P' Colom 1

1
DS4-T2 T3Signal conditioning RFI mitigation

• Achieved milestones and deliverables
• DS4T2 (INAF-IRA, ASTRON, CSIRO)
• Deliverable Planned Achieved
• 1 Wide band, high dynamic range A/D blocks 9 9
• 2 Digital Down Converters 9 9
• 4 Low cost Poly-Phase filter banks 9 9
• 5 Data distribution and synchronization 6 12
• Next milestone and deliverable
• Sizing of the digital word at the different
  levels of the system chain (T018)

2
RFI and digitisation requirement around 408 MHz
in Medicina (Italy)
In Europe, the RFI environment is dominated by
ground-based emissions TV, telecom,
radars... To avoid ADC saturation, need for high
dynamic range 10 (true) bits in Medicina
3
RFI and digitisation requirement Potential SKA
site

• Expectation the ground-based emissions are much
  lower
• the RFI environment is dominated by satellite
  emissions
• (GPS, GLONASS, Iridium )
• a lower dynamic range is required
• Iridium around 1620 MHz is the most powerful
• Depending on the required instantaneous bandwidth
  and the required nr. of bits in the noise level
• 4-6 bits would be enough (ASTRON preliminary
  analysis)

4
RFI and digitisation requirement Distance
Measuring Equipment

• Frequency range (1000-1400 MHz)
• pulsed signals of high peak power level.
• If it will be required to handle these signals
  without distortion, the number of bits has to
  increase
• same stands for lightning
• time occupancy of these signals ?

5
Digital Down Conversion Undersampling

• Sampling frequency lt Nyquist frequency
• It works, but
• concern is the added noise due to the ADC clock
  jitter

6
Digital Down Conversion This is crucial for a
high undersampling factor

• a low jitter clock is fundamental to achieve a
  high SNR
• undersampling in radio astronomical applications
  seems to be possible, but it is very important to
  take care of the clock source and the clock
  distribution to ADC.

7
Low cost polyphase filter bank PCI board
developed in Medicina (VIIP)

• Two analog inputs, one clock input
• two ADCs, 105 MSPS, 14 bits
• one FPGA implements the polyphase filter bank
• out of band rejection ratio of 60 dB
• Xilinx FPGA, from the Virtex-II family.
• Low cost, driven by the FPGA and the PCB

8
RFI mitigation DS4T3 (OPAR, ASTRON, INAF-IRA,
UORL, CSIRO)

• Achieved milestones and deliverables
• Deliverable Planned Achieved
• 1 RFI mitigation inventory 12 6
• 2 Influence on data quality 24 Y3Q4
• 3 Impact of moving interference sources 24 Y2Q4
• 4 Cost effect. and tech. Requirements SKA
  site 36 Y3Q4
• 5 Demonstrations with EMBRACE, BEST 48 Y4Q4
• 6 RFI mitigation strategies for the SKA
  phased-arrays Y4Q4
• Next milestone and deliverable
• RFI mitigation inventory end of 06
  (rescheduled)
• impact of moving interference sources July 07

9
RFI mitigationresults (1)

• Work started on the Inventory of RFI mitigation
  methods
• under ASTRON supervision overview, spatial
  excision and filtering
• UORL detection, cancellation and estimation
  techniques using cyclostationary properties of
  interference sources in t-f domain
• evaluation and influence of RFI mitigation on the
  data quality
• impact of moving interferers on SKA a study was
  conducted (conference paper) in which the use of
  NOAA weather satellites for aperture array
  calibration was investigated (ASTRON)
• cost effectiveness and requirements an ASTRON
  study on signal processing requirements for SKA
  (memo)

10
RFI mitigation results (2)

• demonstrations of RFI mitigation techniques
• design (UORL) and implementation (OPAR) of
  real-time detection and blanking in both time and
  frequency domains with the RDH digital receiver
  on the decimetre wave Radio Telescope and the
  decametre wave array at the Nançay Station.
  Observations of galaxies in frequency bands with
  radar emissions.
• elaboration of a test plan for EMBRACE, under
  discussion (ASTRON)
• design of deterministic and adaptive beam nulling
  techniques, and studies of the possibility to
  implement them in the BEST (DS6) demonstrator.
  RFI cancellation has been obtained with the use
  of a reference antenna, at frequencies around 408
  MHz (INAF)

11
RFI mitigation results (3)

• CSIRO
• a prototype FPGA implementation of a real-time
  adaptive filter for RFI mitigation (designed to
  be used for pulsar observations) has been built.
  This unit has a 50 MHz bandwidth and a 2048
  channel polyphase filter.
• a second team has been investigating the
  cancellation of digital TV signals in the 50cm
  wavelength band at Parkes Observatory using dual
  "reference antenna" methods. The aim is RFI
  cancellation down to sensitivity levels that are
  radiometer noise limited.
• UORL
• detection and cancellation using cyclostationary
  properties of interference sources. Results were
  obtained on simulated and real data.

12
RFI mitigation next steps

• regular exchanges with the EMBRACE test group, to
  insure RFI mitigation demonstrations will be
  included in the test plan (OPAR, ASTRON)
• looking at the variability of the spatial
  signature of moving sources (ASTRON)
• assessing the cost effectiveness and requirements
  of the most promising RFI mitigation methods
  (ASTRON)
• implementation of a synthesis filter to convert
  the RFI-filtered spectral data to a baseband IF,
  in order to match the RFI-filter to the pulsar
  backend to be completed in 2007 (CSIRO)
• The work on spatial filtering techniques using
  cyclostationary properties will start in
  September 2006 (UORL).