Comparison of Reference Frequencies Using CGGTTS at Quasar-KVO Radio Observatories

K. V. Kuznetsov, A. V. Vytnov, A. S. Karpichev

Transactions of IAA RAS, issue 75, 40–44 (2025)

DOI: 10.32876/ApplAstron.75.40-44

Keywords: CGGTTS, GLONASS, GPS, active hydrogen maser, frequency comparison

Abstract

Very-long-baseline radio interferometry (VLBI) is based on independent signal recording. Each radio interferometer element operates with autonomous timing systems, synchronized by independent atomic frequency standards. Over time, due to the instability of these standards, their frequencies diverge, requiring periodic adjustment. A key factor is that the magnitude of the instability of the average relative frequency difference depends on the measurement interval. This work examines the comparison of reference frequencies at the Quasar-KVO radio astronomy observatories using the Common GNSS Generic Time Transfer Standard (CGGTTS). The study presents results on the instability (measured via Allan deviation) of frequencies across various observatories within the complex, relative to the GLONASS and GPS system scales, the State Standard of Time and Frequency, and UTC. Data from the Time Department of the International Bureau of Weights and Measures (BIPM) are utilized. The influence of observation duration on the accuracy of the results obtained is analyzed. It is shown that daily measurements enable frequency comparisons with an accuracy of approximately (4...6) × 10⁻¹⁵ when using GPS signals and 1 × 10⁻¹⁴ when using GLONASS signals. Extending the data collection period to 10–20 days improves comparison accuracy to roughly 1 × 10⁻¹⁵. The study also indicates that the main cause of frequency drift is linear drift, with a magnitude of approximately 1 × 10⁻¹⁵ per day.

Citation