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The structure and material of cable

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-02-11

The electrical properties of the cable is the most important low attenuation, impedance uniformity, high return loss, the leaky cable and it is the key point is the best coupling loss. The main function of the transmission signal cable is, therefore, should make the cable construction and materials that have good properties of cable transmission in the whole period of use, this point is very important

1, the inner conductor

Copper is the main material of the inner conductor, may be in the form of: annealed copper wire, annealing brass, copper clad aluminum wire. Usually, small cable inner conductor is a copper or copper clad aluminum wire, and cable with copper cable, to reduce the weight and cost. Conductor of cable and embossing, so that you can get enough good bending performance.

The inner conductor has great influence on signal transmission, because the attenuation is mainly caused by the inner conductor resistance loss. The electrical conductivity, especially the surface conductivity, should be as high as possible, the general requirements for 58MS/m (+20 ℃), because in the high frequency current transmission, only in a thin layer of conductor surface, this phenomenon is called the skin effect, the effective thickness of the current layer called the skin depth. Table 1 shows the brass and copper clad aluminum wire as inner conductor in the specific frequencies where the skin depth value.

Copper conductor with quality requirement is very high, requirement of copper should be free of impurities, surface clean, smooth, smooth. The inner conductor diameter should be stable and very small tolerances. Any change in the diameter will reduce the impedance uniformity and return loss, so it should be precise control of the manufacturing process.

2, the outer conductor

The outer conductor has two basic functions: the first is a loop conductor, the second shielding. The outer conductor of the leaky coaxial cable also determines its leakage performance. Coaxial feeder cable and the outer conductor super soft cable is made of corrugated copper tube outer conductor is welded, the cable is completely closed, not allowed to have any radiation cable.

The outer conductor is usually made of copper coated vertically into. In the outer conductor layer, a longitudinal or transverse notches or holes.

The outer conductor groove is common in corrugated type cable. Through along the axial direction of corrugated crest distance cutting slot form. Cut part of the proportion of very small, the wavelength of the electromagnetic wave and the slot spacing is far less than the transmission.

Apparently, the non leaky cable processing can be made according to the following method: leaky coaxial cable outer conductor wave ordinary wrinkles type cable at a 120 degree angle on non leaky cable in common by cutting, get a set of optimum slot structure. The shape, width and slot leakage cable determines its performance index.

The outer conductor of copper should be of good quality, high conductivity, free of impurities. The outer conductor size should be strictly controlled in the tolerance range, to ensure that the characteristic impedance of a uniform and high return loss.

3, an insulating medium

Radio frequency coaxial cable medium not only from the insulation, transmission performance is mainly to determine the final after insulating medium, so the choice of materials and the structure is very important. All the important properties, such as attenuation, impedance and return loss, and insulating great relationship. The most important requirements for insulation:

Low relative dielectric constant, dielectric loss angle factor is small, to ensure that the attenuation
The structure, in order to ensure uniform impedance, return loss
Stable mechanical properties to ensure long service life
Waterproof and moistureproof

Insulation Physical high foaming can achieve all the above requirements. For extrusion and gas injection technology advanced and special material, foaming degree can reach above 80%, close to the electrical properties and air such insulated cable. Gas injection method, nitrogen is injected directly into the dielectric material extrusion machine in the process, also known as physical foaming method. Chemical foaming method and the relative, the foaming degree can reach about 50%, dielectric loss. Foaming structure are consistent and gas injection method, means the uniform impedance, return loss.

Our RF cable for dielectric loss of insulating material angle is small, foaming degree and has very good electrical performance. Foaming medium characteristics are more important at high frequencies, it is this kind of special foaming structure determines the attenuation properties of very low frequency cables.

Unique multilayer insulation (inner layer foaming layer and outer layer coextrusion process) can obtain uniform, sealed foam structure, moistureproof performance, stable mechanical properties, high strength and good. In order to make the cable in a humid environment remains electrical performance very good, we have designed a cable foaming insulation layer: in the outer surface with a thin layer of solid core PE. The outer layer can effectively prevent moisture intrusion, protect the electrical characteristics of cable from the start of production, the design is especially important for the leaky cable outer conductor hole. In addition, the insulating layer by layer tightly the inner conductor, and further improve the mechanical stability of the cable. Moreover, thin layer contains special stabilizer, which can ensure the compatibility and copper, and can ensure long service life of our cable. The inner layer material suitable, can obtain satisfactory performance, such as: moisture-proof, adhesion and stability.

Insulation design of the multilayer (inner layer foaming layer and outer layer) can be obtained at the same time mechanical electrical performance is excellent and stable, so as to improve the long-term service life of our RF cable and *.

4, sheath

Outdoor cable sheath material is the most commonly used black linear low density polyethylene, its density is similar to LDPE, but the strength is equivalent to HDPE. On the contrary, in some cases, we tend to use HDPE, it can be sheathed performance to provide better mechanical properties and wear resistance, chemical, moisture and different environmental conditions.

UV Black HDPE can withstand such as caused by high temperature and strong ultraviolet climate stress. When the fire safety stressed cable, should use the low smoke halogen-free flame retardant materials. In the leaky cable, in order to reduce the spread of fire, fire retardant belt can be used between the outer conductor and the sheath, so easy to melt insulating layer remains on the cable.

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