{"history":[],"article":{"id":"90f307d6-b2c4-4ac8-aee0-f3167a23331b","title":"Transmission medium","slug":"transmission-medium","content":":::summary\n:::\n\n# \nA **transmission medium** is a system or substance that can mediate the [propagation](https://bliptext.com/articles/wave-propagation) of [signals](https://bliptext.com/articles/signal) for the purposes of [telecommunication](https://bliptext.com/articles/telecommunication).\nSignals are typically imposed on a wave of some kind suitable for the chosen medium.\nFor example, data can modulate sound, and a transmission medium for [sounds](https://bliptext.com/articles/sound) may be [air](https://bliptext.com/articles/air), but solids and liquids may also act as the transmission medium.\n[Vacuum](https://bliptext.com/articles/vacuum) or air constitutes a good transmission medium for [electromagnetic waves](https://bliptext.com/articles/electromagnetic-wave) such as [light](https://bliptext.com/articles/light) and [radio waves](https://bliptext.com/articles/radio-wave).\nWhile a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by [absorption](https://bliptext.com/articles/absorption-electromagnetic-radiation) or [reflection](https://bliptext.com/articles/reflection-physics) or [refraction](https://bliptext.com/articles/refraction) at the [interfaces](https://bliptext.com/articles/interface-chemistry) between media.\nTechnical devices can therefore be employed to transmit or guide waves.\nThus, an optical fiber or a copper cable is used as transmission media.\n[Electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) can be transmitted through an [optical medium](https://bliptext.com/articles/optical-medium), such as [optical fiber](https://bliptext.com/articles/optical-fiber), or through [twisted pair](https://bliptext.com/articles/twisted-pair) wires, [coaxial cable](https://bliptext.com/articles/coaxial-cable), or [dielectric](https://bliptext.com/articles/dielectric)-slab [waveguides](https://bliptext.com/articles/waveguide).\nIt may also pass through any physical material that is transparent to the specific [wavelength](https://bliptext.com/articles/wavelength), such as [water](https://bliptext.com/articles/water), [air](https://bliptext.com/articles/air), [glass](https://bliptext.com/articles/glass), or [concrete](https://bliptext.com/articles/concrete).\n[Sound](https://bliptext.com/articles/sound) is, by definition, the vibration of matter, so it requires a physical medium for transmission, as do other kinds of mechanical waves and [heat](https://bliptext.com/articles/heat) energy.\nHistorically, science incorporated various [aether theories](https://bliptext.com/articles/aether-theories) to explain the transmission medium.\nHowever, it is now known that electromagnetic waves do not require a physical transmission medium, and so can travel through the vacuum of [free space](https://bliptext.com/articles/free-space).\nReg[ions](https://bliptext.com/articles/ion) of the [insulative](https://bliptext.com/articles/electrical-insulation) vacuum can become [conductive](https://bliptext.com/articles/conductive) for [electrical conduction](https://bliptext.com/articles/electrical-conduction) through the presence of free [electrons](https://bliptext.com/articles/electron), [holes](https://bliptext.com/articles/electron-hole), or [ions](https://bliptext.com/articles/ion).\n# [Cutaway diagram of Coaxial cable, one example of a transmission medium | upload.wikimedia.org/wikipedia/commons/f/f4/Coaxial///cable///cutaway.svg]\n\n# Optical medium\n\n# Telecommunications\nA physical medium in data communications is the transmission path over which a signal propagates.\nMany different types of transmission media are used as [communications channel](https://bliptext.com/articles/communications-channel).\nIn many cases, communication is in the form of electromagnetic waves.\nWith guided transmission media, the waves are guided along a physical path; examples of guided media include phone lines, [twisted pair](https://bliptext.com/articles/twisted-pair) cables, [coaxial cables](https://bliptext.com/articles/coaxial-cable), and optical fibers.\nUnguided transmission media are methods that allow the transmission of [data](https://bliptext.com/articles/data) without the use of physical means to define the path it takes.\nExamples of this include [microwave](https://bliptext.com/articles/microwave), [radio](https://bliptext.com/articles/radio) or [infrared](https://bliptext.com/articles/infrared).\nUnguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and seawater.\nThe term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitters to receivers with no intermediate devices, other than amplifiers or repeaters used to increase signal strength.\nThis term can apply to both guided and unguided media.