What are coaxial cables and ordinary cables? What is the difference between coaxial cable and ordinary cable?
1. Introduction of coaxial cable
Coaxial cable refers to a cable with two concentric conductors, and the conductor and shield share the same axis. The most common coaxial cable consists of copper conductors separated by insulating material, on the outside of the inner insulating material is another layer of ring conductor and its insulator, and then the whole cable is covered by a sheath of PVC or Teflon material .
Classification of coaxial cables:
Coaxial cables can be divided into two basic types, baseband coaxial cables and broadband coaxial cables. At present, the baseband is a commonly used cable, and its shielding wire is a mesh made of copper, with a characteristic impedance of 50 (such as RG-8, RG-58, etc.); the shielding layer of a cable commonly used in broadband coaxial cables is usually made of aluminum. Stamped, the characteristic impedance is 75 (such as RG-59, etc.).
Coaxial cables can be divided into thick coaxial cables and thin coaxial cables according to their diameters. The thick cable is suitable for a relatively large local network. It has a long standard distance and high reliability. Since the cable does not need to be cut during installation, the network access position of the computer can be flexibly adjusted according to the needs. However, the thick cable network must be installed with transceiver cables. The difficulty is high, so the overall cost is high. On the contrary, the thin cable installation is relatively simple and the cost is low, but because the cable needs to be cut off during the installation process, the basic network connector (BNC) must be installed on both ends, and then connected to the two ends of the T-shaped connector, so when there are many connectors, it is easy to produce bad results. Hidden danger, this is one of the most common faults that occur in the Ethernet in operation at present.
Whether it is a thick cable or a thin cable, it is a bus topology, that is, multiple machines are connected to one cable. This topology is suitable for an environment with dense machines, but when a fault occurs at one contact, the fault will affect the entire cable in series. on all machines. The diagnosis and repair of faults are troublesome, so they will be gradually replaced by unshielded twisted pair or optical cables.
How coaxial cables work:
The coaxial cable is divided into four layers from the inside to the outside: the central copper wire (single-strand solid wire or multi-strand wire), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh conductive layer form a current loop. It is named because the central copper wire and the mesh conductive layer are in a coaxial relationship.
Coaxial cables conduct alternating current rather than direct current, which means the direction of the current reverses several times per second.
If you use ordinary wires to transmit high-frequency currents, this wire will act as an antenna that transmits radio to the outside. This effect consumes the power of the signal and reduces the strength of the received signal.
Coaxial cables were designed to solve exactly this problem. The radio emitted by the central wire is isolated by the mesh conductive layer, and the mesh conductive layer can control the emitted radio by grounding.
There is also a problem with coaxial cables, that is, if a certain section of the cable undergoes relatively large extrusion or twisting deformation, the distance between the central wire and the mesh conductive layer will not be consistent, which will cause the internal radio waves to be blocked. Reflected back to the source from which the signal was sent. This effect reduces the received signal power. To overcome this problem, a plastic insulator is inserted between the central wire and the mesh conductive layer to ensure a consistent distance between them. This also contributes to the relatively rigid nature of the cable and makes it less prone to bending.
Advantages and disadvantages of coaxial cable:
The advantage of coaxial cable is that it can support high-bandwidth communication on a relatively long line without repeaters, and its disadvantages are also obvious: one is that it is bulky, and the diameter of a thin cable is 3/8 inches thick, and it takes up a lot of space for the cable. There is a lot of space for the pipeline; the second is that it cannot withstand tangles, pressure and severe bending, which will damage the cable structure and prevent the transmission of signals; the last is the high cost, and all these shortcomings are exactly what twisted pairs can overcome, so now In the local area network environment, it has basically been replaced by the Ethernet physical layer specification based on twisted pair.
The parameter index of the coaxial cable:
Main Electrical Parameters
(1) The characteristic impedance of the coaxial cable The average characteristic impedance of the coaxial cable is 50±2Ω, the periodic change of the impedance along the single coaxial cable is a sine wave, the center average value is ±3Ω, and its length is less than 2 meters.
(2) The attenuation of a coaxial cable generally refers to the attenuation value of a 500-meter-long cable segment. When measured with a 10MHz sine wave, its value does not exceed 8.5db (17db/km); and when measured with a 5MHz sine wave, its value does not exceed 6.0db (12db/km).
(3) The propagation speed of the coaxial cable requires a minimum propagation speed of 0.77C (C is the speed of light).
(4) Coaxial cable DC loop resistance The sum of the resistance of the center conductor of the cable and the resistance of the shielding layer does not exceed 10 milliohms/m (measured at 20°C).
physical parameters
A coaxial cable consists of a central conductor, a layer of insulating material, a shield made of mesh fabric, and an outer layer of insulating material.
