Satellite Coordination, Link Margins Jim Cohen and Mike Davis

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.

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 n th -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 GEOs LEOs Sun 48 hours continuous scanning

Satellite Spectrum Leeheim, Germany Monitor Station Detrimental Level, Rec. 769 Measured Signal Level 40 dB RAS Allocation GHz FSS Allocation

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

Reduction in RAS Channel Capacity caused by interference Relative Channel Capacity (  r /  ri ) =  r 2 /(  r 2 +  i 2 ) Recommended Level 99% 50% 10 dB 7D86, 4 Feb 2002

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.