Multifunctional Digital Backend for Quasar VLBI network

The new 13-meters radio telescope recently built at Svetloe observatory (Russia) required a backend device that could digitize wideband signals from the receiving system, process the signal appropriately, prepare and transmit the resulting signal to the recorder. The previously existing backends, also used at other radio telescopes of Quasar VLBI network, could not provide compatibility with VGOS (VLBI Global Observing System) requirements. We developed Multifunctional Digital Backend (MDBE) with superior performance, flexibility and functions to equip the new antenna and other radio telescopes of the network with the same backend compatible with both domestic and international systems. The MDBE contains up to 12 input channels with 2 GHz bandwidth, powerful and remotely configurable Field programmable gate arrays (FPGA) for digital signal processing, and optical transceivers with total throughput of 50 Gbps per channel. The digital downconverters implemented in FPGA can form sub channels with 0.5, 2, 4, 8, 16, and 32 MHz bandwidth freely tuned with 10 kHz step. In wideband mode a single channel with 512, 1024 or full 2048 MHz bandwidth can be recorded. The MDBE also supports single-dish applications, such as radiometric and spectrometric observations. The paper presents the results of hardware and firmware development of the system, and the experimental results received with the MDBE in Svetloe observatory. (paper)