Type of communcation cable.
communication Cables are used in many different environments, so that the appearance of the cable looks very different. But regardless of the type of cable, they are used as a signal transmission conductor. These different types of cable, transmission of different signals in the quality of performance is different, in addition to some special applications, is currently used in audio and video transmission cable roughly a single wire, twisted pair, coaxial and fiber-based.
1.1. Single wire.
Single wire is the most basic type of cable (such as wire), which consists of one or a group of plastic protective layer surrounded by wires, this cable is generally used to transmit low-frequency signals, such as power, audio, computer ID code.
Twisted pair is a common name, the number of wires and the type of stranding is not limited, but the cable structure is only two types: shielded twisted pair (STP: ShieldedTwistedPair) and non-shielded network Twisted Pair (UTP: UunshieldedTwistedPair).
Twisted pair generally in the telecommunications, Internet, professional audio in the universal application of this cable from two or more independent of each other insulated cable continuous twist composed of twisted two of these cables is called the group , Transmission impedance is generally 100_, a single wire diameter specifications in the 20AWG (US cable standard: 0.91mm) to 24AWG (0.61mm) between. Twisted pair is a relatively cheap cable, each set of wires with the same anti-interference ability, can effectively suppress the outside electromagnetic interference (EMI), but also effectively shield the transmission signal to the outside world of electromagnetic interference.
UTP cables are most commonly used in telecommunications transmission and computer network environments. They are divided into five categories according to the type of stranding. Cat- egories for CAT5 and CAT6 can typically achieve transmission rates of 100Mbps (100 million bits per second). STP cable in the outer wire group to add a layer of woven metal mesh or tin foil, but also help to improve the signal to suppress the impact of external radio waves. The metal housing of each connector of the STP cable must remain in good contact with the screen.
1.3. Coaxial cables.
Coaxial cable (Coaxial) is a composite composed of two conductors, as shown in the following figure: The center wire of the coaxial cable is used to transmit the signal, the metal shield net plays two roles: First, the public ground of the signal is Signal to provide current loop, and second, as a signal shielding network to suppress electromagnetic noise on the signal interference. The center conductor and the screen mesh are interposed between the semi-foamed polypropylene insulation layers, which determine the transmission characteristics of the cable and are effective in protecting the intermediate conductors.
Coaxial cable is widely used in audio and video or radio frequency transmission, transmission impedance is generally 75_, has become the standard video impedance (early also use 50_ impedance characteristics of video transmission). High-quality standard coaxial cable is generally more expensive than twisted pair, because the coaxial cable reliable physical properties, can provide excellent audio and video performance. The signal frequency, resolution and cable effective transmission distance in the audio and video systems play a decisive role.
1.4. Optical fiber cable.
OpticCable (OpticCable) signal the best choice for long-distance transmission, optical transmission is based on photoelectric conversion to replace the electronic transmission of technical means. The simple principle of optical fiber transmission is: analog electrical signal to the optical transmitter, the signal buffer circuit and drive circuit, the input voltage signal into a current signal, drive LED or laser. In this way, the incoming electrical signal is converted into an optical signal, which is coupled into the optical fiber by precise optical alignment and guidance.
After the optical signal is transmitted through the optical fiber, the optical signal is converted into the original electron source by a wavelength matched photodiode at the receiving end, then amplified by the low noise linear amplifier and then output.
Optical fiber signal transmission to avoid the many shortcomings of traditional cable transmission, with many cable transmission can not be compared to the advantages;
Excellent anti-electromagnetic interference: long-distance cable transmission, the cable itself is a huge antenna, will pick up the existing electromagnetic signals around the space, especially in the display system is more prominent, such interference signal in the image display can not Elimination of particle noise, fiber optic cable is the core of glass, and the transmission of optical signals, not susceptible to external electromagnetic interference.
Very small volume: most of the fiber with the human body hair thickness.
Very low attenuation: Because the optical fiber transmission is to rely on the glass tube to complete, there is no signal because the cable resistance, capacitance caused by a significant attenuation, fiber greatly improves the transmission bandwidth capacity and transmission distance. The high security of the optic fiber: The signal content of optic fiber transmission is not easy to be eavesdropped.
Although fiber seems to be the ultimate method of signal transmission, but there are some disadvantages;
Higher prices: fiber optic cables, transmitters, receivers are expensive.
High labor: in the cable routing process, requires a lot of human resources and special tools. Although the optical signal in the optical fiber transmission loss is very low, but in the transmitter and receiver to carry out electro-optical, photoelectric conversion of the signal attenuation is very powerful. So to ensure no insertion loss transmission, it must be added in the transmission of high-gain multi-stage amplifier, but also to ensure stable operation of the circuit.