Currently, there are six transmission methods for video transmission in the surveillance system: video baseband transmission, balanced twisted pair transmission, optical fiber transmission, network transmission, microwave transmission, and broadband common cable transmission.
1 Video baseband transmission: It is the most traditional television monitoring transmission method. It does not do any processing on 0~6MHz video baseband signals and directly transmits analog signals through coaxial cables (unbalanced). Its advantages are: the short-distance transmission image signal loss is small, the cost is low. Disadvantages: The transmission distance is short, high-frequency components above 300 meters are attenuated greatly, and the image quality cannot be guaranteed; one cable is required for one-way video signals, and an additional cable is required for transmission of control signals; its structure is a star structure, and the wiring volume is large and maintained. Difficulties and poor scalability.
2 Twisted Pair Transmission (Balanced Transmission): It is one of the solutions to solve the problem of transmitting electromagnetic signals within 1Km of the surveillance image and dealing with complex situations of the electromagnetic environment. The signal processing of surveillance images is transmitted in a balanced and symmetrical manner. Its advantages are: simple wiring, low cost, and strong anti-common-mode performance. Its disadvantages are that it can only solve the monitoring image transmission within 1Km, and a twisted pair can only transmit one image, which is not suitable for large and medium-sized monitoring; the texture of the twisted pair is weak and has poor anti-aging ability, and is not suitable for field transmission; The high-frequency component of the twisted wire transmission attenuates greatly, and the color of the image suffers a great loss.
3 Optical fiber transmission: Common analog optical transceivers and digital optical transceivers are the best solutions to solve tens or even hundreds of kilometers of television monitoring transmissions. The video and control signals are converted into optical signals for transmission in optical fibers. Its advantages are: long transmission distance, low attenuation, best anti-interference performance, suitable for long-distance transmission. The disadvantages are: it is not economical to transmit monitoring signals within a few kilometers; the optical welding and maintenance require professional technicians and equipments to handle, and the maintenance technical requirements are high, so it is difficult to upgrade and expand.
4 Network transmission: It is a monitoring transmission method that solves the long-distance and extremely-distributed points between metropolitan areas. It uses the MPEG audio and video compression format to transmit monitoring signals. Its advantages are: the use of network video server as a monitoring signal upload device, Internet monitoring and monitoring software can be installed on the remote monitoring and control. The disadvantages are: limited by the network bandwidth and speed, can only transmit small images and low quality images; only a few to a dozen frames of images can be transmitted per second, the animation effect is very obvious and there is a delay, and real-time monitoring cannot be achieved. .
5Microwave transmission: It is one of the solutions to solve the problem of monitoring and transmission in places where several kilometers or even tens of kilometers are not easy to be wired. Using FM modulation or AM modulation, the image is loaded on a high-frequency carrier and converted into high-frequency electromagnetic waves for transmission in the air. Its advantages are: the cost of wiring and cable maintenance is eliminated, and broadcast-level images can be dynamically transmitted in real time. The disadvantages are: due to the use of microwave transmission, the frequency band above 1 GHz is commonly used in the L-band (1.0 ~ 2.0 GHz), S-band (2.0 ~ 3.0 GHz), Ku-band (10 ~ 12 GHz) transmission environment is open space is very vulnerable External electromagnetic interference; Microwave signals are transmitted in a straight line, and mountains and buildings cannot be blocked in the middle; Ku band is affected by the weather more severely, especially in rain and snow weather.
6Broadband common cable transmission: It is the best solution to solve the transmission of several kilometers to several tens of kilometers of monitoring signals. It adopts advanced technologies such as amplitude modulated modulation, audio frequency modulation, FSK data signal modulation, etc. It can provide 40 channels of monitoring images, audio, control and alarm. The signal is integrated into the "one" coaxial cable in both directions. Its advantages are: full use of the coaxial cable's resource space, 40-way audio and video and control signals in the same cable in two-way transmission, to achieve a wide-band common cable "first pass"; construction is simple, easy maintenance, substantial savings in material costs and construction costs Frequency division multiplexing technology solves the problem of dispersion of distant transmission points, and the difficulty in monitoring and transmission of wiring; RF transmission mode only attenuates carrier signals, image signal attenuation is very small, and luminance and chrominance transmission are synchronously nested, ensuring that the image quality reaches above 4.5. National standards; The use of 75Ω coaxial unbalanced transmission makes it have a very strong anti-interference ability, the electromagnetic environment can still guarantee image quality in complex occasions. The disadvantages are: the use of weak signal transmission, the need for external AC220V AC power supply broadband modulation end, but most monitoring sites have this condition.
