In surveillance systems, the transmission of surveillance images is a vital part of the entire system. Selecting which media and equipment to transfer images and other control signals will directly affect the quality and reliability of the surveillance system. At present, the media used to transmit image signals in surveillance systems are mainly coaxial cables, twisted pairs and optical fibers. The corresponding transmission devices are coaxial video amplifiers, twisted-pair video transmission devices and optical transceivers.
Coaxial cable is used earlier and it is also the longest transmission time. 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. As far as twisted-pair wires are used in image monitoring networks, it is a recent thing. Its emergence has mainly solved two problems: On the one hand, it solved high-quality maps within a range of 200 meters to 2000 meters. Like the problem of signal transmission, because coaxial cable transmission is difficult to achieve in this distance range, optical fiber transmission is not economical; on the other hand, it solves the wiring problem of large-scale intensive monitoring networks, and the twisted pair itself The size and softness overcome the cabling challenges when using a large number of coaxial cables. Of course, the twisted pair also has the advantages of strong resistance to common mode interference and low price. It is because twisted-pairs solve the problems that have plagued people for a long time. Therefore, its application in monitoring networks has attracted widespread attention in the industry. It has been widely used in engineering practice in a short period of time, and Has achieved very good application results.
Each monitoring project has its own characteristics and particularities. Therefore, when setting up a monitoring network, it is necessary to fully consider these specific situations and use the most suitable image and signal transmission methods. Given that coaxial cable, twisted pair, and fiber are the three most widely used transmission media in current surveillance systems, we can analyze and compare them in several ways.
First, the characteristics and transmission characteristics of the analysis 1, coaxial cable is generally in a small range of monitoring systems, because the transmission distance is very close, the use of coaxial cable direct transmission of monitoring images of the image quality of the damage is not large, to meet the actual requirements. However, according to the analysis of the characteristics of the coaxial cable itself, when the signal is transmitted in the coaxial cable, its attenuation is related to the transmission distance and the frequency of the signal itself. In general, the higher the signal frequency, the greater the attenuation. Therefore, the coaxial cable is only suitable for transmitting the image signal at a short distance. When the transmission distance reaches about 200 meters, the image quality will obviously decrease, especially the color becomes dull, and there is a sense of distortion.
In engineering practice, coaxial amplifiers are used to extend the transmission distance. The coaxial amplifier has a certain amplification to the video signal, and can also compensate different magnitudes of the different frequency components by equalization adjustment, so as to minimize the distortion of the video signal output by the receiver. However, coaxial amplifiers cannot be cascaded without limitation. Generally, in a point-to-point system, coaxial amplifiers can only cascade at most 2 to 3, otherwise the quality of video transmission cannot be guaranteed, and adjustment is also very difficult. Therefore, when the coaxial cable is used in the monitoring system, the range of the transmission distance is generally limited to about four or five hundred meters in order to ensure a good image quality.
In addition, there are some disadvantages in the coaxial cable transmission of image signals in the surveillance system:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected.
2) The coaxial cable is relatively thick, and the wiring is not convenient in dense monitoring applications;
3) Coaxial cable can only transmit video signals. If the system needs to transmit control data, audio and other signals at the same time, additional wiring is required.
4) Coaxial cable has limited anti-jamming capability and cannot be used in strong jamming environments;
5) Coaxial amplifiers also have the disadvantage of being difficult to adjust.
2. Twisted Pair Twisted Pairs have been used for a long time. Twisted pairs have been used in many industrial control systems and in places with large interference and in long-distance transmission. The LANs we use widely today also use twisted pairs. . The reason why twisted-pair cables are so widely used is that they have many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Twisted pair signal also has a large attenuation, if the video signal is directly transmitted in the twisted pair, it will also decay greatly, so the video signal in the twisted pair to achieve long-distance transmission, must be amplified and compensated, Twisted pair video transmission equipment is to complete this function. With a pair of twisted pair video transceivers, the image can be transmitted to 1 to 2 km. Twisted pair and twisted pair video transmission equipment are very cheap, not only does not increase the system cost, but when the distance increases, its cost is much lower than the coaxial cable. Therefore, the use of twisted pair transmission in monitoring systems has obvious advantages:
1) The transmission distance is long and the transmission quality is high. Thanks to the advanced processing technology used in the twisted pair transceivers, the attenuation of the amplitude of the video signal and the difference in attenuation between different frequencies of the twisted pair are perfectly compensated, and the brightness and color of the original image and the real-time performance are maintained. When the transmission distance reaches 1km or more, the image signal is substantially free of distortion. If relay mode is used, the transmission distance will be further away.
