Adaptive filters revisited: Radio frequency interference mitigation in pulsar observations

Abstract

[1] Pulsar detection and timing experiments are applications where adaptive filters seem eminently suitable tools for radio frequency interference (RFI) mitigation. We describe a novel variant which works well in field trials of pulsar observations centered on an observing frequency of 675 MHz and a bandwidth of 64 MHz and with 2-bit sampling. Adaptive filters have generally received bad press for RFI mitigation in radio astronomical observations with their most serious drawback being a spectral echo of the RFI embedded in the filtered signals. Pulsar observations are intrinsically less sensitive to this as they operate in the (pulsar period) time domain. The field trials have allowed us to identify those issues which limit the effectiveness of the adaptive filter. We conclude that adaptive filters can significantly improve pulsar observations in the presence of RFI.

The North American Nanohertz Observatory for Gravitational Waves

“…Our group has demonstrated initial success with broadband and narrowband software RFI identification and excision before and during coherent dedispersion (Stairs et al 2000), but we need efficient versions of these algorithms in order to implement them routinely in the wideband real-time instruments. Achieving this goal and exploring alternate RFI mitigation schemes based on FPGA technology (Kesteven et al 2005) are some of our priorities for the next few years ( §4.1). We will also determine the exact effect of such techniques on the final recorded signal and TOAs by performing an end-to-end simulation of the pulsar signal path encompassing everything from propagation effects to calibration corrections.…”

“…• Radio-frequency interference (RFI) excision ( §3.1), efficiently implementing existing software algorithms (Stairs et al 2000), and exploring hardware-based solutions (Kesteven et al 2005). …”

Field Trials of a RFI adaptive filter for Pulsar Observations

“…The result is a practical tool, available on-line for routine pulsar observations. A proof-of-concept demonstration was reported in 2005 [4].…”

RFI Mitigation in Radio Astronomy (invited)

“…The suppression of the interfering signal can be about equal to its instantaneous INR. Adaptive filters are effective when spectral information is unimportant, such as in pulsar [33] and continuum studies. This method has also been used effectively with multi-feed or focal plane arrays on single dishes (see next section).…”