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/ 05.14.2010 12:00AM
Cable TV Networks Could Survive Rogue Satellite
From Doug Lung’s Most Excellent RF Report: The mainstream press finally picked up on the failure of Galaxy 15, first covered in RF Report almost a month ago. While those stories focused
on the impact Galaxy 15 transponders will have on AMC-11 satellite, the popular
press articles are short on technical details. AMC-11 is home to popular cable
nets Lifetime, Food Network, HGTV, A&E, MTV, Nickelodeon, BBC America and more.
Will these popular channels disappear from cable channels when Galaxy 15 moves
into AMC-11’s location? Perhaps not. After all, you didn’t see a major
disruption of the cable networks at 133 degrees west longitude.when traffic was
moved from Galaxy 15 to Galaxy 12. The 133 degree location is home to many cable
feeds, including Turner networks, HBO, and NBC networks USA, Syfy, Sleuth and
Oxygen. I’ll explain how after a little history.
When Galaxy 15 was in between Galaxy 12 and AMC 11, Intelsat and Orbital
Sciences engineers tried to regain control of it. When that failed, they had to
take more drastic measures. Uplink operators know they have to be in contact
with the satellite operator and gradually increase power when transmitting to a
satellite.
The fear is that if there is too much power, not only will it cause
interference to other users but it could damage the power amplifiers in the
satellite. As I suspected they would do, it appears Intelsat attempted to kill
Galaxy 15 by transmitting strong signals and overloading its power circuits.
Unfortunately, the protection circuits worked better than the telemetry,
tracking and telecommand (TT&C) payload. This attempt required careful
coordination between Intelsat and SES New Skies, the owner of AMC-11 to avoid
interfering with AMC-11.
Intelsat is posting data on Galaxy 15’s movement towards AMC-11. Go to
Intelsat
Owned/Operated Satellites Ephemeris Data and scroll down to “Galaxy Region
(W)”. Using the dropdown menus, select “Galaxy 15” to view the data. The “Center
of Box” has the predicted location of the satellite for the next two weeks.
According to the May 11 prediction, Galaxy 15 will be within 0.5 degree of 131
degrees west longitude around 17:00 UTC on May 24.
Many cable downlinks operate with antennas as small as 4.5m. At this size, the –3
dB beamwidth is around 1.3 degrees. In less than two weeks Galaxy 15 will be
sitting in the main beam of these antennas. Will Food Network be toast when
this happens? Perhaps not!
Two things could help viewers of programs on AMC 11. First, Galaxy 15 is not
tumbling through space. Its transponders are cross-polarized with AMC 11. This
helps in both directions--uplinks aimed at AMC 11 will put less signal into
Galaxy 15 and Galaxy 15 signals will be attenuated at downlinks polarized for
AMC 11. Because adjacent transponders overlap, this won’t completely eliminate
interference.
The best hope of Intelsat and SES New Skies may be the size of the uplink
dishes used to access these cable satellites. For example, a Vertex 9m C-band
uplink dish has a –3 dB beamwidth of 0.36 and a –15 dB beamwidth of 0.76
degrees. Up the dish size to 11.1 meters and the beamwidth is even smaller
–0.28 degrees at –15 dB. As long as AMC 11 can stay 0.5 degrees or so away from
Galaxy 15, the amount of energy hitting Galaxy 15 and, as a result, the amount
of interference from Galaxy 15 to AMC-11 downlinks, will be greatly reduced.
Operating a satellite this far out of its normal 0.1 degree box will require FCC
approval.
Keeping MTV viewers happy will require a celestial dance of the satellites; SES
New Skies will need to move AMC 11 around Galaxy 15, maintaining enough
distance from it for uplinks to minimize the signal into Galaxy 15 while
staying close enough to 131 degrees west longitude so cable operators don’t
have to adjust their antennas to follow it.
Engineers at uplinks looking at AMC 11 will be busy, as they will need to move
their uplink dishes to follow AMC 11 as it dances around Galaxy 15. Other steps
SES New Skies could take to minimize interference would be to have uplinks
lower power so they can remove attenuators from the transponder input, further
reducing the amount of signal into Galaxy 15. Will they be able to pull it off?
I think there is a good chance they will. The cable nets have a big incentive
to make it work!
Find more of Doug Lung’s work at
TV
Technology’s RF
Report.
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