Narrow-band Operation Mode of the Multifunctional Digital Backend System

S. A. Grenkov, A. E. Melnikov, L. V. Fedotov

Transactions of IAA RAS, issue 72, 20–32 (2025)

DOI: 10.32876/ApplAstron.72.20-32

Keywords: radio telescope, data acquisition system, digital signal processing, VLBI data conditioning

Abstract

In many astrophysical and geodetic studies using radio interferometry with very large bases (VLBI), as well as in VLBI observations of spacecraft, narrow-band signal registration is used. For such registration, narrow-band signal conversion systems are designed, which until recently were equipped with radio telescopes of the Quasar VLBI Network. Currently, new Multifunctional Digital Backend systems (MDBE) are installed on them, which provide for the possibility of organizing a narrow-band signal recording mode by downloading specialized firmware into programmable logic integrated circuits (FPGAs). Experimental studies of these systems were conducted in 2022–23 and described in the relevant publications. However, the features of the narrow-band mode of operation of the multifunctional system, the algorithms implemented in the corresponding FPGA configurations and results of their effective use have not yet been considered in the literature. The paper discusses the principles of signal conversion in digital converters of MDBE channels, and also provides a detailed description of the structure of FPGA configurations that provide a narrow-band mode of operation of the system and the corresponding algorithms for its functioning. The characteristics of the obtained narrow-band channels of the system are given. The real work of MDBE on the RT-32 radio telescope is considered, which made it possible to significantly improve the results of VLBI observations. To assess the effectiveness of replacing standard narrowband systems with MDBE in the narrowband signal recording mode, a series of three-station geodetic VLBI sessions were conducted. Using the method proposed by the authors, the effectiveness of using MDBE in narrow-band recording mode has been confirmed. The FPGA configuration developed for digital converters of MDBE channels implements new technical and software solutions that provide a narrow-band mode of operation of the system. They make it possible to completely abandon the use of outdated narrow-band systems on the radio telescopes of the Quasar VLBI Network. The use of MDBE with these FPGA configurations makes it a completely universal system, compatible with almost any domestic and foreign Data Acquisition Systems on radio telescopes. The practical results of using MDBE in narrow-band mode have confirmed the operability of the algorithms proposed and the correctness of the solutions included in the development.

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