## 3 Results and Discussion  
In the analysed data (clock correction rates) after removal of the outliers and trend, numerous discontinuities are clearly visible (e.g., Figure 3e). These jumps are less visible for the older BDS-2 than for the BDS-3 satellites because of the relatively higher noise level in the clock correction time series. As the offsets are the same for all satellites (see Appendix C), their origin is also common and must be connected with some maintenance works or with a processing strategy adopted for clock correction determination. Moreover, as is indicated in the clock data files obtained, during the analysed time span, the reference clock for the WUM clock products was switched 44 times (Figure 4). The clock switch occurs at the end/beginning of the day and eight different clocks--hydrogen masers--worked as a reference clock. The switching of the reference clock leads to jumps in analysed clock data, visible for all BDS-3 satellites (e.g., Figure 3e).  
Figure 4: Reference clock for the WUM clock product swapping. Vertical black lines indicate the instant of reference clock switch.  
For verification, if the presence of this effect had an impact on the resulting power spectrum, we performed an analysis of the simulated data. Simulated data were Gaussian noise of amplitude \(2\times 10^{-13}\) s (similar to the BDS-3 satellite clock rate signal) with jumps of 0.2 ns added in the same epochs as the jumps occurring in the real data (Figure 5). These discontinuities are visible in the BDS-3 satellite clock data only. Simulated data processed the same way as real clock data (described in Section 2.2) allows us to confirm that the signals of periods of 17 h and 30-40 h are caused by frequent reference clock swapping. An L-S periodogram of the simulated data is presented in Figure 5. It shows a similar pattern for higher periods as periodograms for all of the analysed satellite clocks (Appendix C). The same effect is visible on the time\(-\)frequency spectrograms (see Appendix D).  
An example spectrogram for satellite C32 is shown in Figure 6. Visible is a component with a period of about 6.4 h, which appears from about 7200 h and continues until the end of the period analyzed.  
This component is also visible in the L-S periodogram in Figure 3f. In addition, signals with periods of 18 h and over than 30 h are noticeable in the time interval 6700-8000 h. These signals are caused by frequent changes of the reference clock (cf. Figures 3e and 5). Spectrograms for all of the analyzed satellites are shown in Appendix D.  
The identified periods in the clock correction rate depend on the satellite orbit type. For GEO and IGSO satellites, the main period of 23.935 h correspo  
Figure 5: Simulated data with jumps (**left**) and its Lomb-Scargle periodogram (**right**).  
Figure 6: CWT spectrogram for the C32 satellite.  
is present. Moreover, higher harmonics are visible--up to the ninth in the case of the C01 satellite--which shows that the periodic changes are not sinusoidal. The orbital period for the BeiDou MEO satellites is about 12.887 h. All BDS-3 MEO satellites have dominant second harmonics for this period (Appendices B-D).  
The IGSO BDS-3 satellites (C38, C39, and C40) equipped with H-maser clock exhibit many low power spectrum peaks around 24 h and 12 h. In the case of these satellites, orbital periods close to the sidereal day and its harmonics are of course natural. In the BDS-3 segment, only these three satellites are IGSO and they all have an H-maser clock. The presence of signals with periods between 12 and 24 h, which are not visible in the other BDS-3 satellites data, may depend on these factors. Several BDS-2 satellites' clock corrections oscillate with very low periods, e.g., C10, 1.02 h; C11, 1.21 h; and C14, around 1.8 h, not connected with their orbital periods. These effects require further investigation.