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| | == Pandora Anelli don preoccuparti == |
| [[File:RG-59.jpg|thumb|right|400px|<center>[[RG-59]] '''flexible coaxial cable''' composed of:</center><ol type="A" style="list-style-type: upper-latin;"><li>Outer plastic sheath</li><li>Woven copper shield</li><li>Inner dielectric insulator</li><li>Copper core</li></ol>]]
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| {{Antennas|Components of Antenna Systems}}
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| '''Coaxial cable''', or '''coax''' (pronounced [[Help:IPA|'ko.æks]]), is a type of [[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.<ref>{{cite book|last=Nahin|first=Paul J.|title=Oliver Heaviside: The Life, Work, and Times of an Electrical Genius of the Victorian Age|year=2002|isbn=0-8018-6909-9}}</ref> | | Durante il periodo coloniale vi era una leggenda parlata tra le popolazioni indigene in Guatemala di una città perduta all'interno della giungla dove i loro antenati avevano prosperato. Nel 1848 questa leggenda è diventata una realtà. Jeffrey DouchebagIdiot: Sei sia divertente o ignoranti? Hai capirlo. Abbiamo più problemi con ObamaC allora siamo ora. <br><br>Yh destra (!). E la ragione per cui abbiamo sentito alcun rifugio menziona del Silenzio o Trenzalore è dovuto a Steven Moffat iniziare una storia e non finirlo. Parte della Wake County Public School di sistema, con più di 130.000 studenti in 156 scuole (il più grande dello stato), questo sistema razziale ed economicamente diversificata è anche sede di tre scuole superiori che offrono l'esigente, ben rispettato il programma International Baccalaureate. In realtà, l'intero quartiere è focalizzata sulla [http://www.metallipressofusi.it/web_ted/include/datebase.asp Pandora Anelli] preparazione all'università, oltre il 90% degli studenti ha intenzione di continuare una qualche forma di istruzione superiore, con ben oltre la metà di partire per quattro anni college.. <br><br>Il risultato è stato variamente interpretato come una vittoria per la laicità, una rivolta della 'AAM sistema amministrativo' contro i ricchi, e l'affermazione della stiva continua della dinastia Nehru Gandhi sull'immaginazione popolare. Nel più ampio contesto della storia mondiale, tuttavia, ciò che è importante non è il motivo per cui gli elettori hanno votato come hanno fatto, ma il fatto che hanno votato affatto. <br><br>Christie [http://www.landa.it/web_fra/config.asp Air Max 90] ha detto che non ripagherà ARC-prezzo: il NJ gov ha detto che il 271 milioni dollari in fondi federali che erano stati designati per il tunnel ARC "Non è il [http://www.mieascensori.com/web/client.asp Oakley Italia] denaro che dovrebbe essere restituita al governo federale." La sua decisione può costare lo stato 52 mila dollari a settimana in interesse. Non si sa ancora la sua prossima mossa. <br><br>Oltre a camminare, ho iniziato il sollevamento pesi. All'inizio ero un po 'confuso, perché sembrava che stavo guadagnando più peso. Il Coomealla aperto sarà l'ultimo campionato Open dell'anno in Sunraysia Golf e il club sta [http://www.mieascensori.com/web/client.asp Oakley Holbrook] promuovendo come un campione onofficial di evento Champion witin il torneo. New golfista Ilker Deli ha rotto 100 per la prima volta le riprese di 49 punti per il vincitore Sunraysia Golf Tour del Round della Settimana. <br><br>Una donazione di è stato fatto verso il progetto ei fondi sono stati utilizzati molto efficacemente dal Ten. Col. E 'la battuta più densamente imballati Greenwich Natale offrendo finora se indossate come il bavaglio attualmente sul palco, don preoccuparti, ci sarà un altro lungo in un secondo ti piacerà ancora meno. Ho questa immagine di Andrew Pollard passare il resto dell'anno vive in una fabbrica di cracker di Natale, sopravvivendo con motti carta di scarto raschiato fino al largo della terra fatto un sacco di battute sono così veloce, è quasi perdere. |
| Coaxial cable differs from other [[shielded cable]] used for carrying lower-frequency signals, such as [[audio signal]]s, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a [[radio frequency]] [[transmission line]].
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| ==Applications== | | == Louis Vuitton Roma si concentrano sulla propria terra == |
| Coaxial cable is used as a [[transmission line]] for [[radio frequency]] signals. Its applications include [[feedline]]s connecting [[radio transmitter]]s and [[Radio receiver|receivers]] with their antennas, computer network ([[Internet]]) connections, 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 [[electrical conductor|conductor]]s. 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]].
