Workshop on Mitigation of Radio Frequency Interference in Radio Astronomy (RFI2004)
held at DRAO (Penticton, BC, Canada) July 16-18, 2004.

Note: Many of the papers appearing here are now available as peer-reviewed papers in a Special Section of Radio Science.

Table of Contents

Introductory Session
Regulatory Session
Radar and Iridium
Precorrelation Array Techniques
Postcorrelation Techniques
Characterization and Algorithms
Mitigating RFI at RF
Workshop Recap and Discussion

Introductory Session

Session Chair: S. Ellingson, Virginia Tech
  1. "The Future of our Radio Window to the Universe"(Invited)
    R. Ekers (ATNF).
    This will be a very broad overview of issues related to the future use of the radio spectrum for astronomy. I will cover international activities, sharing use of the spectrum, impact of new technology, requirements for new telescopes, regulation versus mitigation, environmental credits, and other social issues.
    Presentation (PDF, 1.7MB)

  2. "Overview of Technical Approaches to RFI Mitigation"
    F. Briggs (ANU/MSO)
    The goal of this introductory presentation will be to explore the commonality of different approaches to RFI mitigation, in order to help build intuition on some of the conditions under which interfering signals can be cancelled or subtracted without damaging the celestial signals that radio astronomers strive to receive.(more)
    Presentation (PDF, 5.4MB)

  3. "Getting RFI Mitigation into the Workplace" (Invited),
    J.R. Fisher (NRAO)
    Over the past few years we have seen some impressive demonstrations of excision of RFI from radio telescope data. The techniques used include parametric signal synthesis and subtraction, adaptive filtering, post correlation subtraction, and pulse blanking. However, relatively little of this work has made its way into astronomical use. (more)
    Presentation (PDF, 40KB)

Table of Contents

Regulatory Session

Session Chair: S. Ellingson, Virginia Tech
  1. ``Quiet, please'' - introduction to regulatory protection of the SKA"
    Wim van Driel (Obs. de Paris)
    The saying that ``Prevention is better than a cure'' also applies to the RFI situation for the SKA - the quieter its RFI environment, the higher the sensitivity that could be achieved and the easier it will be to mitigate residual RFI problems. An introduction will be given to the astronomical spectrum management situation, focused on different possible strategies for regulatory means to limit the levels of various kinds of RFI at the SKA site.(more)
    Presentation (PDF, 480KB), Paper (PDF, 192KB)

  2. "SKA and ITU Regulations"
    Tomas Gergely (NSF)
    The International Telecommunication Union (ITU) provides the international regulatory framework that governs the uses of the radio spectrum that the SKA will cover. The primary instrument used by the ITU to accomplish its task is the Radio Regulations (RR), an international treaty.(more).
    Presentation (PDF, 184KB), Paper (PDF, 116KB)

  3. "Radio Quiet Zones - past, present and future"
    Tasso Tzioumis (ATNF)
    The first step of RFI mitigation should always be avoidance of RFI to the maximum practicable extent. One way to do this is to attempt to define the RF characteristics in the environment around our observatories, and that is the basic concept of a "radio quiet zone" (RQZ). In this contribution, I will review the past and present instances of RQZs and their operational characteristics.(more).
    Presentation (PDF, 256KB)

Table of Contents

Radar and Iridium

Session Chair: F. Briggs, ANU/MSO
  1. "Examination of a Simple Pulse Blanking Technique for RFI Mitigation"
    N. Niamsuwan (Ohio State), J.T. Johnson (Ohio State), and S.W. Ellingson (Virginia Tech)
    Radio frequency interference (RFI) mitigation is very important for spectroscopy at L-band due to the presence of numerous interference sources, including strong pulsed RFI from ground-based aviation radars (GBARs). A simple strategy for reducing pulsed RFI is to remove incoming data whose power exceeds the mean power by a specified number of standard deviations.(more)
    Presentation (PDF, 652KB), Paper (PDF, 700KB).

