Usually in a surveillance display system, the video signals obtained by a camera need to be simultaneously transmitted to video matrix switchers, hard disk recorders, monitors and other equipment in order to realize real-time monitoring of information. If other signal processing equipment is used, it will not be able to divide the signal while ensuring signal quality. The video splitter can meet this requirement very well. Also in some spliced large-screen display systems, users also choose distributors as the main signal processing equipment. Of course, the signal processing equipment required for LCD splicing walls is often determined by the actual user needs. In addition to distributors, video matrices, processors, switchers, etc. are commonly used.
What are the reasons why the signal quality output by the video splitter is not affected:
First, let’s talk about the signal amplitude requirements: according to international standards, the matching impedance between all video equipment is 75Ω, the video composite signal is 1VP-P (video signal amplitude + line cut synchronization signal amplitude), and the synchronization signal amplitude is 0.3 VP-P. The subcarrier signal amplitude is 0.3 VP-P. When the synchronization signal is less than the allowed value, it will cause the display image to jitter or jump. When the subcarrier signal is less than the allowed value, the image displayed on the splicing screen will flicker or be intermittent.
The second is the channel bandwidth of the video signal: usually 10MHZ, but in some special circumstances it can reach 7MHZ and can be used. According to the empirical statistics between video signal display image resolution and bandwidth, it can be seen that 1MHZ bandwidth is equivalent to 80 lines. However, the bandwidth of the video signal distributor is only 3MHZ~4MHZ, and when the used camera image resolution can reach 480 lines, even if it passes through the video signal distributor, it can only display an image effect of 240~320 lines. It is obvious to choose such a video Signal splitters are worth the loss.
Also, the phase-frequency characteristics of the video signal distributor are represented by differential gain and differential phase. Normally, the differential gain index is 3% to 5%, and the differential phase index is 3° to 5°. If it is lower than this value, the color of the displayed color image will be different from the original image. In severe cases, the big red will appear purple, and the blue and green colors will be confused.
During the construction process of the LCD splicing surveillance TV wall system, video cables are used to transmit the image signals of each camera to the monitoring center. The short cables can range from dozens of meters to hundreds of meters long. And in most cases there will be a lot of interference around the cable, some of which will be superimposed on the image transmitted by the cable. Weak interference will reduce the system signal-to-noise ratio, while heavy interference will directly affect the display effect on the LCD splicing unit.
Therefore, on the basis of ensuring their electrical performance, some video distributors on the market now add anti-interference suppression circuits to their signal input ports, so that the common mode suppression capability of each input port reaches 50db. In this way, while ensuring the image quality of video signal distribution, it can also play a certain role in suppressing common mode interference during video signal transmission.
