Plenum Cable

From Wikipedia, the free encyclopedia

Plenum cable /ˈplɛnəm/ is electrical cable that is laid in the plenum spaces of buildings. In the United States, plastics used in the construction of plenum cable are regulated under the National Fire Protection Association standard NFPA 90A: Standard for the Installation of Air Conditioning and Ventilating Systems. All materials intended for use on wire and cables to be placed in plenum spaces are designed to meet rigorous fire safety test standards in accordance with NFPA 262 and outlined in NFPA 90A.

Plenum cable is jacketed with a fire-retardant plastic jacket of either a low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP). Polyolefin formulations, specifically based on polyethylene compounding had been developed by at least two companies in the early to mid-1990s; however, these were never commercialized, and development efforts continue in these yet-untapped product potentials. Development efforts on a non-halogen plenum compound were announced in 2007 citing new flame-retardant synergist packages that may provide an answer for a yet-underdeveloped plenum cable market outside the United States.

In 2006, significant concern developed over the potential toxicity of FEP and related fluorochemicals including the process aid perfluorooctanoic acid (PFOA) or C8 such that California has proposed some of these materials as potential human carcinogens. The NFPA Technical Committee on Air Conditioning, in response to public comment, has referred the issue of toxicity of cabling materials to the NFPA Committee on Toxicity for review before 2008.

In 2007, a development program specifically targeting the production of a non-halogen plenum cable compound was announced to specifically address lingering toxicity concerns presented by halogenated compounds for use in European and other global markets.

Riser Cable

Cable that is run between floors in non-plenum areas is rated as riser cable. The fire requirements on riser cable are not as strict. Thus, plenum cable can always replace riser cable, but riser cable cannot replace plenum cable in plenum spaces.

Both plenum and riser cables commonly include a rope or polymer filament with high tensile strength, which helps support the weight of the cable when it is dangling in an open chute.

Cables like twisted-pair, coaxial, HDMI, and DVI are available in both plenum and riser versions. The cable cost is often significantly higher than general-use cable due to the special restricted-use flame retardant materials.

Cable Stiffness

Plenum-rated and riser-rated cables are restricted to only allow certain chemicals for manufacture of the wire insulation and cable sheath. Typically this results in reduced flexibility of plastic cables, making it stiff and hard to bend. The bend radius may also be increased, and tight bends can potentially crack or tear the insulation and sheathing.


Optical Fiber Cable

From Wikipedia, the free encyclopedia


A TOSLINK optical fiber cable with a clear jacket. These cables are used mainly for digital audio connections between devices.

An optical fiber cable, also known as fiber optic cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed. Different types of cable are used for different applications, for example long distance telecommunication, or providing a high-speed data connection between different parts of a building.

1 Design
2 Capacity and market
3 Reliability and quality
4 Cable types
5 Jacket material
6 Fiber material
7 Color coding
7.1 Patch cords
7.2 Multi-fiber cables
8 Propagation speed and delay
9 Losses
10 Safety
11 Hybrid cables
12 Innerducts
12.1 Types
12.2 Placement
13 Fiber optic coupler
14 Optical Power Meter
15 Optical Time-Domain Reflectometer (OTDR)



A Multi-Fiber Cable

Optical fiber consists of a core and a cladding layer, selected for total internal reflection due to the difference in the refractive index between the two. In practical fibers, the cladding is usually coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties. Individual coated fibers (or fibers formed into ribbons or bundles) then have a tough resin buffer layer and/or core tube(s) extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable. Rigid fiber assemblies sometimes put light-absorbing (“dark”) glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications.


Left: LC/PC connectors – Right: SC/PC connectors. All four connectors have white caps covering the ferrules.

For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid (e.g. Twaron or Kevlar), in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment.


Fiber-optic cable in a Telstra pit


Investigating a fault in a fiber cable junction box. The individual fiber cable strands within the junction box are visible.


An optical fiber breakout cable

For use in more strenuous environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself. This protects the fiber from tension during laying and due to temperature changes. Loose-tube fiber may be “dry block” or gel-filled. Dry block offers less protection to the fibers than gel-filled, but costs considerably less. Instead of a loose tube, the fiber may be embedded in a heavy polymer jacket, commonly called “tight buffer” construction. Tight buffer cables are offered for a variety of applications, but the two most common are “Breakout” and “Distribution”. Breakout cables normally contain a ripcord, two non-conductive dielectric strengthening members (normally a glass rod epoxy), an aramid yarn, and 3 mm buffer tubing with an additional layer of Kevlar surrounding each fiber. The ripcord is a parallel cord of strong yarn that is situated under the jacket(s) of the cable for jacket removal. Distribution cables have an overall Kevlar wrapping, a ripcord, and a 900 micrometer buffer coating surrounding each fiber. These fiber units are commonly bundled with additional steel strength members, again with a helical twist to allow for stretching.

A critical concern in outdoor cabling is to protect the fiber from contamination by water. This is accomplished by use of solid barriers such as copper tubes, and water-repellent jelly or water-absorbing powder surrounding the fiber.

Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals. Undersea cables are more heavily armored in their near-shore portions to protect them from boat anchors, fishing gear, and even sharks, which may be attracted to the electrical power that is carried to power amplifiers or repeaters in the cable.

Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, dual use as power lines, installation in conduit, lashing to aerial telephone poles, submarine installation, and insertion in paved streets.

Capacity and Market

In September 2012, NTT Japan demonstrated a single fiber cable that was able to transfer 1 petabit per second (1015bits/s) over a distance of 50 kilometers.

Modern fiber cables can contain up to a thousand fibers in a single cable, with potential bandwidth in the terabytes per second. In some cases, only a small fraction of the fibers in a cable may be actually “lit”. Companies can lease or sell the unused fiber to other providers who are looking for service in or through an area. Companies may “overbuild” their networks for the specific purpose of having a large network of dark fiber for sale, reducing the overall need for trenching and municipal permitting. They may also deliberately under-invest to prevent their rivals from profiting from their investment.

The highest strand-count singlemode fiber cable commonly manufactured is the 864-count, consisting of 36 ribbons each containing 24 strands of fiber.

Reliability and Quality

Optical fibers are very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging.

Telcordia GR-20, Generic Requirements for Optical Fiber and Optical Fiber Cable, contains reliability and quality criteria to protect optical fiber in all operating conditions. The criteria concentrate on conditions in an outside plant (OSP) environment. For the indoor plant, similar criteria are in Telcordia GR-409, Generic Requirements for Indoor Fiber Optic Cable.

Cable Types

This section needs expansion. You can help by adding to it. (June 2008)

  • OFC: Optical fiber, conductive
  • OFN: Optical fiber, nonconductive
  • OFCG: Optical fiber, conductive, general use
  • OFNG: Optical fiber, nonconductive, general use
  • OFCP: Optical fiber, conductive, plenum
  • OFNP: Optical fiber, nonconductive, plenum
  • OFCR: Optical fiber, conductive, riser
  • OFNR: Optical fiber, nonconductive, riser
  • OPGW: Optical fiber composite overhead ground wire
  • ADSS: All-Dielectric Self-Supporting
  • OSP: Fiber optic cable, outside plant
  • MDU: Fiber optics cable, multiple dwelling unit

Jacket Material

The jacket material is application specific. The material determines the mechanical robustness, aging due to UV radiation, oil resistance, etc. Nowadays PVC is being replaced by halogen free alternatives, mainly driven by more stringent regulations.


Fiber Material

There are two main types of material used for optical fibers: glass and plastic. They offer widely different characteristics and find uses in very different applications. Generally, plastic fiber is used for very short range and consumer applications, glass fiber is used for short/medium range (multi-mode) and long range (single-mode) telecommunications.

Color Coding

Patch Cords

The buffer or jacket on patchcords is often color-coded to indicate the type of fiber used. The strain relief “boot” that protects the fiber from bending at a connector is color-coded to indicate the type of connection. Connectors with a plastic shell (such as SC connectors) typically use a color-coded shell. Standard color codings for jackets (or buffers) and boots (or connector shells) are shown below:

Cord Jacket (or Buffer) Color


Connector Boot (or Shell) Colors


Remark: It is also possible that a small part of a connector is additionally color-coded, e.g. the lever of an E-2000 connector or a frame of an adapter. This additional colour coding indicates the correct port for a patchcord, if many patchcords are installed at one point.

Multi-fiber Cables

Individual fibers in a multi-fiber cable are often distinguished from one another by color-coded jackets or buffers on each fiber. The identification scheme used by Corning Cable Systems is based on EIA/TIA-598, “Optical Fiber Cable Color Coding.” EIA/TIA-598 defines identification schemes for fibers, buffered fibers, fiber units, and groups of fiber units within outside plant and premises optical fiber cables. This standard allows for fiber units to be identified by means of a printed legend. This method can be used for identification of fiber ribbons and fiber subunits. The legend will contain a corresponding printed numerical position number and/or color for use in identification.


The colour code used above resembles PE copper cables used in standard telephone wiring.

In the UK the colour codes for COF200 and 201 are different. Each 12 fibre bundle or element within a Cable Optical Fibre 200/201 cable is coloured as follows:

  • Blue
  • Orange
  • Green
  • Red
  • Grey
  • Yellow
  • Brown
  • Violet
  • Black
  • White
  • Pink
  • Turquoise

Each element is in a tube within the cable (not a blown fibre tube) The cable elements start with the red tube and are counted around the cable to the green tube. Active elements are in white tubes and yellow fillers or dummies are laid in the cable to fill it out depending on how many fibres and units exists – can be up to 276 fibres or 23 elements for external cable and 144 fibres or 12 elements for internal. The cable has a central strength member normally made from fiberglass or plastic. There is also a copper conductor in external cables.

Propagation Speed and Delay

Optical cables transfer data at the speed of light in glass. This is the speed of light in vacuum divided by the refractive index of the glass used, typically around 180,000 to 200,000 km/s, resulting in 5.0 to 5.5 microseconds of latency per km. Thus the round-trip delay time for 1000 km is around 11 milliseconds.