  2. "Kalman Tracking and Bayesian Detection for Radar RFI Blanking"
    W. Dong (Brigham Young U.), B.D. Jeffs (Brigham Young U.), J.R. Fisher (NRAO)
    L-Band observations at the Green Bank Telescope (GBT) and other radio observatories are plagued with interference from pulsed aviation RADAR transmissions. Several researchers have studied the problem and proposed time gated blanking and parametric signal subtraction as mitigation strategies.(more)
    Presentation (PDF, 848KB), Paper (PDF, 960KB)

  3. "Iridium: Characterization and Countermeasures"
    S. Ellingson (Virginia Tech), P. McDougle (Virginia Tech)
    RFI from the Iridium satellite communication system complicates observations in 1610-1630 MHz band. In this paper, we present a detailed analysis of Iridium downlink signal observed at 1624 MHz using coherently-sampled data from Argus, a 24-element array of broadbeam antennas capable of instantaneous all-sky field of view, currently operating on the campus of the Ohio State University. (more)
    Presentation (PDF, 1.3MB)

  4. "RFI Mitigation and Burst Detection with a Digital Receiver"
    R. Weber, LESI/Polytech'Orleans; L. Denis, Nanšay; C. Dumez-Viou, LESI/Nanšay.
    RDH (Reconquest of Radio Spectrum) is a high dynamic receiver currently developed at the Nanšay Observatory in France. It is currently connected to 2 instruments that observe 10 to 30 cm long wavelength for the Nanšay Radio Telescope (NRT) and 3 to 30 m long for the Nanšay Decameter Array (NDA).(more)
    Presentation (PDF, 3.8MB), Paper (PDF, 1.3MB)

Table of Contents


Session Chair: F. Briggs, ANU/MSO
  1. "Ten Years of RFI - Project Phoenix at Parkes, Green Bank and Arecibo"
    M.M. Davis, SETI Institute; P.R. Backus, SETI Institute; J. Tarter, SETI Institute.
    Between 1995 and 2004 Project Phoenix detected and recorded narrowband, drifting CW and pulsed signals between 1200 and 3000 MHz, in a search for extraterrestrial intelligence. The observations were carried out at three major radio observatories, with frequency resolutions of 1 kHz, 1 Hz and, for candidate signals, a few mHz.(more)
    Presentation (PDF, 1.0MB)

  2. "Post-Correlation RFI Excision at Low Frequencies"
    W. Lane (NRL); A. Cohen (NRL); N. Kassim (NRL); J. Lazio (NRL); R. Perley (NRAO); B. Cotton (NRAO); E. Greisen (NRAO)
    We describe some RFI excision schemes which are currently being used in low frequency (<1 GHz) radio astronomy. We present examples from our experience with editing of single dish and interferometric data, and discuss specialized procedures employed for targetted observations, as well as broader brush, pipe-line schemes developed for surveys such as the VLA Low Frequency Sky Survey (VLSS). (more)
    Presentation (PDF, 736KB)

  3. "Adaptive Filters Revisited - RFI Mitigation in Pulsar Observations"
    M. Kesteven (ATNF), G. Hobbs (ATNF), R. Clement.
    Pulsar detection and timing experiments are applications where adaptive filters seem eminently suitable tools for RFI mitigation. We describe a novel variant which has worked well in field trials - with observations at 700 MHz, 64 MHz bandwidth, 2-bit sampling.(more)
    Presentation (PDF, 272KB), Paper (PDF, 520KB)

  4. "RFI Mitigation for the Deuterium Experiment"
    G. Bower (UC Berkeley)
    One of the first scientific goals of the Allen Telescope Array is the detection of interstellar deuterium through the DI transition at 327 MHz. This is a novel experiment for RFI mitigation since we accumulate the astronomy signal from autocorrelations from each antenna but also compute cross-correlations.(more)
    Presentation (PDF, 1.5MB), Conference paper (PDF, 356KB)
    Also available as: RADIO SCIENCE, VOL. 40, RS5S07, doi:10.1029/2004RS003141, 2005

  5. "RFI Mitigation Strategies for LOFAR and SKA"
    W.A. Baan, Astron; A.-J. Boonstra, Astron; P. Fridman, Astron; R. Millenaar, Astron.
    The leap in sensitivity of the new generation telescopes and the intensifying commercial and public use of the spectrum warrant a new and innovative approach towards RFI Mitigation. An RFI Mitigation strategy using multiple layers of applications during the data-processing flow is found to be optimal. (more)
    Presentation (PDF, 1.8MB)

Table of Contents

Precorrelation Array Techniques

Session Chair: B. Jeffs, BYU
  1. "RFI mitigation at WSRT: algorithms, test observations, system implementation"
    W. Baan (ASTRON), P. Fridman (ASTRON), R. Millenaar (ASTRON).
    An RFI mitigation subsystem (RFIMS) based on real-time digital signal processing is proposed here for the Westerbork Synthesis Radio Telescope (WSRT). RFIMS is based on a powerful field programmable gate array (FPGA) processor Altera Stratix S80.(more)
    Presentation (Warning: 9MB PowerPoint file!)

