Multi-channel digital video optical transceivers can have multiple functions, and each type of function has corresponding technical index requirements, such as video index, audio index, asynchronous data index, Ethernet index, telephone index and so on. Specific technical indicators can require the manufacturer to provide a third-party test certificate, and qualified engineers should conduct retests in accordance with the indicators provided by the manufacturer before purchasing equipment to check the actual technical indicators of the equipment and the integrity of the manufacturer. Here focuses on briefly explaining the following two video indicators from an engineering perspective.

Video bandwidth is one of the most frequently mentioned issues. Insufficient video bandwidth, the details of the monitoring screen are not clear enough, the horizontal resolution is low, and serious color distortion or video loss occurs. It is precisely because of the importance of video bandwidth to image quality that some unscrupulous manufacturers deliberately exaggerate the video bandwidth of their products to deceive customers. For example, a digital video optical transceiver produced by a certain manufacturer claims that its video bandwidth is 8M, but its publicly announced video sampling frequency is 12.5M. According to the Nyquist sampling law, to truly restore the signal, its sampling frequency should be at least twice the signal frequency , calculated in this way, the theoretical video bandwidth of this manufacturer’s optical transceiver cannot exceed 6.25M in any case. For general engineering companies and users by observing the details of the image, they can roughly judge the video bandwidth of the device.

APL is the average image level, and many engineering companies don’t pay much attention to or are not familiar with this indicator.  However, if we talk about a problem encountered in some projects: the video signal is transmitted through the optical transceiver, when there is a large area of white in the picture (such as when the camera is illuminated by strong light), the picture on the monitor will shake horizontally, then The engineering staff must be no strangers.  This is because the APL range of video optical transceivers produced by some manufacturers is too narrow. When there is a large area of white in the image signal, the DC component in each line of the image signal increases, and the APL will increase, resulting in a decrease in the amplitude of the horizontal synchronization signal. Or lost, the monitor cannot detect the line synchronization and the screen shakes.