Typical modern multimode graded-index fibers have 3 dB/km of attenuation loss (50% loss per km) at 850 nm and 1 dB/km at 1300 nm. Singlemode 9/125 loses 0.4 dB/km at 1310 nm and 0.25 dB/km at 1550 nm. Very high quality singlemode fiber intended for long distance applications is specified at a loss of 0.19 dB/km at 1550 nm. POF (plastic optical fiber) loses much more: 1 dB/m at 650 nm. Plastic optical fiber is large core (about 1mm) fiber suitable only for short, low speed networks such as within cars.

Each connection made adds about 0.6 dB of average loss, and each joint (splice) adds about 0.1 dB. Depending on the transmitter power and the sensitivity of the receiver, if the total loss is too large the link will not function reliably.

Invisible IR light is used in commercial glass fiber communications because it has lower attenuation in such materials than visible light. However, the glass fibers will transmit visible light somewhat, which is convenient for simple testing of the fibers without requiring expensive equipment. Splices can be inspected visually, and adjusted for minimal light leakage at the joint, which maximizes light transmission between the ends of the fibers being joined.

The charts at “Understanding wavelengths In fiber optics” and “Optical power loss (attenuation) in fiber” illustrate the relationship of visible light to the IR frequencies used, and show the absorption water bands between 850, 1300 and 1550 nm.


The infrared light used in telecommunications cannot be seen, so there is a potential laser safety hazard to technicians. The eye’s natural defense against sudden exposure to bright light is the blink reflex, which is not triggered by infrared sources. In some cases the power levels are high enough to damage eyes, particularly when lenses or microscopes are used to inspect fibers that are emitting invisible infrared light. Inspection microscopes with optical safety filters are available to guard against this. More recently indirect viewing aids are used, which can comprise a camera mounted within a handheld device, which has an opening for the connectorized fiber and a USB output for connection to a display device such as a laptop. This makes the activity of looking for damage or dirt on the connector face much safer.

Small glass fragments can also be a problem if they get under someone’s skin, so care is needed to ensure that fragments produced when cleaving fiber are properly collected and disposed of appropriately.

Hybrid Cables

There are hybrid optical and electrical cables that are used in wireless outdoor Fiber To The Antenna (FTTA) applications. In these cables, the optical fibers carry information, and the electrical conductors are used to transmit power. These cables can be placed in several environments to serve antennas mounted on poles, towers, and other structures.

According to Telcordia GR-3173, Generic Requirements for Hybrid Optical and Electrical Cables for Use in Wireless Outdoor Fiber To The Antenna (FTTA) Applications, these hybrid cables have optical fibers, twisted pair/quad elements, coaxial cables and/or current-carrying electrical conductors under a common outer jacket. The power conductors used in these hybrid cables are for directly powering an antenna or for powering tower-mounted electronics exclusively serving an antenna. They have a nominal voltage normally less than 60 VDC or 108/120 VAC. Other voltages may be present depending on the application and the relevant National Electrical Code (NEC).

These types of hybrid cables may also be useful in other environments such as Distributed Antenna System (DAS) plants where they will serve antennas in indoor, outdoor, and roof-top locations. Considerations such as fire resistance, Nationally Recognized Testing Laboratory (NRTL) Listings, placement in vertical shafts, and other performance-related issues need to be fully addressed for these environments.

Since the voltage levels and power levels used within these hybrid cables vary, electrical safety codes consider the hybrid cable to be a power cable, which needs to comply with rules on clearance, separation, etc.


Innerducts are installed in existing underground conduit systems to provide clean, continuous, low-friction paths for placing optical cables that have relatively low pulling tension limits. They provide a means for subdividing conventional conduit that was originally designed for single, large-diameter metallic conductor cables into multiple channels for smaller optical cables.


Innerducts are typically small-diameter, semi-flexible subducts. According to Telcordia GR-356, there are three basic types of innerduct: smoothwall, corrugated, and ribbed. These various designs are based on the profile of the inside and outside diameters of the innerduct. The need for a specific characteristic or combination of characteristics, such as pulling strength, flexibility, or the lowest coefficient of friction, dictates the type of innerduct required.

Beyond the basic profiles or contours (smoothwall, corrugated, or ribbed), innerduct is also available in an increasing variety of multiduct designs. Multiduct may be either a composite unit consisting of up to four or six individual innerducts that are held together by some mechanical means, or a single extruded product having multiple channels through which to pull several cables. In either case, the multiduct is coilable, and can be pulled into existing conduit in a manner similar to that of conventional innerduct.


Innerducts are primarily installed in underground conduit systems that provide connecting paths between manhole locations. In addition to placement in conduit, innerduct can be directly buried, or aerially installed by lashing the innerduct to a steel suspension strand.

As stated in GR-356, cable is typically placed into innerduct in one of three ways. It may be

  1. Pre-installed by the innerduct manufacturer during the extrusion process,
  2. Pulled into the innerduct using a mechanically assisted pull line, or
  3. Blown into the innerduct using a high air volume cable blowing apparatus.

Fiber Optic Coupler

A fiber optic coupler is a device used in optical fiber systems with one or more input fibers and one or several output fibers. Light entering an input fiber can appear at one or more outputs and its power distribution potentially depending on the wavelength and polarization. Such couplers can be fabricated in different ways, for example by thermally fusing fibers so that their cores get into intimate contact. If all involved fibers are single-mode (supporting only a single mode per polarization direction for a given wavelength), there are certain physical restrictions on the performance of the coupler. In particular, it is not possible to combine two or more inputs of the same optical frequency into one single-polarization output without significant excess losses. However, such a restriction does not occur for different input wavelengths: there are couplers that can combine two inputs at different wavelengths into one output without exhibiting significant losses. Wavelength-sensitive couplers are used as multiplexers in wavelength-division multiplexing (WDM) telecom systems to combine several input channels with different wavelengths, or to separate channels.

Optical Power Meter


Optical power meter in use

An optical power meter (OPM) is a device used measure the power in an optical signal. The term usually refers to a device for testing average power in fiber optic systems. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power meters (can be photodiode sensors or thermopile laser sensors), light meters or lux meters.

A typical optical power meter consists of a calibrated sensor, measuring amplifier and display. The sensor primarily consists of a photodiode selected for the appropriate range of wavelengths and power levels. On the display unit, the measured optical power and set wavelength is displayed. Power meters are calibrated using a traceable calibration standard such as a NIST standard.

A traditional optical power meter responds to a broad spectrum of light, however the calibration is wavelength dependent. This is not normally an issue, since the test wavelength is usually known, however it has a couple of drawbacks. Firstly, the user must set the meter to the correct test wavelength, and secondly if there are other spurious wavelengths present, then wrong readings will result.

Sometimes optical power meters are combined with a different test function such as an Optical Light Source (OLS) or Visual Fault Locator (VFL), or may be a sub-system in a much larger instrument. When combined with a light source, the instrument is usually called an Optical Loss Test Set.

Optical Loss Test Sets (OLTS) are available in dedicated hand held instruments and platform-based modules to suit various network architectures and test requirements. They are used to measure optical power and power loss, and reflectance and reflected power loss. The products may also be used as optical sources or optical power meters, or to measure optical return loss or event reflectance.

Three types of equipment can be used to measure optical power loss:

  1. Component equipmentOptical Power Meters (OPMs) and Stabilized Light Sources (SLSs) are packaged separately, but when used together they can provide a measurement of end-to-end optical attenuation over an optical path. Such component equipment can also be used for other measurements.
  2. Integrated test set – When an SLS and OPM are packaged in one unit, it is called an integrated test set. Traditionally, an integrated test set is usually called an OLTS. GR-198, Generic Requirements for Hand-Held Stabilized Light Sources, Optical Power Meters, Reflectance Meters, and Optical Loss Test Sets, discusses OLTS equipment in depth.
  3. An Optical Time Domain Reflectometer (OTDR) can be used to measure optical link loss if its markers are set at the terminus points for which the fiber loss is desired. However a single-direction measurement may not be accurate if there are multiple fibers in a link, since the back-scatter coefficient is variable between fibers. The accuracy of such a measurement can be increased if the measurement is made as a bidirectional average of the fiber. GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment, discusses OTDR equipment in depth.

Optical Time-Domain Reflectometer (OTDR)




An OTDR in use

An Optical Time-Domain Reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. An OTDR is the optical equivalent of an electronic time domain reflectometer. It injects a series of optical pulses into the fiber under test and extracts, from the same end of the fiber, light that is scattered (Rayleigh backscatter) or reflected back from points along the fiber. The scattered or reflected light that is gathered back is used to characterize the optical fiber. This is equivalent to the way that an electronic time-domain meter measures reflections caused by changes in the impedance of the cable under test. The strength of the return pulses is measured and integrated as a function of time, and plotted as a function of fiber length.

Parallel Optical Interface

A Parallel Optical Interface is a form of fiber optic technology aimed primarily at communications and networking over relatively short distances (less than 300 meters), and at high bandwidths.

Parallel optic interfaces differ from traditional fiber optic communication in that data is simultaneously transmitted and received over multiple fibers. Different methods exist for splitting the data over this high bandwidth link. In the simplest form, the parallel optic link is a replacement for many serial data communication links. In the more typical application, one byte of information is split up into bits and each bit is coded and sent across the individual fibers. Needless to say, there are many ways to perform this multiplexing provided the fundamental coding at the fiber level meets the channel requirement.

The main applications for parallel optical interfaces are found in telecommunications and supercomputers, also being introduced to consumer applications. It displaces copper backplanes that are commonly used for large switching equipment design.

There are two forms of commercially available products for parallel optic interfaces. The first is a twelve channel system consisting of an optical transmitter and an optical receiver. The second is a four channel transceiver product that is capable of transmitting four channels and receiving four channels in one product.

