Weak current College】 【common video interference】.

<br> <br> Speaking of video interference, to talk about video signal transmission of traditional video baseband transmission. The so-called video baseband transmission refers to the video signal does not pass through any process such as frequency converters from image intake-side .through coaxial cable directly to the monitoring side of the transmission mode, the image is transmitted directly by using the coaxial cable of 0 ~ 6MHz to transport, very susceptible to interference, which makes the image appear Anilox, striated and noise impacts monitoring results. For .baseband video interference, the angle from the source of interference into AC acoustic interference and electromagnetic interference, and space from interference entry way into conduction-type interference and radiating interference. The following analysis of some common video interference phenomenon and its causes. <br> .1, power frequency interference <br> Interference: image appears snowflake noise, Anilox or very wide dark transverse band continuous scrolling. <br> Interference cause: this is when the camera-to-end monitoring equipment, grounding resistance due to its cable jacketing .resistance, in between the power systems each phase load imbalance or grounding differences 50Hz potential difference, creating power-frequency interference. Ground potential that exists both earthing terminal voltage drop, the voltage drop on both ends and the shield and the Earth (ground resistance) .constitutes a ground current loops generate, ground current through the cable shield formation interference voltage, and current section harmonic components fall into video cores, core and the shielding of the interference potential between layers, so that the interference signal to join the video signal to the .monitor image formation. <br> 2. space electromagnetic interference <br> Interference: image appears relatively dense of oblique Anilox, severe flooding when the image. <br> Interference cause: when monitoring cable erection in the air, the air wave interference signal .generated by the electric field is applied control transmission line, the line ends rather considerable electromagnetic interference voltage, its frequency in 200Hz ~ 2.3MHz. Due to the potential difference exists in the cable, the cable shield produce interference current, general photography and monitoring devices .are for grounding status, this allows interference current location through the cable ends and ground looped cause interference voltage Terminal load, interference signal coupling into the video signal of the resulting image interference. <br> 3. low-frequency interference (20Hz-nKHz low .frequency noise interference) <br> Interference: image appears static horizontal stripes. <br> Reasons: because of the voice, data, and other signal belongs to low-frequency signals, their band stenosis during transmission using only to 20Hz ~ nKHZ, almost .any type of cable you can transfer, generally only Exchange sound interference. For the transmission of video signal coaxial cable, its shield anti-interference characteristics indicate that the interference signal curves of the higher the frequency, the better its shielding properties, such as carrier .telephone, cable radio, and other low frequency signal interference but pales. Low-frequency interference signal same will transfer cable interference voltage on, thus affecting image quality. <br> 4, high-frequency interference (high-frequency noise interference) <br .> Interference: image appears snow or highlight point. <br> Phenomenon causes: Although the video transmission using coaxial high-frequency interference resistance than strong resistance to low-frequency interference, but a strong high-frequency interference signals also interfere with the image transfer .. Big charge load switch, frequency and high frequency machines at work in addition to output high-intensity-based wave, it also produces high-strength of second harmonic generation. Although the fundamental wave harmonic intensity ratio is much lower, but the higher harmonic .frequency band is wide and the components of complex, so fundamental to the harmonic will use video baseband transmission (ie 6MHZ bandwidth) video signal caused by different levels of interference. After many experimental precision, high-frequency interference signal for fundamental and harmonic frequency within .the 45MHz. <br> 5, reflection interference <br> Interference: image ghosting. <br> Interference cause: video signal during the transfer process color, brightness and saturation will have corresponding attenuation, and when transport video coaxial network impedance mismatch (also .called a mismatch), the video signal is transmitted to the terminal will be part of the chroma, brightness and saturation produces micro-reflective, reflected signal will come back to launch Office formation and reflection, and video signal superposition after delay and loss arrived at .the Terminal. More reflective signal will be at the receiving end result Intersymbol interference (ISI), ISI will cause the monitor to receive the wrong input signal amplitude and phase and displayed, which makes uploading back image seems clear image on the first floor blurred image .phenomenon, that is, the ghost phenomena. <br> 6, electrostatic interference <br> Interference phenomenon: when the image has a noise, Anilox and patchy. <br> Interference cause: in power plants, coal mines and industrial enterprises, and .other high voltage (1000V) output, severe mechanical friction and high electromagnetic environment places earthed with potential difference when on are 400VP-P ~ 1500VP-P. Ground and ground potential difference exists between the phenomenon is an electrostatic phenomena, phenomenon, it exists the .electrostatic grounding Terminal (including cool and heat) and the Earth as a positively and negatively charged capacitor. According to the capacitor works, when the charge capacity reaches a certain level will discharge. Then the electrostatic discharge will end in different ground potential difference between the .transmission line to the current shield formation, so that the interference signal coupling into the video signal and is fed into the monitoring device. Electrostatic interference on video transmission depends on the size of the electrostatic voltage difference, serious would create an interface chip for injury or .damage. <br> <br>.