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87-423: A tee connector is an electrical connector that connects three cables together. It is usually in the shape of a capital T. It is usually used for coax cables and the three connector points can be either female or male gender, and could be different or the same standard, such as F type , BNC or N type . Tee connectors can be used to split radio frequency power from a cable into two. They can be used to attach

174-449: A displacement current ; therefore it stores and returns electrical energy as if it were an ideal capacitor. The electric susceptibility χ e {\displaystyle \chi _{e}} of a dielectric material is a measure of how easily it polarises in response to an electric field. This, in turn, determines the electric permittivity of the material and thus influences many other phenomena in that medium, from

261-791: A characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the lowest insertion loss impedance drops down to a value between 52 and 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

348-423: 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

435-437: A consequence of causality , imposes Kramers–Kronig constraints on the real and imaginary parts of the susceptibility χ e ( ω ) {\displaystyle \chi _{e}(\omega )} . In the classical approach to the dielectric, the material is made up of atoms. Each atom consists of a cloud of negative charge (electrons) bound to and surrounding a positive point charge at its center. In

522-416: 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

609-465: A frequency-dependent response of a medium for wave propagation. When the frequency becomes higher: In the frequency region above ultraviolet, permittivity approaches the constant ε 0 in every substance, where ε 0 is the permittivity of the free space. Because permittivity indicates the strength of the relation between an electric field and polarisation, if a polarisation process loses its response, permittivity decreases. Dielectric relaxation

696-409: 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

783-493: A good choice both for carrying weak signals that cannot tolerate interference from the environment, and for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits. Larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections. The characteristic impedance of

870-413: A high polarisability . The latter is expressed by a number called the relative permittivity . Insulator is generally used to indicate electrical obstruction while dielectric is used to indicate the energy storing capacity of the material (by means of polarisation). A common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor . The polarisation of

957-549: A material cannot polarise instantaneously in response to an applied field. The more general formulation as a function of time is P ( t ) = ε 0 ∫ − ∞ t χ e ( t − t ′ ) E ( t ′ ) d t ′ . {\displaystyle \mathbf {P} (t)=\varepsilon _{0}\int _{-\infty }^{t}\chi _{e}\left(t-t'\right)\mathbf {E} (t')\,dt'.} That is,

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1044-444: 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

1131-434: A piece of electronic test equipment . Tee connectors were used to attach end stations to 10BASE2 Ethernet networks. This electronics-related article is a stub . You can help Misplaced Pages by expanding it . Coax cable Coaxial cable , or coax (pronounced / ˈ k oʊ . æ k s / ), is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield , with

1218-408: A result, when lattice vibrations or molecular vibrations induce relative displacements of the atoms, the centers of positive and negative charges are also displaced. The locations of these centers are affected by the symmetry of the displacements. When the centers do not correspond, polarisation arises in molecules or crystals. This polarisation is called ionic polarisation . Ionic polarisation causes

1305-485: 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 outside of the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. When using differential signaling , coaxial cable provides an advantage of equal push-pull currents on

1392-423: 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

1479-547: A type of waveguide . Power is transmitted through the radial electric field and the circumferential magnetic field in the TEM mode. This is the dominant mode from zero frequency (DC) to an upper limit determined by the electrical dimensions of the cable. 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

1566-606: 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

1653-453: Is a delay or lag in the response of a linear system , and therefore dielectric relaxation is measured relative to the expected linear steady state (equilibrium) dielectric values. The time lag between electrical field and polarisation implies an irreversible degradation of Gibbs free energy . In physics , dielectric relaxation refers to the relaxation response of a dielectric medium to an external, oscillating electric field. This relaxation

1740-522: Is a good approximation at radio frequencies however for frequencies below 100 kHz (such as audio ) it becomes important to use the complete telegrapher's equation : Applying this formula to typical 75 ohm coax we find the measured impedance across the audio spectrum will range from ~150 ohms to ~5K ohms, much higher than nominal. The velocity of propagation also slows considerably. Thus we can expect coax cable impedances to be consistent at RF frequencies but variable across audio frequencies. This effect