Parallel optics is often the most cost effective solution for getting 40 Gigabit per second transmission of data over distances exceeding 100 meters. 100GE Optical Transceiver comes with 100 Gigabit of data transmit. Data is delivered in both duplex and parallel mechanism with 100GE.



Coaxial Cable

From Wikipedia, the free encyclopedia


RG-59 flexible coaxial cable composed of:

A. Outer plastic sheath
B. Woven copper shield
C. Inner dielectric insulator
D. Copper core

Coaxial cable, or coax (pronounced /ˈkoʊ.æks/), is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who patented the design in 1880. Coaxial cable differs from other shielded cables because the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line.


Oliver Heaviside invented coaxial cable in 1880

1 Applications
2 Description
3 Construction
4 Signal propagation
5 Connectors
6 Important parameters
6.1 Physical parameters
6.2 Fundamental electrical parameters
6.3 Derived electrical parameters
6.4 Choice of impedance
7 Issues
7.1 Signal leakage
7.2 Ground loops
7.3 Noise
7.3.1 Transformer effect
7.4 Common mode current and radiation
8 Standards
9 Uses
10 Types
10.1 Hard line
10.2 Radiating
10.3 RG-6
10.4 Triaxial cable
10.5 Twin-axial cable
10.6 Semi-rigid
10.7 Rigid line
10.8 Cables used in the UK
11 Interference and troubleshooting
12 History


Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network (Internet) connections, digital audio (S/PDIF), and distributing cable television signals. 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. 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. Coaxial cable also provides protection of the signal from external electromagnetic interference.



Coaxial cable cutaway (not to scale)

Coaxial cable conducts electrical signal 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. The cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. The advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable. Larger diameter cables and cables with multiple shields have less leakage. This property makes coaxial cable a good choice for carrying weak signals that cannot tolerate interference from the environment or for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits.

Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections.

The characteristic impedance of the cable ( {\displaystyle Z_{0}} Z_{0}) is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer and minimum standing wave ratio. Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality.


Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. The inner conductor might be solid or stranded; stranded is more flexible. To get better high-frequency performance, the inner conductor may be silver-plated. Copper-plated steel wire is often used as an inner conductor for cable used in the cable TV industry.

The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of the dielectric insulator determine some of the electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE) is also used as an insulator. Some coaxial lines use air (or some other gas) and have spacers to keep the inner conductor from touching the shield.

Many conventional coaxial cables use braided copper wire forming the shield. 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. Sometimes the braid is silver-plated. For better shield performance, some cables have a double-layer shield. The shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as “quad-shield”, which uses four alternating layers of foil and braid. Other shield designs sacrifice flexibility for better performance; some shields are a solid metal tube. Those cables cannot be bent sharply, as the shield will kink, causing losses in the cable. When a foil shield is used a small wire conductor incorporated into the foil makes soldering the shield termination easier.

For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor is corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. One brand name for such cable is Heliax.

Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield. The dielectric losses increase in this order: Ideal dielectric (no loss), vacuum, air, polytetrafluoroethylene (PTFE), polyethylene foam, and solid polyethylene. A low relative permittivity allows for higher-frequency usage. An inhomogeneous dielectric needs to be compensated by a non-circular conductor to avoid current hot-spots.

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. Foam coax will have about 15% less attenuation but some types of foam dielectric can absorb moisture—especially at its many surfaces — in humid environments, significantly increasing the loss. Supports shaped like stars or spokes are even better but more expensive and very susceptible to moisture infiltration. Still more expensive were the air-spaced coaxials used for some inter-city communications in the mid-20th century. The center conductor was suspended by polyethylene discs every few centimeters. In some low-loss coaxial cables such as the RG-62 type, the inner conductor is supported by a spiral strand of polyethylene, so that an air space exists between most of the conductor and the inside of the jacket. 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. Inner conductors are sometimes silver-plated to smooth the surface and reduce losses due to skin effect. A rough surface prolongs the path for the current and concentrates the current at peaks and, thus, increases ohmic losses.

The insulating jacket can be made from many materials. A common choice is PVC, but some applications may require fire-resistant materials. Outdoor applications may require the jacket resist ultraviolet light, oxidation, rodent damage, or direct burial. Flooded coaxial cables use a water blocking gel to protect the cable from water infiltration through minor cuts in the jacket. For internal chassis connections the insulating jacket may be omitted.

Signal Propagation

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Twin-lead transmission lines have the property that the electromagnetic wave propagating down the line extends into the space surrounding the parallel wires. These lines have low loss, but also have undesirable characteristics. They cannot be bent, tightly twisted, or otherwise shaped without changing their characteristic impedance, causing reflection of the signal back toward the source. They also cannot be buried or run along or attached to anything conductive, as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line. Coaxial lines largely solve this problem by confining virtually all of the electromagnetic wave to the area inside the cable. Coaxial lines can therefore be bent and moderately twisted without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

In radio-frequency applications up to a few gigahertz, the wave propagates primarily in the transverse electric magnetic (TEM) mode, which means that the electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain cutoff frequency, transverse electric (TE) or transverse magnetic (TM) modes can also propagate, as they do in a waveguide. It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other. The outer diameter is roughly inversely proportional to the cutoff frequency. A propagating surface-wave mode that does not involve or require the outer shield but only a single central conductor also exists in coax but this mode is effectively suppressed in coax of conventional geometry and common impedance. Electric field lines for this [TM] mode have a longitudinal component and require line lengths of a half-wavelength or longer.

Coaxial cable may be viewed as a type of waveguide. Power is transmitted through the radial electric field and the circumferential magnetic field in the TEM00 transverse mode. This is the dominant mode from zero frequency (DC) to an upper limit determined by the electrical dimensions of the cable.




A male F-type connector used with common RG-6 cable


A male N-type connector

The ends of coaxial cables usually terminate with connectors. Coaxial connectors are designed to maintain a coaxial form across the connection and have the same impedance as the attached cable. Connectors are usually plated with high-conductivity metals such as silver or tarnish-resistant gold. Due to the skin effect, the RF signal is only carried by the plating at higher frequencies and does not penetrate to the connector body. Silver however tarnishes quickly and the silver sulfide that is produced is poorly conductive, degrading connector performance, making silver a poor choice for this application.

Important Parameters

Coaxial cable is a particular kind of transmission line, so the circuit models developed for general transmission lines are appropriate. See Telegrapher’s equation.


Schematic representation of the elementary components of a transmission line.


Schematic representation of a coaxial transmission line, showing the characteristic impedance {\displaystyle Z_{0}} Z_{0}.

Physical Parameters

In the following section, these symbols are used:

  • Length of the cable, {\displaystyle h} h.
  • Outside diameter of inner conductor, {\displaystyle d} d.
  • Inside diameter of the shield, {\displaystyle D} D.
  • Dielectric constant of the insulator, {\displaystyle \epsilon } \epsilon . The dielectric constant is often quoted as the relative dielectric constant {\displaystyle \epsilon _{r}} \epsilon_r referred to the dielectric constant of free space {\displaystyle \epsilon _{0}} \epsilon _{0}: {\displaystyle \epsilon =\epsilon _{r}\epsilon _{0}} \epsilon = \epsilon_r \epsilon_0. When the insulator is a mixture of different dielectric materials (e.g., polyethylene foam is a mixture of polyethylene and air), then the term effective dielectric constant {\displaystyle \epsilon _{eff}} \epsilon _{{eff}} is often used.
  • Magnetic permeability of the insulator, {\displaystyle \mu } \mu . Permeability is often quoted as the relative permeability {\displaystyle \mu _{r}} \mu _{r} referred to the permeability of free space {\displaystyle \mu _{0}} \mu _{0}: {\displaystyle \mu =\mu _{r}\mu _{0}} \mu =\mu _{r}\mu _{0}. The relative permeability will almost always be 1.

Fundamental Electrical Parameters

Shunt capacitance per unit length, in farads per metre.


Series inductance per unit length, in henrys per metre.


  • Series resistance per unit length, in ohms per metre. The resistance per unit length is just the resistance of inner conductor and the shield at low frequencies. At higher frequencies, skin effect increases the effective resistance by confining the conduction to a thin layer of each conductor.
  • Shunt conductance per unit length, in siemens per metre. The shunt conductance is usually very small because insulators with good dielectric properties are used (a very low loss tangent). At high frequencies, a dielectric can have a significant resistive loss.

Derived Electrical Parameters

  • Characteristic impedance in ohms (Ω). The complex impedance Z of an infinite length of transmission line is:


Where R is the resistance per unit length, L is the inductance per unit length, G is the conductance per unit length of the dielectric, C is the capacitance per unit length, and s = jω = j2πf is the frequency. The “per unit length” dimensions cancel out in the impedance formula. At very low frequencies (s≈0), the two reactive terms are negligible, so the impedance is real-valued and looks like

With increasing frequency, the reactive components take effect and the impedance of the line is complex-valued. At higher frequences, the reactive terms usually dominate R and G, and the cable impedance again becomes real-valued. That value is Z0, the characteristic impedance of the cable:


Assuming the dielectric properties of the material inside the cable do not vary appreciably over the operating range of the cable, the characteristic impedance is frequency independent above about five times the shield cutoff frequency. For typical coaxial cables, the shield cutoff frequency is 600 (RG-6A) to 2,000 Hz (RG-58C).

The parameters L and C are determined from the ratio of the inner (d) and outer (D) diameters and the dielectric constant (ε). The characteristic impedance is given by


  • Attenuation (loss) per unit length, in decibels per meter. This is dependent on the loss in the dielectric material filling the cable, and resistive losses in the center conductor and outer shield. These losses are frequency dependent, the losses becoming higher as the frequency increases. Skin effect losses in the conductors can be reduced by increasing the diameter of the cable. A cable with twice the diameter will have half the skin effect resistance. Ignoring dielectric and other losses, the larger cable would halve the dB/meter loss. In designing a system, engineers consider not only the loss in the cable but also the loss in the connectors.
  • Velocity of propagation, in meters per second. The velocity of propagation depends on the dielectric constant and permeability (which is usually 1).


