A System Approach to Synchronous Detection

System considerations in synchronous detection of the composite video signal are analyzed. It is shown that the bandwidth of the reference channel influences the quality of the synchronous detection system. The bandwidth that is practical in the reference channel depends upon the type of tuning system employed. A closed loop frequency synthesizer tuning system with quartz crystal stability and accuracy is the best solution. However, it is possible to improve the performance of quasi-synchronous detection with a conventional type of tuning system by reducing staticphase error in the estimated carrier and retaining or re-establishing the integrity of the AM sideband pairs in the reference channel before amplitude limiting.