coaxial-cables

Coaxial Cables are made of two concentric wires having some dielectric material between them, and are cylindrically shaped. The dielectric is either solid type, or foam type containing as much as possible the content of air to reduce current losses by increasing the cross-sectional area of inner conductor. Sometimes the inner conductor is made silver-coated to smooth its surface which results in minimum occurrence of skin effect. In many coaxial cables, there is an outer insulating sheath which, protects the cables from erosion, makes them water-proof, ensures safe operation, and maintains their durability. The sheath is not specifically of just one form; it is available in different forms like solid plastic, foam plastic, and air with spacers covering the inner wire. Descriptive figure of a coaxial cable is shown in figure 1.

 

The power losses in the foam type coaxial cables are 15% lesser, but some of its types are prone to moisture absorption, thus significantly decreasing its efficiency. This problem can be overcome by using a spiral strand of Polythene wrapped around the inner conductor so that cavity exists between the conductors and the inside of the sheath. However, their use is limited due to its cost as they are very expensive.

coaxial-cables-02Fig.1. Parts of Coaxial Cable

Since coaxial cables are supposed to carry less/more electric power, they must be made connectable to some device, port, or another cable etc. To do this, the ends of coaxial cables are joined with some connecting devices known as Coax Connectors. Impedance of Coax connector is the same as that of the attached cable. To increase their conductivity, the connectors are plated with silver or tarnish-resistant gold. However, silver soon tarnishes producing silver sulfide which has poor conductivity, thus degrading the connector performance. A 3D view of a typical Coaxial Connector is show in figure 2.

coaxial-cables-03Fig.2. 3D View of typical Coaxial Connector

There are plenty of different connectors available in market like F-Series, N-Series, The BNC, etc. Below is their brief construction.

F-Series

F-series are the coax connectors used in conjunction with video equipment. They have ferrule that enwraps around the outer sheath of coaxial cable and remain fixed in its position. The inner conductor of the cable is little bit extruded from the connector. The extruded part is supposed to play major part during plugging.  A threaded collar on the plug screws down on the jack thus forms a solid connection. The F-connectors are mainly used in RG-58, RG-59, and RG-6 coaxial cables which are supposed to provide security camera, CATV, and many more services. It’s typical layout is shown in figure 3.

coaxial-cables-04Fig.3. F-Series Coax Connector

N-Series

The N-Series is similar to F-series except that it has an extra pin. The pin is fixable on the inner conductor. It is supposed to be inserted in the jack. It is to be noted that if the inner conductor is stranded, it must be fixed into this pin to avoid damage. Like F-series, they are also collar-screwed which enables reliable connection with the jack. The N-type connectors are frequently used in data, video applications which employ RG-8, RJ-11U coaxial cables. General layout of N-series connectors is shown in figure 4.

coaxial-cables-05

Fig.4. N-Series Coax Connector

Some more types of Coaxial Connectors along with their general layout are in figure 5.

                   coaxial-cables-06            

coaxial-cables-07

 

Fig.5. the BNC Connector.    Twisted-pair Connector

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