NRAO is nearing completion of a VLBA Sensitivity Upgrade project that significantly enhances the instrument's capabilities. The project's goal is to expand the VLBA's continuum bandwidth to 512 MHz per polarization by 2011, and thereby improve the signal/noise ratio of a typical continuum observation by factors of 2.8-5.6. The latter is equivalent to nearly two optical magnitudes. The corresponding recorded data rate of 4 Gigabits per second (Gbps) is a 32-fold increase over the sustainable rate of 128 Megabits per second (Mbps) that was available when the instrument was inaugurated, and 8 times the current standard data rate. New technologies for digital signal processing, data transmission and recording, and correlation, make this an achievable goal for a fairly modest investment. Overviews of the VLBA sensitivity upgrade are given by Romney (2007) and Walker et al. (2007b).
The first of the Sensitivity Upgrade developments, the DiFX software correlator described in Section 7, has been in routine operational use for over a year. This edition of the Observational Status Summary introduces two additional elements, in Sections 6.9 and 6.10. The new instrumentation, currently being installed across the VLBA, will enable an interim bandwidth of 256 MHz per polarization (2 Gbps recording rate) for observations during semester 2011-B. Further information on the Sensitivity Upgrade project is available in a memo series, at http://www.vlba.nrao.edu/memos/sensi/ . Interim updates of this document will be issued as further details on the transition become clear. Questions can be addressed to the cognizant staff members via the NRAO Helpdesk, at https://help.nrao.edu/ .
A new project, initiated recently, will replace the VLBA's 6 cm receivers. The new systems, with an expanded tuning range of 4.1 - 7.9 GHz, will enable observations of the 6.7 GHz transition of methanol. An expedited installation schedule, beginning as early as June 2011 and complete approximately one year later, will limit the VLBA's complement of 6 cm receivers to 8 or 9 at most times during that period. Proposals for 6 cm observations that require an array of 9 or 10 stations should include a careful justification.