Video interference of main manifestation


1 and in the monitor the screen appears a black poles or white bar, and upward or downward scrolling. The so-called 50HZ power frequency interference. This interference are largely due front-end and control center two equipment grounding undeserved, forming a loop erps self-citation of entering system caused by, Also may be due to the device itself power performance degradation cause.


2, the images have snowflakes pixels. This kind of interference resulted from transmission line and the coupling attenuation caused by high-frequency interference.


3, video images have double, or white, character image dithering, or on the monitors the screen produces several spacing equal ShuTiao interference. This is due to video transmission lines or equipment between the characteristic impedance not 75 Ω caused impedance mismatch cause.


4, twill interference, beating interference, power supply interfere. This interference, the emergence of mild won't drown normal image, and the serious when image distortion can't watch. This fault the reasons of this phenomenon also is relatively complicated, such as more video transmission line quality is bad, especially shielding performance is poor, or because the power supply system of power have clutter and cause, still have even system have strong interference source near.


5, large-area anilox interference, also called single-rate interference. This phenomenon is mainly due to the video cable HPVV and shielding network short-circuit, breakers caused malfunction or is due to improper BNC connector contact.


At the scene encountered in the video interference is simply the above five status, so we encountered at the scene of this kind of phenomenon, must first appeared calm analysis of interference genre, identify possible interferences with roughly reason, eventually to exclude it. Through the example below to analyze the causes of video interference.




Grounding jam


Front-end equipment "earth" and control equipment to "ground" relative "network", namely the potential in two different ground point relative power grid "land" DianShiCha different, then through power in the camera and matrix formed between the power circuit, video cable shielding layer is grounded, such 50Hz work frequency interference into the matrix, the disturbance. For such interference, because it is so hard to make everywhere "ground" potential and "power grid land" erps identical, more effective method is to cut off to have formed the path, using cut circulation to ring circuit method, in the camera end are ungrounded and do well with the mounting bracket insulation measures, so can basically eliminate grounding the disturbance caused. What is worth mentioning, because coaxial cable is too long, intermediate are inevitable joints, such as joint processes is not good, shielding network encounters metal trough also can produce such interference, so in processing also want to notice to this case.


Power supply interfere


Because of the power supply system of power supply is not "clean" and cause. Citcc power not to "clean" refers to the normal power superimposed on have jamming signal. But this power source, the jamming signal from the electric equipment, especially use silicon controlled high current, high voltage silicon-controlled equipment, the pollution to power network is very serious, and that has made the same in the grid power not to "clean". As the grid in high-power SCR FM silicon-controlled rectifier equipment, speed device, SCR ac-dc mapping device etc, can produce pollution to power. For example, a site systems installed appeared after the images have twill interference phenomenon, how also find a reason. Because of this system is found out later in the summer, when installation installed the room had air-conditioned, and air conditioning in the automatic operation. Have a chance to turn off the switch, when air conditioning miracle, the monitors image unexpectedly as normal. Again the air conditioning power plug in, interference appeared again, trapped crossly. good period of time the problem finally discovered. Then install UPS power system and air conditioning power will be separated, interference excluded. This kind of situation of solving method is simpler, as long as the whole system adopt ac purifying or online UPS power supply was basically can be solved.


By introducing the transmission line space radiation interference


This interference phenomenon of generation, mostly because in transmission systems, system headend or central control room near a stronger and higher frequencies of space radiation sources. This solution in a system, answer peripheral environment to understand somewhat, try to avoid or away from radiation sources, Another way is unable to avoid emitter, when in front and center for transmission line, strengthen shielding device pipeline steel pipe and mining have good grounding.


Impedance mismatch


Because of the characteristic impedance mismatch transmission line caused by fault phenomena. This is due to the video transmission characteristic impedance not 75 Ω or the device itself characteristic impedance not 75 Ω caused impedance mismatch cause. For such interference should try to make the system within the equipment impedance matching.