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Satellite Coordination and Link Margins Algorithm for Radio Astronomy

Learn about the Equivalent Power Flux Density (epfd) Algorithm that ensures proper coordination between satellites and radio telescopes. Understand the significance of Link Margins in maintaining signal integrity and preventing interference in radio astronomy bands.

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Satellite Coordination and Link Margins Algorithm for Radio Astronomy

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  1. Satellite Coordination,Link Margins Jim Cohen and Mike Davis

  2. 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.

  3. 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!

  4. 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?

  5. RFI Survey at the RPAG. R. Harp and R. F. Ackermann 48 hours continuous scanning LEOs Sun GEOs

  6. 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

  7. Radio Astronomy Maps Before and After TV Satellite Operation Before 1995 After 1995 IUCAF Doc 7D85, 4 Feb 2002

  8. 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

  9. 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.

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