Technical RFI Mitigation

1
Technical RFI MitigationSpectrum Management

• Rick Fisher
• NRAO

2
RFI Mitigation Research StatusDemonstration
Projects

• Array Image Processing
• local interference VLA
• Parametric Subtraction
• GLONASS - ATCA Radar - Arecibo
• Pulse Blanking
• Radar - Arecibo, GBT, Nancay DME - GBT
• Post-correlation Subtraction
• TV repeater - ATCA Sun - Parkes
• Multi-station Coincidence
• Various 1200-1800 MHz signals - Arecibo/GBT
• Adaptive Filtering/Nulling
• individual satellites - ATA, GBT, ATCA TV
  repeater - Parkes

3
NGC6251, 333 MHz, VLACornwell, Perley, Golap,
Bhatnagar RFI2004
RFI from ABQ glide slope transmitter
Mitigated with all-sky self-cal
4
RFI Mitigation Research StatusDemonstration
Projects

• Array Image Processing
• local interference VLA
• Parametric Subtraction
• GLONASS - ATCA Radar - Arecibo
• Pulse Blanking
• Radar - Arecibo, GBT, Nancay DME - GBT
• Post-correlation Subtraction
• TV repeater - ATCA Sun - Parkes
• Multi-station Coincidence
• Various 1200-1800 MHz signals - Arecibo/GBT
• Adaptive Filtering/Nulling
• individual satellites - ATA, GBT, ATCA TV
  repeater - Parkes

5
RFI Mitigation Research StatusDemonstration
Projects

• Array Image Processing
• local interference VLA
• Parametric Subtraction
• GLONASS - ATCA Radar - Arecibo
• Pulse Blanking
• Radar - Arecibo, GBT, Nancay DME - GBT
• Post-correlation Subtraction
• TV repeater - ATCA Sun - Parkes
• Multi-station Coincidence
• Various 1200-1800 MHz signals - Arecibo/GBT
• Adaptive Filtering/Nulling
• individual satellites - ATA, GBT, ATCA TV
  repeater - Parkes

6
Top Half of Aircraft Navigation Band (DME)
7
Two-hour Integration on GBT, Quasar 0952176with
and without Pulse Blanking
8
RFI Mitigation Research StatusDemonstration
Projects

• Array Image Processing
• local interference VLA
• Parametric Subtraction
• GLONASS - ATCA Radar - Arecibo
• Pulse Blanking
• Radar - Arecibo, GBT, Nancay DME - GBT
• Post-correlation Subtraction
• TV repeater - ATCA Sun - Parkes
• Multi-station Coincidence
• Various 1200-1800 MHz signals - Arecibo/GBT
• Adaptive Filtering/Nulling
• individual satellites - ATA, GBT, ATCA TV
  repeater - Parkes

9
RFI Mitigation Research StatusDemonstration
Projects

• Array Image Processing
• local interference VLA
• Parametric Subtraction
• GLONASS - ATCA Radar - Arecibo
• Pulse Blanking
• Radar - Arecibo, GBT, Nancay DME - GBT
• Post-correlation Subtraction
• TV repeater - ATCA Sun - Parkes
• Multi-station Coincidence
• Various 1200-1800 MHz signals - Arecibo/GBT
• Adaptive Filtering/Nulling
• individual satellites - ATA, GBT, ATCA TV
  repeater - Parkes

10
Adaptive Filtering on TV RFI to Pulsar at Parkes,
680 MHzKesteven, Hobbs, Clement
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Lessons Learned So Far

• Considerable processing power required
• 2x to 10x of no-RFI processing (cost)
• Greater than 20 dB suppression gets rapidly
  tougher
• Currently an enthusiasts game
• Case-by-case solutions
• Non-expert use will require considerable
  development
• Observer demand so far is soft
• Lots of other science to do
• RFI mitigation requires effort and resources
• Development ahead of the perceived need
• Common situation in spectrum management

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Derivative Thoughts

• Some types of signals are more harmful than
  others
• ITU-R R.A.769 is too simplistic, even with
  de-correlation caveats
• Radio service separation better done as a broader
  design problem
• Include transmitter, receiver, and temporal
  requirements adaptively
• Transmitters can know where they are
• Receivers and transmitters from all services can
  communicate
• Some types of signals are easier to excise than
  others
• Radio Science has outgrown its cm-wave frequency
  allocations
• Much wider bandwidths than R.A. bands below 30
  GHz
• Need to optimize our protection requirements with
  trade-offs
• Geography, time, frequency, signal compatibility,
  etc.
• We dont need or want narrow bands all the time,
  everywhere
• New set of rules and protocols need to be
  developed
• Both risks and rewards, but status quo is highest
  long term risk