Registration of Narrowband Cosmic Radio Emissions with Multifunctional Digital Backend System

S. A. Grenkov, I. A. Rahimov, L. V. Fedotov

Transactions of IAA RAS, issue 66, 11–17 (2023)

DOI: 10.32876/ApplAstron.66.11-17

Keywords: radio telescope, data acquisition system, digital signal processing, spectrometric signal recording

Abstract

Since 2006 the observations of radio emissions in the spectral lines of hydroxyl and water masers have been carried out at the “Svetloe” observatory. In order to record the spectra of signal at "Svetloe" the prototype samples of various equipment were used. The samples of equipment that used at "Svetloe" based on the spectrum calibration method that developed at the IAA RAS specifically for digital spectrometers. At present day all radio telescopes of “Quasar” VLBI network are equipped with new multifunctional digital backend systems (MDBE). On the RT-32 radio telescope in obs. “Svetloe” the MDBE has already installed. The MDBE provides digital processing of signals with intermediate frequencies from the radio telescope by field-programmable logic integrated circuits (FPGA). MDBE can replace any system responsible for converting signals on a radio telescope by used specialized FPGA firmware that provides signal condition not only for VLBI, but also for radiometric and spectral observations. For spectrometric observations the FPGA firmware with different bands has been developed to provide observations of hydroxyl (18 cm) and water (1.35 cm) maser radio emissions. The article describes the principle of operation of spectrometric modules based on the 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 a reception band of up to 2 GHz and allows using the developed FPGA firmware to get 32768 spectral components with a frequency resolution of up to ≈ 61.035 Hz. The software and firmware of the module implement digital registration and measurement of the power of radiometric signals, analysis of signal spectra, as well as detection, analysis and elimination of interference within the signal spectrum. The multifunctional system with the developed FPGA firmware and software was tested at the “Svetloe” observatory on the RT-32 radio telescope. For this the special spectrometric observations were carried out using a spectrometer based on channels of R1002M and the main results of which are presented in the article. Tests have shown the possibility of using a new MDBE for spectrometric registration of radio astronomy signals. The developed FPGA firmware for the channels of the MDBE will be used in prototypes that put into operation on the radio telescopes of “Quasar” VLBI network. The main parameters of the spectrometric module and the results of test observations with its use at the Svetloe observatory are presented.

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