At present, there are many ways to transmit image signals in the security surveillance industry, but the main transmission media are coaxial cables, twisted pairs, and optical fibers. The corresponding transmission devices are coaxial video amplifiers and twisted pair video transmission devices, respectively. And optical transceivers. Coaxial cable is used earlier and is the most traditional video transmission method. Later, due to the need for long-distance and large-scale image monitoring and people's increasing requirements for the quality of surveillance images, a large number of optical fibers have been used in surveillance networks to transmit image signals. Although the use of twisted pairs in image monitoring networks is a recent matter, the video balance transmission technology of twisted pair has emerged very early. It is also a branch of video transmission technology. The following describes the following common video transmission methods:
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: small loss of image signals transmitted over short distances, low cost, and stable system. Disadvantages: short transmission distance, high-frequency component attenuation of more than 300 meters, can not guarantee the image quality; all the way to install a video signal cable, transmission control signal to be additional cable; its structure is a star structure, large amount of wiring, maintenance Difficult and poorly scalable, suitable for small systems.
2. 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. They convert the video and control signals into laser signals for transmission in optical fibers. Its advantages are: long transmission distance, low attenuation, good anti-interference performance, and 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 equipment to operate and process, and the maintenance technical requirements are high, so it is difficult to upgrade and expand capacity.
3, network transmission: is to solve the long-distance metropolitan area, a very scattered monitoring transmission point, using MPEG2/4, H. 264 audio and video compression format transmission monitoring signal. Its advantages are: the use of network video server as a monitoring signal upload device, as long as there is an Internet network, the installation of remote monitoring software can monitor and control. The disadvantages are: limited by the network bandwidth and speed, the current ADSL can only transmit small pictures 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, it can not be done. Real-time monitoring.
4. Microwave transmission: It is one of the solutions to the problem of monitoring and transmission of difficult cabling places that are several kilometers or even several tens of kilometers away. 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. The advantages are: low overall cost, more stable performance, eliminating the need for wiring and cable maintenance costs; real-time transmission of broadcast-level images, good image transmission clarity, and complete real-time; flexible networking, good scalability, and plug-in Ready to use; low maintenance costs. The disadvantages are: Due to the use of microwave transmission, the frequency band is above 1 GHz. Commonly used are L-band (1.0 to 2.0 GHz), S-band (2.0 to 3.0 GHz), and Ku-band (10 to 12 GHz), and the transmission environment is an open space. If used in a big city, radio waves are relatively complex and relatively easy to be affected by external electromagnetic interference; microwave signals are transmitted in a straight line, and mountains and buildings cannot be blocked in the middle; if there are obstacles, they need to be relayed and solved, and Ku band is affected by the weather. More serious, especially rain and snow weather will have more serious rain attenuation. However, there are also digital microwave video transmission products, which have improved the anti-interference ability and scalability.
5. Twisted-pair transmission (balanced transmission): It is also a type of video baseband transmission. It converts 75Ω unbalanced mode to balanced mode for transmission. It is to solve the problem that the monitoring image is transmitted within 1Km, and the electromagnetic environment is relatively complicated and the situation is better. The monitoring image signal processing 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 problem of 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.
6, broadband cable transmission: video using AM modulation, audio frequency modulation equipped with FSK data signal modulation technology, dozens of monitoring images, audio, control and alarm signals integrated into the "one" coaxial cable in two-way transmission. Its advantages are: full use of the coaxial cable resource space, 30-way audio and video and control signals in the same cable in two-way transmission, to achieve "one-line pass"; construction is simple, easy maintenance, substantial savings in material costs and construction costs; Frequency Division Multiplexing technology to solve the long-distance transmission point dispersion, wiring difficulties to monitor transmission problems; RF transmission mode only attenuate the carrier signal, the image signal attenuation is relatively small, brightness, chroma transmission synchronization nested to ensure that the image quality to reach 4 or so; using 75Ω The coaxial non-equilibrium transmission makes it have strong anti-interference ability, and the image quality can still be guaranteed in complex electromagnetic environments. The disadvantages are: the use of weak signal transmission, system debugging technology requirements are high, must use professional equipment, if there is a problem with the main line of a device, may result in no image of the entire system, in addition to the need for external AC220V AC power supply broadband modulation terminal (but most The monitoring point has the condition of AC220V AC power supply).
