and northeast African radio and television stations, as well as
Agence France-Presse's news service. All transferred their satellite
transmissions to another frequency to resume operations.
Theresa Hitchens of the Center for Defense Information think-tank in
Washington DC, US, says there have been cases of deliberate satellite
jamming in the past, but it is hard to see what motivation there would
be in this instance.
"It's really puzzling to me," she told New Scientist. "If it was
accidental, why would they be so secretive about saying what the source
was and if it's deliberate, you've got to wonder why – it just seems to
me to be an odd target, unless someone's ticked off at the French," she
says.
Hitchens points out that there have been cases of deliberate jamming,
including one in the 1990s when Indonesia and Tonga had a dispute over
which country had the rights to a particular satellite orbital slot.
Tonga had leased the slot to a satellite firm based in Hong Kong, but
Indonesia had its own satellite in the same slot and proceeded to jam
the Hong Kong satellite.
In a more recent incident, the US claimed in 2003 that Cuba was jamming
its satellite broadcasts into Iran.
Listen and repeat
There are a variety of ways to interfere with a satellite's
communications. One is to broadcast a stronger signal, either from the
ground or from another satellite, that drowns what the satellite is
sending to the ground, preventing people from receiving its signal.
Another is to blast a signal at the satellite itself so that it cannot
hear what the ground is trying to tell it.
Communications satellites act like conduits, listening to the ground and
re-broadcasting what they hear. If someone drowns out the uplink signal
with noise, then the satellite will re-broadcast the noise instead of
the intended television or radio program.
Military satellites use methods like encryption and frequency hopping to
prevent jamming, but many commercial communications satellites lack such
safeguards, Hitchens says. "Given the fact that militaries increasingly
rely on commercial satellites for communication, this has generated a
lot of discussion," she says.
A 2004 report of the satellite task force of the US President's National
Security Telecommunications Advisory Committee highlighted potential
jamming of satellites as a key concern.
Nothing nefarious
Richard DalBello, vice-president of government affairs for satellite
operator Intelsat General says accidental interference occurs all the
time. Intelsat deals with thousands of such events each year, he says.
The equipment at ground stations used to communicate with satellites can
malfunction, interfering with other people's efforts to communicate with
the same satellite, he says.
Given this, the fact that Eutelsat does not know the source of the
interference yet is "really not indicative of anything nefarious", he
says. "Obviously if something persists or as you move traffic [to other
satellites] it follows you, there are some things that give you pretty
clear clues," he adds.
Deliberate interference may be more common than is widely recognised,
however. The website of the Satellite Users Interference Reduction
Group, whose members include Intelsat and other industry players, lists
11 incidents of deliberate interference with satellite communication
since January 2005, although this comprises only 0.7% of the total
transmissions.