Q: What is VD sync., VBS Sync., EXT sync., Gen. lock and AC line lock? 

A: There are different ways to do synchronization among cameras.

General lock is the best way to fully synchronize two cameras for most dedicated application such as broadcasting studio. It will synchronize Vertical, Horizontal, Even/Odd field, and Color burst frequency and Phase.

VD sync. is the most simple way to synchronize two cameras by vertical drive frequency to ensure video can be processed by plan old switcher or quad machine to display several image sources on the same monitor. VD signal is usually constructed by a pulse on the repeat rate of 20/16.7ms ( 50/60 Hz) and with pulse width of 1~ 3 ms.

VBS stands for video and color burst signal. It means the camera will synchronize an external composite color video signal. Although it is read as VBS sync. it is actually doing H sync. and V sync. only , and does not do color burst synchronization.

External sync. is almost the same as VBS sync. A camera can be synchronized by video signal supplied by another camera. An External sync camera will take an incoming VBS video, and extract the vertical and horizontal sync. signal for sync. purpose. 

Many our cameras have VD sync. or VBS/External sync. feature but because surveillance cameras never need Gen lock, CCTV cameras scarcely have general lock feature. In Mintron, there is only one OEM model has Gen lock feature that is not open for distribution channel.

AC line lock is an old technology for synchronizing camera by AC 50/60 Hz power line current. AC 24 volts power is widely used for fire-fighting alarm system in most of the buildings and is very easy to get. Therefore, it is widely used in north American. Because old style switcher and quad system have no digital memory, synchronization among cameras is necessary to maintain stable picture. The trade off for AC line lock is camera synching to ac 50/60 hertz. The timing relation between color sub carrier and horizontal /vertical signal will be disengaged and cause bad color rendering ( color phase draft )Therefore, all user that enjoying AC line lock will unavoidably scarify good color rendering. Fortunately, modern quad, 16-channel multiplexer and DVR have internal memory to overcome this difficulty and need no sync. signal so AC line lock might be obsolete couple years later.