1827-423: Is also used as an insulator, and exclusively in plenum-rated cables. 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

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1914-433: Is applied, the distance between charges within each permanent dipole, which is related to chemical bonding , remains constant in orientation polarisation; however, the direction of polarisation itself rotates. This rotation occurs on a timescale that depends on the torque and surrounding local viscosity of the molecules. Because the rotation is not instantaneous, dipolar polarisations lose the response to electric fields at

2001-568: 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. An inhomogeneous dielectric needs to be compensated by

2088-551: Is more convenient in a linear system to take the Fourier transform and write this relationship as a function of frequency. Due to the convolution theorem , the integral becomes a simple product, P ( ω ) = ε 0 χ e ( ω ) E ( ω ) . {\displaystyle \mathbf {P} (\omega )=\varepsilon _{0}\chi _{e}(\omega )\mathbf {E} (\omega ).} The susceptibility (or equivalently

2175-454: Is often described in terms of permittivity as a function of frequency , which can, for ideal systems, be described by the Debye equation. On the other hand, the distortion related to ionic and electronic polarisation shows behaviour of the resonance or oscillator type. The character of the distortion process depends on the structure, composition, and surroundings of the sample. Debye relaxation

2262-418: 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)

2349-550: Is referenced in IEC 61917. 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

2436-611: Is related to the polarisation density P {\displaystyle \mathbf {P} } by D   =   ε 0 E + P   =   ε 0 ( 1 + χ e ) E   =   ε 0 ε r E . {\displaystyle \mathbf {D} \ =\ \varepsilon _{0}\mathbf {E} +\mathbf {P} \ =\ \varepsilon _{0}\left(1+\chi _{e}\right)\mathbf {E} \ =\ \varepsilon _{0}\varepsilon _{r}\mathbf {E} .} In general,

2523-400: Is roughly inversely proportional to the cutoff frequency . A propagating surface-wave mode that only involves the central conductor also exists, but is effectively suppressed in coaxial cable 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

2610-456: Is roughly the inverse of the time it takes for the molecules to bend, and this distortion polarisation disappears above the infrared. Ionic polarisation is polarisation caused by relative displacements between positive and negative ions in ionic crystals (for example, NaCl ). If a crystal or molecule consists of atoms of more than one kind, the distribution of charges around an atom in the crystal or molecule leans to positive or negative. As

2697-439: 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

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2784-449: 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 extends

2871-590: Is the electric permittivity of free space . The susceptibility of a medium is related to its relative permittivity ε r {\displaystyle \varepsilon _{r}} by χ e   = ε r − 1. {\displaystyle \chi _{e}\ =\varepsilon _{r}-1.} So in the case of a classical vacuum , χ e   = 0. {\displaystyle \chi _{e}\ =0.} The electric displacement D {\displaystyle \mathbf {D} }

2958-603: Is the dielectric relaxation response of an ideal, noninteracting population of dipoles to an alternating external electric field. It is usually expressed in the complex permittivity ε of a medium as a function of the field's angular frequency ω : ε ^ ( ω ) = ε ∞ + Δ ε 1 + i ω τ , {\displaystyle {\hat {\varepsilon }}(\omega )=\varepsilon _{\infty }+{\frac {\Delta \varepsilon }{1+i\omega \tau }},} where ε ∞

3045-468: Is the momentary delay (or lag) in the dielectric constant of a material. This is usually caused by the delay in molecular polarisation with respect to a changing electric field in a dielectric medium (e.g., inside capacitors or between two large conducting surfaces). Dielectric relaxation in changing electric fields could be considered analogous to hysteresis in changing magnetic fields (e.g., in inductor or transformer cores ). Relaxation in general

3132-419: Is the permittivity at the high frequency limit, Δ ε = ε s − ε ∞ where ε s is the static, low frequency permittivity, and τ is the characteristic relaxation time of the medium. Separating into the real part ε ′ {\displaystyle \varepsilon '} and the imaginary part ε ″ {\displaystyle \varepsilon ''} of

