Multi-channel digital video fiber transceiver has various functions, and each of them has their corresponding technical indicator requirements,such as video indicator, audio indicator, asynchronous data indicator, Ethernet indicator, telephone indicator. For specific technical indicators, the manufacturer can be required to provide a third-party test certificate. The projector available for retesting need to retest based on the indicators provided by manufacturer before purchasing to check the true technical indicators of device and the integrity of the manufacturer. Here is description focusing on the following two video indicators from an engineering point of view.
Video bandwidth is a issue which is usually talked about. When the video bandwidth is insufficient, the details of monitoring picture is not clear enough, the horizontal solution is low, even color distortion or video loss will happen. Due to the importance of video bandwidth for picture quality, some dishonest manufacturers cheat customers by exaggerated video bandwidth indicator. For example, a claimed 8M video bandwidth video bandwidth digital video fiber transceiver, but be announced to customers that is 12.5M video sampling frequency. According to Nyquist Sampling Law, the sampling frequency must be at least the twice of signal frequency to signal. So, the video bandwidth of the fiber transceiver above involved is impossible to be over 6.25M. Obviously, this is a lie for customers. The manufacturer like that should not be considered in the scope of purchase. But it is not easy for all customers to identify the lies of manufactures, to roughly judge the bandwidth, general engineers and users can observe the details of the image.
APL, average picture level, is not familiar indicator for many contractors. However, it must not be strange when talking about the problem that there is large-area white in picture(such as when the camera is illuminated by strong light), the picture on the monitor will occur horizontal jitter when video signal transmits by fiber transceiver. This is because the range of APL of video optical transceiver produced by some of manufacturers is too small. When there is a large-area white in the picture signal, the DC component in the image signal of each line will increase, and the APL will increase, resulting in a decrease in the amplitude of the line synchronization signal. Or lost, the monitor can not detect the line synchronization and the picture flicker occurs.