Coaxial video transmission technology theory and practical application - Coaxial transmission, video - broadcasting industry
Coaxial cable is an ultra-wideband transmission media, from DC to microwave can be transmitted. Coaxial transmission electromagnetic theory is the theoretical basis, and general electrical circuit theory has important differences. Such as a cable connection using wire, shield welding, respectively, twist, and as with the "three links" Video Signal distribution, electrical circuit from the point of view this is reasonable, but from the perspective of a coaxial transmission theory of error. Then if the cable manufacturers to reduce the cable attenuation, the SYV75-5 0.75-0.8mm solid cable's core wire, to 1.0mm, the following reasons: physical foaming cable wire is 1.0mm, solid cable can also be made 1.0mm, as if I could choose RVV wire cable as thick thin election not work why not? Do not know, this way the cable characteristic impedance is no longer a 75 ohm to 60 ohms or so, and do not match, can not be used in 75 ohm transmission system. This is not a "pure theory", but the complete reunification of the practice and theory of scientific conclusions.
Coaxial video cable transmission, there are two main ways: base-band transmission and RF coaxial coaxial transmission, there is a "digital video transmission," such as the Internet, is an integrated transport. It is worth mentioning that there is now Digital TV Transmission technology, will develop to monitor the industry to, worthy of our discussion and concern. Here to talk about the first two major technical principle. From the engineering point of view, it is important to grasp the cable transmission characteristics and transmission equipment, basic performance, but also to pay special attention to the cable transmission equipment composed of Canada, "the video transmission channel characteristics."
Radio transmission, that is, Cable television Mature transmission, the video signal through the RF carrier for amplitude modulation, and video information carrying RF signals hidden in the magnitude of change, the formation of a 8M standard bandwidth channels, different Video camera Video signal modulated to a different radio frequency channels, then use the multi-mixer, mix all the channels in one of the broadband RF output, to achieve a transmission cable with multiple signal transmission with the Village, in the end, and then divided into multiple radio frequency adapter per signals demodulated with a demodulator, a channel of video signal. On one channel (8M) generated within the cable transmission frequency distortion, should be Modem The weighted completion of the internal circuit, for broadband transmission frequency between the channel distortion, the equalizer by a dedicated on-site testing and adjusting the completion of the project; for transmission attenuation, through the calculation and completion of testing and adjusting the field strength, including long-range transport cascade Amplifiers , Field strength before and after the equalizer level control; RF multiplexing within a few kilometers in the remote video transmission has an advantage. Inherited the RF transmission cable transmission of maturity, in the surveillance industry applications, their feasibility, credibility and reliability, is technically no doubt. But the technology matures, does not mean the specific product and the specific projects will definitely succeed, RF network design and debugging of knowledge and experience, the level of engineering and technical personnel, test equipment supporting such projects is key to the success factors; in monitoring project video transmission system should pay attention to other transmission methods, collocation, and not to be "unified" design. The present situation is: a lot of products, the pursuit of low cost, low price, reducing the original Broadcasting The technical performance, and actual monitoring applications is outdoor all-weather environment. Manufacturers that overwhelming, but this surface is also less, because in addition to system complexity and engineering companies with little experience outside the factory is just propaganda emphasized that "a total of multi-cable", "multi-Link" the benefits people feel this transmission sound, and simple, and cheap price, there is no RF transmission network focuses on the design and installation techniques of difficulty, the results are not used do not understand, bought to do well, screaming, "fools!" inevitably affect the expand the applications.
Baseband coaxial video transmission: This is a most basic, the most common application of the first, the most widely used means of transmission, jokingly, "is people will do" the transmission. In fact it is about the most superficial kind of technological progress the slowest transmission. This slow technological progress which is the main factor. Low attenuation coaxial cable, high-frequency attenuation, as everyone is aware of the truth, but the radio as early as 20 years ago to achieve a multi-distance transmission, and video base-band transmission is going through a long stay in the single 10 m below the level; monitoring project the image quality requirements in the lower case, and can only use 3,4 meters.
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