2) Easy wiring and high cable utilization. A pair of ordinary telephone lines can be used to transmit video signals. In addition, one of the five types of unshielded twisted pairs widely installed in a building can transmit one video signal without the need for additional wiring. Even with rerouting, category 5 cables are easier than coaxial cables. In addition, a Category 5 cable has 4 pairs of twisted pair cables. If a pair of cables is used to transmit video signals, the other pairs of cables can also be used to transmit audio signals, control signals, power supply, or other signals to improve the cable. The utilization rate, at the same time avoids the trouble caused by the separate wiring of various signals, and reduces the project cost.
3) Strong anti-interference ability. Twisted pair can effectively suppress common-mode interference. Even in strong interference environments, twisted-pair cables can transmit excellent image signals. In addition, several pairs of twisted pairs in a cable are used to transmit different signals and no interference occurs between them.
4) High reliability and easy to use. Utilize twisted pair to transmit the video signal, need to insert the special transmitter in the front end, want to insert the special receiver in the control center. This type of twisted-pair transmission equipment is cheap and easy to use, requires no specialized knowledge, and does not require much operation. It can be installed once and work stably for a long time.
5) The price is cheap, easy to draw. Due to the use of common 5 types of unshielded cables or ordinary telephone lines which are widely used at present, the purchase is easy and the price is also very cheap, which brings great convenience to engineering applications.
3. The application of fiber optics and optical transceivers in the field of surveillance is mainly to solve two problems: First, transmission distance, and first, environmental interference. Twisted pair and coaxial cable can only solve the problem of transmission of surveillance images in short distances and small areas. If it is necessary to transmit image signals of distances of several kilometers or even hundreds of kilometers, it needs to use optical fiber transmission methods. In addition, for some super-disturbing sites, in order to be free from environmental interference, optical fiber transmission must also be used. Because the optical fiber has many advantages such as wide transmission bandwidth, large capacity, immunity to electromagnetic interference, and small influence from the external environment, an optical fiber can transmit all the signals required in the monitoring system, and the transmission distance can reach hundreds of kilometers. The optical transceiver provides a flexible transmission and networking method for the monitoring system, with good signal quality and high stability.
However, the use of optical fiber and optical transceivers requires a certain amount of expertise and special equipment, which brings certain difficulties for construction and user use. In addition, for short-range, small-scale monitoring systems, the use of optical fiber transmission is also not economical.
Second, technical performance analysis 1, coaxial cable In the monitoring system, using 75Ω, -5 coaxial cable is more common.
In general, the distributed capacitance of this kind of coaxial cable is about 50-60pF/m, plus the DC resistance of the cable, which will cause the transmitted signal to be attenuated. Tests have shown that a signal with a frequency of 5 MHz will be attenuated by about 5 dB when transmitted over a coaxial cable of 75 Ω and -5, and the higher the signal frequency, the greater the attenuation. The image signal is a high-frequency broadband signal. The color part of the image is located at the high end of the frequency. When the coaxial cable is used to transmit the color image signal, the brightness and color will be attenuated, especially as the transmission distance increases the color of the image. Will become lighter or even distorted. Tests conducted in the laboratory revealed that the amplitude and color of the color image signal have been significantly attenuated when transmitting a color image signal of about 200 m in a coaxial cable of 75Ω or -5. If you want to transmit more distance, only join the coaxial video amplifier.