\n\n# Simplex versus duplex\nA [signal transmission](https://bliptext.com/articles/signal-transmission) may be [simplex](https://bliptext.com/articles/simplex-communication), half-[duplex](https://bliptext.com/articles/duplex-telecommunications), or full-[duplex](https://bliptext.com/articles/duplex-telecommunications).\nIn simplex transmission, signals are transmitted in only one direction; one station is a transmitter and the other is the receiver.\nIn the half-duplex operation, both stations may transmit, but only one at a time.\nIn full-duplex operation, both stations may transmit simultaneously.\nIn the latter case, the medium is carrying signals in both directions at the same time.\n\n# Types\nIn general, a transmission medium can be classified as\nThere are two main types of transmission media:\nOne of the most common physical media used in networking is [copper wire](https://bliptext.com/articles/copper-wire).\nCopper wire to carry signals to long distances using relatively low amounts of power.\nThe [unshielded twisted pair](https://bliptext.com/articles/unshielded-twisted-pair) (UTP) is eight strands of copper wire, organized into four pairs.\n\n## Guided media\n\n### Twisted pair\nTwisted pair cabling is a type of wiring in which two conductors of a single [circuit](https://bliptext.com/articles/electronic-circuit) are twisted together for the purposes of improving [electromagnetic compatibility](https://bliptext.com/articles/electromagnetic-compatibility).\nCompared to a [single conductor](https://bliptext.com/articles/single-ended-signaling) or an untwisted [balanced pair](https://bliptext.com/articles/balanced-pair), a twisted pair reduces [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) from the pair and [crosstalk](https://bliptext.com/articles/crosstalk) between neighboring pairs and improves rejection of external [electromagnetic interference](https://bliptext.com/articles/electromagnetic-interference).\nIt was invented by [Alexander Graham Bell](https://bliptext.com/articles/alexander-graham-bell).\n\n### Coaxial cable\nCoaxial cable, or coax (pronounced ) is a type of [electrical cable](https://bliptext.com/articles/electrical-cable) that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield.\nMany coaxial cables also have an insulating outer sheath or jacket.\nThe term [coaxial](https://bliptext.com/articles/coaxial) comes from the inner conductor and the outer shield sharing a geometric axis.\nCoaxial cable was invented by English physicist, engineer, and mathematician [Oliver Heaviside](https://bliptext.com/articles/oliver-heaviside), who patented the design in 1880.\nCoaxial cable is a type of [transmission line](https://bliptext.com/articles/transmission-line), used to carry high [frequency](https://bliptext.com/articles/frequency) [electrical signals](https://bliptext.com/articles/electrical-signal) with low losses.\nIt is used in such applications as [telephone trunk lines](https://bliptext.com/articles/trunking), [broadband internet](https://bliptext.com/articles/broadband-internet) networking cables, high-speed computer [data busses](https://bliptext.com/articles/bus-computing), carrying [cable television](https://bliptext.com/articles/cable-television) signals, and connecting [radio transmitters](https://bliptext.com/articles/radio-transmitter) and [receivers](https://bliptext.com/articles/radio-receiver) to their [antennas](https://bliptext.com/articles/antenna-radio).\nIt differs from other [shielded cables](https://bliptext.com/articles/shielded-cable) 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.\n# [RG-59 flexible coaxial cable composed of:

Outer plastic sheath
Woven copper shield
Inner dielectric insulator
Copper core

| upload.wikimedia.org/wikipedia/commons/7/73/RG-59.jpg]\n\n### Optical fiber\nOptical fiber, which has emerged as the most commonly used transmission medium for long-distance communications, is a thin strand of glass that guides light along its length.\nFour major factors favor optical fiber over copper: data rates, distance, installation, and costs.\nOptical fiber can carry huge amounts of data compared to copper.\nIt can be run for hundreds of miles without the need for signal repeaters, in turn, reducing maintenance costs and improving the reliability of the communication system because repeaters are a common source of network failures.\nGlass is lighter than copper allowing for less need for specialized heavy-lifting equipment when installing long-distance optical fiber.\nOptical fiber for indoor applications cost approximately a dollar a foot, the same as copper.\n[Multimode](https://bliptext.com/articles/multi-mode-optical-fiber) and [single mode](https://bliptext.com/articles/single-mode-optical-fiber) are two types of commonly used optical fiber.\nMultimode fiber uses LEDs as the light source and can carry signals over shorter distances, about 2 kilometers.\nSingle mode can carry signals over distances of tens of miles.