The coaxial cable uses hard copper wire as the core and a layer of insulating material. This layer of insulating material is surrounded by a densely woven mesh conductor, and the net is covered with a layer of protective material. There are two widely used coaxial cables. One is a 50-ohm cable, which is used for digital transmission, and is also called baseband coaxial cable because it is mostly used for baseband transmission; the other is a 75-ohm cable, which is used for analog transmission, which is the broadband coaxial cable to be discussed in the next section. This difference is caused by historical reasons, not technical reasons or manufacturers.