Tracking-mode synchronisation for a switching satellite

Synchronisation of earth stations to a switching satellite in the tracking mode is examined in detail. After completion of the fine-search mode, a timing error may exist due to satellite motion, which can be large compared to noise in the system. To overcome this source of error, a tracking-mode network is included in the timing-circuit configuration. By applying a small correction voltage to the voltage-controlled oscillator (v.c.o.) at all times, an offset frequency shift occurs, which can be used to eliminate the timing error due to constant-velocity satellite motion. Both p.s.k. and f.s.k. synchronisation-burst implementations are considered. It is shown that steady-state conditions are reached after about 4.5 s and the ultimate timing accuracy is limited only by uplink and downlink signal-to-noise ratios.