  2. "RFI mitigation for tied-array configuration with phase-only adaptive beamforming"
    P. Fridman (ASTRON)
    There are several specific features of large aperture synthesis radio interferometers (ASRI) like (WSRT, VLA, GMRT) which make a straightforward application of RFI mitigation adaptive beam-forming difficult and different from classic phased arrays: 1) ASRI are the highly sparsed arrays...(more)
    Presentation (PDF, 656KB)

  3. "Spatial Filtering of Interfering Signals at the Initial LOFAR Phased Array Test Station"
    A.J. Boonstra, ASTRON; S. van der Tol, TU Delft.
    The Low Frequency Array (LOFAR) is a radio telescope currently being designed and planned. Its targeted observational frequency window lies in the range 10-250 MHz. The initial test station (ITS) is a full scale prototype of a LOFAR station, and it became operational in December 2003.(more)
    Presentation (PDF, 1.8MB), Paper (PDF, 2.4MB).

  4. "Design Constraints for RFI Nulling at the ATA"
    Gerry Harp (SETI Inst.)
    The Allen Telescope Array is a new 350-element radio telescope currently under construction in Northern California. Single-tap beamformers combine signals from all these elements to provide 16 simultaneous dual-polarization beams on the sky.(more).
    Presentation (PDF, 696KB), Paper (PDF, 180KB)

Table of Contents

Postcorrelation Techniques

Session Chair: B. Jeffs, BYU
  1. "Reference Antenna Techniques for Cancelling Interference from Moving Sources"
    D. Mitchell (U. Sydney)
    Interference mitigation techniques which modify signals from auxiliary reference antennae to model and cancel interference from an astronomical observation can be applied in the time domain, where the RFI voltage is modelled and subtracted from the astronomy signal path (adaptive noise cancelling)... (more)
    Presentation (PDF, 352KB), Paper (PDF, 272KB)

  2. "Correlations of Spectral Intensity Fluctuations: Application to RFI mitigation"
    A.A. Deshpande, NAIC and RRI
    This paper describes a technique involving correlations between fluctuations in spectral intensities. When applied to intensity data available as a function of time and frequency, the result can be viewed in form of a correlation map, wherein the temporal correlation between fluctuations in every possible pair of spectral channels is represented.(more)
    Paper (PDF, 2.7MB)

  3. "Post-correlation ripple removal and RFI rejection for Parkes Telescope survey data"
    D.G. Barnes, U. Melbourne; F.H. Briggs, ANU; M.R. Calabretta, ATNF.
    The Multibeam receiver on the Parkes telescope has been used for many neutral hydrogen (HI) imaging projects, for example the HI Parkes All Sky Survey (HIPASS) and the Southern Galactic Plane Survey.(more)
    Presentation (PDF, 2.2MB), Paper (PDF, 5.1MB)

  4. "Post-Correlation RFI Excision with the VLA and the EVLA"
    R. Perley, NRAO; T. Cornwell, NRAO; S. Bhatnagar, NRAO; K. Golap, NRAO.
    To a synthesis interferometer, a source of RFI differs from a distant unresolved astronomical source primarily in its rapid differential phase rate. Providing that the correlator sampling is sufficiently rapid, and that the RFI emissions do not drive the signal transmission or processing components to non-linear behavior...(more)
    Presentation (PDF, 976KB)

Table of Contents

Characterization and Algorithms

Session Chair: A.-J. Boonstra, Astron
  1. "RFI Identification and Mitigation Using Simultaneous Dual Station Observations"
    R. Bhat, MIT/Haystack; J. Cordes, Cornell; S. Chatterjee, NRAO; J. Lazio, NRL.
    RFI mitigation is a critically important issue in the development of next-generation radio telescopes including the SKA. Most designs for the SKA involve multiple stations with spacings up to a few thousands of kilometers and thus will need to deal with RFI environments drastically different from that of conventional single-station telescopes.(more)
    Presentation (PDF, 1.5MB), Paper (Postscript, 15MB), Paper (PDF, 1.4MB)

  2. "Cyclostationary Detectors for RFI Mitigation in Radio Astronomy"
    S. Bretteil (LESI/Polytech Orleans), R. Weber (LESI/Polytech'Orleans).
    This paper presents a scheme for removing efficiently cyclostationary radio frequency interferences (RFI) from astronomical data. Various methods have been experimented to eliminate those RFI depending on the type of interferences and the type of instruments. The present study focuses on time-frequency blanking on data coming from a single dish.(more)
    Presentation (PDF, 256KB), Paper (PDF, 220KB)