The coaxial cable is flexible enough to support a bend radius of 254mm (10 inches). The central conductor is a solid copper wire with a diameter of 2.17mm±0.013mm. The insulating material must meet the electrical parameters of the coaxial cable. The shielding layer is composed of metal strips or sheets that meet the transmission impedance and ECM specifications. The inner diameter of the shielding layer is 6.15mm and the outer diameter is 8.28mm. The external isolation material generally uses polyvinyl chloride (such as PVC) or similar materials.
The main parameters of the test
(1) Open circuit condition of conductor or shielding layer.
(2) Short circuit between conductor and shielding layer.
(3) Conductor grounding condition.
(4) Short-circuit conditions between shielded joints.
2. Ordinary cable introduction
Cable (electriccable; powercable): usually consists of several or several groups of wires.
Definition 1: A wire made of one or more mutually insulated conductors and an outer insulating layer to transmit power or information from one place to another.
Definition 2: It is usually a rope-like cable twisted by several or several groups of wires (at least two in each group). Each group of wires is insulated from each other and is often twisted around a center, and the entire outer wrap Has a highly insulating covering. The cable has the characteristics of internal electrification and external insulation.
Cable classification:
Cables include power cables, control cables, compensation cables, shielded cables, high-temperature cables, computer cables, signal cables, coaxial cables, fire-resistant cables, marine cables, mining cables, aluminum alloy cables, etc. They are all composed of single or multi-strand wires and insulation layers, and are used to connect circuits, electrical appliances, etc.
Cables can be divided into DC cables and AC cables according to the system of photovoltaic power plants, and are classified as follows according to different uses and environments:
1. DC cable
(1) Serial cables between components.
(2) Parallel cables between the strings and between the strings and the DC distribution box (combiner box).
(3) The cable between the DC distribution box and the inverter.
The above cables are all DC cables, and they are often laid outdoors. They need to be protected from moisture, sun exposure, cold, heat, and ultraviolet rays. In some special environments, they also need to be resistant to chemical substances such as acids and alkalis.
2. AC cable
(1) The connecting cable from the inverter to the step-up transformer.
(2) The connecting cable from the step-up transformer to the power distribution device.
(3) Connecting cables from the power distribution device to the power grid or users.
This part of the cable is an AC load cable, which is often laid in the indoor environment, and can be selected according to the general power cable selection requirements.
Application of the cable:
1. Power system
The wire and cable products used in the power system mainly include overhead bare wires, busbars (busbars), power cables (plastic cables, oil-paper cables (basically replaced by plastic power cables), rubber-sheathed cables, overhead insulated cables), branch cables (replacing some busbars), electromagnetic wires, and electrical equipment wires and cables for power equipment, etc.
2. Information transmission
The wires and cables used in the information transmission system mainly include local telephone cables, TV cables, electronic cables, radio frequency cables, optical fiber cables, data cables, electromagnetic wires, power communication or other composite cables, etc.
3. Instrument system
Except for overhead bare wires, almost all other products in this part are used, but mainly power cables, magnet wires, data cables, instrumentation cables, etc.
What is the difference between coaxial cable and ordinary cable
Coaxial cable refers to a cable with two concentric conductors, and the conductor and shield share the same axis. It is often used in the connection between devices, or in the bus network topology. The central axis of the coaxial cable is a copper conductor, plus a layer of insulating material. Outside this layer of insulating material, it is wrapped by a hollow cylindrical mesh copper conductor, and the outermost layer is an insulating layer. Compared with twisted pair, coaxial cable has strong anti-interference ability, good shielding performance, stable data transmission, and cheap price, and it can be used without connecting to a hub or switch. Ordinary cables are usually rope-like cables twisted by several or groups of wires (at least two in each group). Each group of wires is insulated from each other and is often twisted around a center. Highly insulating overlay. Most of them are erected in the air or installed underground or underwater for telecommunications or power transmission.
Coaxial cables (CoaxtalCabLe) are often used for connections between devices, or in bus-type network topologies. The central axis of the coaxial cable is a copper conductor, plus a layer of insulating material. Outside this layer of insulating material, it is wrapped by a hollow cylindrical mesh copper conductor, and the outermost layer is an insulating layer. Compared with twisted pair, coaxial cable has strong anti-interference ability, good shielding performance, stable data transmission, and cheap price, and it can be used without connecting to a hub or switch.
Ordinary cables are usually rope-like cables twisted by several or groups of wires, each group of at least two], each group of wires is insulated from each other, and is often twisted around a center, and the entire outer wrap has a height Insulating covering. Most of them are erected in the air or installed underground or underwater for telecommunications or power transmission.
