Coaxial cable is an ultra-wideband transmission medium that can be transmitted from DC to microwave. The theoretical basis of coaxial transmission is the electromagnetic field theory, which is very different from the general electrical circuit theory. For example, if the cable connection is made of core wire or shielded mesh, it is welded and twisted separately, and if the "three links" are used for video signal distribution, this is reasonable from the perspective of electrical circuits, but it is a principle from the perspective of coaxial transmission. error. In order to reduce the cable attenuation, the cable manufacturer of the SYV75-5 solid cable is changed to 1.0mm for the SYV75-5 solid cable. The reason is: the physical foam cable core is 1.0mm, and the solid cable can also be made. 1.0mm, it seems that the RVV cable can be chosen just like the wire diameter. What can't be done with a thin one? I don't know, so the characteristic impedance of the cable is no longer 75 ohms, it becomes 60 ohms, no Matching, can not be used in the 75 ohm transmission system. This is not a "pure theory" problem, but a scientific conclusion that is completely unified in practice and theory.
This article refers to the address: http://
There are two main ways of coaxial video cable transmission: baseband coaxial transmission and radio frequency coaxial transmission, and a kind of "digital video transmission", such as the Internet, which is an integrated transmission mode. It is worth mentioning that there is already a digital TV transmission technology, will it develop into the monitoring industry, it is worthy of discussion and attention. Here mainly talk about the technical principles of the first two categories. From the perspective of engineering application, it is important to grasp the transmission characteristics of the cable and the basic performance of the transmission equipment. It is also necessary to pay special attention to the "video transmission channel characteristics" composed of the cable plus transmission equipment.
Radio frequency transmission, which is the mature transmission mode of cable TV, is to modulate the RF carrier by video signal. The video information is carried and hidden in the amplitude variation of the RF signal to form a channel of 8M standard bandwidth. Different camera video signals are modulated. Different RF channels, then use a multi-channel mixer to mix all the channels into one broadband RF output, realize the transmission of multiple signals in the same cable with one transmission cable, and then divide the multi-channel with the RF adapter at the end, and use one signal for each signal. The demodulator demodulates the video signal of one channel. The frequency distortion generated by cable transmission within a channel (8M) should be completed by the internal weighting circuit of the modem. For the broadband transmission frequency distortion between channels, the special equalizer is used to detect and debug at the engineering site; for transmission attenuation, the calculation is performed. And on-site field strength detection and debugging, including remote transmission of series amplifiers, field strength level control before and after the equalizer; RF multiplex transmission has obvious advantages for medium and long distance video transmission within a few kilometers. The radio frequency transmission method inherits the mature transmission mode of cable TV, and its feasibility, credibility and reliability are not doubtful in the technical application of the monitoring industry. However, the maturity of technology does not mean that specific products and specific projects will be successful. The knowledge and experience of RF network design and debugging, the level of engineering and technical personnel, and the supporting equipment are also the key factors for the success of the project. When designing the transmission system, pay attention to the reasonable matching with other transmission methods, and avoid the design scheme of “unifying the worldâ€. The current status quo is: many products, the pursuit of low cost, low price, reduce the technical performance of the original broadcast equipment, and the actual monitoring of the application is an outdoor all-weather environment. The manufacturers announced that they are overwhelming, but the application surface is still less. In addition to the complexity of the system and the lack of experience of the engineering business, the propaganda of the factory only emphasizes the benefits of “multi-channel common cable†and “multi-channel first-line communicationâ€, which makes people feel this transmission method. Good, simple, and cheap, there is no emphasis on the design, installation and debugging techniques and difficulties of the RF transmission network. The result is that I don’t know how to use it. If I don’t know how to buy it, I’m going to be fooled! Promote the application.
