Causes of common video signal interference
Led Floodlight,Indoor Lighting,Led Street Light,LED Grow Lighting Guangzhou ZG Scaffolding.co.Ltd , https://www.zgscaffolding.com
The use of video baseband transmission in television surveillance systems is the most common transmission method. Baseband transmission refers to a method of directly transmitting full-television signals without any processing such as frequency conversion. The advantage of this transmission method is that the transmission system is simple; within a certain distance range, the distortion is small; the additional noise is low (the system signal-to-noise ratio is high); additional devices such as modulators, demodulators, etc. need not be added. The disadvantage is that the transmission distance cannot be too far; a video coaxial cable can only transmit one TV signal.
Due to the advantages of stable operation and simple equipment, this transmission method has been widely used in practice. However, the frequency band of the video signal is very wide, and the start frequency is very low, so when the cable is transmitted, its amplitude and phase will be very different in the low frequency band and the high frequency band. Especially when the phase distortion is too large, it is difficult to compensate with a simple circuit. At the same time, the low-frequency part of the baseband transmission is easily disturbed by low-frequency interference sources such as power, telephone, and broadcasting.
Broadcast interference:
Because of practical application needs, when the cable must be erected in the air, the cable itself is equivalent to a long antenna. As a result of the antenna effect, a considerable broadcast interference voltage is generated in the cable, and an interference current is generated on the cable sheath. This current forms a loop through the grounding point at both ends of the cable and the ground, thus causing broadcast interference on the terminal load. The voltage of the signal causes the interfering signal to mix in the video signal. This type of interfering signal appears in the image as a tightly slanted screen, even when the image is overwhelmed. If the cable is buried underground, or using lead-sheathed cable, balanced symmetrical cable, etc. can better overcome this interference. 
Low-frequency interference:
The shielding effectiveness of the cable shielding layer is lower for signals with lower frequencies. For this reason, the interference signals introduced include carrier telephones and radio signals. They cause horizontal streaks in the image.
50Hz power interference:
When the system needs both the beginning and the end of the system to be grounded at the same time, due to the difference in the grounding potential at both ends and the presence of the cable sheath resistance, a 50-Hz ground potential difference is caused between the two grounds, thereby generating an interference signal voltage. When the interference signal is superimposed on the video signal, a wide dark band appears on the normal image.
Second harmonic and third harmonic interference of 50Hz power frequency:
Harmonic interference is mainly manifested around the power line with large current or high voltage. It is a radiation signal from the power cable to the surrounding area. Its frequency is 2500 Hz and 125000 Hz, and it mainly interferes with the low frequency band of the video signal.
Transmission line interference:
The quality of the video transmission line is not good, especially the shielding performance is poor (the shielding network is not a good quality copper network, or the shielding network is too thin to be used for shielding). At the same time, the line resistance of such a video line is too large, which results in a large attenuation of the signal, which is also a cause of the increase in failure. In addition, the characteristic impedance of such a video line is not 75 Ω and one of the causes of the malfunction is that the parameter is out of specification. The manifestation of this phenomenon is that a number of vertical bars with equal spacing are generated on the screen of the monitor, and the frequency of the interference signal is basically an integral multiple of the line frequency. 
Unclean power interference:
The power source referred to here is not "clean" and means that an interference signal is superimposed on a normal power source (a 50-cycle sine wave). This type of interference signal on the power supply is mostly caused by equipment that uses thyristors in the power grid, especially high-current, high-voltage thyristor equipment. The pollution to the power grid is very serious, which leads to the power supply in the same power grid. Not "clean". For example, in this power grid, there are high-power thyristor frequency modulation speed control devices, thyristor rectifier devices, thyristor AC-DC converter devices, and so on, all of which will cause pollution to the power supply. Unclean power makes the camera and other active devices unstable and interfere.