the cable is designed to carry a high-frequency or broadband signal, as a high-frequency transmission line. Every now and again DC power (called bias) is added to the signal to supply a devices at the more prevent, when inside direct broadcast satellite receivers. Because a electromagnetic field carrying a signal is (ideally) simply in the space between the inner & outer conductors, it just can't interfere by using or even suffer interference from external electromagnetic fields.

Coaxial cables may be rigid or even flexible. Rigid types have a firm sheath, when flexible types have a braided sheath, both commonly of thinly copper wire. A inner insulator, also known as a dielectric, has a important burden on the cable's properties, like its characteristic impedance and its attenuation. A insulator even can be firm or perforated by using airspace. Modems to the stops of coaxial cables come normally manufactured by using RF connectors.

Signal propagation in coaxial cable
Open wire cable stand a property that a electromagnetic wave propagating down a line extends into the space surrounding the parallel wires. These lines keep around moo loss, however as well stand unsuitable characteristics. It can't become bent, twisted or even otherwise shaped while forgoing changing their characteristic resistivity. It besides can't become line or even connected to anything conductive, as a extended fields might cause currents in the nearby conductors inducing unwanted radiation & detuning of the line.

Coaxal lines solve this condition by confining a electromagnetic wave to a locality in a cable, between a center conductor & the shield. A transmission of energy in a line occurs wholly through a nonconductor within the cable between the conductors. Coaxal lines may so become bent & twisted (subject to restricts) forgoing veto results, & it may be strapped to conductive supports forswearing getting unwanted currents around the two.

Within radio-frequency applications as much as two or three gigahertz, a wave propagates in the transverse electric automobile magnetic (TEM) mode, which means that the electric & magnetic fields come each perpendicular to the counsel of propagation. Nevertheless, above a certain frequency known as the cutoff frequency, a cable behaves as a waveguide, and propagation switches to either the transverse electric (TE) or even even the transverse magnetic (TM) mode or the mixture of modes. This symptom enables coaxial cables to become utilized at microwave frequencies, although they are non when effective when a other expensive, purpose-purpose-made wave guide.

Coaxial cables take an internal structure of an insulating (insulator) lesson to maintain a spacing between a center conductor & shield. Unluckily, everthing dielectrics have loss associated with the children, which is the causal agent of virtually all coaxal lines to exist as lossier than open wire lines. Virtually all cables have a firm insulator; others have a foam nonconductor which contains when much air as conceivable to reduce a losses. Foam coaxial cable have had just about 15% less attenuation however could take inside wet in humid environments, increasing a loss.

Important parameters
The characteristic impedance in ohms (Ω) is calculated from either a ratio of a inner & outer diameters & the dielectric constant. Assuming a insulator properties of a poop in a cable doesn't alter appreciably above the operational range of the cable, this electrical resistance is frequency independent. Capacitance, in farads per metre. Resistance, in ohms by the metre. Attenuation or even loss, around decibels per metre. This is depending on a loss in the nonconductor poop filling the cable, & insubordinate losses in the center conductor & shield. These losses come frequency dependant, a losses becoming higher when a frequency increases. Inside designing the patterns, engineers must consider non simply a loss in a actual cable itself, however likewise the insertion loss in the connectors. Outside across, which dictates which connectors must be utilized to terminate a cable. Velocity of propagation, which depends on the type of nonconductor.

Standard cable types
Virtually all coaxial cables have a characteristic ohmic resistance of either L, 52, 75, or even 93 ohms. A RF industry utilizes standard nature and severity-list for coaxial cables.

The series of standard types of coaxial cable were specified for military uses, in the form "RG-#" or "RG-#/U" (RG from either Radio Cure, /U indicates multiple utilizes). It last back to World War II and were listed within MIL-HDBK-216 published inside 1962. These desigations come okay, obsolete. A todays military standard is MIL-SPEC MIL-C-17. MIL-C-17 counts, like M17/75-RG214.come given for military cables & manufacturer's catalog totals for civilian applications. however, the RG-series designations were then green for generations that it is still utilized, although critical users should become caring that since a vade mecum is withdrawn no standard to assure a electrical & physical characteristics of a cable described when "RG=# type". A RG designators come mostly wont to identify compatible connectors that fit a inner conductor, nonconductor, & jacket dimensions of the old RG-series cables. For instance:

A select few standard types

nature and severity	impedence	outside across	comments
RG-6/U	75Ω	0.332" in (8.5mm)	low loss at high frequency for satellite television and cablemodem
RG-6/UQ	75Ω		This is 'quad' shield RG 6. Apparently it has twice as much shielding as regular RG-6/U
RG-8/U	50Ω	0.405 in (10.287 mm)	used for Thick Ethernet (10base5)
RG-9/U	51Ω	0.42 in (10.668 mm)
RG-11/U	75 Ω	0.405 in (10.287 mm)
RG-58/U	50 or 52 Ω	0.2 in (5 mm)	used for Thin Ethernet (10base2)
RG-59/U	75 Ω	0.242 in (6.15 mm)
RG-62/U	92 Ω	0.242 in (6.15 mm)	used for ARCNET
RG-178/U	50 Ω	0.079 in (2.00 mm)
RG-179/U	75 Ω	0.094 in (2.38 mm)

