Coaxial Cables

Coaxial cables are used for the simultaneous transmission of many telephone messages, for transmitting television programs, for connecting radio transmitters to the sending antennas, and for connecting radio-receiving antennas to the receiving sets. Since the beginning of communication, coaxial cables have been used for transoceanic telegraph circuits.

The construction details of a coaxial cable depend on the purpose to which it will be put. The common features are the copper conductor held at the center of the outer copper sheath by insulators of hard rubber, ceramic, plastic, or other suitable material. The sheath acts as one side of the transmitting circuit and also as an effective shield. Because of skin effect, the high-frequency signal current being transmitted travels along the inside of the sheath and the unwanted currents induced by extraneous sources travel along the outside of the sheath, which is usually at ground potential.

Figure 23. A coaxial cable consists of a conductor (often solid as shown) at the center of a conducting sheath. The dimensions a and b are usually as indicated.