For more than four years, fluctuations in the deflection angle\ud θ(t) of novel type of tor-\ud sion balance have been monitored at the Main Astronomical Observatory of National\ud Academy of Sciences in Kiev, Ukraine. During this all-year recording, unpredictable\ud spontaneous high-frequency oscillations were observed occasionally. The aim of the\ud present paper was to investigate four of these high-frequency oscillatory events by per-\ud forming a detailed time-frequency analysis. From the overall available\ud θ\ud (\ud t\ud ) signal, we\ud selected four 24-hour long segments containing a clearly visible oscillations observed\ud on 20 and 21 November 2009 (data segments 1 and 2) and on 24 and 2\ud 5 December\ud 2012 (data segments 3 and 4). High-resolution time-frequency analysis was performed\ud for each of the four data segments using the generalized S-transform with a hyperbolic\ud window. The oscillation of\ud θ\ud (\ud t\ud ) present in data segment 1 shows clearly an increase\ud in frequency, starting at 0.0002205 Hz (period length\ud T\ud =\ud 75.59 min) and ending at\ud 0.0002325 Hz (T=71.68 min). The oscillation of\ud θ\ud (\ud t\ud ) present in data segment 2 has\ud instead a stable frequency of\ud f\ud =\ud 0.000243 Hz (T=68.59 min). Both high frequency\ud oscillations of\ud θ(t) of data segment 3 and 4 show an increase in frequency, starting at\ud 0.006179 Hz (T=161.84 s) and ending at 0.006859 Hz (T=145.79 s) for data segment\ud 3, and starting at 0.005379 Hz (T=185.91 s) and ending at 0.005939 Hz (T=168.38 s)\ud for data segment 4, respectively. In addition, the oscillation present in data segment 3 is\ud periodically amplitude-modulated with a period length of\ud T=57±4.2 min. Regarding\ud the origin of the observed high frequency oscillation we discuss possible technical or\ud natural factors that could be related to these oscillations
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