References for this section [http://www.dscc.dla.mil/Programs/MilSpec/ListDocs.asp?BasicDoc=MIL-HDBK-216 Withdrawal Notice for MIL-HDBK-216 2001]

H. P. Westman et al, (ed), Reference Data for Radio Engineers, Fifth Edition, 1968, Howard W. Sams and Co., no ISBN, Library of Congress Card No. 43-14665

Uses of coaxial cable
Short coaxial cables are commonly used to connect home video equipment, or in ham radio setups. They used to be common for implementing computer networks, in particular Ethernet, but twisted pair cables have replaced them in most applications.

Long distance coaxial cable is used to connect radio networks and television networks, though this has largely been superseded by other more high-tech methods (fibre optics, T1/E1, satellite). It is still common for carrying cable television signals.

Types of coaxial cable
In broadcasting and other forms of radio communication, hard line is a very heavy-duty coaxial cable, where the outside shielding is a rigid or semi-rigid pipe, rather than flexible and braided wire. Hard line is very thick, typically at least a half inch or 13 mm and up to several times that, and has low loss even at high power. It is almost always used in the connection between a transmitter on the ground and the antenna or aerial on the tower. Hard lines are often made to be pressurised with nitrogen or desiccated air, which provide an excellent dielectric even at the high temperatures generated by thousands of watts of RF power, especially during intense summer heat and sunshine. Physical separation between the inner conductor and outer shielding is maintained by spacers, usually made out of tough solid plastics like nylon.

Triaxial cable or triax is coaxial cable with a third layer of shielding, insulation and sheathing. The outer shield, which is earthed, protects the inner shield from electromagnetic interference from outside sources.

Twin-axial cable or twinax is a balanced, twisted pair within a cylindrical shield. It allows a nearly perfect differential signal which is both shielded and balanced to pass through. Multi-conductor coaxial cable is also sometimes used.

'Biaxial cable or biax is a figure-8 configuration of two 50 ohm coaxial cables, used in some proprietary computer networks.

Semi-rigid cable is a coaxial form using a solid copper outer sheath. This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies. The major disadvantage is that the cable, as its name implies, is not very flexible, and is not intended to be flexed after initial forming.

Interference and troubleshooting

Despite being shielded, interference can occur on coaxial cable lines. Eventually, the insulation degrades and the cable must be replaced, especially if it has been exposed to the elements on a continuous basis. The copper screen is normally grounded, and if even a single thread touches the inner copper core, the signal will be shorted out. This most often occurs at improperly installed end connectors and splices. Also, the connector or splice must be properly attached to the copper screen, as this provides the return electrical path for the signal.

For cable television it is important to use the correct type of coaxial cable. RG-59/U should be avoided, and only RG-6/U, or in cases of severe interference, RG-6/UQ (quad-shield) used. Many consumers have purchased the cheaper RG-59/U to use as an extension for cable television, only to find it causes severe interference. Also, unknown to most cable television customers, leakage of signals can cause interference to aircraft communications which operate on the same frequency as several cable channels. This may even be a violation of the law.

In the United States and some other countries, cable channels 2-13 share the same frequency as those from television broadcast towers. If the cable consumer is too close to a television tower and the cable company provides the same station on the like channel, interference and 'ghosting' may result. The solution is to make sure the cable signal is at the maximum allowed strength (especially if splitters are use for multiple TV sets), as this will increase the signal-to-noise level (the "noise" being the pickup of the broadcast tower). Using the more expensive quad-shield coaxial cable also helps reduce interference. Only industrial-quality cable TV amplifiers (generally not available at retail) should be used to amplify weak signals. Cheaper ones, sold at consumer electronics stores, often cause more problems than they solve.

Timeline
1884 - Coaxial cable patented in Germany by Ernst Werner von Siemens, but with no known application. [unverified: more details needed] 1894 - Oliver Lodge demonstrates waveguide transmission at the Royal Institution. Nikola Tesla receives , Electrical Conductor, on February 6. 1929 - First modern coaxial cable patented by Lloyd Espenschied and Herman Affel of AT&T's Bell Telephone Laboratories. 1934 - First transmission of TV pictures on coaxial cable, from the Berlin Olympic Games to Leipzig. 1936 - AT&T installs experimental coaxial TV cable between New York and Philadelphia. 1936 - Coaxial cable laid by the Post Office (now BT) between London and Birmingham, providing 40 telephone channels. [Source: archives at http://www.bt.com] 1941 - First commercial use in USA by AT&T, between Minneapolis, Minnesota and Stevens Point, Wisconsin. L1 system with capacity of one TV channel or 480 telephone circuits. 1956 - First transatlantic coaxial cable laid, TAT-1.