  • Single-mode band. In coaxial cable, the dominant mode (the mode with the lowest cutoff frequency) is the TEM mode, which has a cutoff frequency of zero; it propagates all the way down to d.c. The mode with the next lowest cutoff is the TE11 mode. This mode has one ‘wave’ (two reversals of polarity) in going around the circumference of the cable. To a good approximation, the condition for the TE11 mode to propagate is that the wavelength in the dielectric is no longer than the average circumference of the insulator; that is that the frequency is at least
    Hence, the cable is single-mode from to d.c. up to this frequency, and might in practice be used up to 90% of this frequency.
  • Peak Voltage. The peak voltage is set by the breakdown voltage of the insulator. One website gives:
    Smils is the insulator’s breakdown voltage in volts per mil
    din is the inner diameter in inches
    The 1150 factor converts inches (diameter) to mils (radius) and log10 to ln.
    The above expression may be rewritten as
    S is the insulator’s breakdown voltage in volts per meter
    d is the inner diameter in meters
    The calculated peak voltage is often reduced by a safety factor.

Choice of Impedance

The best coaxial cable impedances in high-power, high-voltage, and low-attenuation applications were experimentally determined at Bell Laboratories in 1929 to be 30, 60, and 77 Ω, respectively. For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give a characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the best-loss impedance drops down to a value between 52–64 Ω. Maximum power handling is achieved at 30 Ω.

The approximate impedance required to match a centre-fed dipole antenna in free space (i.e., a dipole without ground reflections) is 73 Ω, so 75 Ω coax was commonly used for connecting shortwave antennas to receivers. These typically involve such low levels of RF power that power-handling and high-voltage breakdown characteristics are unimportant when compared to attenuation. Likewise with CATV, although many broadcast TV installations and CATV headends use 300 Ω folded dipole antennas to receive off-the-air signals, 75 Ω coax makes a convenient 4:1 balun transformer for these as well as possessing low attenuation.

The arithmetic mean between 30 Ω and 77 Ω is 53.5 Ω; the geometric mean is 48 Ω. The selection of 50 Ω as a compromise between power-handling capability and attenuation is in general cited as the reason for the number. 50 Ω also works out tolerably well because it corresponds approximately to the drive impedance (ideally 36 ohms) of a quarter-wave monopole, mounted on a less than optimum ground plane such as a vehicle roof. The match is better at low frequencies, such as for CB Radio around 27 MHz, where the roof dimensions are much less than a quarter wavelength, and relatively poor at higher frequencies, VHF and UHF, where the roof dimensions may be several wavelengths. The match is at best poor, because the antenna drive impedance, due to the imperfect ground plane, is reactive rather than purely resistive, and so a 36 ohm coaxial cable would not match properly either. Installations which need exact matching will use some kind of matching circuit at the base of the antenna, or elsewhere, in conjunction with a carefully chosen (in terms of wavelength) length of coaxial, such that a proper match is achieved, which will be only over a fairly narrow frequency range.

RG-62 is a 93 Ω coaxial cable originally used in mainframe computer networks in the 1970s and early 1980s (it was the cable used to connect IBM 3270 terminals to IBM 3274/3174 terminal cluster controllers). Later, some manufacturers of LAN equipment, such as Datapoint for ARCNET, adopted RG-62 as their coaxial cable standard. The cable has the lowest capacitance per unit-length when compared to other coaxial cables of similar size. Capacitance is the enemy of square-wave data transmission (in particular, it slows down edge transitions), and this is a much more important factor for baseband digital data transmission than power handling or attenuation.

All of the components of a coaxial system should have the same impedance to avoid internal reflections at connections between components. Such reflections may cause signal attenuation and ghosting TV picture display; multiple reflections may cause the original signal to be followed by more than one echo. In analog video or TV systems, this causes ghosting in the image. Reflections also introduce standing waves, which cause increased losses and can even result in cable dielectric breakdown with high-power transmission (see Impedance matching). Briefly, if a coaxial cable is open, the termination has nearly infinite resistance, this causes reflections; if the coaxial cable is short-circuited, the termination resistance is nearly zero, there will be reflections with the opposite polarity. Reflection will be nearly eliminated if the coaxial cable is terminated in a pure resistance equal to its impedance.


Signal Leakage

Signal leakage is the passage of electromagnetic fields through the shield of a cable and occurs in both directions. Ingress is the passage of an outside signal into the cable and can result in noise and disruption of the desired signal. Egress is the passage of signal intended to remain within the cable into the outside world and can result in a weaker signal at the end of the cable and radio frequency interference to nearby devices. Severe leakage usually results from improperly installed connectors or faults in the cable shield.

For example, in the United States, signal leakage from cable television systems is regulated by the FCC, since cable signals use the same frequencies as aeronautical and radionavigation bands. CATV operators may also choose to monitor their networks for leakage to prevent ingress. Outside signals entering the cable can cause unwanted noise and picture ghosting. Excessive noise can overwhelm the signal, making it useless.

An ideal shield would be a perfect conductor with no holes, gaps, or bumps connected to a perfect ground. However, a smooth solid highly conductive shield would be heavy, inflexible, and expensive. Such coax is used for straight line feeds to commercial radio broadcast towers. More economical cables must make compromises between shield efficacy, flexibility, and cost, such as the corrugated surface of flexible hardline, flexible braid, or foil shields. Since shields cannot be perfect conductors, current flowing on the inside of the shield produces an electromagnetic field on the outer surface of the shield.

Consider the skin effect. The magnitude of an alternating current in a conductor decays exponentially with distance beneath the surface, with the depth of penetration being proportional to the square root of the resistivity. This means that, in a shield of finite thickness, some small amount of current will still be flowing on the opposite surface of the conductor. With a perfect conductor (i.e., zero resistivity), all of the current would flow at the surface, with no penetration into and through the conductor. Real cables have a shield made of an imperfect, although usually very good, conductor, so there must always be some leakage.

The gaps or holes, allow some of the electromagnetic field to penetrate to the other side. For example, braided shields have many small gaps. The gaps are smaller when using a foil (solid metal) shield, but there is still a seam running the length of the cable. Foil becomes increasingly rigid with increasing thickness, so a thin foil layer is often surrounded by a layer of braided metal, which offers greater flexibility for a given cross-section.

Signal leakage can be severe if there is poor contact at the interface to connectors at either end of the cable or if there is a break in the shield.

To greatly reduce signal leakage into or out of the cable, by a factor of 1000, or even 10,000, superscreened cables are often used in critical applications, such as for neutron flux counters in nuclear reactors.

Superscreened cables for nuclear use are defined in IEC 96-4-1, 1990, however as there have been long gaps in the construction of nuclear power stations in Europe, many existing installations are using superscreened cables to the UK standard AESS(TRG) 71181 which is referenced in IEC 61917.

Ground Loops

A continuous current, even if small, along the imperfect shield of a coaxial cable can cause visible or audible interference. In CATV systems distributing analog signals the potential difference between the coaxial network and the electrical grounding system of a house can cause a visible “hum bar” in the picture. This appears as a wide horizontal distortion bar in the picture that scrolls slowly upward. Such differences in potential can be reduced by proper bonding to a common ground at the house. See ground loop.


External fields create a voltage across the inductance of the outside of the outer conductor between sender and receiver. The effect is less when there are several parallel cables, as this reduces the inductance and, therefore, the voltage. Because the outer conductor carries the reference potential for the signal on the inner conductor, the receiving circuit measures the wrong voltage.

Transformer Effect

The transformer effect is sometimes used to mitigate the effect of currents induced in the shield. The inner and outer conductors form the primary and secondary winding of the transformer, and the effect is enhanced in some high-quality cables that have an outer layer of mu-metal. Because of this 1:1 transformer, the aforementioned voltage across the outer conductor is transformed onto the inner conductor so that the two voltages can be cancelled by the receiver. Many sender and receivers have means to reduce the leakage even further. They increase the transformer effect by passing the whole cable through a ferrite core one or more times.

Common Mode Current and Radiation

Common mode current occurs when stray currents in the shield flow in the same direction as the current in the center conductor, causing the coax to radiate.

Most of the shield effect in coax results from opposing currents in the center conductor and shield creating opposite magnetic fields that cancel, and thus do not radiate. The same effect helps ladder line. However, ladder line is extremely sensitive to surrounding metal objects, which can enter the fields before they completely cancel. Coax does not have this problem, since the field is enclosed in the shield. However, it is still possible for a field to form between the shield and other connected objects, such as the antenna the coax feeds. The current formed by the field between the antenna and the coax shield would flow in the same direction as the current in the center conductor, and thus not be canceled. Energy would radiate from the coax itself, affecting the radiation pattern of the antenna. With sufficient power this could be a hazard to people near the cable. A properly placed and properly sized balun can prevent common mode radiation in coax. An isolating transformer or blocking capacitor can be used to couple a coaxial cable to equipment, where it is desirable to pass radio-frequency signals but to block direct current or low-frequency power.


Most coaxial cables have a characteristic impedance of either 50, 52, 75, or 93 Ω. The RF industry uses standard type-names for coaxial cables. Thanks to television, RG-6 is the most commonly used coaxial cable for home use, and the majority of connections outside Europe are by F connectors.

A series of standard types of coaxial cable were specified for military uses, in the form “RG-#” or “RG-#/U”. They date from World War II and were listed in MIL-HDBK-216 published in 1962. These designations are now obsolete. The RG designation stands for Radio Guide; the U designation stands for Universal. The current military standard is MIL-SPEC MIL-C-17. MIL-C-17 numbers, such as “M17/75-RG214”, are given for military cables and manufacturer’s catalog numbers for civilian applications. However, the RG-series designations were so common for generations that they are still used, although critical users should be aware that since the handbook is withdrawn there is no standard to guarantee the electrical and physical characteristics of a cable described as “RG-# type”. The RG designators are mostly used to identify compatible connectors that fit the inner conductor, dielectric, and jacket dimensions of the old RG-series cables.