Coaxial video baseband transmission: This is one of the most basic, most common, the earliest applications, the most used one, and the so-called "it is what people will do" transmission. In fact, it is a transmission method that understands the most superficial and the slowest technological progress. The slow progress of this technology is also a major factor. The low-frequency attenuation of the coaxial cable is small, and the high-frequency attenuation is large. It is also the truth that everyone understands. However, the radio has realized multiple long-distance transmissions more than 20 years ago, while the video baseband transmission has stayed in the single-channel one hundred and eighty. At the level below the meter; in the case of reducing the image quality requirements in the monitoring project, only 3 or 4 meters can be used.
The difficulty in the advancement of this technology is the problem that the frequency distortion of the coaxial video baseband transmission is too serious. For RF transmission, the relative bandwidth (8M) of a channel is only a few percent, and the difference between high and low frequencies is small, which can be neglected. However, in the coaxial video baseband transmission mode, the low frequency is 10-50 Hz and the high frequency is 6M. The difference between high and low frequencies is hundreds of thousands - hundreds of thousands of times, high and low frequency attenuation (frequency distortion) is too large, and the attenuation difference of cables of different lengths is also different. It is impossible to correct the cable with a simple, fixed frequency weighting network. Frequency distortion, with wideband and other gain video amplifiers, can not solve the frequency distortion problem. Therefore, in order to realize coaxial long-distance baseband transmission, it is necessary to solve the problem of weighted amplification technology, and the "compensation characteristic" of such frequency-weighted amplification must be opposite, complementary, and continuously adjustable with the attenuation and frequency distortion characteristics of the cable. Adapting to the different models of engineering and the compensation of cables of different lengths, this is the historical reason for the slowest technological progress. This technology was breakthrough in the EIE laboratory of Yantai Development Zone in 2000, and obtained national patents. After several years of productization and promotion, technology and products have matured and have been successfully applied in all provinces and cities in China and Hong Kong. . The direct engineering application effect is: greatly improving the distance and range of coaxial video surveillance - from more than 100 meters to 2, 3 kilometers; effectively improving the image transmission quality and reducing the cost of long-distance transmission cables; The compensation "simplifies the transmission system, facilitates the installation and commissioning of the project, and realizes the on-site adjustable control of the image quality in the project for the first time. However, such video recovery products can only be used one-to-one, and cannot be used as a multi-channel cable or as an anti-jamming device.
In January 2005, EIE Lab's patented frequency-weighted anti-jamming video transmission technology realized the dual functions of suppressing interference and video response. On the basis of solving the problem of frequency-weighted amplification technology, it further promoted the transmission of coaxial video baseband. The development and application of technology.
15.6 inch Laptop is one of the most important sizes on the market, more than 85% clients choose this size for business, teachers, middle or high school students, university students projects. 15.6 inch Gaming Laptop is ranking the first level of custom laptop, you can see i5 15.6 inch laptop, intel celeron n5095 Cheap 15.6 Inch Laptop, i7 11th 15.6 Inch Laptop In cm, etc.
15inch gaming Laptop with 11th Gen Intel Core i5-1135G7 processor ( up to 4.2GHZ, 4core, 8threads, 8MB caches) or 15.6 inch i7 1165G7 8 512gb Solid State Drive laptop ( up to 4.7GHZ, 4core, 8threads, 12MB Caches) should attractive your eyes when choose a competitive and hot gaming laptop.
Of course, other parameters levels, like 14 inch n4020 64gb laptop for online classes, 10.1 Inch Laptop equipped with 64gb rom, android 11 or windows 10 , or 11 Inch Windows Laptop in metal with 360 rotating, celeron quad core cpu, etc.
Except, 8 inch Android Tablet, Mini PC host, All In One Desktop also available here. So just share your idea about what you exactly need, then we do following for you.
15.6 Inch Laptop,15.6 Inch Gaming Laptop,15.6 Inch Laptop In Cm,I5 15.6 Inch Laptop,Cheap 15.6 Inch Laptop
Henan Shuyi Electronics Co., Ltd. , https://www.shuyielectronictech.com