Construction

• Coaxial cables carry a signal over a single copper wire. A layer of plastic covers the copper, insulating the signal wire from the shielding. The shield itself is made of a braided metal mesh that enshrouds the length of the cable. The braid offers a path for interference to reach ground without having to enter the signal-carrying wire or exit into adjacent cables. Finally, an outer thick plastic insulates the entire cable from external contact and protects it from physical damage.
  
  

Electromagnetic Interference

• Shielding on a coaxial cable serves to protect the inner copper wire from external interference. Though the majority of any electric current in cabling systems travels through the wire, some current may leak out as an electromagnetic field. Because of this, having one cord carrying a large amount of electricity, such as an AC power cable, adjacent to an unshielded signal cable will cause distortion in the second cable's signal. The mesh shield on a coaxial cable reduces the amount of interference from such external sources.
  
  

Signal Loss

• In addition to external interference, the coaxial cable itself would naturally leak its own signal as an electromagnetic field without shielding. Over long cable systems, enough could leak out to degrade the quality of the final signal. This leakage could also negatively effect other nearby cables. The shielding on the coaxial cable helps keep the signal within the inner copper wire from leaking as much.
  
  

Combination Shielding

• While standard coaxial cables found within the home use mesh shielding, due to low price and ease of use, mesh alone does not prevent 100 percent of interference. For extremely sensitive systems or those in areas of high electromagnetic interference, a technician may use a coaxial cable shielded with both a mesh and a foil lining. The foil offers complete protection from electromagnetic interference, while the mesh blocks out radio frequency interference that would pass through foil alone.