Selection of coaxial cable, twisted pair and optical fiber

Coaxial cable, twisted pair and optical fiber are all commonly used transmission media in integrated wiring, so what is the difference between them? How should we use them in engineering?

One. Coaxial cable

 Coaxial cable is a cable with a central copper conductor wrapped in layers of insulated wires. It is characterized by good anti-interference ability, stable data transmission, and low price, so it is widely used, such as closed-circuit television lines.
 However, according to the analysis of the characteristics of the coaxial cable itself, the attenuation of the signal when it is transmitted in the coaxial cable is related to the transmission distance and the frequency of the signal itself. Generally speaking, the higher the signal frequency, the greater the attenuation. Therefore, the coaxial cable is only suitable for short-distance transmission of image signals. When the transmission distance reaches about 200 meters, the image quality will be significantly reduced, especially the color becomes dim and there is a sense of distortion.
 In actual engineering, in order to extend the transmission distance, a coaxial amplifier is used. The coaxial amplifier has a certain degree of amplification for the video signal, and can also compensate different frequency components in different sizes through equalization adjustment, so that the distortion of the video signal output by the receiving end is as small as possible. However, coaxial amplifiers cannot be cascaded indefinitely. Generally, only 2 to 3 coaxial amplifiers can be cascaded in a point-to-point system. Otherwise, the video transmission quality cannot be guaranteed and adjustment is difficult. Therefore, when using a coaxial cable in a monitoring system, in order to ensure a better image quality, the transmission distance range is generally limited to about four or five hundred meters.

Two, twisted pair

Common twisted-pair cables are category 3, category 5, over category 5, category 6, and category 7.
1. Category 5 cable: This type of cable has increased winding density, a high-quality insulating material in the jacket, and a transmission rate of 100MHz. It is used for voice transmission and data transmission at a transmission rate of 100Mbps, mainly used for 100BASE-T and 10BASE. -T network. This is a commonly used Ethernet cable.
2. Super Class 5 line: Super Class 5 has low attenuation, less crosstalk, higher attenuation to crosstalk ratio and signal-to-noise ratio, smaller delay error, and performance is greatly improved. The transmission rate of Super Category 5 cable is 250Mbps.
3. Category 6 cable: The transmission frequency of this type of cable is 1MHz～250MHz. The comprehensive attenuation crosstalk ratio (PS-ACR) of Category 6 wiring system should have a large margin at 200MHz, which provides 2 times that of Category 5 bandwidth. The transmission performance of Category 6 cabling is much higher than the Category 5 Super Standard, and it is suitable for applications with a transmission rate higher than 1Gbps.
4. Super Category 6 wire: Super Category 6 wire is an improved version of Category 6 wire, which is also an unshielded twisted pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards. Mainly used in gigabit networks. In terms of transmission frequency, it is also 200-250 MHz like Category 6 lines, and the transmission speed can also reach 1,000 Mbps, but it has been greatly improved in terms of crosstalk, attenuation and signal-to-noise ratio.
5. Category 7 line: This line is a twisted pair in the ISO 7/F standard. It is mainly used to adapt to the application and development of 10 Gigabit Ethernet technology. But it is no longer an unshielded twisted pair, but a shielded twisted pair, so its transmission frequency can reach at least 500 MHz, which is more than twice that of Category 6 and Super Category 6 cables. Up to 10 Gbps.
The reason why twisted pair is so widely used is that it has many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Since the twisted pair also has a large attenuation of the signal, the frequency of the signal cannot be too high when the transmission distance is long, while the high-speed signal such as Ethernet can only be limited to within 100m.

Three, optical fiber

Optical fiber transmits signals in the form of light pulses, so the material is mainly glass or plexiglass. It consists of a fiber core, a cladding and a protective cover.
The structure of the optical fiber is very similar to that of a coaxial cable, and the center is an optical fiber made of glass or transparent plastic, surrounded by a protective material, and multiple optical fibers can be combined in one optical cable as required.
According to different optical signal generation methods, optical fibers can be divided into single-mode fibers and multi-mode fibers (the so-called "mode" refers to a beam of light entering the fiber at a certain angle). Multimode fiber is generally used for network connections in the same office building or in a relatively close area. The single-mode optical fiber transmits data with higher quality and longer transmission distance, and is usually used to connect office buildings or geographically dispersed networks. If optical fiber and cable are used as the network transmission medium, it is necessary to add equipment such as optical transceivers, so the cost investment is greater, and it is less used in general applications.
The characteristic of optical fiber is that it conducts optical signals, so it is not interfered by external electromagnetic signals, and the attenuation speed of the signal is very slow. Therefore, the transmission distance of the signal is much longer than the various network cables that transmit electrical signals above, and it is especially suitable for electromagnetic Places with harsh environment.