\nAn optical fiber is a flexible, [transparent](https://bliptext.com/articles/transparency-and-translucency) fiber made by [drawing](https://bliptext.com/articles/drawing-manufacturing) [glass](https://bliptext.com/articles/glass) ([silica](https://bliptext.com/articles/silica)) or plastic to a diameter slightly thicker than that of a [human hair](https://bliptext.com/articles/hair-s-breadth).\nOptical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in [fiber-optic communications](https://bliptext.com/articles/fiber-optic-communication), where they permit transmission over longer distances and at higher [bandwidths](https://bliptext.com/articles/bandwidth-computing) (data rates) than electrical cables.\nFibers are used instead of [metal](https://bliptext.com/articles/metal) wires because signals travel along them with less [loss](https://bliptext.com/articles/attenuation); in addition, fibers are immune to [electromagnetic interference](https://bliptext.com/articles/electromagnetic-interference), a problem from which [metal](https://bliptext.com/articles/metal) wires suffer excessively.\nFibers are also used for [illumination](https://bliptext.com/articles/illumination-lighting) and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a [fiberscope](https://bliptext.com/articles/fiberscope).\nSpecially designed fibers are also used for a variety of other applications, some of them being [fiber optic sensors](https://bliptext.com/articles/fiber-optic-sensor) and [fiber lasers](https://bliptext.com/articles/fiber-laser).\nOptical fibers typically include a [core](https://bliptext.com/articles/core-optical-fiber) surrounded by a transparent [cladding](https://bliptext.com/articles/cladding-fiber-optics) material with a lower [index of refraction](https://bliptext.com/articles/index-of-refraction).\nLight is kept in the core by the phenomenon of [total internal reflection](https://bliptext.com/articles/total-internal-reflection) which causes the fiber to act as a [waveguide](https://bliptext.com/articles/waveguide).\nFibers that support many propagation paths or [transverse modes](https://bliptext.com/articles/transverse-mode) are called [multi-mode fibers](https://bliptext.com/articles/multi-mode-fiber), while those that support a single mode are called [single-mode fibers](https://bliptext.com/articles/single-mode-fiber) (SMF).\nMulti-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted.\nSingle-mode fibers are used for most communication links longer than 1000 m.\nBeing able to join optical fibers with low loss is important in fiber optic communication.\nThis is more complex than joining electrical wire or cable and involves careful [cleaving](https://bliptext.com/articles/cleave-fiber) of the fibers, precise alignment of the fiber cores, and the coupling of these aligned cores.\nFor applications that demand a permanent connection a [fusion splice](https://bliptext.com/articles/fusion-splice) is common.\nIn this technique, an electric arc is used to melt the ends of the fibers together.\nAnother common technique is a [mechanical splice](https://bliptext.com/articles/mechanical-splice), where the ends of the fibers are held in contact by mechanical force.\nTemporary or semi-permanent connections are made by means of specialized [optical fiber connectors](https://bliptext.com/articles/optical-fiber-connector).\nThe field of applied science and engineering concerned with the design and application of optical fibers is known as **fiber optics**.\nThe term was coined by Indian physicist [Narinder Singh Kapany](https://bliptext.com/articles/narinder-singh-kapany), who is widely acknowledged as the father of fiber optics.\n# [A bundle of optical fiber | upload.wikimedia.org/wikipedia/commons/e/ec/fibreoptic.jpg]\n# [Fiber crew installing a 432-count fiber cable underneath the streets of Midtown Manhattan, New York City | upload.wikimedia.org/wikipedia/commons/1/1b/Stealth///Fiber///Crew///installing///fiber///cable///underneath///the///streets///of///Manhattan.jpg]\n# [A TOSLINK fiber optic audio cable with red light being shone in one end transmits the light to the other end | upload.wikimedia.org/wikipedia/commons/8/85/Fiber///optic///illuminated.jpg]\n# [A wall-mount cabinet containing optical fiber interconnects. The yellow cables are single mode fibers; the orange and aqua cables are multi-mode fibers: 50/125 μm OM2 and 50/125 μm OM3 fibers respectively. | upload.wikimedia.org/wikipedia/commons/b/b4/Optical-fibre-junction-box.jpg]\n\n## Unguided transmission media\n\n### Radio\nRadio propagation is the behavior of [radio waves](https://bliptext.com/articles/radio-wave) as they travel, or are [propagated](https://bliptext.com/articles/wave-propagation), from one point to another, or into various parts of the [atmosphere](https://bliptext.com/articles/atmosphere).