Monitoring system of video signal transmission in brief (1)

Monitoring system, video signal transmission is the whole system is very important, is also very broad engineering, head of one thing, as project monitoring equipment, price transparency and engineering competition intensifies, signal transmission part of everyone's attention more and more; at present, the supervisory system of the most common transmission medium is coaxial cable, twisted pair, fiber, and other ways, for different occasions and different transmission distance, how to guarantee that the transmission quality, reduce costs, according to many years of engineering experience, here we made some presentations for reference.

1 coaxial transmission

(A) through coaxial cable transfer video baseband signal

Video baseband signal that is often speak of the video signal, it's bandwidth is 0-6MHZ, generally speaking, the higher the signal frequency, the greater the attenuation, General design time only need to take into account the guarantee of high-frequency signals will be able to satisfy the system requirements for video signal attenuation in 5.8MHZ: SYV75-3 96 series GB video cable attenuation 30dB/1000 meters, SYV75-5 96 series GB video cable attenuation 19dB/1000 meters, the 96 series SYV75-7 GB video cable attenuation 13dB/1000 m; if the image quality is very high, surrounding non-intrusive, 75-3 cables can only transport 100 meter, 75-5 transmission 160 m, 75-7 transmission 230 meters; practical applications, there are some uncertain factors, such as selecting camera different ambient noise, and so on, generally speaking, 75-3 cable can transmit 150 m, 75-5 can transport 300 m, 75-7 can transfer 500 m; longer distances for the transport, you can use video amplifiers (video Restorer) and other equipment, to zoom in on the signal and compensation, can transmit 2-3 km; in addition, through a coaxial cable can also implement a video signal and control signal transmission, i.e. coaxial together as controlled transmission technology, following a brief introduction to the technology:

In the monitoring system, the need for transmission of signals major has two, one is the image signal, the other is a control signal.

Which video signal flows from the front of the camera to control center; and control signal from the control centre to the front of the camera (including lens), head, and other managed objects; and, to the front of the control signal, and is set in front of the decoder to decode and then go to the control of camera and PTZ etc managed objects. Coaxial transmission as control technology is the use of a video cable to transmit both from the camera's video signal as well as on the head and camera control functions such transmission in material savings and cost, construction convenient, the service is simple, system expansion and renovation is more flexible; coaxial depending on the control implementation method in two categories:

One is the use of frequency division, that is, the control signal modulation in and video signal a different frequency range, and then with a composite video signal transmission, together again in the scene will distinguish between the demodulation; as the use of frequency segmentation technique, in order to fully split two different frequencies, the need to use a band-pass filter, band-pass notch filter and low-pass filter, low-pass notch filter, which affects the video signal transmission effects; as the control signal modulation in the video signal frequency, the higher the frequency, the greater the thus transmit attenuation distance is limited; the other way is to double your way, the video signal and control signal modulation in different frequency, and cable TV in principle the same, and in the front and back-end demodulation.

Second, the use of video signal during blanking signal to transmit control, similar to TV teletext transmissions; the control signals directly into the video signal of blanking period, the video signal of blanking period section is not displayed on the monitor, the images show the interference will not occur without affecting the image quality of transmission, the video signal through the front end of the pre amplifier and receiver signal amplification of weighted, can greatly extend the video signal transmission distance, where that 75-5 video cable, you can implement 2000 m, 75-7 cable for 3500 m, 75-9 cable 5000 m video transmission and reverse control.

(Ii) transmit RF signal through a coaxial cable

Video signal is modulated video signal to a frequency transmission, that is, the use of cable television transmission mode, typically by a line of "specialists", "signal transmission" and "broadband transmission", and so is the use of this technology.

Using this technique is particularly suitable for monitoring points more and the relative concentration, distant of the system, the use of the system is simple, wiring strong anti-interference ability, but debugging is relatively cumbersome, because a cable transmission of multi-channel signal, and there's also a amplifier, if debugging is not good there will be mutual interference (alternating); in addition, reliability in relation to the optical cable, video cable is marginal, because common cable system is in-line, connector, especially near the engine room of the section, if the problem affects all previous signal (video direct communication programme is one-to-one, one cable out of the problem will only affect the way signal).

Therefore adopts the programme, be sure to set the system detailed device location map to the "signal transmission" device manufacturers to help design the system transmission scheme, you need to be equipped with 1 field strength meter.

[1] [2] [3] [4]