Satellite Coordination, Link Margins

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Satellite Coordination,Link Margins

• Jim Cohen and Mike Davis

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SATELLITE COORDINATION Equivalent Power Flux
Density (epfd) Algorithm
Takes into account the gain and pointing
directions of both the Satellite and the Radio
Telescope. Must be run repeatedly to cover full
range.
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Link Margins

• The satellite operators require a Link Margin,
  the maximum S/N in the intended receiver after
  all free-space link losses are accounted for.
• IRIDIUM used 16 dB as their link margin, for
  example. Transmitter power on a given connection
  can be increased as needed, up to this level.
• Note that if nth-order intermods are causing
  interference, increasing the transmitter power 1
  dB generally increases the intermod level n dB!

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Basic Requirements

• A satellite system needs to place a certain power
  flux density PFDsat on the ground in the
  satellite allocated band, to provide its
  legitimate service.
• The signal becomes detrimental if it exceeds
  PFDrec769 in a radio astronomy band
• PFDsat PFDrec769 dB attenuation or more is
  needed between the satellite band and the RAS
  band. Basic to the work of Task Group 1-7.
• PFDrec769 is published, but
• PFDsat generally is not publicly available.
• Measure it?

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RFI Survey at the RPA G. R. Harp and R. F.
Ackermann
48 hours continuous scanning
LEOs
Sun
GEOs
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Satellite SpectrumLeeheim, Germany Monitor
Station
FSS Allocation
RAS Allocation 10.68-10.7 GHz
Measured Signal Level
40 dB
Detrimental Level, Rec. 769
Unwanted Emission
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Radio Astronomy Maps Before and After TV
Satellite Operation
Before 1995
After 1995
IUCAF Doc 7D85, 4 Feb 2002
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Relative Channel Capacity (?r/?ri) ?r2/(?r2
?i2)
7D86, 4 Feb 2002
99
50
10 dB
Recommended Level
Reduction in RAS Channel Capacity caused by
interference
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CONCLUSION

• Measure the satellite emission ON THE GROUND,
  before launch.
• Do it carefully.
• Do it thoroughly.
• Once the satellites are up, its too late.