2. When using twisted pair as a transmission medium for twisted-pair cables, commonly used Category 5 UTP cables are generally used. Its characteristic impedance is about 100Ω, and the distributed capacitance is about 15pF/m. Different from the coaxial cable, the signal is transmitted in a balanced manner in the twisted pair. With the use of twisted pair video transmission equipment and twisted pair, it can be guaranteed. High-quality video signals can be transmitted within a distance of 1.5Km. In the laboratory, a dedicated instrument was used to test the performance of the image signal transmitted by the twisted pair. The results are as follows:
Test Instruments: Tektronix TSG-271PAL signal generator, Tektronix VN700A video signal analyzer Tested equipment: Wuhan MicroPort Optoelectronics Technology Co., Ltd. (027-87462996) WTC S-03C10 twisted pair video transmission equipment, Category 5 UTP cable (1) transmission When the distance is 300m, the index: DG ≤ 1%; DP ≤ 1°; SNR ≥ 65dB
(2) When the transmission distance is 1200m: Index: DG ≤ 2%; DP ≤ 2°; SNR ≥ 60dB
3, fiber optic fiber is an inevitable choice for remote monitoring of image transmission, it can provide a transmission distance of hundreds of kilometers, and can provide a good image transmission quality. The use of special instruments in the laboratory tested the performance of the Wuhan Slight Optoelectronic Technology Co., Ltd. WTOS-02S4000 uncompressed digital video transmission equipment, as follows:
DG ≤ 1%; DP ≤ 1°; SNR ≥ 70dB
Third, economic analysis Optical fiber transmission is the highest cost of the three transmission methods, and now the price of single-mode fiber is generally about 2 yuan per fiber per meter, the price of optical transceiver is about 2,000 yuan per image, plus The auxiliary materials in the project such as optical fiber jumpers, optical flanges, and optical fiber fusion splicing expenses, etc., make the cost of the optical fiber monitoring network relatively high. However, optical fiber transmission has many outstanding advantages. Therefore, in monitoring networks with transmission distances of two to three kilometers or more, some places with strong environmental interference, and monitoring sites that require high quality and reliability, most of them use optical fiber as the transmission medium. .
Coaxial cables are widely used within a distance of one or two hundred meters. In this range, the use of coaxial cables does not require other equipment. It is easy to use and the transmission quality can basically meet the requirements. However, when the transmission distance increases, the coaxial cable is inferior to the twisted pair in cost performance. In general, 75Ω, -5 coaxial cable market price is 1.5 yuan / m, coaxial amplifier price is 300 yuan / Taiwan; Category 5 UTP cable price is 0.8 yuan / m, the price of twisted pair video transmission equipment is 600 yuan / In the following, the transmission costs of coaxial cable and twisted pair are compared in terms of distances of 300m and 600m.
(1) It is assumed that there are 8 monitoring points in a monitoring network, and each monitoring point is about 300m from the control center.
When using coaxial cable:
1.5 yuan/m×300m×8=3600 yuan When using twisted pair:
Since each four-way image can share a Category 5 UTP cable, only two Category 5 UTP cables are required in the network. 0.8 yuan/m×300m×2+600 yuan/set×8=5280 yuan (2) It is assumed that there are 8 monitoring points in a monitoring network, each monitoring point is about 600m away from the control center when the coaxial cable is used:
To ensure image quality, an amplifier is added to each image. 1.5 yuan / m × 600m × 8 + 300 yuan / Taiwan × 8 = 9600 yuan When using twisted pair:
Since each four-way image can share a Category 5 UTP cable, only two Category 5 UTP cables are required in the network. 0.8 yuan/m×600m×2+600 yuan/set×8=5760 yuan It can be seen from the above analysis that as the transmission distance increases, the advantages of twisted pair transmission in terms of cost are increasingly displayed. If there are other signal transmissions such as control signals in the network, the cost advantage of twisted pair transmission will be more obvious. In addition, when the transmission distance is further increased, for example, up to about 1 km, the coaxial cable transmission has been difficult to meet the transmission quality requirements, and the twisted pair can still ensure good image quality when the transmission is about 1.5 kilometers.
IV. Project Recommendations In actual projects, the choice of transmission method needs to be considered in conjunction with the specific conditions of the project and the project budget.
For monitoring networks with transmission distances exceeding 2 Km, optical and optical transceivers should be considered. If the transmission distance reaches several kilometers or dozens of kilometers, only the optical fiber is used. In addition, in places where there is strong interference, such as where industrial interference and electromagnetic interference occur, optical fiber transmission is also recommended to ensure image quality.
The selection of coaxial cables and twisted pairs requires more analysis and comparison. As twisted pair transmission is a new emerging technology, and the use of coaxial cable has a long history, it is necessary to fully explore the characteristics and advantages of twisted pair transmission, providing convenience for engineering design and construction, and saving cost. . When the transmission distance is from four to five hundred meters to about 1.5 kilometers, the twisted pair can undoubtedly exert excellent performance and price advantages. For a monitoring network within two or three hundred meters, if the scale is small, it is reasonable to use the coaxial cable. The cost of construction is also lower. However, the actual project will also have its specificity. Even if the distance is very close, if the network is very large, for example, there are hundreds of monitoring points, then it will be difficult to use coaxial cable, and twisted pair can make This problem has been solved. Furthermore, if there is a large amount of interference in the environment, using twisted-pair cables can effectively prevent interference and ensure image transmission quality. In addition, the convenience and flexibility of twisted-pair cabling make some short-distance, intensive monitoring networks such as building buildings gradually begin to use it instead of coaxial cable, and it is well integrated into the integrated cabling project.
