Ku-BAND SATELLITE TWO-WAY TIMING USING A VERY SMALL APERTURE TERMINAL (VSAT)"

The NBS Boulder Laboratory has recently completed installation of a 6.1 meter Ku-band (14/12 GHz) satellite earth station and has acquired two 1.8 meter portable earth terminals and commercial spreadspectrum modems. This equipment was procured for the purpose of doing two-way time transfer experiments in collaboration with other timekeeping laboratories. Each portable earth terminal, often called VSAT for "very small aperture terminal" when the dish diameter is 1.8 meters or less, is a complete Ku-band earth station. The VSAT can provide full duplex capability to transmit to and receive from a geostationary satellite of the Fixed Satellite Service (FSS). Thus, two-way time comparisons can be done directly between NBS and a portable VSAT through a Ku-band satellite. Phase measurements have been performed of earth station and VSAT facilities in various looparound schemes using a satellite simulator. Frequency stability o (T) at various carrier-to-noise density (C/No) ratios will be reported. Stability plots have shown that performance is 4 x 10-lo~-l for a C/No ratio of 65 dB-Hz and that this white noise behavior continues to a few days where a is 3 x Absolute phase delay measuremenes show reproducibility to better than 1 ns over a 16 day sample time. This suggests the potential for accuracy to this level given an appropriate calibration. Preliminary results of loop tests through a satellite will be reported.