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| | Ciò include i pulsanti casa, Accensione / Spegnimento e Volume. Naturalmente, alcuni di loro potrebbe essere ancora migliore, vale a dire il bilanciere del volume, ma non causerà alcun problema il loro modo di lavorare now.If dobbiamo descrivere i nostri sentimenti verso il design del SGS4 in una sola frase, diremmo . <br><br>Con solo 3 di noi e 5 bambini per gestire insieme, ci isn tempo per fare tutto, mi sono concentrato sul fare alcune marche aspetto migliore, blog un po ', tweeting un po', parlare con i clienti al telefono e Max hanno fatto tutte le cose che fa meglio che è ciò che mantiene tutto in esecuzione più agevole e senza problemi come fa. Mi piace essere il super impegnata tipo di social media che alcune piccole imprese possono riescono ad essere ma stiamo a volte catturato in un posto complicato troppo piccolo per avere un sacco di personale, ma abbastanza grande da avere bisogno di essere tutte le mani sul ponte maggior parte del tempo . <br><br>Alcuni anni fa abbiamo avuto una riunione di soli coro varsity e che era così divertente. Sarà bello vedere il resto della classe 69. Principali risultati Le alterne fortune del programma SCR nel suo primo anno sono stati ampiamente spiegate da otto influenze interagenti. Il primo era proprietà del materiale del SCR [http://www.gardailmelograno.com/web_eng/content.asp Louis Vuitton Roma] (immaturità soprattutto tecnica e la mancanza di interoperabilità) e gli attributi (in particolare la misura in cui i potenziali adottanti credevano i benefici superavano i rischi). <br><br>Tutti i paesi europei sono sopravvissuti volte molto approssimativa nella loro storia. Se l'Europa, che è un'astrazione, non è ciò che è necessario, si concentrano sulla propria terra, il proprio [http://www.omfb.it/includi/content.asp Prada Gucci Uomo] territorio, i propri [http://www.bertellicostruzioni.it/redirect/web/search.asp Longchamp Roma] metodi. Potreste essere a metà strada in tutto il mondo e non essere in grado di venire a Waco. Questo è comprensibile. <br><br>C'è un avvertimento circa tossica scossa sindrome sulla confezione di tamponi che uso proprio come elencano gli effetti collaterali in ogni medicina, nulla è privo di rischi. Non ho mai avuto un problema con loro. JL Graves smonta Rushton scenario evolutivo per tenere conto di queste differenze presunte (capitolo 3, e Intelligence: Separazione della scienza dal mito Rushton problema importante è che lui pensa capisce teoria della storia di vita, quando in realtà egli doesn Inoltre, i suoi collegamenti tra i climi freddi e selezione [http://www.landa.it/area_riservata/mailing_list/search.asp Bracciali Tiffany] per l'intelligenza sono molto discutibili. Teoria r K separa tutti biodiversità lungo un unico asse, naturalmente, è proprio così semplice! [sarcasmo nota]. |
| [[File:Coaxial cable cutaway.svg|thumb|right|300px|Coaxial cable cutaway (not to scale)]] | | 相关的主题文章： |
| 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 voltage is applied to the center conductor to carry electrical signals. The advantage of coaxial design is that electric and magnetic fields are confined to the dielectric with little [[Crosstalk (electronics)|leakage]] outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from causing interference to 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 higher electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits.<ref name="Hdbk87_20">{{cite book|chapter=Chapter 20: Transmission Lines|title=The ARRL Handbook for Radio Communications|edition=87th|publisher=[[ARRL|The American Radio Relay League]]|year=2010|isbn=0-87259-144-1|editor=H. Ward Silver, N0AX, and Mark J. Wilson, K1RO}}</ref>
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| Common applications of coaxial cable include video and [[CATV]] distribution, RF and microwave transmission, and computer and instrumentation data connections.<ref>{{cite web|url=http://www.belden.com/pdfs/Techpprs/CoaxialCablesandApplications.pdf|title= Coaxial Cables and Applications|author=Martin J. Van Der Burgt|publisher=Belden|accessdate=11 July 2011|page=4}}</ref>
| | == Christian Louboutin Milano insieme a Facebook == |
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| The [[characteristic impedance]] of the cable (<math>Z_0</math>) 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 [[Impedance matching|matched]] to ensure [[Maximum power transfer theorem|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.<ref name="Hdbk87_20"/>
