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...
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Transcript of 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...
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 AssociateRadio 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 regionGPSGalileoPR Radars in bandRFI 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
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 L2 L1
General coverage -158 dBWSpot Beam -138 dBW Alfa 1225 - 1525
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
GPSL1 & L2 -157 dBW for C/A -160 dBW for YL5 -154 dBW ≈24 MHz, full time occupancy
This is 6 dB stronger than present L1 & L2
L5 spfd ~-205 dBW/m^2/Hz 1164-1188 MHz~-197 dBW/m^2/Hz in center
5 - 8 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 1164-1215 MHz (WRC2000)E6 1260-1300 MHz (WRC2000)E2,L1,E1 1559-1591 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 2001-5 2/4 satellites
Deployment 2006-7 26-28 sats
Commercial Ops. 2008
Concern is their presence at 1260-1300 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 1200-1450 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 1400-1427 MHz band
(i) US has proposed a satellite feeder-link system Uplink 1390-2 MHz, downlink 1430-2 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 GORoosveldt Roads closureTethered Aerostat ~1260 MHz gone
-- New systems arriveUWB!
-- Sporadic Incursionsdaily rfi complaintsvaried 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 1330-1350 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 http://www.iucaf.org/sschool/peterf/fridmanpaper4.pdf)