Time & frequency system for satellites ground stations

A highly redundant time & frequency generation and distribution system which has been developed for satellite ground stations (or Stratum 1 for digital telecommunication) is described. The system has a reliability of millions of hours mean time between failure (MTBF). A majority vote occurs among 3 frequency sources which are phase aligned and from which a master is selected under microprocessor control. No dead time, amplitude or phase jump, occurs during a master changeover. The selected master is used as a source for a distribution amplifier. The system is designed to meet CCITT Rec. G811 and features exceptional phase stability, low noise and high isolation between outputs. All three frequency sources are phase locked to the jittered output of a Global Positioning System receiver, using a very slow time constant to filter out the jitter. Thus, excellent short- and long-term stabilities (5×10^{2 m-12} per month, 1×10¹¹ per life) are achieved