Coaxial cable is used earlier and it is also the longest transmission time. 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. As far as twisted-pair wires are used in image monitoring networks, it is a recent thing. Its emergence has mainly solved two problems: On the one hand, it solved high-quality maps within a range of 200 meters to 2000 meters. Like the problem of signal transmission, because coaxial cable transmission is difficult to achieve in this distance range, optical fiber transmission is not economical; on the other hand, it solves the wiring problem of large-scale intensive monitoring networks, and the twisted pair itself The size and softness overcome the cabling challenges when using a large number of coaxial cables. Of course, the twisted pair also has the advantages of strong resistance to common mode interference and low price. It is because twisted-pairs solve the problems that have plagued people for a long time. Therefore, its application in monitoring networks has attracted widespread attention in the industry. It has been widely used in engineering practice in a short period of time, and Has achieved very good application results.
Each monitoring project has its own characteristics and particularities. Therefore, when setting up a monitoring network, it is necessary to fully consider these specific situations and use the most suitable image and signal transmission methods. Given that coaxial cable, twisted pair, and fiber are the three most widely used transmission media in current surveillance systems, we can analyze and compare them in several ways.
First, the characteristics and transmission characteristics of the analysis 1, coaxial cable is generally in a small range of monitoring systems, because the transmission distance is very close, the use of coaxial cable direct transmission of monitoring images of the image quality of the damage is not large, to meet the actual requirements. However, according to the analysis of the characteristics of the coaxial cable itself, when the signal is transmitted in the coaxial cable, its attenuation is related to the transmission distance and the frequency of the signal itself. In general, the higher the signal frequency, the greater the attenuation. Therefore, the coaxial cable is only suitable for transmitting the image signal at a short distance. When the transmission distance reaches about 200 meters, the image quality will obviously decrease, especially the color becomes dull, and there is a sense of distortion.
In engineering practice, coaxial amplifiers are used to extend the transmission distance. The coaxial amplifier has a certain amplification to the video signal, and can also compensate different magnitudes of the different frequency components by equalization adjustment, so as to minimize the distortion of the video signal output by the receiver. However, coaxial amplifiers cannot be cascaded without limitation. Generally, in a point-to-point system, coaxial amplifiers can only cascade at most 2 to 3, otherwise the quality of video transmission cannot be guaranteed, and adjustment is also very difficult. Therefore, when the coaxial cable is used in the monitoring system, the range of the transmission distance is generally limited to about four or five hundred meters in order to ensure a good image quality.
In addition, there are some disadvantages in the coaxial cable transmission of image signals in the surveillance system:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected.
2) The coaxial cable is relatively thick, and the wiring is not convenient in dense monitoring applications;
3) Coaxial cable can only transmit video signals. If the system needs to transmit control data, audio and other signals at the same time, additional wiring is required.
4) Coaxial cable has limited anti-jamming capability and cannot be used in strong jamming environments;
5) Coaxial amplifiers also have the disadvantage of being difficult to adjust.
2. Twisted Pair Twisted Pairs have been used for a long time. Twisted pairs have been used in many industrial control systems and in places with large interference and in long-distance transmission. The LANs we use widely today also use twisted pairs. . The reason why twisted-pair cables are so widely used is that they have many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Twisted pair signal also has a large attenuation, if the video signal is directly transmitted in the twisted pair, it will also decay greatly, so the video signal in the twisted pair to achieve long-distance transmission, must be amplified and compensated, Twisted pair video transmission equipment is to complete this function. With a pair of twisted pair video transceivers, the image can be transmitted to 1 to 2 km. Twisted pair and twisted pair video transmission equipment are very cheap, not only does not increase the system cost, but when the distance increases, its cost is much lower than the coaxial cable. Therefore, the use of twisted pair transmission in monitoring systems has obvious advantages:
1) The transmission distance is long and the transmission quality is high. Thanks to the advanced processing technology used in the twisted pair transceivers, the attenuation of the amplitude of the video signal and the difference in attenuation between different frequencies of the twisted pair are perfectly compensated, and the brightness and color of the original image and the real-time performance are maintained. When the transmission distance reaches 1km or more, the image signal is substantially free of distortion. If relay mode is used, the transmission distance will be further away.