| | Egli ha anche abbinato il suo career high con tre intercettazioni. Ha detto Sandusky è solo nella sua cella per 23 ore al giorno durante la settimana e tutto il giorno nei fine settimana.. Parte della stazione della transazione è di aggiungere canzoni indie raccomanda alle loro playlist. <br><br>Lei e suo marito mai lanciato verbali (o in alcuni casi fisiche) attacchi contro Upshaw e l'unione come molti dei suoi coetanei in pensione [http://www.satu.it/web_eng/include/config.asp Christian Louboutin Milano] lo ha fatto spesso. '. Oltre a questo, è possibile aggiungere il link al sito con un testo di ancoraggio. Ma Io non capisco come questo aiuta il SEO del mio sito web. <br><br>Stewart ancora una volta ha suscitato un sacco di dramma. Ora che è cool!. Immaginate se quasi la metà della squadra 1972 era stato preso in ostaggio e ucciso, e il CIO ha rifiutato di onorare adeguatamente i morti americani.. Alcuni slumlords ingiustamente sfrattare gli inquilini o utilizzare tattiche intimidatorie per costringere gli inquilini a basso reddito di un edificio in modo che il proprietario può legittimamente ristrutturarlo e trasformarlo in un hotel o appartamenti a prezzi elevati.. <br><br>I genitori, le imprese, i politici (alcuni dei quali sono chiaramente troppo agio con la tecnologia), anche Wilford Brimley, o almeno una manciata di impostori in posa come il settantenne portavoce Quaker Oats hanno saltato il treno per Twitter Town, unendo la rete di social media che, insieme a Facebook, sta cambiando il modo di comunicare, 140 caratteri alla volta.. <br><br>Il luogo più ideale che questo tipo di albero preferisce è una zona ombreggiata anche se può sopportare illuminazione luminosa se è lentamente permesso di adattarsi alla luce solare. Essa si traduce anche in più morti di seno, della prostata e del colon combinati. <br><br>Childress ha ringraziato il suo autista e rispose sempre pensato che nel 2001 dobbiamo ancora essere qui in esecuzione per un campionato? Lasciate che chiude con una vittoria! ha portato otto giri, ha perso la manipolazione sulla sua auto, ma recuperato un top 10 la 209 della sua carriera nel n ° 29 Chevy. <br><br>'E fa un sacco di senso. Sezione 3 (1) della etc legge sulla salute e la sicurezza sul lavoro 1974 afferma: 'Ha il dovere di ogni datore di lavoro a svolgere il suo impegno in modo tale da garantire, per quanto ragionevolmente possibile, che le persone non in suo rapporto di lavoro [http://www.satu.it/webOLD/include/helper.asp Timberland Milano] che possono essere inficiata non sono quindi esposto a [http://www.mutuisi.it/area_riservata/gestione_news/editor.asp Ray Ban Occhiali] rischi per la salute o la sicurezza. <br><br>Molti studi supportano il fatto che i cani si annoiano facilmente con l'ambiente circostante. E trascorrere qualche ora cercare di capire perché hai speso tanto per cominciare. In realtà, se sei una donna e beve alcolici, si rivolga al medico di prendere acido folico supplementare per aiutare [http://www.mieascensori.com/includi/config.asp Nike Free 5.0] a ridurre il rischio di cancro al seno associato all'uso di alcol. |
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| ==Construction==
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| 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.<ref name=UHFMAN90>''The ARRL UHF/Microwave Experimenter's Manual'', American Radio Relay League, Newington CT USA,1990 ISBN 0-87259-312-6, Chapter 5 ''Transmission Media'' pages 5.19 through 5.21</ref>
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| The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of dielectric control some 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.
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| 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.<ref name=UHFMAN90/> 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.
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| 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 rippled like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric.<ref name=UHFMAN90/>
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| 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.
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| 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 [[Permittivity|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 [[ohms law|ohmic losses]]. Inner conductors are sometimes silver-plated to smooth the surface and reduce losses due to [[skin effect]].<ref name=UHFMAN90/> A rough surface prolongs the path for the current and concentrates the current at peaks and, thus, increases ohmic losses.
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| 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]] and rodent damage. 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.
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| ==Signal propagation==
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| {{Unreferenced section|date=June 2009}}
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| Open-wire [[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, 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.