Dielectric material codes

  • FPE is foamed polyethylene
  • PE is solid polyethylene
  • PF is polyethylene foam
  • PTFE is polytetrafluoroethylene;
  • ASP is air space polyethylene

VF is the Velocity Factor; it is determined by the effective {\displaystyle \epsilon _{r}} \epsilon_r and {\displaystyle \mu _{r}} \mu _{r}

  • VF for solid PE is about 0.66
  • VF for foam PE is about 0.78 to 0.88
  • VF for air is about 1.00
  • VF for solid PTFE is about 0.70
  • VF for foam PTFE is about 0.84

There are also other designation schemes for coaxial cables such as the URM, CT, BT, RA, PSF and WF series.


RG-6 Coaxial cable


RG-142 Coaxial cable


RG-405 semi-rigid coaxial cable


High-end coaxial audio cable (S/PDIF)


Short coaxial cables are commonly used to connect home video equipment, in ham radio setups, and in measurement electronics. While formerly common for implementing computer networks, in particular Ethernet (“thick” 10BASE5 and “thin” 10BASE2), twisted pair cables have replaced them in most applications except in the growing consumer cable modem market for broadband Internet access.

Long distance coaxial cable was used in the 20th century to connect radio networks, television networks, and Long Distance telephone networks though this has largely been superseded by later methods (fibre optics, T1/E1, satellite).

Shorter coaxials still carry cable television signals to the majority of television receivers, and this purpose consumes the majority of coaxial cable production. In 1980s and early 1990s coaxial cable was also used in computer networking, most prominently in Ethernet networks, where it was later in late 1990s to early 2000s replaced by UTP cables in North America and STP cables in Western Europe, both with 8P8C modular connectors.

Micro coaxial cables are used in a range of consumer devices, military equipment, and also in ultra-sound scanning equipment.

The most common impedances that are widely used are 50 or 52 ohms, and 75 ohms, although other impedances are available for specific applications. The 50 / 52 ohm cables are widely used for industrial and commercial two-way radio frequency applications (including radio, and telecommunications), although 75 ohms is commonly used for broadcast television and radio.

Coax cable is often used to carry data/signals from an antenna to a receiver—from a satellite dish to a satellite receiver, from a television antenna to a television receiver, from a radio mast to a radio receiver, etc. In many cases, the same single coax cable carries power in the opposite direction, to the antenna, to power the low-noise amplifier. In some cases a single coax cable carries (unidirectional) power and bidirectional data/signals, as in DiSEqC.


Hard Line


1 5⁄8 in (41 mm) flexible line


1-5/8″ Heliax coaxial cable

Hard line is used in broadcasting as well as many other forms of radio communication. It is a coaxial cable constructed using round copper, silver or gold tubing or a combination of such metals as a shield. Some lower-quality hard line may use aluminum shielding, aluminum however is easily oxidized and unlike silver oxide, aluminum oxide drastically loses effective conductivity. Therefore, all connections must be air and water tight. The center conductor may consist of solid copper, or copper-plated aluminum.

ince skin effect is an issue with RF, copper plating provides sufficient surface for an effective conductor. Most varieties of hardline used for external chassis or when exposed to the elements have a PVC jacket; however, some internal applications may omit the insulation jacket. Hard line can be 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.

These large-scale hard lines are almost always used in the connection between a transmitter on the ground and the antenna or aerial on a tower. Hard line may also be known by trademarked names such as Heliax (CommScope), or Cablewave (RFS/Cablewave). Larger varieties of hardline may have a center conductor that is constructed from either rigid or corrugated copper tubing.

The dielectric in hard line may consist of polyethylene foam, air, or a pressurized gas such as nitrogen or desiccated air (dried air). In gas-charged lines, hard plastics such as nylon are used as spacers to separate the inner and outer conductors.

The addition of these gases into the dielectric space reduces moisture contamination, provides a stable dielectric constant, and provides a reduced risk of internal arcing. Gas-filled hardlines are usually used on high-power RF transmitters such as television or radio broadcasting, military transmitters, and high-power amateur radio applications but may also be used on some critical lower-power applications such as those in the microwave bands.

However, in the microwave region, waveguide is more often used than hard line for transmitter-to-antenna, or antenna-to-receiver applications. The various shields used in hardline also differ; some forms use rigid tubing, or pipe, others may use a corrugated tubing, which makes bending easier, as well as reduces kinking when the cable is bent to conform. Smaller varieties of hard line may be used internally in some high-frequency applications, in particular in equipment within the microwave range, to reduce interference between stages of the device.


Radiating or leaky cable is another form of coaxial cable which is constructed in a similar fashion to hard line, however it is constructed with tuned slots cut into the shield. These slots are tuned to the specific RF wavelength of operation or tuned to a specific radio frequency band. This type of cable is to provide a tuned bi-directional “desired” leakage effect between transmitter and receiver. It is often used in elevator shafts, US Navy Ships, underground transportation tunnels and in other areas where an antenna is not feasible. One example of this type of cable is Radiax (CommScope).


RG-6 is available in four different types designed for various applications. In addition, the core may be copper clad steel (CCS) or bare solid copper (BC). “Plain” or “house” RG-6 is designed for indoor or external house wiring. “Flooded” cable is infused with waterblocking gel for use in underground conduit or direct burial. “Messenger” may contain some waterproofing but is distinguished by the addition of a steel messenger wire along its length to carry the tension involved in an aerial drop from a utility pole. “Plenum” cabling is expensive and comes with a special Teflon-based outer jacket designed for use in ventilation ducts to meet fire codes. It was developed since the plastics used as the outer jacket and inner insulation in many “Plain” or “house” cabling gives off poison gas when burned.

Triaxial Cable

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

Twin-axial Cable

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.



Semi-Rigid coax assembly


Semi-Rigid coax installed in an Agilent N9344C 20GHz spectrum analyser

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. (See “hard line”)

Conformable cable is a flexible reformable alternative to semi-rigid coaxial cable used where flexibility is required. Conformable cable can be stripped and formed by hand without the need for specialized tools, similar to standard coaxial cable.

Rigid Line

Rigid line is a coaxial line formed by two copper tubes maintained concentric every other meter using PTFE-supports. Rigid lines can not be bent, so they often need elbows. Interconnection with rigid line is done with an inner bullet/inner support and a flange or connection kit. Typically rigid lines are connected using standardised EIA RF Connectors whose bullet and flange sizes match the standard line diameters, for each outer diameter either 75 or 50ohm inner tubes can be obtained. Rigid line is commonly used indoors for interconnection between high power transmitters and other RF-components, but more rugged rigid line with weatherproof flanges is used outdoors on antenna masts, etc. In the interests of saving weight and costs, on masts and similar structures the outer line is often aluminium, and special care must be taken to prevent corrosion. With a flange connector it is also possible to go from rigid line to hard line. Many broadcasting antennas and antenna splitters use the flanged rigid line interface even when connecting to flexible coaxial cables and hard line. Rigid line is produced in a number of different sizes:


Cables used in the UK

At the start of analogue satellite TV broadcasts in the UK by BskyB, a 75 ohm cable referred to as RG6 was used. This cable had a 1 mm copper core, air-spaced polyethylene dielectric and copper braid on an aluminium foil shield. When installed outdoors without protection, the cable was affected by UV radiation, which cracked the PVC outer sheath and allowed moisture ingress. The combination of copper, aluminium, moisture and air caused rapid corrosion, sometimes resulting in a ‘snake swallowed an egg’ appearance. Consequently, despite the higher cost, the RG6 cable was dropped in favour of CT100 when BSKYB launched its digital broadcasts.

From around 1999 to 2005 (when CT100 manufacturer Raydex went out of business), CT100 remained the 75 ohm cable of choice for satellite TV and especially BskyB. It had an air-spaced polyethylene dielectric, a 1 mm solid copper core and copper braid on copper foil shield. CT63 was a thinner cable in ‘shotgun’ style, meaning that it was two cables moulded together and was used mainly by BskyB for the twin connection required by the Sky+ satellite TV receiver, which incorporated a hard drive recording system and a second, independent tuner.

In 2005, these cables were replaced by WF100 and WF65, respectively, manufactured by Webro and having a similar construction but a foam dielectric that provided the same electrical performance as air-spaced but was more robust and less likely to be crushed.

At the same time, with the price of copper steadily rising, the original RG6 was dropped in favour of a construction that used a copper-clad steel core and aluminium braid on aluminium foil. Its lower price made it attractive to aerial installers looking for a replacement for the so-called low-loss cable traditionally used for UK terrestrial aerial installations. This cable had been manufactured with a decreasing number of strands of braid, as the price of copper increased, such that the shielding performance of cheaper brands had fallen to as low as 40 percent. With the advent of digital terrestrial transmissions in the UK, this low-loss cable was no longer suitable.

The new RG6 still performed well at high frequencies because of the skin effect in the copper cladding. However, the aluminium shield had a high DC resistance and the steel core an even higher one. The result is that this type of cable could not reliably be used in satellite TV installations, where it was required to carry a significant amount of current, because the voltage drop affected the operation of the low noise block downconverter (LNB) on the dish.

A problem with all the aforementioned cables, when passing current, is that electrolytic corrosion can occur in the connections unless moisture and air are excluded. Consequently, various solutions to exclude moisture have been proposed. The first was to seal the connection by wrapping it with self-amalgamating rubberised tape, which bonds to itself when activated by stretching. The second proposal, by the American Channel Master company (now owned by Andrews corp.) at least as early as 1999, was to apply silicone grease to the wires making connection. The third proposal was to fit a self-sealing plug to the cable. All of these methods are reasonably successful if implemented correctly.

Interference and Troubleshooting

Coaxial cable insulation may degrade, requiring replacement of the cable, especially if it has been exposed to the elements on a continuous basis. The shield is normally grounded, and if even a single thread of the braid or filament of foil touches the center conductor, the signal will be shorted causing significant or total signal loss. This most often occurs at improperly installed end connectors and splices. Also, the connector or splice must be properly attached to the shield, as this provides the path to ground for the interfering signal.

