VHF-band RFI
in Geographically Remote Areas
Judd D. Bowman
Hubble Fellow, Caltech
Alan E. E. Rogers
Haystack Observatory
With support from:
CSIRO/MRO and Curtin University
Thanks to:
The organizers and Murray Lewis and the NSF
31 March 2010
RFI2010
Groningen
Outline
• Experiment to Detect the Global EoR Signature (EDGES)
• RFI at Murchison Radio-astronomy Observatory (MRO)
• Quick surveys in the US
Rural New England
Catlow Valley, Oregon
• A few words on meteor scattering
Experiment to Detect the
Global Epoch of Reionization Signature
(EDGES)
Exotic Telescopes Prepare to Probe Era of First Stars and Galaxies
Science, Vol. 325. no. 5948, pp. 1617 – 1619, 25 September 2009
The approach for LOFAR, MWA, PAPER, SKA…
“Science with the MWA”
Greenhill, Bowman, et al. (2010, in prep)
Figure by Matt McQuinn
The approach for EDGES
 [MHz]
50
100
10
500
Tb [mK]
50
0
-50
21 cm global brightness temperature
-100
100
10
z [redshift]
Pritchard & Loeb 2008
EDGES
EDGES
Bowman & Rogers (in prep)
Deep VHF-band integrations at the MRO
Murchison Radio-astronomy Observatory
Radio Frequency Interference (RFI)
Integrated spectrum at MRO by EDGES
+15 dB
Murchison Radio-Astronomy
Observatory (MRO)
Aug 20 – Oct 20, 2009
1440 wall-clock hours on sky
~50 hours actual integration
+40 dB
Orbcomm LEO satellite constellation (136-138 MHz)
Total power in band vs. time
Sum antenna temperature 90-205 MHz
Orbcomm band ~138 MHz
Anomalous propagation – DTV 7 and 9
EDGES Memo#058, AEER, 2010
Integrated RFI
(time excision only – by broadband power level in
FM, Orbcomm, DTV bands: 30% removal)
Note: shows every channel that ever had RFI over 3 months
Conservatively excise any channel that had RFI: 11% removal
Example excision rates
Shallow surveys in remote areas of the US
US TV and FM radio “pollution”
West Forks, Maine
D1 Array – Haystack Obs.
Rural New England, US
D1 Array – Haystack Obs.
West Forks, Maine
EDGES Memo#044, AEER, 2009
US TV and FM radio “pollution”
EDGES Memo#052, AEER, JDB, 2009
Catlow Valley, Oregon, US
60 dB
10 dB
80 MHz 200
Meteor scattering
Time-variable FM RFI
FM band
Meteor scatter rates vs. elevation angle
horizon
zenith
EDGES Memo#054, AEER, 2009
Summary
• 3 month deployment in MRO
– Deepest broadband spectrum ever acquired:
5 mK rms
(-220 dBW/m2/Hz)
– First redshifted 21 cm EoR science
– Simple time and spectral flagging sufficient to remove RFI
– FM band a good indicator of anomalous transmission events
– Total power in band varies strongly with Orbcomm and aircraft
• Quiet sites in US – not as good as MRO
– Meteor scatter a significant source of RFI, dependent on
elevation angle of sky coverage
Aircraft at MRO
FM at MRO
RFI observed in Oregon, US
Summary
• 3 month deployment in MRO
– Deepest broadband spectrum ever acquired:
5 mK rms
(-220 dBW/m2/Hz)
– First redshifted 21 cm EoR science
– Simple time and spectral flagging sufficient to remove RFI
– FM band a good indicator of anomalous transmission events
– Total power in band varies strongly with Orbcomm and aircraft
• Quiet sites in US – not as good as MRO
– Meteor scatter a significant source of RFI, dependent on
elevation angle of sky coverage