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Key points that can not be ignored when selecting a video signal dispenser

Sep 07, 2017

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Key points that can not be ignored when selecting a video signal dispenser


A video distributor is a device that distributes a source equally into multiple video signals.

 

Basic introduction

 

All the video signal corresponds to a monitor or video recorder, if you want a camera image given to a number of managers to see, it is recommended to select the video distributor, because the parallel video signal attenuation is large, given to multiple output devices due to impedance Match and other reasons, the image will be seriously distorted, the line is not stable.

 

Video splitter in addition to impedance matching, as well as video gain, so that the video signal can be sent to multiple output devices at the same time short distance and not affected, to a certain extent, to ensure the synchronization of video transmission. But there is no practical effect on the branch of the long-distance coaxial cable transmission.

 

For example, the front-end camera to capture the video signal through the video distributor can access the central matrix at the same time, and then access the hard disk video recorders or display devices. Video splitter usually has 1 input 2 output (ie 1 in 2 out), 1 into 4 out, 1 into 8 and so on.

 

Common video splitter there are 4 into 8 out, 16 into 32 and other models. Some models also feature character overlays and video isolators.

 

There are 2 points 4 8 minutes 24 16 minutes 48 and so on

 

The video signal dispenser can not be ignored when selecting points

 

When a video signal corresponds to a monitor or video recorder, do not need to use video distributor. However, in the video security monitoring system construction project, all the way camera images need to be sent to the video matrix switcher, hard disk recorders, monitors and other equipment, then you must use the video signal distributor. Because the parallel video signal attenuation is large, after transmission to multiple output devices due to impedance mismatch and other reasons, the image will be seriously distorted, the line is not stable. Video splitter in addition to impedance matching, as well as video gain function, so that the video signal can be transmitted to multiple output devices at the same time without being affected.

 

The video signal distributor has an important technical requirement that many users can not ignore:

 

First, the signal amplitude requirements, according to international standards, all video equipment between the matching impedance of 75Ω, the video composite signal is 1VP-P (video signal amplitude + line sync signal amplitude), the synchronization signal amplitude of 0.3VP-P , The subcarrier signal amplitude is 0.3VP-P. When the synchronization signal is less than the allowable value will cause the display image jitter or beating; subcarrier signal is less than the allowable value, the display image color will flash or sometimes no time.

 

Followed by the video channel bandwidth, channel bandwidth is generally 10MHz, at least not less than 7MHz. According to the video signal display image clarity and bandwidth between the experience of statistical data, 1MHz bandwidth equivalent to 80 lines. It can be seen that if the bandwidth of the video signal distributor is only 3MHz ~ 4MHz, and the selected camera image resolution can reach 480 lines, after such a video signal distributor can only show the 240 ~ 320 line image effect, obviously Choose such a video signal distributor is worth the candle.

 

The phase-frequency characteristics of the video signal distributor are expressed in terms of differential gain and differential phase, typically with a differential gain index of 3% to 5% and a differential phase index of 3 ° to 5 °. If below this value will make the color image and the original image color to produce color.

 

Most of the video signal distributors are 8 or 16 integrated together, because the process design is unreasonable, adjacent two images will be crosstalk, which is the partition between the road isolation does not meet the requirements caused by the requirements. Therefore, the video signal distributor of the road between the degree of isolation is generally required in more than 50db.

 

A video surveillance system is a combination of many related equipment, people tend to pay more attention to the camera, control equipment, hard disk recorders, monitor performance options, do not pay attention to the video signal distributor performance requirements, obviously this is wrong.

 

Video signal distributor is the first to receive the camera image signal and its distribution of the equipment out, if its various electrical performance indicators are not up to the basic requirements, then choose the other good equipment will be meaningless. Therefore, the user must pay attention to the technical performance requirements of the video signal distributor, so as to ensure that the video security monitoring system indicators can meet the specifications and related standards of technical requirements.

 


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