Despite being shielded, interference can occur on coaxial cable lines. Susceptibility to interference has little relationship to broad cable type designations (e.g. RG-59, RG-6) but is strongly related to the composition and configuration of the cable’s shielding. For cable television, with frequencies extending well into the UHF range, a foil shield is normally provided, and will provide total coverage as well as high effectiveness against high-frequency interference. Foil shielding is ordinarily accompanied by a tinned copper or aluminum braid shield, with anywhere from 60 to 95% coverage. The braid is important to shield effectiveness because (1) it is more effective than foil at preventing low-frequency interference, (2) it provides higher conductivity to ground than foil, and (3) it makes attaching a connector easier and more reliable. “Quad-shield” cable, using two low-coverage aluminum braid shields and two layers of foil, is often used in situations involving troublesome interference, but is less effective than a single layer of foil and single high-coverage copper braid shield such as is found on broadcast-quality precision video cable.

In the United States and some other countries, cable television distribution systems use extensive networks of outdoor coaxial cable, often with in-line distribution amplifiers. Leakage of signals into and out of cable TV systems can cause interference to cable subscribers and to over-the-air radio services using the same frequencies as those of the cable system.



Early coaxial antenna feedline of 50 kW radio station WNBC, New York, in 1930s


AT&T coaxial cable trunkline installed between East Coast and Midwest in 1948.

  • Each of the 8 coaxial subcables could carry 480 telephone calls or one television channel.
  • 1880 — Coaxial cable patented in England by Oliver Heaviside, patent no. 1,407.
  • 1884 — Siemens & Halske patent coaxial cable in Germany (Patent No. 28,978, 27 March 1884).
  • 1929 — First modern coaxial cable patented by Lloyd Espenschied and Herman Affel of AT&T’s Bell Telephone Laboratories.
  • 1936 — First closed circuit transmission of TV pictures on coaxial cable, from the
  • 1936 Summer Olympics in Berlin to Leipzig.
  • 1936 — World’s first underwater coaxial cable installed between Apollo Bay, near Melbourne, Australia, and Stanley, Tasmania. The 300 km cable can carry one 8.5-kHz broadcast channel and seven telephone channels.
  • 1936 — AT&T installs experimental coaxial telephone and television cable between New York and Philadelphia, with automatic booster stations every ten miles.
  • Completed in December, it can transmit 240 telephone calls simultaneously.
    1936 — Coaxial cable laid by the General Post Office (now BT) between London and
  • Birmingham, providing 40 telephone channels.
  • 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.
  • 1949 — On January 11, eight stations on the US East Coast and seven Midwestern stations are linked via a long-distance coaxial cable.
  • 1956 — First transatlantic coaxial cable laid, TAT-1.

Twisted Pair

From Wikipedia, the free encyclopedia


Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell.

1 Explanation
2 History
3 Unshielded twisted pair
4 Cable shielding
5 Common types
6 Solid-core cable vs. stranded cable
7 Advantages
8 Disadvantages
9 Less common variants


In a balanced line operation, the two wires carry equal and opposite signals, and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is canceled at the receiver when the difference signal is taken.

This method starts to fail when the noise source is close to the signal wires; the closer wire will couple with the noise more strongly and the common-mode rejection of the receiver will fail to eliminate it. This problem is especially apparent in telecommunication cables where pairs in the same cable lie next to each other for many miles. One pair can induce crosstalk in another and it is additive along the length of the cable. Twisting the pairs counters this effect as on each half twist the wire nearest to the noise-source is exchanged.

Providing the interfering source remains uniform, or nearly so, over the distance of a single twist, the induced noise will remain common-mode. Differential signaling also reduces electromagnetic radiation from the cable, along with the associated attenuation allowing for greater distance between exchanges.

The twist rate (also called pitch of the twist, usually defined in twists per meter) makes up part of the specification for a given type of cable. When nearby pairs have equal twist rates, the same conductors of the different pairs may repeatedly lie next to each other, partially undoing the benefits of differential mode. For this reason it is commonly specified that, at least for cables containing small numbers of pairs, the twist rates must differ.

In contrast to shielded or foiled twisted pair (typically F/UTP or S/FTP cable shielding), UTP (unshielded twisted pair) cable is not surrounded by any shielding. UTP is the primary wire type for telephone usage and is very common for computer networking, especially as patch cables or temporary network connections due to the high flexibility of the cables.



Wire transposition on top of pole

The earliest telephones used telegraph lines, or open-wire single-wire earth return circuits. In the 1880s electric trams were installed in many cities, which induced noise into these circuits. Lawsuits being unavailing, the telephone companies converted to balanced circuits, which had the incidental benefit of reducing attenuation, hence increasing range.

As electrical power distribution became more commonplace, this measure proved inadequate. Two wires, strung on either side of cross bars on utility poles, shared the route with electrical power lines. Within a few years, the growing use of electricity again brought an increase of interference, so engineers devised a method called wire transposition, to cancel out the interference.

In wire transposition, the wires exchange position once every several poles. In this way, the two wires would receive similar EMI from power lines. This represented an early implementation of twisting, with a twist rate of about four twists per kilometre, or six per mile. Such open-wire balanced lines with periodic transpositions still survive today in some rural areas.

Twisted-pair cabling was invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.

Unshielded twisted pair


Cross-section of cable with four unshielded twisted pairs

Unshielded twisted pair (UTP) cables are found in many Ethernet networks and telephone systems. For indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T Corporation. A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables. The cables are typically made with copper wires measured at 22 or 24 American Wire Gauge (AWG), with the colored insulation typically made from an insulator such as polyethylene or FEP and the total package covered in a polyethylene jacket.

For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into small but identical bundles. Each bundle consists of twisted pairs that have different twist rates. The bundles are in turn twisted together to make up the cable. Pairs having the same twist rate within the cable can still experience some degree of crosstalk. Wire pairs are selected carefully to minimize crosstalk within a large cable.


Unshielded twisted pair cable with different twist rates

UTP cable is also the most common cable used in computer networking. Modern Ethernet, the most common data networking standard, can use UTP cables. Twisted pair cabling is often used in data networks for short and medium length connections because of its relatively lower costs compared to optical fiber and coaxial cable.

UTP is also finding increasing use in video applications, primarily in security cameras. Many cameras include a UTP output with screw terminals; UTP cable bandwidth has improved to match the baseband of television signals. As UTP is a balanced transmission line, a balun is needed to connect to unbalanced equipment, for example any using BNC connectors and designed for coaxial cable.

Cable Shielding


F/UTP cable


S/FTP cable


U/FTP, F/UTP and F/FTP are used in Cat 6a cables

Twisted pair cables are often shielded in an attempt to prevent electromagnetic interference. Shielding provides an electrically conductive barrier to attenuate electromagnetic waves external to the shield, and provides a conduction path by which induced currents can be circulated and returned to the source, via ground reference connection.

This shielding can be applied to individual pairs or quads, or to the collection of pairs. Individual pairs are foiled, while overall cable may use braided screen, foil, or braiding with foil.

When shielding is applied to the collection of pairs, this is usually referred to as screening, but different vendors and authors use “screening”, “shielding”, and “STP” (shielded twisted pair), inconsistently, in attempting to denote various shielded cable types.

ISO/IEC 11801:2002 (Annex E) attempts to internationally standardize the various designations for shielded cables by using combinations of three letters – U for unshielded, S for braided shielding (in outer layer only), and F for foil shielding – to explicitly indicate the type of screen for overall cable protection and for protecting individual pairs or quads, using a two-part abbreviation in the form of x/xTP.

Shielded Cat 5e, Cat 6/6A, and Cat 8/8.1 cables typically have F/UTP construction, while shielded Cat 7/7A and Cat 8.2 cables use S/FTP construction.

Because the shielding is made of metal, it may also serve as a ground. Usually a shielded twisted pair cable has a special grounding wire added called a drain wire which is electrically connected to the shield or screen. The drain wire simplifies connection to ground at the connectors.

Common shield construction types used include:

Individual Shield (U/FTP)

Individual shielding with aluminum foil for each twisted pair or quad. Common names: pair in metal foil, shielded twisted pair, screened twisted pair. This type of shielding protects cable from external EMI entering or exiting the cable and also protects neighboring pairs from crosstalk.

Overall Shield (F/UTP, S/UTP, and SF/UTP)

Overall foil, braided shield or braiding with foil across all of the pairs within the 100 ohm twisted pair cable. Common names: foiled twisted pair, shielded twisted pair, screened twisted pair. This type of shielding helps prevent EMI from entering or exiting the cable.

Individual and overall shield (F/FTP, S/FTP, and SF/FTP)

Individual shielding using foil between the twisted pair sets, and also an outer foil and/or braided shielding. Common names: fully shielded twisted pair, screened foiled twisted pair, shielded foiled twisted pair, screened shielded twisted pair, shielded screened twisted pair. This type of shielding helps prevent EMI from entering or exiting the cable and also protects neighboring pairs from crosstalk.

An early example of shielded twisted-pair is IBM STP-A, which was a two-pair 150 ohm S/FTP cable defined in 1985 by the IBM Cabling System specifications, and used with token ring or FDDI networks.

Common industry abbreviations for cable construction

The code before the slash designates the shielding for the cable itself, while the code after the slash determines the shielding for the individual pairs:

U = unshielded
F = foil shielding
S = braided shielding (outer layer only)
TP = twisted pair
TQ = twisted pair, individual shielding in quads

Common Types

Common types

Solid-core cable vs. stranded cable

A solid-core cable uses one solid wire per conductor and in a four pair cable there would be a total of eight solid wires. Stranded conductor uses multiple wires wrapped around each other in each conductor and in a four pair with seven strands per conductor cable, there would be a total of 56 wires (2 per pair × 4 pairs × 7 strands).

