Excision of broadband arcing power-line RFI Ryan Monroe - - PowerPoint PPT Presentation

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excision of broadband arcing power line rfi
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Excision of broadband arcing power-line RFI Ryan Monroe - - PowerPoint PPT Presentation

Oct 17, 2022 353 likes •534 views

Excision of broadband arcing power-line RFI Ryan Monroe rmonroe@caltech.edu The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) 288 Dual-pol Antennas Full sky viewing @ ~25-85 MHz The Owens Valley Radio Observatory

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SLIDE 1

Excision of broadband arcing power-line RFI

Ryan Monroe

rmonroe@caltech.edu

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SLIDE 2

The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA)

  • 288 Dual-pol

Antennas

  • Full sky viewing

@ ~25-85 MHz

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SLIDE 3

The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA)

  • 4 pols* 2400 channels* 33000 baselines =

1.2558e+09 visibility measurements per integration!

  • Flagging of RFI and bad data

– {antenna, channel, visibility}

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RFI seen from OVRO

  • Minimal RFI from intentional broadcasters - easily flagged
  • However, power-line arcing produces broadband, time-

variable RFI

  • Fitting for near-field emitters produces candidate sources.
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SLIDE 5
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RFI seen from OVRO

  • Unlike most RFI, this is on often and broadband –

hard to remove with time/frequency flagging

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SLIDE 7

Beamformed detection

  • Beamform in the direction of source for

detection and analysis

  • Easy to see RFI events with integrated power

detector

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SLIDE 8

Beamformed detection

  • Pulses unresolved at 41.6 microseconds
  • Clear 60 Hz trend to pulse groupings
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SLIDE 9

Results

  • Flag in time @ 41.6 us, correlate in software
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Results

  • Easy to implement on GPU correlator; for large

arrays is often computationally efficient = real-time processing

  • OVRO-LWA will use this for final 352-antenna array
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SLIDE 11

Flagging Bad Data

  • Antennas: 288 (easy)
  • Frequencies: 2398 (easy)
  • Baselines: 165600 (much harder!)

– Most baseline-driven issues are stable in time

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Baseline flagging

  • Insight: visibilities smooth in

{u,v,w,time,frequency}

  • Instrumental effects violate this
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Baseline flagging

  • Insight: visibilities smooth in

{u,v,w,time,frequency}

  • Fit low-order polynomial to surface, look for

large residuals

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Baseline flagging

  • Limitation: require sufficient visibility

density

– In our case, long baselines too sparse

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SLIDE 15

Baseline flagging

  • Discovered: a few bad antennas,

frequencies

– Also, adjacent ARX line leakage – (was already planning on designing

improved ARX boards)

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SLIDE 16

Conclusions

  • You might need evidence to convince

utilities companies to clean their power lines: look for something like this

  • Created realtime RFI mitigator which is

easy to implement in software

  • Used smoothness assumption in visibility

space to flag bad baselines

  • Email me at rmonroe@caltech.edu