A Study on Using SDR Receivers for the Europe- Europe and Transatlantic TWSTFT Links

The International Bureau of Weights and Measures and the Consultative Committee for Time and Frequency Working Group on Two-Way Satellite Time and Frequency Transfer (TWSTFT) have stimulated a pilot study on using software defined radio (SDR) receivers for TWSTFT in the framework of the realization of Coordinated Universal Time. The SDR receivers based on a software developed by TL have been set up at PTB, OP and NIST during the summer and fall of 2016. Continuous SDR TWSTFT measurements have been established for the OP/PTB, NIST/OP and NIST/PTB links. From the SDR TWSTFT clock comparison results (TWSTFT difference), we observed that the commonly present but undesired diurnal pattern in the OP/PTB SDR TWSTFT difference is greatly reduced compared to the diurnal pattern in the difference obtained from the regular (nonSDR) TWSTFT equipment. However, the diurnal reduction in the NIST/OP and NIST/PTB SDR TWSTFT differences is not as significant as in the OP/PTB link. This is a strong indication that the application of SDR receivers has the ability to significantly improve the stability of some TWSTFT links, but is not a solution for all links. In this paper, we will analyze the diurnal reduction using the SDR receivers for the three links and study the dominant causes for the diurnal effect in the EuropeEurope and transatlantic TWSTFT links.