Solid core cable is intended for permanently installed runs. It is less flexible than stranded cable and is more prone to failure if repeatedly flexed. Stranded cable is used for fly leads at patch panel and for connections from wall-ports to end devices, as it resists cracking of the conductors.

Connectors are designed differently for solid core than for stranded. Use of a connector with the wrong cable type can lead to unreliable cabling. Plugs designed for solid and stranded core are readily available, and some vendors even offer plugs designed for use with both types. The punch-down blocks on patch-panel and wall-port jacks are designed for use with solid core cable.


  • Electrical noise going into or coming from the cable can be prevented.
  • Crosstalk is minimized.
  • Cheapest form of cable available for networking purposes.
  • Easy to handle and install.


  • Deformation: twisted pair’s susceptibility to electromagnetic interference greatly depends on the pair twisting schemes (sometimes patented by the manufacturers) staying intact during the installation. As a result, twisted pair cables usually have stringent requirements for maximum pulling tension as well as minimum bend radius. This fragility of twisted pair cables makes the installation practices an important part of ensuring the cable’s performance.
  • Delay skew: different pairs within the cable have different delays, due to different twist rates used to minimize crosstalk between the pairs. This can degrade image quality when multiple pairs are used to carry components of a video signal. Low skew cable is available to mitigate this problem.
  • Imbalance: differences between the two wires in a pair can cause coupling between the common mode and the differential mode. Differential to common mode conversion produces common mode currents that can cause external interference and can produce common mode signals in other pairs. Common mode to differential mode conversion can produce differential mode signals from common mode interference from other pairs or external sources. Imbalance can be caused by asymmetry between the two conductors of the pair from each other and in relationship to other wires and the shield. Some sources of asymmetry are differences in conductor diameter and insulation thickness. In telephone jargon, the common mode is called longitudinal and the differential mode is called metallic.

Less Common Variants

Loaded Twisted Pair

A twisted pair that has intentionally added inductance, formerly common practice on telecommunication lines. The added inductors are known as load coils and reduce attenuation for voiceband frequencies but increase it on higher frequencies. Load coils reduce distortion in voiceband on very long lines. In this context a line without load coils is referred to as an unloaded line.

Bonded Twisted Pair

A twisted pair variant in which the pairs are individually bonded to increase robustness of the cable. Pioneered by Belden, it means the electrical specifications of the cable are maintained despite rough handling.

Twisted Ribbon Cable

A variant of standard ribbon cable in which adjacent pairs of conductors are bonded and twisted together. The twisted pairs are then lightly bonded to each other in a ribbon format. Periodically along the ribbon there are short sections with no twisting to enable connectors and PCB headers to be terminated using the usual ribbon cable IDC techniques.

Networking Cables

From Wikipedia, the free encyclopedia

Networking cables are networking hardware used to connect one network device to other network devices or to connect two or more computers to share printers, scanners etc. Different types of network cables, such as coaxial cable, optical fiber cable, and twisted pair cables, are used depending on the network’s physical layer, topology, and size. The devices can be separated by a few meters (e.g. via Ethernet) or nearly unlimited distances (e.g. via the interconnections of the Internet).

There are several technologies used for network connections. Patch cables are used for short distances in offices and wiring closets. Electrical connections using twisted pair or coaxial cable are used within a building. Optical fiber cable is used for long distances or for applications requiring high bandwidth or electrical isolation. Many installations use structured cabling practices to improve reliability and maintainability. In some home and industrial applications power lines are used as network cabling.

1 Twisted pair
2 Fiber optic
3 Coaxial
4 Patch
5 Power lines

Twisted Pair

Twisted pair cabling is a form of wiring in which pairs of wires (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from other wire pairs and from external sources. This type of cable is used for home and corporate Ethernet networks. Twisted pair cabling is used in short patch cables and in the longer runs in structured cabling.

An Ethernet crossover cable is a type of twisted pair Ethernet cable used to connect computing devices together directly that would normally be connected via a network switch, Ethernet hub or router, such as directly connecting two personal computers via their network adapters. Most current Ethernet devices support Auto MDI-X, so it doesn’t matter whether you use crossover or straight cables.

Fiber Optic

An optical fiber cable consists of a center glass core surrounded by several layers of protective material. The outer insulating jacket is made of Teflon or PVC to prevent interference. Optical fiber deployment is more expensive than copper but offers higher bandwidth and can cover longer distances.

There are two major types of optical fiber cables: short-range multi-mode fiber and long-range single-mode fiber.


Coaxial cables confine the electromagnetic wave inside the cable, between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

The most common use for coaxial cables is for television and other signals with a bandwidth of several hundred megahertz to gigahertz. Although in most homes coaxial cables have been installed for transmission of TV signals, new technologies (such as the ITU-T standard) open the possibility of using home coaxial cable for high-speed home networking applications (Ethernet over coax).

In the 20th century they carried long distance telephone connections.


A patch cable is an electrical or optical cable used to connect one electronic or optical device to another or to building infrastructure for signal routing. Devices of different types (e.g. a switch connected to a computer, or a switch connected to a router) are connected with patch cords. Patch cords are usually produced in many different colors so as to be easily distinguishable, and most are relatively short, no longer than a few meters. In contrast to on-premises wiring, patch cables are more flexible but may also be less durable.

Power Lines

Although power wires are not designed for networking applications, new technologies like Power line communication allows these wires to also be used to interconnect home computers, peripherals or other networked consumer products. On December 2008, the ITU-T adopted Recommendation as the first worldwide standard for high-speed powerline communications. also specifies communications over phonelines and coaxial wiring.

Ethernet Cable Identification and Use

Category 5, Cat. 5e, Cat. 6, Cat. 6a, Cat. 7, and Cat. 7a Cable Comparison

So you’ve got a bundle of ethernet cables and you’re not really sure if you should use them in your network, this short guide should help you identify and correctly use any of the common ethernet cables you are likely to run across.

Identify the Cable




Category 6 Ethernet Cable Category 5 Ethernet Cable Category 5e Ethernet Cable
As you see above almost all ethernet cabling has the category of cabling printed on the side (hover over an image for the caption). The category shows what bandwidth the cable is rated to carry. If you encounter anything other than the categories listed in the table below, you probably should not use them in your network.

Below you can see that the various categories of cable can be relatively reliably identified by the end connector and the diameter of the cable, however, this is not a be all end all. In general a higher category of cable is thicker because it uses thicker wire for better transmission quality. If you are at all unsure, always check the printing on the side of the cable.


From top to bottom: Cat. 6, Cat. 5e, Cat. 5, and a standard telephone cable for comparison.

Common Ethernet Categories, Speed, and Usage

Common Ethernet Categories


MbE stands for Megabit Ethernet, 100MbE means that the cable can carry 100 Megabits per second of Ethernet trafic.
GbE stands for Gigabit Ethernet, 10GbE is equivalent to 10000MbE.
* Speeds marked with a star are possible over a short run (less than 10 meters) on that category, however for longer runs up to 100m it is reconmended to use a higher quality cable.

General Tips For Using Ethernet Cables

  • Do run cables over distances up to 100 meters with their rated speed.
  • Do mix different cable types as long as the minimum cable category supports the maximum speed of your network. As noted in the table above, all the cables are backward combatible with prior ethernet standards.
  • Do make your own cable if you need lots of varying lengths. More information can be found here.
  • Do buy cables that have no-catch connectors, as seen in the two left-most images of Cat. 6 cable below (hover over the image for the caption). A no-catch connector won’t snag on carpets, clothing, and other cables when you are installing it. The right-most image indicates a traditional connector.


  • Category 6 Ethernet Cable with no-snag connector Category 6 Ethernet Cable with no-snag connector Category 5e cable with traditional snagging connector
  • Don’t order anything less than Cat. 5e cable.
  • Don’t use cable in your network if it is rated less than the maximum speed of the network.
  • In most cases don’t buy cable from retail stores. BestBuy sells 25′ of Cat. 6 cable for $30, you can buy the same from online stores for ~$10 shipped.
  • Don’t buy overpriced “super-high-quality” cable. This $500(!) cable comes to mind. If a cable is rated as Cat. 5e then it will perform at that rating.
  • Don’t crimp or staple cable, this can easily cause breaks in the cable which are sometimes hard to track down.
  • Ethernet cables are not directional in any way, you cannot install one backwards.
  • Lighter colored cables are usually a better choice for two reasons: They are easier to see in the dark, and it’s easier to read the cable catogory stamped on the side.
  • Use a patch cable when connecting a computer to a router or hub, use a cross over cable when connecting two computers directly together. If you are unsure, buy a patch cable, if the cable is not labled as “patch” or “cross over” it is a patch cable.

Kevin Castor July 10th 2008
Last Updated May 21st 2011

Media Introduction

1 Ethernet Overview
2 Common Network Cabling
3 Physical Network Communication Mediums
3.1 Twisted-Pair Cable
3.2 Unshielded Twisted-Pair Cable
3.3 Shielded Twisted-Pair Cable
3.4 Coaxial Cable
3.5 Fiber Optic
4 Wiring Diagrams and Schematics

Ethernet Overview

Ethernet has been with us since 1980. Early Ethernet was carried over stiff coax and later more malleable thin coax. Coax Ethernet installations require that the cable be snaked past each network device and that the device tap into the cable as it goes past. Although this wiring scheme reflects the way Ethernet uses a shared media to allow network communications, the station to station coax has serious real-world reliability problems. 10BASE-T was introduced in 1990 to address these problems. 10BASE-T uses durable and inexpensive twisted pair cable. Two pairs are required for each station: one pair for incoming traffic and one for outgoing. Home runs from each station to a central concentrator carry data to and from each station. With 10BASE-T, the vulnerable shared media portion of the network is now safely hidden in the closet and is not strewn all across the office. In a 10BASE-T system, a wiring fault typically takes out network service only to a single station.

10BASE-T includes diagnostic indicators that allow wiring faults to be easily identified. Because 10BASE-T offers both reliability and cost advantages over the original coax, most new Ethernet installations are of the twisted pair variety.

