Coax was originally invented in 1929. Its most common use today is in cable television and Ethernet applications. Coax cable is called coaxial because it includes one physical channel surrounded by another concentric physical channel. Both of these channels run along the same axis allowing information to be transmitted.
Coax cable has one inner conductor which is typically copper or a copper covered iron or steel. The insulator, or dielectric as it is called, can have an effect on the electrical characteristics of the cable. There are various types if dielectrics such as solid and foamed polyethylene or Teflon.Over the dielectric you will have a shield of some type. The most common types of shields are either a braid or a foil or some type of combination of both. The shield can affect the flexibility of the coax as well as determine how protective it is from interference from electromagnetic fields.
The coax will then have a jacket of some type placed over the core and insulator. A common jacket is PVC but you will find many jacket variations as well. Each part of the coax is decided by the individuals application so will find many different styles available for many different usages.
Here are some common styles of coax, the approximate impedance of each measured in ohms and common applications of each. The two most common impedances are 50 and 75 ohms.
RG 6 – 75 ohms – Used frequently in cable TV, satellite TV, and cable modemsRG 8 – 50 ohms – Thicknet (10 Base 5) and amateur radio
RG 11 – 75 ohms – Underground applications and longer runs or drops
RG 58 – 50 ohms – Thin Ethernet (10 Base 2) and radio communication
RG 62 – 92 ohms – Computer networking and automotive radio antennas
RG 213 – 50 ohms – Radio communication and amateur radio
These are only a few styles of the types of coax cables available today. Almost all of these will come in multiple styles including direct burial (flooded), plenum and messengered for overhead applications. It is worth mentioning that coax has been replaced in many data transmission applications by either a twisted paired cable or fiber optics. These can provide a more reliable, faster and cost effective wiring option in lieu if coaxial cable in many situations. However, coax is still very popular in the growing consumer market of cable modems and broadband internet access.
When determining the coax you require, the most important factor is your application. After you have that information, you can decide on the dielectric, shielding and jacket construction for your coax that suits your needs the best.
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