Digital Back End for the NRAO VLBA
Steven Durand, Mike Revnell
The ten antenna VLBA was originally designed to sustain a long-term mean bandwidth of 32 MHz (128 Mbit/s). The present plan is to replace the original VLBA backend equipment, including the samplers, BBCs, and formatter, with a 4Gbit/s, all digital backend. The VLBA DBE is based on the Center for Astronomy Signal Processing and Electronics Research (CASPER) University of California, Berkeley ROACH Board. The ROACH board contains a Virtex-5 FPGA from Xilinx, a power PC and external analog to digital converters. The DBE will support 4 IFs, each with a nominal bandwidth of 550 MHz. The DBE will have at least two personalities, a polyphase filter bank that will output the full bandwidth and a digital downconverter filter bank which can select portions of the received bandwidth. The 10GE output format is compatible with the MARK5C recorders.
This paper will discuss the status of the VLBA DBE project and performance of the ROACH general purpose board.