Application of Vondrak Filtering Method to the Two-Way Satellite Time and Frequency Transfer Based on Software Defined Receiver

The SDR-TWSTFT (Two-Way Satellite Time and Frequency Transfer based on Software Defined Receiver) link collects measurement data per second and then fits the raw data into 300 seconds by mathematical model. The time transfer results of the link are therefore affected by short-term measurement noise and non-model errors, and exhibit certain characteristics of random noise. A frequency domain amplitude analysis method is proposed to determine the filtering factor and construct a low-pass Vondrak filter to meet the requirements. By analyzing the measured data of the SDR-TWSTFT link between the NTSC (National Time Service Center) of Chinese Academy of Sciences and the PTB (Physikalisch-Technische Bundesanstalt) of Germany, it is found that the method is effective in filtering the high frequency noise in the average time of the link, can improve the confidence of the link time transfer results, and also the short-term frequency and time stability of the filtered link is significantly improved.