3219-432: Is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers to their antennas, computer network (e.g., Ethernet ) connections, digital audio ( S/PDIF ), and distribution of 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

3306-418: 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

3393-465: The ferroelectric effect as well as dipolar polarisation. The ferroelectric transition, which is caused by the lining up of the orientations of permanent dipoles along a particular direction, is called an order-disorder phase transition . The transition caused by ionic polarisations in crystals is called a displacive phase transition . Ionic polarisation enables the production of energy-rich compounds in cells (the proton pump in mitochondria ) and, at

3480-533: The plasma membrane , the establishment of the resting potential , energetically unfavourable transport of ions, and cell-to-cell communication (the Na+/K+-ATPase ). All cells in animal body tissues are electrically polarised – in other words, they maintain a voltage difference across the cell's plasma membrane , known as the membrane potential . This electrical polarisation results from a complex interplay between ion transporters and ion channels . In neurons,

3567-533: 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. Coaxial cable is a particular kind of transmission line , so the circuit models developed for general transmission lines are appropriate. See Telegrapher's equation . In

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3654-418: 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

3741-465: 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

3828-400: The above equation for ε ^ ( ω ) {\displaystyle {\hat {\varepsilon }}(\omega )} is sometimes written with 1 − i ω τ {\displaystyle 1-i\omega \tau } in the denominator due to an ongoing sign convention ambiguity whereby many sources represent the time dependence of

3915-457: 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, so long as provisions are made to ensure differential signalling push-pull currents in the cable. In radio-frequency applications up to a few gigahertz , the wave propagates primarily in the transverse electric magnetic (TEM) mode , which means that

4002-466: 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

4089-535: The cable ( Z 0 ) is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss. The source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio . Other important properties of coaxial cable include attenuation as

4176-401: The cable can cause unwanted noise and picture ghosting. Excessive noise can overwhelm the signal, making it useless. In-channel ingress can be digitally removed by ingress cancellation . 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

4263-505: The cable from water infiltration through minor cuts in the jacket. For internal chassis connections the insulating jacket may be omitted. 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

4350-529: 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

4437-594: The capacitance of capacitors to the speed of light . It is defined as the constant of proportionality (which may be a tensor ) relating an electric field E {\displaystyle \mathbf {E} } to the induced dielectric polarisation density P {\displaystyle \mathbf {P} } such that P = ε 0 χ e E , {\displaystyle \mathbf {P} =\varepsilon _{0}\chi _{e}\mathbf {E} ,} where ε 0 {\displaystyle \varepsilon _{0}}

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4524-478: 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. The characteristic impedance formula above

4611-425: The coaxial cable is terminated in a pure resistance equal to its impedance. 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

4698-842: The complex dielectric permittivity yields: ε ′ = ε ∞ + ε s − ε ∞ 1 + ω 2 τ 2 ε ″ = ( ε s − ε ∞ ) ω τ 1 + ω 2 τ 2 {\displaystyle {\begin{aligned}\varepsilon '&=\varepsilon _{\infty }+{\frac {\varepsilon _{s}-\varepsilon _{\infty }}{1+\omega ^{2}\tau ^{2}}}\\[3pt]\varepsilon ''&={\frac {(\varepsilon _{s}-\varepsilon _{\infty })\omega \tau }{1+\omega ^{2}\tau ^{2}}}\end{aligned}}} Note that

4785-792: The complex electric field with exp ⁡ ( − i ω t ) {\displaystyle \exp(-i\omega t)} whereas others use exp ⁡ ( + i ω t ) {\displaystyle \exp(+i\omega t)} . In the former convention, the functions ε ′ {\displaystyle \varepsilon '} and ε ″ {\displaystyle \varepsilon ''} representing real and imaginary parts are given by ε ^ ( ω ) = ε ′ + i ε ″ {\displaystyle {\hat {\varepsilon }}(\omega )=\varepsilon '+i\varepsilon ''} whereas in