\nAs a form of [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation), like light waves, radio waves are affected by the phenomena of [reflection](https://bliptext.com/articles/reflection-physics), [refraction](https://bliptext.com/articles/refraction), [diffraction](https://bliptext.com/articles/diffraction), [absorption](https://bliptext.com/articles/absorption-electromagnetic-radiation), [polarization](https://bliptext.com/articles/polarization-waves), and [scattering](https://bliptext.com/articles/scattering).\nUnderstanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international [shortwave](https://bliptext.com/articles/shortwave) [broadcasters](https://bliptext.com/articles/broadcasting), to designing reliable [mobile telephone](https://bliptext.com/articles/mobile-telephone) systems, to [radio navigation](https://bliptext.com/articles/radio-navigation), to operation of [radar](https://bliptext.com/articles/radar) systems.\nDifferent types of propagation are used in practical radio transmission systems.\n[Line-of-sight propagation](https://bliptext.com/articles/line-of-sight-propagation) means radio waves that travel in a straight line from the transmitting antenna to the receiving antenna.\nLine of sight transmission is used to medium-range radio transmission such as [cell phones](https://bliptext.com/articles/cell-phone), [cordless phones](https://bliptext.com/articles/cordless-phone), [walkie-talkies](https://bliptext.com/articles/walkie-talkie), [wireless networks](https://bliptext.com/articles/wireless-network), [FM radio](https://bliptext.com/articles/fm-radio) and [television broadcasting](https://bliptext.com/articles/television-broadcasting) and [radar](https://bliptext.com/articles/radar), and [satellite communication](https://bliptext.com/articles/satellite-communication), such as [satellite television](https://bliptext.com/articles/satellite-television).\nLine-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, which depends on the height of transmitting and receiving antennas.\nIt is the only propagation method possible at [microwave](https://bliptext.com/articles/microwave) frequencies and above.\nAt microwave frequencies, moisture in the atmosphere ([rain fade](https://bliptext.com/articles/rain-fade)) can degrade transmission.\nAt lower frequencies in the [MF](https://bliptext.com/articles/medium-frequency), [LF](https://bliptext.com/articles/low-frequency), and V[LF](https://bliptext.com/articles/low-frequency) bands, due to [diffraction](https://bliptext.com/articles/diffraction) radio waves can bend over obstacles like hills, and travel beyond the horizon as [surface waves](https://bliptext.com/articles/surface-wave) which follow the contour of the Earth.\nThese are called [ground waves](https://bliptext.com/articles/ground-wave).\n[AM broadcasting](https://bliptext.com/articles/am-broadcasting) stations use ground waves to cover their listening areas.\nAs the frequency gets lower, the attenuation with distance decreases, so [very low frequency](https://bliptext.com/articles/very-low-frequency) (VLF) and [extremely low frequency](https://bliptext.com/articles/extremely-low-frequency) (ELF) ground waves can be used to communicate worldwide.\nVLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.\nAt [medium wave](https://bliptext.com/articles/medium-wave) and [shortwave](https://bliptext.com/articles/shortwave) frequencies ([MF](https://bliptext.com/articles/medium-frequency) and [HF](https://bliptext.com/articles/high-frequency) bands) radio waves can refract from a layer of [charged particles](https://bliptext.com/articles/charged-particle) ([ions](https://bliptext.com/articles/ion)) high in the atmosphere, called the [ionosphere](https://bliptext.com/articles/ionosphere).\nThis means that radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances.\nThis is called [skywave](https://bliptext.com/articles/skywave) propagation.\nIt is used by [amateur radio](https://bliptext.com/articles/amateur-radio) operators to talk to other countries and shortwave broadcasting stations that broadcast internationally.\nSkywave communication is variable, dependent on conditions in the upper atmosphere; it is most reliable at night and in the winter.\nDue to its unreliability, since the advent of [communication satellites](https://bliptext.com/articles/communication-satellite) in the 1960s, many long-range communication that previously used skywaves now use satellites.\nIn addition, there are several less common radio propagation mechanisms, such as [tropospheric scattering](https://bliptext.com/articles/tropospheric-scattering) (troposcatter) and [near vertical incidence skywave](https://bliptext.com/articles/near-vertical-incidence-skywave) (NVIS) which are used in specialized communication systems.\n\n# Digital encoding\nTransmission and reception of data is typically performed in four steps:","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T17:41:20.022Z","updated_at":"2025-01-25T17:41:20.022Z","search_vector":"'medium':2 'transmiss':1","search_content":" \n \n\n# \nA **transmission medium** is a system or substance that can mediate the [propagation](https://bliptext.com/articles/wave-propagation) of [signals](https://bliptext.com/articles/signal) for the purposes of [telecommunication](https://bliptext.com/articles/telecommunication).