New Developments
The VLBA Sensitivity Upgrade project is now complete, with the VLBA's original observing system having been decommissioned at the end of 2013.
The Sensitivity Upgrade project traced its origins to a two-year internal NRAO study of the scientific goals (Romney 1999; VLBA Sensitivity Upgrade Memo # 2) and the derived technical requirements (Romney 2000; VLBA Sensitivity Upgrade Memo # 3), for an upgrade of the VLBA. These concepts were subsequently cited among the initial steps recommended in Phase II of the VLBI Future Committee report "Mapping the Future of VLBI Science in the U.S." (Taylor, Lonsdale, et al. 2004; VLBA Sensitivity Upgrade Memo # 4), upon which the initial Sensitivity Upgrade proposal (Walker et al. 2007; VLBA Sensitivity Upgrade Memo # 15) was based. Funding to begin implementation of these goals became available in 2007.
The Sensitivity Upgrade instrumentation now in full operational use addresses, finally, many of the VLBI Future Committee recommendations. The primary discrepancy lies in the achieved maximum recording rate being limited to 2 Gigabits/sec (Gbps), rather than the desired minimum 4-Gbps capability. A roll-out of new Mark 6 recorders is underway which will raise this limit to 4-Gbps initially, with the potential of 16-Gbps (currently limited by available IF bandwidth). The 2-Gbps rate, corresponding to a continuum bandwidth of 256 MHz per polarization, is nevertheless a 16-fold increase over the standard "sustainable rate" at which the VLBA operated for many early years.
Overviews of the new instrumentation are presented in this document in the sections on the ROACH Digital Backend and Mark 5C Recorder. More detailed information is available in the Sensitivity Upgrade memo series. Questions can be submitted via the NRAO Helpdesk.