4872-409: The current path and concentrates the current at peaks, thus increasing ohmic loss. 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 to resist ultraviolet light , oxidation , rodent damage, or direct burial . Flooded coaxial cables use a water-blocking gel to protect

4959-430: 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

5046-420: The dielectric by the applied electric field increases the capacitor's surface charge for the given electric field strength. The term dielectric was coined by William Whewell (from dia + electric ) in response to a request from Michael Faraday . A perfect dielectric is a material with zero electrical conductivity ( cf. perfect conductor infinite electrical conductivity), thus exhibiting only

5133-528: The dielectric now depends on the situation. The more complicated the situation, the richer the model must be to accurately describe the behaviour. Important questions are: The relationship between the electric field E and the dipole moment M gives rise to the behaviour of the dielectric, which, for a given material, can be characterised by the function F defined by the equation: M = F ( E ) . {\displaystyle \mathbf {M} =\mathbf {F} (\mathbf {E} ).} When both

5220-423: The dielectric. (Note that the dipole moment points in the same direction as the electric field in the figure. This is not always the case, and is a major simplification, but is true for many materials.) When the electric field is removed, the atom returns to its original state. The time required to do so is called relaxation time; an exponential decay. This is the essence of the model in physics. The behaviour of

5307-467: The dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line. Coaxial cable was used in the first (1858) and following transatlantic cable installations, but its theory was not described until 1880 by English physicist, engineer, and mathematician Oliver Heaviside , who patented the design in that year (British patent No. 1,407). Coaxial cable

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5394-454: 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 hollow 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

5481-522: The feedpoint impedance of a half-wave dipole, mounted approximately a half-wave above "normal" ground (ideally 73 Ω, but reduced for low-hanging horizontal wires). 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

5568-448: 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

5655-404: The following section, these symbols are used: The best coaxial cable impedances were experimentally determined at Bell Laboratories in 1929 to be 77 Ω for low-attenuation, 60 Ω for high-voltage, and 30 Ω for high-power. 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

5742-482: 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,

5829-436: The frequency of an applied electric field. Because there is a lag between changes in polarisation and changes in the electric field, the permittivity of the dielectric is a complex function of the frequency of the electric field. Dielectric dispersion is very important for the applications of dielectric materials and the analysis of polarisation systems. This is one instance of a general phenomenon known as material dispersion :

5916-445: The highest frequencies. A molecule rotates about 1 radian per picosecond in a fluid, thus this loss occurs at about 10 Hz (in the microwave region). The delay of the response to the change of the electric field causes friction and heat. When an external electric field is applied at infrared frequencies or less, the molecules are bent and stretched by the field and the molecular dipole moment changes. The molecular vibration frequency

6003-406: The image; multiple reflections may cause the original signal to be followed by more than one echo. If a coaxial cable is open (not connected at the end), the termination has nearly infinite resistance, which causes reflections. If the coaxial cable is short-circuited, the termination resistance is nearly zero, which causes reflections with the opposite polarity. Reflections will be nearly eliminated if

6090-399: The inner conductor and inside of the outer conductor that restrict the signal's electric and magnetic fields to the dielectric , with little leakage outside the shield. Further, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, if unequal currents are filtered out at the receiving end of the line. This property makes coaxial cable

6177-426: The inner conductor so that the two voltages can be cancelled by the receiver. Many senders 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 occurs when stray currents in the shield flow in the same direction as the current in the center conductor, causing the coax to radiate. They are

6264-999: The latter convention ε ^ ( ω ) = ε ′ − i ε ″ {\displaystyle {\hat {\varepsilon }}(\omega )=\varepsilon '-i\varepsilon ''} . The above equation uses the latter convention. The dielectric loss is also represented by the loss tangent: tan ⁡ ( δ ) = ε ″ ε ′ = ( ε s − ε ∞ ) ω τ ε s + ε ∞ ω 2 τ 2 {\displaystyle \tan(\delta )={\frac {\varepsilon ''}{\varepsilon '}}={\frac {\left(\varepsilon _{s}-\varepsilon _{\infty }\right)\omega \tau }{\varepsilon _{s}+\varepsilon _{\infty }\omega ^{2}\tau ^{2}}}} This relaxation model

