What Is The Difference Between Coaxial Cable And Ordinary Cable

Coaxial cable refers to a cable with two concentric conductors, and the conductor and the shield share the same axis. The most common coaxial cable consists of a copper wire conductor separated by an insulating material, on the outside of the inner layer of insulating material is another layer of ring conductor and its insulator, and then the entire cable is wrapped 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 shielded wire is made of copper mesh, with a characteristic impedance of 50 (such as RG-8, RG-58, etc.); the shielding layer of cables 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. Thick cable is suitable for relatively large local networks. Its standard distance is long and its reliability is high. Since the cable does not need to be cut during installation, the network access position of the computer can be flexibly adjusted as needed, but the thick cable network must be installed with transceiver cables. Difficulty, so the overall cost is high. On the contrary, the installation of thin cables is relatively simple and the cost is low, but since the cable must be cut off during the installation process, the basic network connector (BNC) must be installed at both ends, and then connected to both ends of the T-type connector, so when there are many connectors, it is easy to produce bad defects. hidden danger, which is one of the most common failures of Ethernet in operation today.

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 a dense machine environment, but when a contact fails, the failure will affect the entire cable in series. on all machines. It is troublesome to diagnose and repair the fault, so it will be gradually replaced by unshielded twisted pair or fiber optic cable.

How coaxial cable works:

Coaxial cable is divided into four layers from the inside to the outside: the central copper wire (single-strand solid wire or stranded wire), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh-like 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 that the direction of the current is reversed several times per second.

If a normal wire is used to transmit high-frequency currents, the wire acts as an antenna that emits radio outwards, an effect that dissipates the power of the signal and reduces the strength of the received signal.

Coaxial cables are designed to solve this problem. The radio emitted by the center wire is isolated by the mesh conductive layer, which can control the emitted radio by grounding.

There is also a problem with coaxial cables, that is, if a certain section of the cable is squeezed or twisted, the distance between the center wire and the mesh conductive layer is not consistent, which will cause the internal radio waves to be blocked. reflected back to the source of the signal. This effect reduces the acceptable signal power. To overcome this problem, a plastic insulator is added between the center wire and the mesh conductive layer to ensure a consistent distance between them. This also causes the cable to be relatively stiff and not easy to bend.

Advantages and disadvantages of coaxial cable:

The advantage of coaxial cable is that it can support high-bandwidth communication on relatively long lines without repeaters, but its disadvantages are also obvious: First, it is bulky, and the diameter of the thin cable is 3/8 inch thick, which takes up the cable. A lot of space for the pipe; second, it cannot withstand tangles, pressure and severe bending, which will damage the cable structure and prevent the transmission of signals; finally, the high cost, and all these shortcomings are what twisted pair can overcome, so in the present In the local area network environment, it has basically been replaced by the Ethernet physical layer specification based on twisted pair.

Parameters of coaxial cable:

Main electrical parameters

(1) Characteristic impedance of coaxial cable The average characteristic impedance of coaxial cable is 50±2Ω, the periodic change of impedance along a 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 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 minimum propagation speed required for the propagation speed of the coaxial cable is 0.77C (C is the speed of light).

(4) Coaxial cable DC loop resistance The sum of the resistance of the central conductor of the cable and the resistance of the shielding layer does not exceed 10 milliohms/meter (measured at 20°C).

Physical parameters:

A coaxial cable is composed of a central conductor, a layer of insulating material, a shielding layer composed of a mesh fabric, and an outer layer of insulating material.

Coaxial cable is flexible enough to support a bend radius of 254mm (10 inches). The center 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. External insulation materials are generally made of polyvinyl chloride (such as PVC) or similar materials.

The main parameters of the test:

(1) Open circuit condition of conductor or shield.

(2) Short circuit between conductor and shield.

(3) Grounding of conductors.

(4) Short-circuit conditions between shielded connectors.

Second, the introduction of ordinary cables

Electric cable (electriccable; powercable): usually consists of several or groups of wires.

Definition 1: A wire that transmits electricity or information from one place to another, made of one or more mutually insulated conductors and an outer insulating protective layer.

Definition 2: It is usually a rope-like cable formed by twisting several or several groups of conductors (at least two in each group), each group of conductors is insulated from each other, and often twisted around a center, the entire outer wrap Has a highly insulating cover. The cable has the characteristics of inner energization and outer 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 and so on. They are all composed of single or multi-strand wires and insulating layers, which are used to connect circuits, appliances, etc.

According to the system of photovoltaic power station, cables can be divided into DC cables and AC cables, which are classified as follows according to different uses and use 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 there are many outdoor installations. They need to be moisture-proof, sun-proof, cold-resistant, heat-resistant, and UV-resistant. In some special environments, they also need to be protected from chemical substances such as acid and alkali.

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) The connecting cable from the power distribution device to the power grid or the user.

This part of the cable is an AC load cable, which is laid in the indoor environment and can be selected according to the general power cable selection requirements.

Application of cable:

1. Power system

The wire and cable products used in the power system mainly include overhead bare wires, busbars (bus bars), power cables (plastic cables, oil-paper power cables (basically replaced by plastic power cables), rubber sheathed cables, overhead insulated cables), branch cables (replacing part of the busbar), magnet wire and electrical equipment wire and cable 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.

3. Instrumentation system

Except for overhead bare wires, almost all other products are used in this part, but mainly power cables, magnet wires, data cables, instrumentation cables, etc.

installation method:

Coaxial cables are generally installed between devices. A connector is provided at each user location to provide an interface for the user. The interface installation method is as follows:

(1) Thin cable, cut the thin cable, install BNC heads on both ends, and then connect to both ends of the T-connector.

(2) Thick cable, thick cable is generally installed with a Tap device similar to a splint, which uses the guide pin on the Tap to penetrate the insulation layer of the cable and directly connect to the conductor. Both ends of the cable are provided with terminators to weaken the reflection of the signal.

Third, the difference between coaxial cable and ordinary cable

Coaxial cable refers to a cable with two concentric conductors, and the conductor and the shield share the same axis. Often used for device-to-device connections, or in bus-type network topologies. The central axis of the coaxial cable is a copper wire, plus a layer of insulating material. The outermost layer of the insulating material 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 low price, and it can be used without connecting to a hub or switch. Ordinary cables are usually rope-like cables that are stranded by several or several groups of conductors (at least two in each group). Each group of conductors is insulated from each other and often twisted around a center. Highly insulating cover. Many are erected in the air or installed underground or underwater for telecommunication or power transmission.

Coaxial cables (CoaxtalCabLe) are often used for connection between devices, or in bus-type network topologies. The central axis of the coaxial cable is a copper wire, plus a layer of insulating material. The outermost layer of the insulating material 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 low price, and it can be used without connecting to a hub or switch.

Ordinary cables are usually rope-like cables composed of several or several groups of conductors that are twisted at least two in each group. Each group of conductors is insulated from each other and often twisted around a center. the covering layer. Many are erected in the air or installed underground or underwater for telecommunication or power transmission.