How Does a Coaxial Cable Work?

Coaxial cable, or coax, is used as a transmission line for radio frequency signals. Coax is made with an inner conductor, usually copper, which is surrounded by a flexible, tubular insulating layer, which is then covered by a tubular conducting shield. The cable is then covered in a protective jacket made of plastic. The name coaxial come from the inner conductor and the outer shield sharing the same geometric axis.

Advantages of using coaxial cable

Coax has distinct advantages over other kinds of transmission lines when used to carry radio signals. In coaxial cable, the electromagnetic field exists only between the inner core and the outer conductors, thus allowing coax to run alongside gutters or other metal objects with no signal loss. Also, the cable protects the signal from external electromagnetic interference. Coaxial cable differs from other shield transmission lines for carrying low frequency signals, such as audio signals, because the dimensions of the cable are precisely controlled to give the constant conductor spacing needed to efficiently conduct radio frequencies.

Coaxial cable construction

The key to how coax works is found in its construction. The inner core is responsible for the frequency transmission. It is frequently made from copper. Silver plated copper is used to improve performance in high-frequency signal transmission. The inner core is either solid wire or braided wire for more flexibility. The insulator that surrounds the inner core is often made of polyethylene. Some coax uses Teflon or even air or other gas as the insulator. If a gas is used, the inner core is supported throughout the length of the cable to prevent it from touching the shield. The critical element of coaxial cable design is the outer shield which prevents signal loss and electromagnetic interference. There are several ways the shield is designed. Braided copper is a common shield design, but when the cable is bent, the braid may gap allowing for signal loss. To prevent this, the shield is sometimes made from multiple layers of braid, or more commonly, it is made from a layer of foil covered with a layer of braid. Coax also comes with solid shields which sacrifice flexibility for better performance. Solid shield cable cannot bend around sharp corners or the shield breaks and allows signal loss or interference.

Coaxial cable's unique design of insulated inner core surrounded by a shield makes it invaluable for radio frequency transmission. It comes in different sizes and construction elements based on the needs of the particular radio frequency transmitted. Every coax cable is designed to reduce signal loss and prevent electromagnetic interference from outside sources.