MARGINS Education/Outreach Activities at the MARGINS-IFREE IBM Workshop, and Beyond
Satellite Coordination, Link Margins Jim Cohen and Mike Davis.
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Transcript of Satellite Coordination, Link Margins Jim Cohen and Mike Davis.
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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
a i
r
N
iir
i
itP
dBi0G G·d
G·epfd
12
1010
410log10
Takes into account the gain and pointing directions of both theSatellite and the Radio Telescope. Must be run repeatedly to coverfull 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
GEOs
LEOs
Sun
48 hours continuous scanning
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Satellite SpectrumLeeheim, Germany Monitor Station
Detrimental Level,Rec. 769
Measured Signal Level
40 dB
RAS Allocation 10.68-10.7 GHz
FSS Allocation
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Radio Astronomy Maps Before and After TV Satellite Operation
IUCAF Doc 7D85,
4 Feb 2002
After 1995
Before 1995
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Reduction in RAS Channel Capacity caused by interference
Relative Channel Capacity (r/ri) = r
2/(r2 + i
2)
Recommended Level
99%
50%10 dB
7D86, 4 Feb 2002
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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, it’s too late.