\nSignals are typically imposed on a wave of some kind suitable for the chosen medium.\nFor example, data can modulate sound, and a transmission medium for [sounds](https://bliptext.com/articles/sound) may be [air](https://bliptext.com/articles/air), but solids and liquids may also act as the transmission medium.\n[Vacuum](https://bliptext.com/articles/vacuum) or air constitutes a good transmission medium for [electromagnetic waves](https://bliptext.com/articles/electromagnetic-wave) such as [light](https://bliptext.com/articles/light) and [radio waves](https://bliptext.com/articles/radio-wave).\nWhile a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by [absorption](https://bliptext.com/articles/absorption-electromagnetic-radiation) or [reflection](https://bliptext.com/articles/reflection-physics) or [refraction](https://bliptext.com/articles/refraction) at the [interfaces](https://bliptext.com/articles/interface-chemistry) between media.\nTechnical devices can therefore be employed to transmit or guide waves.\nThus, an optical fiber or a copper cable is used as transmission media.\n[Electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) can be transmitted through an [optical medium](https://bliptext.com/articles/optical-medium), such as [optical fiber](https://bliptext.com/articles/optical-fiber), or through [twisted pair](https://bliptext.com/articles/twisted-pair) wires, [coaxial cable](https://bliptext.com/articles/coaxial-cable), or [dielectric](https://bliptext.com/articles/dielectric)-slab [waveguides](https://bliptext.com/articles/waveguide).\nIt may also pass through any physical material that is transparent to the specific [wavelength](https://bliptext.com/articles/wavelength), such as [water](https://bliptext.com/articles/water), [air](https://bliptext.com/articles/air), [glass](https://bliptext.com/articles/glass), or [concrete](https://bliptext.com/articles/concrete).\n[Sound](https://bliptext.com/articles/sound) is, by definition, the vibration of matter, so it requires a physical medium for transmission, as do other kinds of mechanical waves and [heat](https://bliptext.com/articles/heat) energy.\nHistorically, science incorporated various [aether theories](https://bliptext.com/articles/aether-theories) to explain the transmission medium.\nHowever, it is now known that electromagnetic waves do not require a physical transmission medium, and so can travel through the vacuum of [free space](https://bliptext.com/articles/free-space).\nReg[ions](https://bliptext.com/articles/ion) of the [insulative](https://bliptext.com/articles/electrical-insulation) vacuum can become [conductive](https://bliptext.com/articles/conductive) for [electrical conduction](https://bliptext.com/articles/electrical-conduction) through the presence of free [electrons](https://bliptext.com/articles/electron), [holes](https://bliptext.com/articles/electron-hole), or [ions](https://bliptext.com/articles/ion).\n# [Cutaway diagram of Coaxial cable, one example of a transmission medium | upload.wikimedia.org/wikipedia/commons/f/f4/Coaxial///cable///cutaway.svg]\n\n# Optical medium\n\n# Telecommunications\nA physical medium in data communications is the transmission path over which a signal propagates.\nMany different types of transmission media are used as [communications channel](https://bliptext.com/articles/communications-channel).\nIn many cases, communication is in the form of electromagnetic waves.\nWith guided transmission media, the waves are guided along a physical path; examples of guided media include phone lines, [twisted pair](https://bliptext.com/articles/twisted-pair) cables, [coaxial cables](https://bliptext.com/articles/coaxial-cable), and optical fibers.\nUnguided transmission media are methods that allow the transmission of [data](https://bliptext.com/articles/data) without the use of physical means to define the path it takes.\nExamples of this include [microwave](https://bliptext.com/articles/microwave), [radio](https://bliptext.com/articles/radio) or [infrared](https://bliptext.com/articles/infrared).\nUnguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and seawater.\nThe term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitters to receivers with no intermediate devices, other than amplifiers or repeaters used to increase signal strength.\nThis term can apply to both guided and unguided media.\n\n# Simplex versus duplex\nA [signal transmission](https://bliptext.com/articles/signal-transmission) may be [simplex](https://bliptext.com/articles/simplex-communication), half-[duplex](https://bliptext.com/articles/duplex-telecommunications), or full-[duplex](https://bliptext.com/articles/duplex-telecommunications).