Institute of Applied Astronomy Project of Direct Sampling

Institute of Applied Astronomy Project of Direct Sampling Digital Backend for Quasar VLBI-network Evgeny Nosov Institute of Applied Astronomy Russian Academy of Sciences (IAA RAS) www. iaaras. ru The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018

Evolution of signal chain at VLBI radio telescopes R 1002 М DAS DBBC, RDBE, ADS 3000+, CDAS, BRAS, MDBE K 6/GALAS, OCTAD BRAND EVN DSDB (Direct Sampling Digital Backend) …? Mark IV DAS, VLBA 4 DAS, R 1000 DAS, etc. The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 2

Direct sampling: pros and cons + Simple and short signal chain + Higher reliability, easier maintenance + Signal chain is perfectly stable and predictable after ADC + Identical channels with good linearity of phase response + Easy implementation of new observation modes - Still very short list of available RF ADCs - Very high data rate from ADC. Not easy to receive and process it in FPGA - Data synchronization issues - Required high end (i. e. expensive) electronic test equipment for hardware debugging The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 3

List of RF ADCs Part, Manufacturer Bits Bandwidth, GHz Data rate, Gsps ADC-30 -NG, Micram 6 20 32 HMCAD 5831, Analog Devices 3 20 26 CHAIS ADC, Fujitsu 8 18 56 ASNT 7123, Adsantec 4 20 16 A 6 B 25 G, Alphacore 6 25 25 EV 5 AS 210, e 2 v 5 8 20 Williamson ADC, Jariet Tech. 10 25 68 The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 4

Signal chain based on DSDB Sampler and DSP units are separated: Ø Digital signals are not affected by group delay variations in cables/fibers (temperature, bending), reflections, EMI, low dynamic range of E/O converter Ø DSP unit has no strong restrictions on size, power consumption, EMI radiation level Ø DSP unit can be based on COTS FPGA boards + specially designed FMC modules Ø CDMS is strongly required to measure/eliminate reference clock variations Analog front-end is specific for a particular receiver. Sampler and DSP units are then compatible with any receiver. The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 5

Analog front-end for RT-32 Fs=20. 48 GHz The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 6

Analog front-end for RT-13 with Tri-band receiver The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 7

Analog front-end for RT-32 The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 8

Digital part of DSDB The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 9

First prototype of DSDB to try key technologies Tasks to achieve using the prototype: Ø Errorless ADC data capture in FPGA Ø Data synchronization with the input 1 PPS signal Ø Efficient firmware implementation of digital RF/IF converter Ø Formulating the requirements for DSDB design The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 10

Summary 1. Direct sampling technique gives valuable advantages over previous generation DBEs. 2. It is desirable to locate the samplers in the antenna cabin, while keeping away the DSP units. 3. CDMS is strongly required! 4. Hardware design of DSP units is flexible. COTS devices can be widely used. 5. DSDB development is in the very beginning. Hardware design scheduled for 2020. The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 11

Thank you! Questions? The 7 th International VLBI Technology Workshop, Thailand, November 12 -15, 2018 12