RFI in the alpha band pass Murray Lewis N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Senior Research Associate Radio Astronomy Group

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Propose to cover FCC frequency allocations in spectral region GPS Galileo PR Radars in band RFI Mitigation possibilities radar blankers! nine level sampling! algorithms! cross correlation between feeds Reinforcement of AO anti-RFI activity!

The frequency range covered by alfa is from 1225 to 1525 MHz N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R

GPS L1, L2, L5 L5 L2L1 General coverage -158 dBW Spot Beam -138 dBW Alfa

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R GPS L1 & L dBW for C/A -160 dBW for Y L dBW ≈24 MHz, full time occupancy This is 6 dB stronger than present L1 & L2 L5 spfd ~-205 dBW/m^2/Hz MHz ~-197 dBW/m^2/Hz in center satellites always available Also, of concern, GPS L3 circa 1381 MHz

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Galileo -- full set due 2008 E5A_E5B MHz (WRC2000) E MHz (WRC2000) E2,L1,E MHz Use of C_band under consideration To have 30 satellites, in 3 planes, inclination 56 deg 14 hr orbits, radius 23,616 km Power 50 W amplifiers peak power 120 W

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Galileo On orbit validation /4 satellites Deployment sats Commercial Ops Concern is their presence at MHz

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Details of Common/Unusual RFI Available on AO Web Page

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Hilltop Monitor MHz

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Examples Blanking San Juan Airport Radars? (1330 & 1350 ) BUT in the Surroundings of MHz band (i) US has proposed a satellite feeder-link system Uplink MHz, downlink MHz (ii) L3 (GPS) at 1381 MHz (iii) Timing explorer in Space Lab was at 1427 MHz

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Fractional occupation of 0.1 MHz bins

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Changeability -- Old systems GO Roosveldt Roads closure Tethered Aerostat ~1260 MHz gone -- New systems arrive UWB! -- Sporadic Incursions daily rfi complaints varied in nature and cause some known, such as GPS L3 activity some site-generated - AO work

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R Countermeasures! -consider radar blanking at least for the airport radars MHz perhaps for others too!! -Sampling sufficiently nine-level sampling for the correlator 12 bits or more for the digitizer -Algorithm developments pipeline excision cross-correlation between pixels robust statistics applied to the signals (eg

N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R

RATAN

Arecibo anti-RFI activity N A T I O N A L A S T R O N O M Y A N D I O N O S P H E R E C E N T E R overwehelming importance of L_band to alfa Should you use the radar blankers? How bothersome is the residual 1350 MHz birdie? Should you be using 9-level sampling? Algorithm development