1. Wood grain interference
The appearance of this kind of interference will not overwhelm the normal image when it is slight, and the image will not be able to be viewed when it is severe (or even break the synchronization). The causes of this failure phenomenon are more and more complex. There are roughly the following reasons:
(1) The quality of the video transmission line is not good, especially the shielding performance is poor (the shielding net is not a good quality copper wire net, or the shielding net is too thin to provide a shielding effect). At the same time, the line resistance of this type of video line is too large, which causes a large attenuation of the signal, which is also the cause of aggravated failure. In addition, the characteristic impedance of this type of video line is not 75Ω and the parameters exceed the regulations are also one of the reasons for the failure. Since the above-mentioned interference phenomenon is not necessarily a fault caused by a poor video cable, the cause of this fault should be judged accurately and cautiously. Only when other possibilities are ruled out, can it be considered from the perspective of poor video lines. If it is really a cable quality problem, the best way is of course to replace all of these cables and replace them with cables that meet the requirements. This is the best way to completely solve the problem.
(2) In the surveillance camera project, the power supply of the power supply system is not "clean". The power supply referred to here is not "clean", which means that interference signals are superimposed on the normal power supply (50-cycle sine wave). And the interference signal on this kind of power source mostly comes from the equipment using thyristor in the power grid. Especially high-current, high-voltage thyristor equipment, pollution to the power grid is very serious, which causes the power supply in the same power grid to be unclean. For example, in this power grid, there are high-power thyristor frequency regulation devices, thyristor rectifier devices, thyristor AC/DC converters, etc., which will cause pollution to the power supply. The solution to this situation is relatively simple, as long as the entire system adopts a clean power supply or online UPS power supply, it can basically be solved.
(3) There is a strong interference source near the system. This can be judged through investigation and understanding. If this is the reason, the solution is to strengthen the shielding of the camera, and ground the video cable pipe.
2. Deeper and more chaotic large-area reticulation interference
In severe cases, all images are destroyed, and images and synchronization signals cannot be formed. This failure is caused by short-circuit or open circuit between the core wire of the video cable and the shielding net. This situation mostly occurs on BNC connectors or other types of video connectors. That is to say, when this kind of failure phenomenon occurs, it is often not that all the signals of the entire system have problems, but only appear on the number of poor connections. As long as you carefully check these connectors one by one, you can solve it.
3. The interference of several vertical bars with equal spacing
The frequency of the interference signal is basically an integer multiple of the horizontal frequency, which is caused by the impedance mismatch caused by the characteristic impedance of the video transmission line not 75Ω. It can also be said that this interference phenomenon is caused by the combination of the characteristic impedance and distribution parameters of the video cable that do not meet the requirements. The solution generally depends on the "start-end series connection resistance" or "terminal parallel connection resistance" method to solve the problem. In addition, it is worth noting that when the video transmission distance is very short (generally within 150 meters), the above-mentioned interference phenomenon may not necessarily occur when the above-mentioned impedance mismatch and the video cable with excessive distribution parameters are used. The fundamental way to solve the above problems is to ensure the quality when purchasing video cables. The cable should be sampled and tested when necessary.
4. Space radiation interference introduced by the transmission line in the surveillance camera project
This kind of interference phenomenon occurs mostly because there are strong and high-frequency space radiation sources near the transmission system, the front end of the system, or the central control room. One solution to this situation is to understand the surrounding environment and try to avoid or stay away from the radiation source when the system is established; The pipeline of the transmission line adopts steel pipe and is well grounded.
How to improve anti-interference ability
Since surveillance cameras generally use the most commonly used transmission method is video baseband transmission (baseband transmission refers to the method of directly transmitting TV signals without any processing such as frequency conversion). The advantage of this transmission method is that the structure of the transmission system is simple, within a certain range, the distortion is low, and the noise is low (the system signal-to-noise ratio is high); One video coaxial cable can only transmit one channel of TV signals at the same time.
