Multifunctional Digital Backend (MDBE) for "Quasar" VLBI-network Evgeny Nosov Institute of Applied Astronomy Russian Academy of Sciences www.iaaras.ru

Backend of RT-32 radio telescopes: R1002M DAS IF: 100-1000 MHz 16 channels Up to 32 MHz/channel Data rate up to 2 Gbps VSI-H Disadvantages: Low data rate No wideband mode Does not support VDIF Does not support fiber Does not support mounting in elevation cabin Past generation

Backend of RT-13 radio telescopes: BRAS IF: 1-1.5 GHz 8 channels 512 MHz/channel Data rate up to 16 Gbps VDIF Disadvantages: Not enough bandwidth for new receivers (2 GHz is desirable) No subchannels (no DDCs) Not compatible with RT-32 equipment No remote firmware reconfiguration No control of internal delays instability (clock synthesizer, clock distributor, ADC)

Temperature variation over antenna elevation Heaters BRAS

Digital, FFT-based RFI filter Backends of “Quasar” VLBI-network, 2017 Op. mode RT-32 RT-13 Sv Zс Bd Zv Bv Svetloe VLBI R1002M DAS BRAS - Radio-metric Digital, FFT-based RFI filter Analog detector Spectro-metric R3902 R3901

Backends of “Quasar” VLBI-network, 2020 Op. mode RT-32 RT-13 Sv Zс Bd Zv Bv Svetloe VLBI MDBE Radio-metric Spectro-metric

Multifunctional Digital BackEnd (MDBE)

MDBE features IF inputs: 0-1 GHz, 1-2 GHz, 2-3 GHz, 0-2 GHz DSP units: Up to 12 DSP units to cover 2-14 GHz in both polarizations Data rate: Up to 96 Gbps (2-bit quantization) Data outputs: VDIF, 10GE, Fiber link Remote reconfiguration Operational modes: VLBI: wideband channels, DDCs, PFB Single-dish: spectrometer, radiometer PCAL extraction, tone phases and pulse group delay estimation Internal delays instability measurement Reference clock delay instability measurement (embedded CDMS)

Current status Circuit design: DONE! PCB design: in progress. March 2018 PCB/hardware production: Spring 2018 Firmware design: in progress… First VLBI with MDBE: End of 2018 (wideband mode, RT-13) Regular observations with RT-13 + MDBE: 2019 Regular observations with RT-32 + MDBE: 2020

Summary MDBE provides… Simple and short (=reliable) signal chain Wide band (=high sensitivity) Delay instability measurement (= can help to achieve required accuracy level) Possibility to cover the whole 2-14 GHz bandwidth (with approp. receivers) Unification of backends and operational modes over RT-13 and RT-32 Compatibility with other DBE Single-dish modes Fast implementation of new features/modes

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