\nIn simplex transmission, signals are transmitted in only one direction; one station is a transmitter and the other is the receiver.\nIn the half-duplex operation, both stations may transmit, but only one at a time.\nIn full-duplex operation, both stations may transmit simultaneously.\nIn the latter case, the medium is carrying signals in both directions at the same time.\n\n# Types\nIn general, a transmission medium can be classified as\nThere are two main types of transmission media:\nOne of the most common physical media used in networking is [copper wire](https://bliptext.com/articles/copper-wire).\nCopper wire to carry signals to long distances using relatively low amounts of power.\nThe [unshielded twisted pair](https://bliptext.com/articles/unshielded-twisted-pair) (UTP) is eight strands of copper wire, organized into four pairs.\n\n## Guided media\n\n### Twisted pair\nTwisted pair cabling is a type of wiring in which two conductors of a single [circuit](https://bliptext.com/articles/electronic-circuit) are twisted together for the purposes of improving [electromagnetic compatibility](https://bliptext.com/articles/electromagnetic-compatibility).\nCompared to a [single conductor](https://bliptext.com/articles/single-ended-signaling) or an untwisted [balanced pair](https://bliptext.com/articles/balanced-pair), a twisted pair reduces [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) from the pair and [crosstalk](https://bliptext.com/articles/crosstalk) between neighboring pairs and improves rejection of external [electromagnetic interference](https://bliptext.com/articles/electromagnetic-interference).\nIt was invented by [Alexander Graham Bell](https://bliptext.com/articles/alexander-graham-bell).\n\n### Coaxial cable\nCoaxial cable, or coax (pronounced ) is a type of [electrical cable](https://bliptext.com/articles/electrical-cable) that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield.\nMany coaxial cables also have an insulating outer sheath or jacket.\nThe term [coaxial](https://bliptext.com/articles/coaxial) comes from the inner conductor and the outer shield sharing a geometric axis.\nCoaxial cable was invented by English physicist, engineer, and mathematician [Oliver Heaviside](https://bliptext.com/articles/oliver-heaviside), who patented the design in 1880.\nCoaxial cable is a type of [transmission line](https://bliptext.com/articles/transmission-line), used to carry high [frequency](https://bliptext.com/articles/frequency) [electrical signals](https://bliptext.com/articles/electrical-signal) with low losses.\nIt is used in such applications as [telephone trunk lines](https://bliptext.com/articles/trunking), [broadband internet](https://bliptext.com/articles/broadband-internet) networking cables, high-speed computer [data busses](https://bliptext.com/articles/bus-computing), carrying [cable television](https://bliptext.com/articles/cable-television) signals, and connecting [radio transmitters](https://bliptext.com/articles/radio-transmitter) and [receivers](https://bliptext.com/articles/radio-receiver) to their [antennas](https://bliptext.com/articles/antenna-radio).\nIt differs from other [shielded cables](https://bliptext.com/articles/shielded-cable) 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.\n# [RG-59 flexible coaxial cable composed of: Outer plastic sheath Woven copper shield Inner dielectric insulator Copper core | upload.wikimedia.org/wikipedia/commons/7/73/RG-59.jpg]\n\n### Optical fiber\nOptical fiber, which has emerged as the most commonly used transmission medium for long-distance communications, is a thin strand of glass that guides light along its length.\nFour major factors favor optical fiber over copper: data rates, distance, installation, and costs.\nOptical fiber can carry huge amounts of data compared to copper.\nIt can be run for hundreds of miles without the need for signal repeaters, in turn, reducing maintenance costs and improving the reliability of the communication system because repeaters are a common source of network failures.\nGlass is lighter than copper allowing for less need for specialized heavy-lifting equipment when installing long-distance optical fiber.\nOptical fiber for indoor applications cost approximately a dollar a foot, the same as copper.\n[Multimode](https://bliptext.com/articles/multi-mode-optical-fiber) and [single mode](https://bliptext.com/articles/single-mode-optical-fiber) are two types of commonly used optical fiber.\nMultimode fiber uses LEDs as the light source and can carry signals over shorter distances, about 2 kilometers.\nSingle mode can carry signals over distances of tens of miles.\nAn optical fiber is a flexible, [transparent](https://bliptext.com/articles/transparency-and-translucency) fiber made by [drawing](https://bliptext.com/articles/drawing-manufacturing) [glass](https://bliptext.com/articles/glass) ([silica](https://bliptext.com/articles/silica)) or plastic to a diameter slightly thicker than that of a [human hair](https://bliptext.com/articles/hair-s-breadth).