2) Easy wiring and high cable utilization. A pair of ordinary telephone lines can be used to transmit video signals. In addition, one of the five types of unshielded twisted pairs widely installed in a building can transmit one video signal without the need for additional wiring. Even with rerouting, category 5 cables are easier than coaxial cables. In addition, a Category 5 cable has 4 pairs of twisted pair cables. If a pair of cables is used to transmit video signals, the other pairs of cables can also be used to transmit audio signals, control signals, power supply, or other signals to improve the cable. The utilization rate, at the same time avoids the trouble caused by the separate wiring of various signals, and reduces the project cost.
3) Strong anti-interference ability. Twisted pair can effectively suppress common-mode interference. Even in strong interference environments, twisted-pair cables can transmit excellent image signals. In addition, several pairs of twisted pairs in a cable are used to transmit different signals and no interference occurs between them.
4) High reliability and easy to use. Utilize twisted pair to transmit the video signal, need to insert the special transmitter in the front end, want to insert the special receiver in the control center. This type of twisted-pair transmission equipment is cheap and easy to use, requires no specialized knowledge, and does not require much operation. It can be installed once and work stably for a long time.
5) The price is cheap, easy to draw. Due to the use of common 5 types of unshielded cables or ordinary telephone lines which are widely used at present, the purchase is easy and the price is also very cheap, which brings great convenience to engineering applications.
3. The application of fiber optics and optical transceivers in the field of surveillance is mainly to solve two problems: First, transmission distance, and first, environmental interference. Twisted pair and coaxial cable can only solve the problem of transmission of surveillance images in short distances and small areas. If it is necessary to transmit image signals of distances of several kilometers or even hundreds of kilometers, it needs to use optical fiber transmission methods. In addition, for some super-disturbing sites, in order to be free from environmental interference, optical fiber transmission must also be used. Because the optical fiber has many advantages such as wide transmission bandwidth, large capacity, immunity to electromagnetic interference, and small influence from the external environment, an optical fiber can transmit all the signals required in the monitoring system, and the transmission distance can reach hundreds of kilometers. The optical transceiver provides a flexible transmission and networking method for the monitoring system, with good signal quality and high stability.
However, the use of optical fiber and optical transceivers requires a certain amount of expertise and special equipment, which brings certain difficulties for construction and user use. In addition, for short-range, small-scale monitoring systems, the use of optical fiber transmission is also not economical.
Second, technical performance analysis 1, coaxial cable In the monitoring system, using 75Ω, -5 coaxial cable is more common.
In general, the distributed capacitance of this kind of coaxial cable is about 50-60pF/m, plus the DC resistance of the cable, which will cause the transmitted signal to be attenuated. Tests have shown that a signal with a frequency of 5 MHz will be attenuated by about 5 dB when transmitted over a coaxial cable of 75 Ω and -5, and the higher the signal frequency, the greater the attenuation. The image signal is a high-frequency broadband signal. The color part of the image is located at the high end of the frequency. When the coaxial cable is used to transmit the color image signal, the brightness and color will be attenuated, especially as the transmission distance increases the color of the image. Will become lighter or even distorted. Tests conducted in the laboratory revealed that the amplitude and color of the color image signal have been significantly attenuated when transmitting a color image signal of about 200 m in a coaxial cable of 75Ω or -5. If you want to transmit more distance, only join the coaxial video amplifier.
2. When using twisted pair as a transmission medium for twisted-pair cables, commonly used Category 5 UTP cables are generally used. Its characteristic impedance is about 100Ω, and the distributed capacitance is about 15pF/m. Different from the coaxial cable, the signal is transmitted in a balanced manner in the twisted pair. With the use of twisted pair video transmission equipment and twisted pair, it can be guaranteed. High-quality video signals can be transmitted within a distance of 1.5Km. In the laboratory, a dedicated instrument was used to test the performance of the image signal transmitted by the twisted pair. The results are as follows:
Test Instruments: Tektronix TSG-271PAL signal generator, Tektronix VN700A video signal analyzer Tested equipment: Wuhan MicroPort Optoelectronics Technology Co., Ltd. (027-87462996) WTC S-03C10 twisted pair video transmission equipment, Category 5 UTP cable (1) transmission When the distance is 300m, the index: DG ≤ 1%; DP ≤ 1°; SNR ≥ 65dB
(2) When the transmission distance is 1200m: Index: DG ≤ 2%; DP ≤ 2°; SNR ≥ 60dB
3, fiber optic fiber is an inevitable choice for remote monitoring of image transmission, it can provide a transmission distance of hundreds of kilometers, and can provide a good image transmission quality. The use of special instruments in the laboratory tested the performance of the Wuhan Slight Optoelectronic Technology Co., Ltd. WTOS-02S4000 uncompressed digital video transmission equipment, as follows:
DG ≤ 1%; DP ≤ 1°; SNR ≥ 70dB
Third, economic analysis Optical fiber transmission is the highest cost of the three transmission methods, and now the price of single-mode fiber is generally about 2 yuan per fiber per meter, the price of optical transceiver is about 2,000 yuan per image, plus The auxiliary materials in the project such as optical fiber jumpers, optical flanges, and optical fiber fusion splicing expenses, etc., make the cost of the optical fiber monitoring network relatively high. However, optical fiber transmission has many outstanding advantages. Therefore, in monitoring networks with transmission distances of two to three kilometers or more, some places with strong environmental interference, and monitoring sites that require high quality and reliability, most of them use optical fiber as the transmission medium. .
