Extension of two-way satellite time- and frequency transfer method to real-time operation and carrier phase measurements

So far, Two-Way Satellite Time and Frequency Transfer (TWSTFT) was mainly used by primary laboratories to compare national time-scales. New concepts make such highly accurate methods available to the less sophisticated user at similar performance levels and in real-time operation. A method called ´Two-Way Time Synchronisation via Satellite´ is introduced, which provides low phase-noise time- and frequency signals synchronised to a remote reference clock. Results show an ADEV of 1E-14 for /spl tau/>10/sup 4/ s. A frequency transfer method via satellite based on carrier phase measurements is presented. Dual receiver channel modems are used to eliminate errors due to the satellite´s local oscillator and due to the satellite´s movement. Initial experiments with two modems indicated the potential to reach a frequency transfer accuracy of 2*10/sup -15/ within 5 minutes. Although the concept of carrier phase was verified by test, these data could not yet be achieved with actual Very Small Aperture Terminal (VSAT) ground stations. Different 2-way operational modes have been tested and verified during a 10 day test campaign. Carrier phase measurements are compared to simultaneous TWSTFT data to prove the concept. Carrier phase data exhibit good short term stability at the level of ADEV 1.2 E-12 /sqrt(/spl tau/) for /spl tau/<100 s. The long-term stability however is in the same order of magnitude as TWSTFT data. This indicates, that significant improvements to RF signal generation and frequency distribution elements are still necessary to achieve the full potential of carrier phase data. Tests have been performed with 10 MChip/s pseudonoise coded signals via a free transponder provided by Societe EuropCene des Satellites, Luxembourg (SES).