\nOptical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in [fiber-optic communications](https://bliptext.com/articles/fiber-optic-communication), where they permit transmission over longer distances and at higher [bandwidths](https://bliptext.com/articles/bandwidth-computing) (data rates) than electrical cables.\nFibers are used instead of [metal](https://bliptext.com/articles/metal) wires because signals travel along them with less [loss](https://bliptext.com/articles/attenuation); in addition, fibers are immune to [electromagnetic interference](https://bliptext.com/articles/electromagnetic-interference), a problem from which [metal](https://bliptext.com/articles/metal) wires suffer excessively.\nFibers are also used for [illumination](https://bliptext.com/articles/illumination-lighting) and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a [fiberscope](https://bliptext.com/articles/fiberscope).\nSpecially designed fibers are also used for a variety of other applications, some of them being [fiber optic sensors](https://bliptext.com/articles/fiber-optic-sensor) and [fiber lasers](https://bliptext.com/articles/fiber-laser).\nOptical fibers typically include a [core](https://bliptext.com/articles/core-optical-fiber) surrounded by a transparent [cladding](https://bliptext.com/articles/cladding-fiber-optics) material with a lower [index of refraction](https://bliptext.com/articles/index-of-refraction).\nLight is kept in the core by the phenomenon of [total internal reflection](https://bliptext.com/articles/total-internal-reflection) which causes the fiber to act as a [waveguide](https://bliptext.com/articles/waveguide).\nFibers that support many propagation paths or [transverse modes](https://bliptext.com/articles/transverse-mode) are called [multi-mode fibers](https://bliptext.com/articles/multi-mode-fiber), while those that support a single mode are called [single-mode fibers](https://bliptext.com/articles/single-mode-fiber) (SMF).\nMulti-mode fibers generally have a wider core diameter and are used for short-distance communication links and for applications where high power must be transmitted.\nSingle-mode fibers are used for most communication links longer than 1000 m.\nBeing able to join optical fibers with low loss is important in fiber optic communication.\nThis is more complex than joining electrical wire or cable and involves careful [cleaving](https://bliptext.com/articles/cleave-fiber) of the fibers, precise alignment of the fiber cores, and the coupling of these aligned cores.\nFor applications that demand a permanent connection a [fusion splice](https://bliptext.com/articles/fusion-splice) is common.\nIn this technique, an electric arc is used to melt the ends of the fibers together.\nAnother common technique is a [mechanical splice](https://bliptext.com/articles/mechanical-splice), where the ends of the fibers are held in contact by mechanical force.\nTemporary or semi-permanent connections are made by means of specialized [optical fiber connectors](https://bliptext.com/articles/optical-fiber-connector).\nThe field of applied science and engineering concerned with the design and application of optical fibers is known as **fiber optics**.\nThe term was coined by Indian physicist [Narinder Singh Kapany](https://bliptext.com/articles/narinder-singh-kapany), who is widely acknowledged as the father of fiber optics.\n# [A bundle of optical fiber | upload.wikimedia.org/wikipedia/commons/e/ec/fibreoptic.jpg]\n# [Fiber crew installing a 432-count fiber cable underneath the streets of Midtown Manhattan, New York City | upload.wikimedia.org/wikipedia/commons/1/1b/Stealth///Fiber///Crew///installing///fiber///cable///underneath///the///streets///of///Manhattan.jpg]\n# [A TOSLINK fiber optic audio cable with red light being shone in one end transmits the light to the other end | upload.wikimedia.org/wikipedia/commons/8/85/Fiber///optic///illuminated.jpg]\n# [A wall-mount cabinet containing optical fiber interconnects. The yellow cables are single mode fibers; the orange and aqua cables are multi-mode fibers: 50/125 μm OM2 and 50/125 μm OM3 fibers respectively. | upload.wikimedia.org/wikipedia/commons/b/b4/Optical-fibre-junction-box.jpg]\n\n## Unguided transmission media\n\n### Radio\nRadio propagation is the behavior of [radio waves](https://bliptext.com/articles/radio-wave) as they travel, or are [propagated](https://bliptext.com/articles/wave-propagation), from one point to another, or into various parts of the [atmosphere](https://bliptext.com/articles/atmosphere).\nAs a form of [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation), like light waves, radio waves are affected by the phenomena of [reflection](https://bliptext.com/articles/reflection-physics), [refraction](https://bliptext.com/articles/refraction), [diffraction](https://bliptext.com/articles/diffraction), [absorption](https://bliptext.com/articles/absorption-electromagnetic-radiation), [polarization](https://bliptext.com/articles/polarization-waves), and [scattering](https://bliptext.com/articles/scattering).