Coaxial cables are widely used within a distance of one or two hundred meters. In this range, the use of coaxial cables does not require other equipment. It is easy to use and the transmission quality can basically meet the requirements. However, when the transmission distance increases, the coaxial cable is inferior to the twisted pair in cost performance. In general, 75Ω, -5 coaxial cable market price is 1.5 yuan / m, coaxial amplifier price is 300 yuan / Taiwan; Category 5 UTP cable price is 0.8 yuan / m, the price of twisted pair video transmission equipment is 600 yuan / In the following, the transmission costs of coaxial cable and twisted pair are compared in terms of distances of 300m and 600m.
(1) It is assumed that there are 8 monitoring points in a monitoring network, and each monitoring point is about 300m from the control center.
When using coaxial cable:
1.5 yuan/m×300m×8=3600 yuan When using twisted pair:
Since each four-way image can share a Category 5 UTP cable, only two Category 5 UTP cables are required in the network. 0.8 yuan/m×300m×2+600 yuan/set×8=5280 yuan (2) It is assumed that there are 8 monitoring points in a monitoring network, each monitoring point is about 600m away from the control center when the coaxial cable is used:
To ensure image quality, an amplifier is added to each image. 1.5 yuan / m × 600m × 8 + 300 yuan / Taiwan × 8 = 9600 yuan When using twisted pair:
Since each four-way image can share a Category 5 UTP cable, only two Category 5 UTP cables are required in the network. 0.8 yuan/m×600m×2+600 yuan/set×8=5760 yuan It can be seen from the above analysis that as the transmission distance increases, the advantages of twisted pair transmission in terms of cost are increasingly displayed. If there are other signal transmissions such as control signals in the network, the cost advantage of twisted pair transmission will be more obvious. In addition, when the transmission distance is further increased, for example, up to about 1 km, the coaxial cable transmission has been difficult to meet the transmission quality requirements, and the twisted pair can still ensure good image quality when the transmission is about 1.5 kilometers.
IV. Project Recommendations In actual projects, the choice of transmission method needs to be considered in conjunction with the specific conditions of the project and the project budget.
For monitoring networks with transmission distances exceeding 2 Km, optical and optical transceivers should be considered. If the transmission distance reaches several kilometers or dozens of kilometers, only the optical fiber is used. In addition, in places where there is strong interference, such as where industrial interference and electromagnetic interference occur, optical fiber transmission is also recommended to ensure image quality.
The selection of coaxial cables and twisted pairs requires more analysis and comparison. As twisted pair transmission is a new emerging technology, and the use of coaxial cable has a long history, it is necessary to fully explore the characteristics and advantages of twisted pair transmission, providing convenience for engineering design and construction, and saving cost. . When the transmission distance is from four to five hundred meters to about 1.5 kilometers, the twisted pair can undoubtedly exert excellent performance and price advantages. For a monitoring network within two or three hundred meters, if the scale is small, it is reasonable to use the coaxial cable. The cost of construction is also lower. However, the actual project will also have its specificity. Even if the distance is very close, if the network is very large, for example, there are hundreds of monitoring points, then it will be difficult to use coaxial cable, and twisted pair can make This problem has been solved. Furthermore, if there is a large amount of interference in the environment, using twisted-pair cables can effectively prevent interference and ensure image transmission quality. In addition, the convenience and flexibility of twisted-pair cabling make some short-distance, intensive monitoring networks such as building buildings gradually begin to use it instead of coaxial cable, and it is well integrated into the integrated cabling project.
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