6351-447: 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

6438-504: The lowest capacitance per unit-length when compared to other coaxial cables of similar size. All of the components of a coaxial system should have the same impedance to avoid internal reflections at connections between components (see Impedance matching ). Such reflections may cause signal attenuation. They introduce standing waves, which increase losses and can even result in cable dielectric breakdown with high-power transmission. In analog video or TV systems, reflections cause ghosting in

6525-405: The nuclei is possible (distortion polarisation). Orientation polarisation results from a permanent dipole, e.g., that arises from the 104.45° angle between the asymmetric bonds between oxygen and hydrogen atoms in the water molecule, which retains polarisation in the absence of an external electric field. The assembly of these dipoles forms a macroscopic polarisation. When an external electric field

6612-490: The old RG-series cables. (7×0.16) (7×0.1) (7×0.1) (7×0.16) (7×0.75) (7×0.75) (7×0.17) Dielectric The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics , optics , solid-state physics and cell biophysics . Although the term insulator implies low electrical conduction , dielectric typically means materials with

6699-457: The opposite of the desired "push-pull" differential signalling currents, where the signal currents on the inner and outer conductor are equal and opposite. 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

6786-476: The permittivity) is frequency dependent. The change of susceptibility with respect to frequency characterises the dispersion properties of the material. Moreover, the fact that the polarisation can only depend on the electric field at previous times (i.e., χ e ( Δ t ) = 0 {\displaystyle \chi _{e}(\Delta t)=0} for Δ t < 0 {\displaystyle \Delta t<0} ),

6873-829: The polarisation is a convolution of the electric field at previous times with time-dependent susceptibility given by χ e ( Δ t ) {\displaystyle \chi _{e}(\Delta t)} . The upper limit of this integral can be extended to infinity as well if one defines χ e ( Δ t ) = 0 {\displaystyle \chi _{e}(\Delta t)=0} for Δ t < 0 {\displaystyle \Delta t<0} . An instantaneous response corresponds to Dirac delta function susceptibility χ e ( Δ t ) = χ e δ ( Δ t ) {\displaystyle \chi _{e}(\Delta t)=\chi _{e}\delta (\Delta t)} . It

6960-413: The presence of an electric field, the charge cloud is distorted, as shown in the top right of the figure. This can be reduced to a simple dipole using the superposition principle . A dipole is characterised by its dipole moment , a vector quantity shown in the figure as the blue arrow labeled M . It is the relationship between the electric field and the dipole moment that gives rise to the behaviour of

7047-414: 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. Standoff insulators are used to keep them away from parallel metal surfaces. Coaxial lines largely solve this problem by confining virtually all of the electromagnetic wave to

7134-413: 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 conducts electrical signals using an inner conductor (usually

7221-627: The two separated by a dielectric ( insulating material); many coaxial cables also have a protective outer sheath or jacket. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis. Coaxial cable is a type of transmission line , used to carry high-frequency electrical signals with low losses. It is used in such applications as telephone trunk lines , broadband internet networking cables, high-speed computer data busses , cable television signals, and connecting radio transmitters and receivers to their antennas . It differs from other shielded cables because

7308-405: The type of electric field and the type of material have been defined, one then chooses the simplest function F that correctly predicts the phenomena of interest. Examples of phenomena that can be so modelled include: Dipolar polarisation is a polarisation that is either inherent to polar molecules (orientation polarisation), or can be induced in any molecule in which the asymmetric distortion of

7395-411: The types of ion channels in the membrane usually vary across different parts of the cell, giving the dendrites , axon , and cell body different electrical properties. As a result, some parts of the membrane of a neuron may be excitable (capable of generating action potentials), whereas others are not. In physics, dielectric dispersion is the dependence of the permittivity of a dielectric material on

7482-413: The wrong voltage. 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

7569-505: Was manifested when trying to send a plain voice signal across the transatlantic telegraph cable , with poor results. 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

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