  3. "Another Algorithm for Phased Array Null Formation"
    L. Kogan (NRAO).
    The phased array beam pattern null towards the RI source can mitigate effect of the RFI. Several algorithms for creating null at the phased array beam pattern have been designed. See for example ATA memos of Geoffrey Bower (1) and G.R. Harp (2). Another algorithm for creating null at the phased array beam pattern is described here.(more)
    (No presentation available), Conference Paper (PDF, 116KB)
    Also available as: RADIO SCIENCE, VOL. 40, RS2S90, doi:10.1029/2004RS003140, 2005

  4. "The Effect of Amplifier Gain Compression on Correlation Coefficient"
    R. Perley, NRAO; R. Hayward, NRAO.
    Modern wideband interferometers will be required to operate in an environment with very strong artificial emissions -- some of which when entering through isotropic sidelobes, will raise the total system power by 20 dB or more above the levels expected from observations of cold sky.(more)
    Presentation (PDF, 136KB)

Table of Contents

Mitigating RFI at RF

Session Chair: A.-J. Boonstra, Astron
  1. "Interference Mitigation Using an Array Feed"
    C.K. Hansen, BYU; K.F. Warnick, BYU; B.D. Jeffs, BYU; J.R. Fisher, NRAO; R. Bradley, NRAO.
    Spatial filtering techniques for RFI mitigation require multiple, spatially separated looks at the interfering signal. For a large reflector, this can be accomplished with an array feed. We show using simulations that an array of electrically small elements in conjunction with a spatial filtering algorithm can provide high antenna sensitivity even in the presence of RFI. (more)
    Presentation (PDF, 352KB), Paper (PDF, 36KB)

  2. "RFI mitigation at a 2GHz band by using a wide-band high-temperature superconductor filter"
    E. Kawai, NICT; J. Nakajima, NICT; H. Takeuchi, NICT; H. Kuboki, NICT; T. Kondo, NICT
    Severe radio frequency interferences (RFIs) at an S-band (2GHz) due to third-generation mobile phone system (IMT-2000) have started since 2002 at a 34-m antenna located at the Kashima Space Research Center, National Institute of Information and Communications Technology (NICT : former Communications Research Laboratory) in Japan.(more)
    Presentation (PDF, 988KB)

  3. "Suppression of Self-Generated RFI Emissions for the EVLA"
    S. Durand, NRAO; R. Ridgeway, NRAO; J. Jackson, NRAO; R. Perley, NRAO.
    The EVLA will be a fully digital radio telescope, with high speed sampling (4 GSamp/sec) done at each antenna, a digital Fiber Optic transmission system to convey the signals from the antenna to the correlator, and a very large digital correlator located at the VLA central site.(more)
    Presentation (PDF, 908KB).

  4. "Determination, control and improvement of an SKA radio environment in South Africa"
    Ne╬l Smuts (South Africa)
    South Africa, in its bid to host the SKA, has adopted a dual approach to determine, assess and improve the radio environment and RFI that would be experienced by the SKA. The one approach was to determine all the transmissions that would provide signals which exceed the various threshold levels...(more)
    Presentation (PDF, 176KB), Paper (PDF, 84KB)

Table of Contents

Workshop Recap and Discussion

Session Chair: W. van Driel, Obs. de Paris
Presentation / Discussion points (PDF, 224KB)

Table of Contents


  1. "Signal Analysis and Blanking Experiments on DME Interference"
    J.R. Fisher (NRAO)
    Paper (PDF, 1.2MB)

  2. "RFI shielding and mitigation techniques for a sensitive search for the 327 MHz line of Deuterium"
    A.E.E. Rogers (Haystack), J.C. Carter (Haystack), P. Pratap (Haystack), M.A. Diaz (Boston U.)
    An array of 25 stations each with 24 crossed-dipoles is being built at the Haystack Observatory in Westford MA. This array has been designed to make a sensitive search for the 327 MHz spectral line of Deuterium. (more)
    Presentation(PowerPoint, 4.9MB), Paper (PDF 464KB)

  3. "Using Multiple Beams to Distinguish RFI From ETI Signals"
    G. Harp (SETI Inst.)
    The Allen Telescope Array is a multi-user instrument and will perform simultaneous radio astronomy and SETI observations. It is a multi-beam instrument, with 16 independently steerable dual-pol beams at 4 different tunings. Given 4 beams at one tuning, it is possible to discriminate RFI from true ETI Signals by pointing the beams in different directions.(more)
    Poster (PowerPoint, 708KB), Paper (PDF, 176KB)

Table of Contents

Maintainer: S.W. Ellingson
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Last Update: May 6, 2005