Prototype WIDAR Correlator Arrives

Michael P. Rupen

Prototype WIDAR Correlator Arrives

Figure 1: The Prototype Correlator for the EVLA in the old correlator room at the VLA site. The right-hand half-rack houses the correlator boards: two Station Boards to filter receive and sub-divide the data from two antennas, and one Baseline Board to perform the cross-correlations. The left-hand rack houses several associated general-purpose computers which control the correlator and process and archive the correlator output data. Two more Station Boards will be added over the next few weeks, giving four antenna and full closure capability.


The first set of boards for the prototype WIDAR correlator arrived at the VLA site on Tuesday, June 24, a week ahead of schedule. The WIDAR correlator is the backend for the Expanded Very Large Array (EVLA), and will cross-correlate the data from the individual antennas over up to 8 GHz of bandwidth in each polarization, divided into 128 independent sub-bands, at a spectral (channel) resolution ranging from 1 MHz to less than 0.1 Hz, with full pulsar binning and gating capabilities. These very demanding requirements are met by an impressively flexible and correspondingly complex design called Wideband Interferometric Digital Architecture (WIDAR).

The WIDAR correlator is the major contribution to the EVLA by Canada, through the Dominion Radio Astronomical Observatory (DRAO). The specially designed correlator chips (ASICs) and prototypes of the main boards have undergone extensive functional testing in the lab; the next step is to perform on-the-sky tests using real data from the antennas, before going to full-scale production. The primary purpose of the Prototype Correlator (PTC, Fig. 1) is to carry out those critical on-the-sky tests. The first boards will allow correlation of 0.8 GHz of bandwidth from two antennas. Boards to handle two additional antennas will be added in a few weeks. The critical tests will keep the DRAO and NRAO - Socorro staff busy for several months, working towards the WIDAR Critical Design Review this fall. Further details on the design and eventual capabilities of the full WIDAR correlator may be found in Chapter 8 of the EVLA Project Book.