This document summarizes the instrumental status of the Expanded Very Large Array (EVLA) until the start of D-configuration on January 25, 2013.  For observations after that date, we refer to the appropriate OSS version.

The OSS intended as a ready reference for those contemplating use of the EVLA for their astronomical research. The information is in summary form - those requiring greater detail should consult the EVLA's staff members, listed in Key Personnel, or refer to the manuals and documentation listed in Documentation. Most of the information contained here, and much more, is available through the EVLA science web pages, and the companion document for the VLBA.

The EVLA is a large and complex modern instrument. Some familiarity with the principles and practices of its operation is necessary for efficient use to be made of it. Although the NRAO strives to make using the EVLA as simple as possible, users must be aware that proper selection of observing mode and calibration technique is often crucial to the success of an observing program. Inexperienced and first-time users are especially encouraged to enlist the assistance of an experienced colleague or NRAO staff member for advice on, or direct participation in, an observing program. Refer to Help for Visitors to the EVLA and DSOC for details. The EVLA will be an extremely flexible instrument, and we are always interested in imaginative and innovative ways of using it.

The EVLA is the product of a program to modernize the electronics of the Very Large Array (VLA) in order to improve several key observational parameters by an order of magnitude or more. Some of the details of the EVLA Project may be found on the web, at http://www.aoc.nrao.edu/evla/. The EVLA is funded jointly by the US National Science Foundation (NSF), the Canadian National Research Council, and the CONACyT funding agency in Mexico. Total funding is approximately $94 million in Year 2006 dollars, including $59 million in new NSF funding, $16 million in redistributed effort from the NRAO Operations budget, $17 million for the correlator from Canada, and $2 million from Mexico. The EVLA project will be completed on time and on budget at the end of 2012, 11 years after it began. Its key observational goals are (1) complete frequency coverage from 1 to 50 GHz; (2) continuum sensitivity improvement by up to an order of magnitude (nearly two orders of magnitude in speed) by increasing the bandwidth from the VLA's 100 MHz per polarization to 8 GHz per polarization; and (3) implementation of a new correlator that can process the large bandwidth with a minimum of 16,384 spectral channels per baseline. A comparison of some of the EVLA performance parameters with those of the VLA is provided in Table 1. The remaining major milestones for the EVLA are shown in Table 2.

Note: The "Factor" gives the factor by which the EVLA parameter will be an improvement over the equivalent VLA parameter.

The year 2010 was extremely exciting for the EVLA. The correlator that was the heart of the VLA for three decades was decommissioned on 11 January, 2010, and replaced with the new EVLA "WIDAR" correlator. The VLA was shut down to outside users until March 2010, during which time hardware was transferred from the old correlator to the EVLA correlator and observing modes commissioned in preparation for EVLA early science. At the same time the direction of the configuration cycles also changed, from A→B→C→D→A to D→C→B→A→D, in order to facilitate the EVLA correlator commissioning and to limit initial EVLA data rates. The last VLA antenna was retrofitted to EVLA specifications in May 2010.

During 2011 the WIDAR correlator was put into full observing mode with commissioning and Resident Shared Risk Observing starting in early 2011. By the end of 2011, up to 2 GHz of bandwidth was provided to the the general public along with 2 tunable bands, each with 8 spectral windows (64 to 256 channels) at S, Ku and X bands.