Spectral-Selective Radiometric Recording by Means of Multifunctional Digital Backend System

S. A. Grenkov, L. V. Fedotov

Transactions of IAA RAS, issue 62, 3–9 (2022)

DOI: 10.32876/ApplAstron.62.3-9

Keywords: radio telescope, data acquisition system, digital signal processing, radiometric spectral-selective signal recording

Abstract

Currently, all radio telescopes of the Quasar VLBI network are equipped with new Multifunctional Digital Backend systems. The operation of each of the channels of such a system is based on digital signal processing in a programmable logic integrated circuit (FPGA). The possibility of remote reprogramming of such FPGA is built into the system of such FPGA, which makes it capable of replacing all the backend equipment of the radio telescope and ensuring the recording of signals not only in the VLBI, but also during radiometric and spectral observations. For these purposes, a special FPGA firmware has been developed that implements a spectral-selective method for recording radiometric signals, which ensures high measurement accuracy even in the presence of radio interference. When each channel of a multifunctional system of such firmware is loaded into the FPGA, this channel is turned to a radiometric signal converter unit without changing the hardware. The article describes the operation principle of spectral-selective radiometric modules based on channels of a multifunctional system, as well as the developed algorithm and FPGA configuration structure. Each such module provides digital signal processing with a sampling rate of up to 4096 MHz in the receiving band up to 2 GHz and allows using the developed FPGA firmware to allocate 32768 spectral components with a frequency resolution of up to 15.625 kHz. The developed software and firmware provides not only digital registration and measurement of radiometric signal power with a coherent accumulation time of up to 600 seconds, but also analysis of signal spectra, monitoring of signal path characteristics, as well as detection, analysis and elimination of radio interference in the signal. The multifunctional system with the developed FPGA firmware was tested at the “Svetloe” Observatory on the RT-32 radio telescope. For this purpose special radiometric observations were carried out. The main results of these observations are reflected in the article. The tests showed the possibility of using a new Multifunctional Digital Backend system for radiometric recording of radio astronomical signals and the effectiveness of using spectral selection of radio interference. The developed FPGA firmware for the channels of the multifunctional system will be used in the prototypes being put into operation on the radio telescopes of the Quasar VLBI network.

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