1 Video baseband transmission: It is the most traditional television monitoring transmission method. It does not do any processing on 0~6MHz video baseband signals and directly transmits analog signals through coaxial cables (unbalanced). Its advantages are: the short-distance transmission image signal loss is small, the cost is low. Disadvantages: The transmission distance is short, high-frequency components above 300 meters are attenuated greatly, and the image quality cannot be guaranteed; one cable is required for one-way video signals, and an additional cable is required for transmission of control signals; its structure is a star structure, and the wiring volume is large and maintained. Difficulties and poor scalability.
2 Twisted Pair Transmission (Balanced Transmission): It is one of the solutions to solve the problem of transmitting electromagnetic signals within 1Km of the surveillance image and dealing with complex situations of the electromagnetic environment. The signal processing of surveillance images is transmitted in a balanced and symmetrical manner. Its advantages are: simple wiring, low cost, and strong anti-common-mode performance. Its disadvantages are that it can only solve the monitoring image transmission within 1Km, and a twisted pair can only transmit one image, which is not suitable for large and medium-sized monitoring; the texture of the twisted pair is weak and has poor anti-aging ability, and is not suitable for field transmission; The high-frequency component of the twisted wire transmission attenuates greatly, and the color of the image suffers a great loss.
3 Optical fiber transmission: Common analog optical transceivers and digital optical transceivers are the best solutions to solve tens or even hundreds of kilometers of television monitoring transmissions. The video and control signals are converted into optical signals for transmission in optical fibers. Its advantages are: long transmission distance, low attenuation, best anti-interference performance, suitable for long-distance transmission. The disadvantages are: it is not economical to transmit monitoring signals within a few kilometers; the optical welding and maintenance require professional technicians and equipments to handle, and the maintenance technical requirements are high, so it is difficult to upgrade and expand.
4 Network transmission: It is a monitoring transmission method that solves the long-distance and extremely-distributed points between metropolitan areas. It uses the MPEG audio and video compression format to transmit monitoring signals. Its advantages are: the use of network video server as a monitoring signal upload device, Internet monitoring and monitoring software can be installed on the remote monitoring and control. The disadvantages are: limited by the network bandwidth and speed, can only transmit small images and low quality images; only a few to a dozen frames of images can be transmitted per second, the animation effect is very obvious and there is a delay, and real-time monitoring cannot be achieved. .
5Microwave transmission: It is one of the solutions to solve the problem of monitoring and transmission in places where several kilometers or even tens of kilometers are not easy to be wired. Using FM modulation or AM modulation, the image is loaded on a high-frequency carrier and converted into high-frequency electromagnetic waves for transmission in the air. Its advantages are: the cost of wiring and cable maintenance is eliminated, and broadcast-level images can be dynamically transmitted in real time. The disadvantages are: due to the use of microwave transmission, the frequency band above 1 GHz is commonly used in the L-band (1.0 ~ 2.0 GHz), S-band (2.0 ~ 3.0 GHz), Ku-band (10 ~ 12 GHz) transmission environment is open space is very vulnerable External electromagnetic interference; Microwave signals are transmitted in a straight line, and mountains and buildings cannot be blocked in the middle; Ku band is affected by the weather more severely, especially in rain and snow weather.
6Broadband common cable transmission: It is the best solution to solve the transmission of several kilometers to several tens of kilometers of monitoring signals. It adopts advanced technologies such as amplitude modulated modulation, audio frequency modulation, FSK data signal modulation, etc. It can provide 40 channels of monitoring images, audio, control and alarm. The signal is integrated into the "one" coaxial cable in both directions. Its advantages are: full use of the coaxial cable's resource space, 40-way audio and video and control signals in the same cable in two-way transmission, to achieve a wide-band common cable "first pass"; construction is simple, easy maintenance, substantial savings in material costs and construction costs Frequency division multiplexing technology solves the problem of dispersion of distant transmission points, and the difficulty in monitoring and transmission of wiring; RF transmission mode only attenuates carrier signals, image signal attenuation is very small, and luminance and chrominance transmission are synchronously nested, ensuring that the image quality reaches above 4.5. National standards; The use of 75Ω coaxial unbalanced transmission makes it have a very strong anti-interference ability, the electromagnetic environment can still guarantee image quality in complex occasions. The disadvantages are: the use of weak signal transmission, the need for external AC220V AC power supply broadband modulation end, but most monitoring sites have this condition.
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