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: small loss of image signals transmitted over short distances, low cost, and stable system. Disadvantages: short transmission distance, high-frequency component attenuation of more than 300 meters, can not guarantee the image quality; all the way to install a video signal cable, transmission control signal to be additional cable; its structure is a star structure, large amount of wiring, maintenance Difficult and poorly scalable, suitable for small systems.
2. 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. They convert the video and control signals into laser signals for transmission in optical fibers. Its advantages are: long transmission distance, low attenuation, good anti-interference performance, and 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 equipment to operate and process, and the maintenance technical requirements are high, so it is difficult to upgrade and expand capacity.
3, network transmission: is to solve the long-distance metropolitan area, a very scattered monitoring transmission point, using MPEG2/4, H. 264 audio and video compression format transmission monitoring signal. Its advantages are: the use of network video server as a monitoring signal upload device, as long as there is an Internet network, the installation of remote monitoring software can monitor and control. The disadvantages are: limited by the network bandwidth and speed, the current ADSL can only transmit small pictures 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, it can not be done. Real-time monitoring.
4. Microwave transmission: It is one of the solutions to the problem of monitoring and transmission of difficult cabling places that are several kilometers or even several tens of kilometers away. 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. The advantages are: low overall cost, more stable performance, eliminating the need for wiring and cable maintenance costs; real-time transmission of broadcast-level images, good image transmission clarity, and complete real-time; flexible networking, good scalability, and plug-in Ready to use; low maintenance costs. The disadvantages are: Due to the use of microwave transmission, the frequency band is above 1 GHz. Commonly used are L-band (1.0 to 2.0 GHz), S-band (2.0 to 3.0 GHz), and Ku-band (10 to 12 GHz), and the transmission environment is an open space. If used in a big city, radio waves are relatively complex and relatively easy to be affected by external electromagnetic interference; microwave signals are transmitted in a straight line, and mountains and buildings cannot be blocked in the middle; if there are obstacles, they need to be relayed and solved, and Ku band is affected by the weather. More serious, especially rain and snow weather will have more serious rain attenuation. However, there are also digital microwave video transmission products, which have improved the anti-interference ability and scalability.
5. Twisted-pair transmission (balanced transmission): It is also a type of video baseband transmission. It converts 75Ω unbalanced mode to balanced mode for transmission. It is to solve the problem that the monitoring image is transmitted within 1Km, and the electromagnetic environment is relatively complicated and the situation is better. The monitoring image signal processing 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 problem of 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.
6, broadband cable transmission: video using AM modulation, audio frequency modulation equipped with FSK data signal modulation technology, dozens of monitoring images, audio, control and alarm signals integrated into the "one" coaxial cable in two-way transmission. Its advantages are: full use of the coaxial cable resource space, 30-way audio and video and control signals in the same cable in two-way transmission, to achieve "one-line pass"; construction is simple, easy maintenance, substantial savings in material costs and construction costs; Frequency Division Multiplexing technology to solve the long-distance transmission point dispersion, wiring difficulties to monitor transmission problems; RF transmission mode only attenuate the carrier signal, the image signal attenuation is relatively small, brightness, chroma transmission synchronization nested to ensure that the image quality to reach 4 or so; using 75Ω The coaxial non-equilibrium transmission makes it have strong anti-interference ability, and the image quality can still be guaranteed in complex electromagnetic environments. The disadvantages are: the use of weak signal transmission, system debugging technology requirements are high, must use professional equipment, if there is a problem with the main line of a device, may result in no image of the entire system, in addition to the need for external AC220V AC power supply broadband modulation terminal (but most The monitoring point has the condition of AC220V AC power supply).