Study of delay instabilities within a Two-Way Satellite Time and Frequency Transfer earth station

The accuracy of the Two-Way Time and Frequency Transfer (TWSTFT) technique has been shown to be limited by propagation delay instabilities present in the earth station hardware. In this paper the National Physical Laboratory (NPL) has investigated a scheme for reducing delay instabilities in order to improve the accuracy of its time and frequency transfer. Tests show that cables propagating signals at 70 MHz or L-band have much lower temperature coefficients than cables propagating at Ku-band when measured with a TWSTFT modem. A scheme for improving earth station stability by propagating signals through cables at 70-MHz or L-band wherever possible has been investigated here. It is found that lower temperature coefficients are possible by adopting this scheme. Comparisons are also presented with tests carried out using a higher chip rate.