VLBI2010 and the Westford station - the path forward

Christopher Beaudoin, MIT Haystack Observatory Arthur Niell, MIT Haystack Observatory Brian Corey, MIT Haystack Observatory Michael Poirier, MIT Haystack Observatory Bruce Whittier, MIT Haystack Observatory

For the past 3 years, the role of the Westford antenna in geodetic VLBI has been two-fold. Over this time, its primary purpose has been to participate in standard S/X-band geodetic VLBI observations. In its secondary role, the Westford antenna is converted into a research instrument, facilitating the development of the broadband geodetic VLBI observing technique. As a research instrument the Westford antenna incorporates a commercially-available ETS-Lindgren 3164 quadridge antenna as a radio telescope feed and uses the VLBI2010 data acquisition system incorporating digital backends (DBEs) which implements a polyphase filter bank processor. The process of converting the station from its mode of operations to a research instrument often introduces subtle anomalies that often must be diagnosed prior to broadband observing. Furthermore, this bifurcation of the station's role is not in line with the goals of the VLBI2010 specifications. Until recently, it has not been possible for the Westford station to serve as both an operational and research instrument without station conversion for two reasons: 1. poor sensitivity and 2. incompatibility of backend baseband filter bandwidths The poor sensitivity of the Westford antenna as a broadband radio telescope is in large part due to the commercial broadband feed which was readily available when the proof-of-concept VLBI2010 observations were initiated. However, with the materialization of the quadridge feed horn (QRFH) by the California Institute of Technology and with the improvements in the DiFX software correlator, the necessary components are now available to upgrade the Westford station to full-broadband capability while also adhering to the mandate to maintain backwards compatibility with the legacy S/X systems. In this presentation we will present the path forward for upgrading the Westford site to full-broadband capability while maintaining S/X compatibility.