Telephone cable

Dielectric Constant

A dielectric core provides an insulation for the center conductor as well as maintains physical support and a constant spacing between the inner conductor and the outer shield. When the insulation affects the signal being carried on the wire, it is called a "dielectric." Plastics, as well as other materials, can be compared with a number that describes dielectric quality, called a "dielectric constant."

Vacuum is the standard by which all other materials are compared, and therefore, has a dielectric constant of one. Since air has a dielectric constant so close to one, air is viewed as the ideal dielectric, in terms of efficiency. Stearns explains, "if you introduce air into a solid compound, you are actually creating foam cells, which is trapping air in the dielectric." However, air does not offer any structural support, so cable companies use hydrocarbon-based materials such as propylenes. Foamed fluorinated ethylene propylene (FEP), otherwise known as Teflon, is close behind air with a dielectric constant of 2.1. "A lower dielectric constant translates to a better transmission at higher frequencies," says Stearns.The dielectric material and its composition are critical as it sets up the electrical properties.

dual-shield coaxial

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