Transcript Satellite Coordination, Link Margins

Satellite Coordination,
Link Margins
Jim Cohen and Mike Davis
SATELLITE COORDINATION
Equivalent Power Flux Density (epfd) Algorithm
 N a Pi

Gt i 

10
epfd Gr 0 dBi  10  log10  10 ·
·Gr i 
2


4

d
i
 i 1

Takes into account the gain and pointing directions of both the
Satellite and the Radio Telescope. Must be run repeatedly to cover
full range.
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!
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?
RFI Survey at the RPA
G. R. Harp and R. F. Ackermann
48 hours continuous scanning
LEOs
Sun
GEOs
Satellite Spectrum
Leeheim, Germany Monitor Station
RAS Allocation
10.68-10.7 GHz
Measured Signal Level
40 dB
Detrimental Level,
Rec. 769
FSS Allocation
Radio Astronomy Maps
Before and After TV Satellite Operation
Before
1995
After
1995
IUCAF Doc
7D85,
4 Feb 2002
Relative Channel Capacity
(r/ri) = r2/(r2 + i2)
7D86, 4 Feb 2002
99%
10 dB
50%
Recommended Level
Reduction in RAS Channel Capacity caused by interference
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.