Antennas continue to be converted to the Expanded Very Large Array (EVLA) design, and 21 antennas are now used routinely for scientific observations. The conversion of the 22nd EVLA antenna was completed in June. EVLA antennas accounted for 72.3% of all antenna hours used in scientific observations in April 2009. The observing statistics are not as favorable as we had forecasted due to the failure of a gear in one of the two azimuth drive gearboxes on EVLA antenna 5. The gearbox is being repaired.
The first subset of the final WIDAR correlator, known as WIDAR-0, was installed at the VLA site. First fringes were recorded with WIDAR-0 using five antennas and 512 MHz of bandwidth on March 6. Fringes from eight antennas were recorded a week later. WIDAR-0 can accept inputs from up to 10 antennas. It is being used to test, verify, and integrate the two WIDAR configurations used in early science observations in Q1 2010. After that, WIDAR capabilities will grow in accordance with the recommendations of the 2008 SAGE (see the Dec 08 eNews article).
The delivery of WIDAR circuit boards is proceeding according to schedule. Nine crossbar boards and 22 station boards were shipped from the Dominion Radio Astrophysical Observatory in Penticton, British Columbia to the VLA site on June 1. Final laboratory tests of WIDAR’s baseline boards were completed in late May. The production order for these boards will be placed this summer.
Good progress has been made with the development and deployment of fully ELVA- compliant receivers. Three EVLA antennas now have the new S-band (2-4 GHz) receiver. First fringes at S-band were recorded on April 8. The production order for the receiver’s wideband orthomode transducer (OMT) was received. Prototype parts (e.g. OMT, phase shifter, circular to square waveguide transitions, and the 45 degree twist) for the Ku-band (12-18 GHz) receiver have been manufactured, and the assembly of the prototype receiver is underway. Ten, fully EVLA-compliant, C-band (4-8 GHz) receivers are installed on antennas in the array. The production order for the C-band OMTs was received in February. Ten Ka-band (26-40 GHz) receivers have been assembled and installed on EVLA antennas, with three more receivers to be installed in the coming month. Tests of the first, fully-EVLA compliant, L-band (1-2 GHz) receiver are underway. The full production of the L-band receiver should commence this year.
A new direct digital synthesizer (DDS) has been designed for use in the L302 frequency synthesizer. The old DDS has thermal dissipation problems, but the new DDS cannot be used with the old correlator due to its frequency resolution. The new DDS will only be used with the new correlator. All of the old DDSs will be changed out as part of a L302 retrofit when the old correlator is turned off.
The production of the sampler modules that contain the 3-bit, 4Gsps digitizers is still delayed due to a clocking problem encountered with a serial-to-parallel converter on the sampler board. The layout of the board has been revised, and the testing of the revised board is underway. If testing goes well, the production of the sampler modules could resume in the early fall 2009.
Work in the monitor and control group has focused on support of WIDAR-0. A new Correlator BackEnd (CBE) cluster for WIDAR-0, and eventually for the full WIDAR, was purchased and installed. The cluster currently consists of four nodes, with different input/output configurations, in order to best investigate how these different configurations affect final system performance. This investigation may allow us to reduce significantly the number of nodes needed in the final version of the cluster. A significant amount of new software, which enabled the handling of auxiliary data products from other parts of the system, was installed on the CBE cluster. The Correlator Power Control Computer (CPCC) software was upgraded to support WIDAR-0. This software supports turning on and off circuit boards, cooling fans, and other correlator room components.
The new web-based Observation Preparation Tool (OPT) is now available to observers and has already been used for science observations. The new OPT is the only supported way to access the extended tuning ranges of the EVLA, such as those provided by the new Ka-band and C-band receivers. A temporary web page has been set up for help on getting started with the OPT. At this moment, Firefox is the only web browser for which the OPT is supported. The OPT is now available via the NRAO User Portal. Users must be registered with that web-site to use the OPT.
An EVLA Advisory Committee meeting was held March 19-20, 2009. The Committee was very impressed with the overall project progress. The Committee findings and recommendations include developing science-driven plans for archiving EVLA data and getting the data to users, taking more action to ensure user acceptance of CASA, maintaining and growing a vibrant science community at Socorro for the EVLA, and quickly developing a vision for high-impact science.
A science workshop on “The EVLA Vision: Stars On and Off the Main Sequence” was held in Socorro May 26-28. Fifty-two scientists from around the world participated. The purpose of the workshop was to explore how the new capabilities provided by the EVLA might be harnessed in stellar studies, such as new source populations, circumstellar chemistry, and fast and sensitive time response to transient events. The workshop program can be found online.