First, the cause of the interference signal
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected. First, the cause of the interference signal
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected. First, the cause of the interference signal
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected.
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected. First, the cause of the interference signal
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected. First, the cause of the interference signal
According to the source of the interference, it can be divided into three sources:
1. The interference caused by the front-end equipment: the interference of the power supply of the front-end camera, the interference caused by the quality problem of the camera itself, the judgment method is directly connected to the monitor at the front end. If the interference caused by the power supply can be replaced by the power supply and the switching power supply In the 220V AC circuit, an AC filter is added to solve the problem.
2. Terminal equipment interference: mainly the power supply of the monitoring room, the interference generated by the equipment itself, the interference caused by the grounding, the interference caused by the connection of the equipment and the equipment, etc. The simple judgment method is to directly connect the camera to observe in the monitoring room.
3. Interference in the transmission process: mainly caused by interference caused by transmission cable damage, electromagnetic radiation interference and ground interference (ground potential difference). For the transmission cable, it can be solved by replacing the cable or adding anti-interference equipment.
Second, the formation and solution of electromagnetic radiation interference and ground potential difference interference during signal transmission.
1. Causes and methods of elimination of electromagnetic radiation interference
1.1 Transmission line to eliminate the principle of external electromagnetic interference Coaxial cable is shielded to resist electromagnetic interference. The coaxial cable is composed of an outer conductor and an inner conductor, and an insulating material is used as a filler between the inner and outer conductors. The outer conductor is usually a wire woven from copper wire, which has a good shielding effect on external electromagnetic interference. The inner conductor is under the tight protection of the outer conductor, so the coaxial cable has good anti-interference ability.
1.2 Interference and elimination of strong electromagnetic radiation on the line As mentioned above, the transmission line has the ability to withstand external electromagnetic interference and can effectively transmit signals. However, when the interference source is too strong, it will interfere with the image signal. There are two main types of these strong electromagnetic interferences:
First, there is a strong source of electromagnetic radiation nearby.
Second, the line is not properly designed, and the interference caused by the strong electric line to the transmission line.
Strong electromagnetic radiation sources are generated by high-power stations or electrical equipment with electromagnetic radiation. The interference caused by strong electromagnetic radiation on the image is mesh ripple interference. For such interference, the following methods can be used to eliminate interference.
First, avoid interference sources as much as possible. System equipment and circuits must be separated from the radiation source by a certain distance.
Second, choose a cable with good shielding performance. The braiding density of the outer shielding net of the coaxial cable directly affects the anti-interference performance of the cable. The greater the weaving density, the stronger the anti-interference ability.
Third, increase anti-jamming equipment.
The main cause of the interference caused by the wiring is that the transmission cable and the high-voltage line are long-distance and nearly parallel to each other, and electromagnetic coupling is generated. The anti-interference ability of the coaxial cable is lower in the low frequency band, and the strong electrical interference component is mainly 50 Hz alternating current and its harmonics, so the threat to the coaxial cable is large. Therefore, it is necessary to avoid the short-distance parallel wiring of the signal line and the strong electric line. The strong electric line and the signal transmission line should be laid in the dividing line slot, and the distance between the line slots should be kept; of course, the short distance between the transmission cable and the strong electric line will not cause large interference. In both ends of the system and in the equipment cabinet, it is inevitable that short-distance parallel wiring of the strong electric line and the signal line will occur, which will not cause large interference.
2. Causes of ground potential difference interference and methods of elimination Ground potential difference interference is a frequent interference of the system. The cause of ground potential difference interference is due to the existence of two or more conflicting grounds in the system. There is a certain voltage difference that forms an interference current through the outer shield of the signal cable, creating interference with the image. The main component of the ground current is the 50 Hz AC and the interference pulse generated by the electrical equipment. The image is characterized by horizontal black stripes, distortion, and cumbersome horizontal clutter, and it is possible to move slowly in the vertical direction.
The solution is:
First, isolate the front-end equipment from the ground, but avoid the risk of possible lightning strikes or electric shocks.
Second, use anti-jamming equipment with isolation function, such as anti-jamming device, video isolator, etc.
Third, the principle of common anti-jamming devices and the solution of interference problems
1. The principle of video amplification directly amplifies the video signal output by the camera, and then compresses it at the terminal. At the same time of compressing the video signal, the interference signal is also compressed to make the video signal reach an acceptable level. It can be seen from the above principle. The higher the front-end video signal is amplified, the better the anti-interference effect is; the anti-jamming device adopting the principle has a good effect on the electromagnetic field interference in the transmission, but if the interference is relatively heavy, the residual of the interference signal is relatively large, and the user is relatively large. Not necessarily acceptable.
2. Frequency shift principle The frequency of the video signal is 0-6 MHz. When the interference frequency falls within the frequency range, interference will occur in the image. The principle of frequency shift is to directly convert the video signal output by the camera. Move to high frequency, avoid the interference frequency, and then convert to a standard video signal of 0-6 MHz at the receiving end. In fact, the principle is the modulation and demodulation principle of cable TV; the anti-jamming device can effectively resist various Interference, no residue, due to the front-end isolation method can effectively resist the interference of ground potential difference; the anti-interference effect depends on the quality of the equipment (how to restore the signal in the modulation and demodulation), in addition to the interference frequency Whether it falls within the frequency range after modulation.
3. Selection of anti-jamming device 3.1 The interference situation in the system is very complicated, and the interference phenomenon is also varied. Generally speaking, if there is such a network interference, the use of these two anti-jamming devices can solve the problem;
3.2 For the video line is thin, the transmission distance is far caused by the moire interference (it is generally recommended that the 75-3 video cable transmission distance does not exceed 300 meters, the 75-5 video cable transmission distance does not exceed 500 meters), you can choose the amplification principle The jammer can not only resist interference but also improve the image quality; of course, the frequency shift principle can also be used, but it is necessary to consult the manufacturer to see if it can meet your transmission distance requirements.
3.3 Due to the interference caused by the damage of the video cable, it is the best way to replace the cable. If it is not replaced, if the interference is snow or moire, you can choose the anti-jamming device of the amplification principle. If the image distortion occurs in the interference phenomenon, The interference bar scrolls up and down, and the frequency shift principle anti-jamming device can be selected.
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