Software for Stability Analysis of Signals in the Receiving and Recording Equipment of a Radio Telescope Based on the Results of Phase Calibration Signal Processing

M. S. Zorin, V. O. Ken

Transactions of IAA RAS, issue 53, 3–8 (2020)

DOI: 10.32876/ApplAstron.53.3-8

Keywords: phase calibration signal, group delay, DiFX, RASFX, delay stability

Abstract

In the majority of radio telescopes which are used for very long baseline interferometry (VLBI), a special signal is injected into a receiver for the phase calibration of the equipment. In order to control the stability of the receiving system, we have elaborated post-processing software for analysis of delay stability of the receiving and recording equipment based on phase calibration data computed by RASFX and DiFX correlators. The software was developed with Python 2.7 and “NumPy” and “Matplotlib” libraries to calculate an instrumental delays, and allows to determine phase calibration signal (PCal) delays with subpicosecond accuracy and to visualize frequency responses of the receiver. The authors used an analytical research methods, methods of imperative programming in Python, as well as mathematical analysis and mathematical statistics. The algorithms and mathematical methods are presented. The plots used for graphical analysis are presented as well. This software may be used for PCal delay stability monitoring in VLBI sessions with long-time intervals in order to control the stability of receiving equipment. In particular, we used the software for the analysis of 30-min Ru0804 session which was carried out on September 20, 2019 on Quasar VLBI network. PCal delay fluctuations do not exceed the formal error value at the Badary radio astronomical observatory. There is a periodic dependence of PCal delay with a 30 ps swing at the Zelenchukskaya observatory, that might be caused by a heterodyne frequency setting error in the receiving system. The paper also describes the mathematical algorithms and implemented features, such as receiver frequency responses visualization and calculation of mean-square deviation of the frequency tones phases.

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