Many Video Operated Relay (VOR) circuits have been published in recent years for use in connection with ATV repeater controllers or automatic videotape logging systems. Unfortunately, many of these circuits fail to properly detect certain video signals depending on their signal-to-noise ratio or their picture content. Most designs rely on using an LM567 phase locked loop (PLL) tone decoder chip to detect the presence of horizontal sync energy in a composite video signal, and this alone is probably the greatest cause of the poor performance provided by many of these circuits.
One of the worst approaches to video sync detection has been the design used by the Micro Computer Concepts VS-100 ATV Repeater Controller. This controller couples baseband video directly into an LM567 PLL tone decoder tuned to the video horizontal sync f