\nUnderstanding the effects of varying conditions on radio propagation has many practical applications, from choosing frequencies for international [shortwave](https://bliptext.com/articles/shortwave) [broadcasters](https://bliptext.com/articles/broadcasting), to designing reliable [mobile telephone](https://bliptext.com/articles/mobile-telephone) systems, to [radio navigation](https://bliptext.com/articles/radio-navigation), to operation of [radar](https://bliptext.com/articles/radar) systems.\nDifferent types of propagation are used in practical radio transmission systems.\n[Line-of-sight propagation](https://bliptext.com/articles/line-of-sight-propagation) means radio waves that travel in a straight line from the transmitting antenna to the receiving antenna.\nLine of sight transmission is used to medium-range radio transmission such as [cell phones](https://bliptext.com/articles/cell-phone), [cordless phones](https://bliptext.com/articles/cordless-phone), [walkie-talkies](https://bliptext.com/articles/walkie-talkie), [wireless networks](https://bliptext.com/articles/wireless-network), [FM radio](https://bliptext.com/articles/fm-radio) and [television broadcasting](https://bliptext.com/articles/television-broadcasting) and [radar](https://bliptext.com/articles/radar), and [satellite communication](https://bliptext.com/articles/satellite-communication), such as [satellite television](https://bliptext.com/articles/satellite-television).\nLine-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, which depends on the height of transmitting and receiving antennas.\nIt is the only propagation method possible at [microwave](https://bliptext.com/articles/microwave) frequencies and above.\nAt microwave frequencies, moisture in the atmosphere ([rain fade](https://bliptext.com/articles/rain-fade)) can degrade transmission.\nAt lower frequencies in the [MF](https://bliptext.com/articles/medium-frequency), [LF](https://bliptext.com/articles/low-frequency), and V[LF](https://bliptext.com/articles/low-frequency) bands, due to [diffraction](https://bliptext.com/articles/diffraction) radio waves can bend over obstacles like hills, and travel beyond the horizon as [surface waves](https://bliptext.com/articles/surface-wave) which follow the contour of the Earth.\nThese are called [ground waves](https://bliptext.com/articles/ground-wave).\n[AM broadcasting](https://bliptext.com/articles/am-broadcasting) stations use ground waves to cover their listening areas.\nAs the frequency gets lower, the attenuation with distance decreases, so [very low frequency](https://bliptext.com/articles/very-low-frequency) (VLF) and [extremely low frequency](https://bliptext.com/articles/extremely-low-frequency) (ELF) ground waves can be used to communicate worldwide.\nVLF and ELF waves can penetrate significant distances through water and earth, and these frequencies are used for mine communication and military communication with submerged submarines.\nAt [medium wave](https://bliptext.com/articles/medium-wave) and [shortwave](https://bliptext.com/articles/shortwave) frequencies ([MF](https://bliptext.com/articles/medium-frequency) and [HF](https://bliptext.com/articles/high-frequency) bands) radio waves can refract from a layer of [charged particles](https://bliptext.com/articles/charged-particle) ([ions](https://bliptext.com/articles/ion)) high in the atmosphere, called the [ionosphere](https://bliptext.com/articles/ionosphere).\nThis means that radio waves transmitted at an angle into the sky can be reflected back to Earth beyond the horizon, at great distances, even transcontinental distances.\nThis is called [skywave](https://bliptext.com/articles/skywave) propagation.\nIt is used by [amateur radio](https://bliptext.com/articles/amateur-radio) operators to talk to other countries and shortwave broadcasting stations that broadcast internationally.\nSkywave communication is variable, dependent on conditions in the upper atmosphere; it is most reliable at night and in the winter.\nDue to its unreliability, since the advent of [communication satellites](https://bliptext.com/articles/communication-satellite) in the 1960s, many long-range communication that previously used skywaves now use satellites.\nIn addition, there are several less common radio propagation mechanisms, such as [tropospheric scattering](https://bliptext.com/articles/tropospheric-scattering) (troposcatter) and [near vertical incidence skywave](https://bliptext.com/articles/near-vertical-incidence-skywave) (NVIS) which are used in specialized communication systems.\n\n# Digital encoding\nTransmission and reception of data is typically performed in four steps:","revisionCount":0},"hasMore":false,"nextCursor":null}

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