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

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)

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

0 500 1000 1500 2000

0 500 1000 1500 2000

400

0

20

0

RATAN-500 1116+28

• 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