Idea of Coaxial Cables

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Definition:

Coaxial cable, or coax, is a type of copper cable that features a central conductor surrounded by braided or foil shielding. An insulator separates the conductor and shield, and the entire package is wrapped in an insulating layer called a jacket. The data signal is transmitted over the central conductor. The outer shielding serves to reduce electromagnetic interference.

Tips: Coaxial cable is so named because the conductor and shield share the central COmmon AXis or are “co-axial.” This arrangement helps prevent electromagnetic interference from reaching the conductor.

Example:

Coaxial_cables

Figure: Coaxial cable.

Coaxial Cable and Connector Types

Coaxial cable comes in various thicknesses that use different connector types.

Example:

Coaxial_connector_type

Figure: Typical Thinnet connectors.

The different types of coaxial cable are described in the following table.

Coaxial Cable Type and Description

5 mm/0.25 inch (“Thinnet”) 

RG-58/U and RG-58A/U, also known as “Thinnet,” are older types of media used for networking. RG-59 is used for cable television transmission. Thinnet connections are made with a twist-lock connector called a BNC connector. Devices connect to the network with T-connectors. Each end of the cable must be terminated with a 50-ohm resistor. Another coax connector type is the F-type connector, which is used to con- nect cable TV and FM antenna cables. Today, F-connectors are also used to connect cable modems to the CATV network.

6.91 mm/ 0.35 inch

RG-6/U has been replacing RG-59 in recent years as the preferred cable for CATV networks. Like RG-59, F-connectors are used to connect cable modems to the CATV network.

10 mm/0.5 inch (“Thicknet”)  

RG8 is a thicker type of coaxial cable often referred to as “Thicknet.” It is not often used today due to its expense and stiffness, but was popular at one time as a “backbone” cable in coaxial network installations. Connections between Thicknet segments are made with a screw-type connector called an N-connector. Thicknet segments must be terminated with a 50-ohm resistor.

Termination

Coax network segments typically must be terminated to prevent signal reflections off the end of the cable. Cables are terminated by installing a resistor of an appropriate rating, typically 50 ohms, on the end of the cable.

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