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

2. Backend of RT-32 radio telescopes: R1002M DAS
IF: 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

3. Backend of RT-13 radio telescopes: BRAS
IF: 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)

4. Temperature variation over antenna elevation
Heaters
BRAS

5. 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

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

7. Multifunctional Digital BackEnd (MDBE)

8. 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)

9. 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

10. 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

11. THANK YOU
FOR YOUR ATTENTION!