Digital transmission system using decision means for selecting the synchronisation mode

摘要

The system incorporates a receiver (14) with synchronisation equipment for estimating and correcting faults in synchronisation between a local carrier and an input signal. The local carrier is generated by a voltage-controlled oscillator (144), and sync faults in the locked and unlocked modes are corrected by separate phase/frequency detectors (140,240). Requests for placement in either mode are determined by a locked/unlocked mode detector (130) activating a selector (135), and a state controller (190) which imposes one or more decision conditions based on the requests, allowing specific adjustments to be safeguarded and restored.