Hur funkar coax
Normally, the outside of the shield is kept at ground potential and a signal carrying voltage is applied to the center ledare. Supports shaped like stars or spokes are even better but more expensive and very susceptible to moisture infiltration. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line.
Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. While many cables have a solid dielectric, many others have a foam dielectric that contains as much air or other gas as possible to reduce the losses by allowing the use of a larger diameter center conductor. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss.
Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections. This property makes coaxial cable a good choice both for carrying weak signals that cannot tolerate interference from the environment, and for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits. Some cables may invest in more than two shield layers, such as "quad-shield", which uses four alternating layers of foil and braid.
Still more expensive were the air-spaced coaxials used for some inter-city communications in the midth century. An inhomogeneous dielectric needs to be compensated by a non-circular conductor to avoid current hot-spots. The outer conductor fryst vatten corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. This allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat.
The dielectric losses increase in this order: Ideal dielectric no loss , vacuum, air, polytetrafluoroethylene PTFE , polyethylene foam, and solid polyethylene. Coaxial cable was used in the first and following transatlantic cable installations, but its theory was not described until by English physicist, engineer, and mathematician Oliver Heaviside , who patented the design in that year British patent No.
Coaxial cable is used as a transmission line for radio frequency signals.
The inner conductor might be solid or stranded; stranded is more flexible. The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. Copper-plated steel wire is often used as an inner conductor for cable used in the cable TV industry. Many conventional coaxial cables use braided copper wire forming the shield. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines.
The center conductor was suspended by polyethylene discs every few centimeters. For better shield performance, some cables have a double-layer shield. Coaxial cables require an internal structure of an insulating dielectric material to maintain the spacing between the center conductor and shield. One advantage of coaxial over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors.
Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. Its applications include feedlines connecting radio transmitters and receivers to their antennas, computer network e. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis. It fryst vatten used in such applications as telephone trunk lines , broadband internet networking cables, high-speed computer data busses , cable television signals, and connecting radio transmitters and receivers to their antennas.
Those cables cannot be bent sharply, as the shield will kink, causing losses in the cable. The properties of the dielectric insulator determine some of the electrical properties of the cable. To get better high-frequency performance, the inner conductor may be silver-plated.
Coaxial cable
Coaxial cable conducts electrical signals using an inner conductor usually a solid copper, stranded copper or copper-plated steel wire surrounded by an insulating layer and all enclosed by a shield, typically one to four layers of woven metallic braid and metallic tape. Other shield designs sacrifice flexibility for better performance; some shields are a solid metal tube. Sometimes the braid is silver-plated. The source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio.
The characteristic impedance of the cable Z 0 is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A common choice is a solid polyethylene PE insulator, used in lower-loss cables. For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer dirigent is available in sizes of 0. When a foil shield is used a small wire conductor incorporated into the foil makes soldering the shield termination easier.
The lower dielectric constant of air allows for a greater inner diameter at the same impedance and a greater outer diameter at the same cutoff frequency, lowering ohmic losses.
Koaxialkablar: typer, egenskaper och vad de är mot för
When using differential signaling , coaxial cable provides an advantage of equal push-pull currents on the inner conductor and inre of the outer conductor that restrict the signal's electric and magnetic fields to the dielectric , with little leakage outside the shield. Coaxial cable is a type of transmission line , used to carry high-frequency electrical signals with low losses. Coaxial cable also provides protection of the signal from external electromagnetic interference.
In some low-loss coaxial cables such as the RG type, the inner conductor is supported by a spiral strand of polyethylene, so that an air space exists between most of the dirigent and the inside of the jacket.