Cobra Overview

Cobra Overview

A.G. Lyne

COBRA is a Coherent On-line Baseband Receiver for Astronomy and its primary function is to perform coherent dedispersion of pulsar data from Jodrell Bank Telescopes. It will have many other on-line and off-line uses, but here we primarily describe its use for on-line pulsar work.

COBRA consists of two main parts. The first is a front-end which provides the signal conditioning and sampling of the radio data and is funded through the PPARC rolling grant to the pulsar group to further their researches. The second part is a powerful cluster of PC processors which has been procured through the HEFCE sponsored Joint Research Equipment Initiative (JREI). The scientific case for this equipment can be found here.

The main aim is to digitise and process 100 MHz or more of dual-polarisation data which will be down-converted to baseband. The I and Q data streams will be sampled and will pass through DMA cards into a cluster of 91 dual-processor compute nodes which will conduct the required processing.

The main features of the system are summarised below:

  • Recording of two polarisations of >100 Mhz total bandwidth each.
  • Each band will be split into several sub-bands of 1.25, 2.5, 5 or 10 MHz. This permits optimisation of the processing efficiency.
  • Data will be sampled with 8-bit precision in order to give the large dynamic range required to maintain the high linearity needed to enable effective interference mitigation techniques.
  • Total input data rate will be >400 MBytes/sec. 16 of the 81 nodes will have DMA cards which are each capable of accepting >40 MBytes/sec.

    The main on-line uses of the system will be as follows:

  • Coherent dedispersion of upto 100 MHz total bandwidth, producing all four Stokes parameters.
  • Filterbanking of upto 200 MHz total bandwidth, again with all four Stokes' parameters, for pulsar searching or incoherent dedispersion.
  • Spectral polarimetry of upto 200 MHz total bandwidth, again with all four Stokes' parameters, with almost any imaginable frequency resolution.
  • Multi-beam spectral polarimetry, with upto 20 beams of 10 MHz bandwidth each.
  • The investigation and application of frequency mitigation techniques in either the frequency or time domains for any of these uses.

    The main off-line uses of the system will be as follows:

  • Pulsar searches in either survey data or in data from targeted observations. These searches may be for pulsars of very short period or which are highly accelerated in binary systems.
  • Hydrodynamical modelling of astrophysical phenomena.
  • Anything else requiring large computing resource.

    This document was generated by Pulsar on November 15, 2001