The newer Fast Ethernet used by CobraNet is wired just like 10BASE-T except that it has ten times the bandwidth, requires a slightly higher grade cable and has some distance limitations not found in 10BASE-T.

Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.

Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from the 1990s to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, is prevalent in home and small office networks and augmenting Ethernet in larger installations.

Ethernet is used in most, but not all, computer networking situations. It is a standard which defines rules that all computers follow to allow successful and efficient communication.

Common Network Cabling

Cable is a medium which provides physical path for data transmission. Several types exist. Some networks use the same type, other use multiple types. A common early cable was the RS-232 D Serial cable. It transmitted one bit at a time, very slow connection. Parallel cables can talk at one bit per line at a time – an 8 pin cable can have 8 bits at once assuming one bit is one line and software handles all handshaking.


RJ-11 is the terminator typically used on plugin phone cables. This cable type has been used for many years by TELCOs all over the world – six pin cable schmatics to follow at a later date.

RJ-45 connectors now terminate most common cables used for hub based or star style TCP/IP networks. RJ-45 terminated cable ends are shown to right. Schematics to follow at a later date. Now that we understand what cables are used the next step is to learn signal processing.

Early TCP/IP networks functioned with looped coax cables or very thick D connector style cables running from one computer to the next rather than via centralized star style hub components.

Physical Network Communication Mediums

Twisted-Pair Cable

Twisted-pair cabling is a copper wire that comes in two forms, shielded and unshielded. It is the most common form of wiring used in a network. It uses 8 wires twisted into pairs to cancel the effect of crosstalk (Noise from the adjacent wires). It is a relatively inexpensive form of LAN cabling. It can accommodate different topologies, but is mostly implemented in a star topology.

Unshielded Twisted-Pair Cable

UTP relies on the cancellation effect of twisting the wires to reduce Electromagnetic Interference (EMI). It is required to have a certain amount of twists per meter and it is connected using a Registered Jack 45 Connecter (RJ-45). UTP can run for 100 meters before the signal needs to be refreshed. UTP has advantages that make it ideal in some networks.

  • Easy to Install
  • Small, it does not take up much space in wiring ducts.
  • Cheapest type of cable.

UTP has 6 Categories.

  • Category 1:
    • Only reliable for transmitting telephone communications, not regular data transmissions.
  • Category 2:
    • Previously used in token rings. Speeds only up to 4kbit
  • Category 3:
    • Works in 10BASE-T networks.. Transfer rate of 10mbit
  • Category 4:
    • Used on 16mbit token ring networks.
  • Category 5:
    • Transfer rate of 100mbit. Unreliable for 1000BASE-T networks.
  • Category 5e:
    • Transfer rate of 1000mbit. Used in Gigabit Ethernet networks.
  • Category 6:
    • Same as Cat 5e but made to a higher standard

Shielded Twisted-Pair Cable

Shielded Twisted-Pair Cable uses twisted pairs along with a metallic foil shielding to reduce the crosstalk and EMI. It is usually connected using an STP connecter but can also be connected with an RJ-45. Although it reduces the interference better than UTP, STP has many drawbacks that keep it from having a mainstream use.

  • More Expensive
  • Must be grounded at both ends
  • Harder to install

Because of these drawbacks it is rarely implemented in Ethernet networks. It is more common in Europe.

Coaxial Cable

Coaxial Cable uses a copper wire for the conductor, on top of this is insulation for the wire. The third layer consists of a metallic foil or woven copper braid as a shielding, followed by a rubber jacket on the top. It is often referred to as Thicknet or Thinnet, depending on the specification. Coaxial cable was found in early Ethernet networks (~1980).


  • It costs less to buy than Fiber Optic
  • It has speeds of 10mb/s to 100mb/s.
  • It costs more to install Coaxial cable.

Fiber Optic

Installation of fiber optic cabling is not the rocket science it once was. Great strides have been made in the durability cost and ease of termination of this media. Fiber optic cable offers two main advantages over twisted pair cable. First, data may be carried much further over fiber. Second, fiber is immune to electromagnetic interference.

There are two basic types of fiber in use today: Multimode and Single Mode. Multimode fiber is used extensively in the data communications industry. Fast Ethernet carried over multimode fiber is known as 100BASE-FX. Ethernet may be carried up to 2 kilometers on this fiber. Single mode fiber is used extensively in the telecom industry. Single mode fiber allows much greater run lengths than multimode fiber. Although there is no official standard for carrying Ethernet over single mode fiber, numerous datacom products offer this capability.

Two strands are required for each Ethernet link; one for transmit and one for receive. Both multimode and single mode fiber cables are available with varying numbers of strands. 4-strand cable costs about $0.80/meter.

Transfer rates of up to 10GB/s and a distance of up to 1000 meters. This is an expensive type of medium and takes a special connector to terminate the signal. It has higher bandwidth possibilities and is best suited for backbone installations. It has 3 parts to the cable: Core, Cladding and Buffer.

  • Core:
    • This is where the light is transmitted
  • Cladding:
    • Just outside the core it traps the light inside the core and helps guide it around corners.
  • Buffer:
    • The hard plastic coating on the outside of the cable that protects the core from moisture and physical damage.

Fiber optic uses include grounding and bonding for:

  • LIghting protection systems
  • Grounding electrode systems
  • Electrical bonding and grounding
  • Power protection
  • Telecom bonding and grounding
  • Telecom circuit protector

Wiring Diagrams and Schematics

RJ-45 Color Codes

RJ-45 modular connectors (AKA “8 Position 8 Contact” or “8P8C”) are the default standard for Ethernet connectivity.

Very Important Note: The T-568B is the current default standard for almost all applications.


RJ-45 Crossover Cable Pinout

A crossover swaps the transmit and receive pairs. Important Note: A crossover cable is not the same as a reverse polarity cable.



RJ-45 Reverse Polarity Cable Pinout

A polarity cable swaps the positive and negative signals on the transmit and receive pairs. Important Note: A polarity cable is not the same as a cross over cable.



Solid color versus banded/striped wiring cross reference

Wiring is usually solid color or banded/striped. Below are the the first three wire pairs and their respective colors.


RJ-11/RJ-14 Color Codes and Wiring

RJ-11 and RJ-14 Female Jack from the outside looking in. RJ-11 is the common standard for most phones and POTS devices.


RJ-11/RJ-14 Wall Plate Jack

Standard RJ-11/RJ-14 Wall Plate Jack.


Swapping Inner and Outer Pairs on an RJ-11 Wall Plate

Some modems are designed to receive the DSL signal on the “outer pairs” (pins 2 and 5) instead of the “inner pairs” (pins 3 and 4) of an RJ-11 jack. You can use a line swapper or you can rewire your wall plate as shown. Note: If you rewire the wall plate as shown you will not be able to use most standard equipment that requires the “inner pairs”.


IFITL (PCDATA) Installation and Connections

IFITL (Integrated Fiber In The Loop) is a 10Mb ethernet connection and does not require a DSL modem. It does however require a PPPoE client for connectivity. You can use a stand alone client such as BellSouth Connection Agent, RasPPPoE, or the native PPPoE client on Windows XP on the computer. You can also use a router as shown here.

IFITL requires a specialized, dedicated 10Base-T Protector and IFITL EBN (Entrance Bridge Network) be placed inside the customer’s NID. Since IFITL installation use a completely separate line there is no need for inline microfilters on the POTS devices.

Important Note: IFITL also requires a crossover be built into the wiring before the NIC. The guidelines for placing the crossover varies and can be wired at the 10base-T protector, the IFITL EBN, or the wall plate inside the house. Most (but not all) technicians rewire the wall plate as the crossover point so standard CAT5 wiring can be used between the wall plate and the NIC or router (if present).




Standard POTS NID (Network Interface Device) Schematic

NIDs (or TNIs) come in a variety of styles as shown here. Depending on the age of the NID and type of the wiring used, the color codes and connections can vary. Please reference these FAQs for more information:

•RJ-11 Color Codes
•RJ-11 Wall Plate Schematic



Telco Wiring Color Code.

Telco color code.

  • B=blue
  • O=orange
  • G=green
  • Br=brown
  • S=slate (not grey)
  • W=white
  • R=red
  • Bk=black
  • Y=yellow
  • V=violet (not purple)

Tip: Pairs

  • White 1-5
  • Red 6-10
  • Black 11-15
  • Yellow 16-20
  • Violet 21-25

Ring: Pairs

  • Blue First Pair 1,6,11,16,21
  • Orange Second Pair 2,7,12,17,22
  • Green Third Pair 3,8,13,18,23
  • Brown Fourth Pair 4,9,14,19,24
  • Slate Fifth Pair 5,10,15,20,25


  • B/W 1-25
  • O/W 26-50
  • G/W 51-75
  • Br/W 76-100

And on and on.

FWIW Telco cable is built in 25 pair groups or binders. Any cable over 25 pairs will have binders which are the 25 pairs twisted and then wrapped in a multi-colored colored string (old days) or two colored plastic binders.

For example a pair in a 25 pair cable consisting of a black wire with blue stripe mated with a blue wire with a black stripe is pair 11. Now lets go to a cable with over twenty five pairs and lets say the same pair was in a binder/group wrapped with a brown/white string it would be pair 86. Make sense?

How do I install DSL filters?

Best Filter Installation Advice:

Due to basic differences in design, it is best to consult the installation instructions and diagrams provided by your ISP or filter manufacturer. It is critical that you install the filters correctly. Failure to do so will create poor performance and speeds. It may even keep the modem from synching at all.

Typically, there are two common types of DSL filters:

  1. Dual Line Filter – One line input and two outputs. One output is marked “Phone” and is used to connect to all POTS devices. The other ouput is marked “DSL/HPN” or “Data” and is used to connect the DSL modem.
  2. Single Line Filter – One line input and one phone only output. The single output marked “Phone” is used to connect to all POTS devices (not modems).


Feedback received on this FAQ entry:

A dual line filter means its designed for a two lines (not that it has two jacks)..Single line 1 line system