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| In radio-frequency applications up to a few [[gigahertz]], the wave propagates primarily in the [[Transverse electric and magnetic mode|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 velocity|phase velocities]] to propagate, [[wave interference|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-wire transmission line|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.
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| Coaxial cable may be viewed as a type of [[Waveguide (electromagnetism)|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.<ref name=jackson>{{cite book|last= Jackson|first=John David|year=1962|title=Classical Electrodynamics|publisher=John Wiley & Sons, Inc.|location=New York|page=244}}</ref>
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| ==Connectors==
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| [[File:N Connector.jpg||thumb|A coaxial connector (male [[N connector|N-type]]).]]
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| {{Main|RF connector}}
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| 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.<ref name=UHFMAN90/> 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.{{citation needed|date=April 2012}}
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| ==Important parameters==
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| Coaxial cable is a particular kind of [[transmission line]], so the circuit models developed for general transmission lines are appropriate. See [[Telegrapher's equation]].
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| [[File:Transmission line element.svg|thumb|Schematic representation of the elementary components of a transmission line.]][[File:Transmission line schematic.svg|thumb|Schematic representation of a coaxial transmission line, showing the characteristic impedance <math>Z_0</math>.]]
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| ===Physical parameters===
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| In the following section, these symbols are used:
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| *Length of the cable, <math>h</math>.
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| *Outside diameter of ''inner'' conductor, <math>d</math>.
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| *Inside diameter of the shield, <math>D</math>.
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| *[[Dielectric constant]] of the insulator, <math>\epsilon</math>. The dielectric constant is often quoted as the relative dielectric constant <math>\epsilon_r</math> referred to the dielectric constant of free space <math>\epsilon_0</math>: <math>\epsilon = \epsilon_r \epsilon_0</math>. 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 <math>\epsilon_{eff}</math> is often used.
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| *[[Magnetic permeability]] of the insulator, <math>\mu</math>. Permeability is often quoted as the relative permeability <math>\mu_r</math> referred to the permeability of free space <math>\mu_0</math>: <math>\mu = \mu_r \mu_0</math>. The relative permeability will almost always be 1.
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| ===Fundamental electrical parameters===
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| *Shunt [[capacitance]] per unit length, in [[farad]]s per metre.<ref>Pozar, David M. (1993). ''Microwave Engineering'' Addison-Wesley Publishing Company. ISBN 0-201-50418-9.</ref>
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| ::<math>\left(\frac{C}{h}\right) = {2 \pi \epsilon \over \ln(D/d)}= {2 \pi \epsilon_0 \epsilon_r \over \ln(D/d)}</math>
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| *Series [[inductance]] per unit length, in [[henry (unit)|henry]]s per metre.
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| ::<math>\left(\frac{L}{h}\right) = {\mu \over 2 \pi} \ln(D/d)= {\mu_0 \mu_r \over 2 \pi} \ln(D/d)</math>
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| *Series [[electrical resistance|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.
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| *Shunt [[Electrical conductance|conductance]] per unit length, in [[siemens (unit)|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.
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| ===Derived electrical parameters===
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| *[[Characteristic impedance]] in ohms (Ω). Neglecting resistance per unit length for most coaxial cables, the characteristic impedance is determined from the capacitance per unit length (<math>C</math>) and the inductance per unit length (<math>L</math>). The simplified expression is (<math>Z_0 = \sqrt{L/C}</math>). Those parameters are determined from the ratio of the inner (d) and outer (D) diameters and the [[dielectric constant]] (<math>\epsilon</math>). The characteristic impedance is given by<ref>{{cite book|last=Elmore|first=William C.|coauthors=Heald, Mark A.|title=Physics of Waves|year=1969|isbn=0-486-64926-1}}</ref>
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| ::<math>Z_0=\frac{1}{2\pi}\sqrt{\frac{\mu}{\epsilon}}\ln\frac{D}{d}\approx\frac {138 \Omega}{\sqrt{\epsilon_r}}\log_{10}\frac {D} {d}</math>
| |
| :Assuming the dielectric properties of the material inside the cable do not vary appreciably over the operating range of the cable, this 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).<ref>{{cite book|last=Ott|first=Henry W.|title=Noise Reduction Techniques in Electronic Systems|year=1976|isbn=0-471-65726-3}}</ref>
| |
| *Attenuation (loss) per unit length, in [[decibel]]s 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).
| |
| ::<math>v={1 \over \sqrt{\epsilon \mu}} = {c \over \sqrt{\epsilon_r \mu_r}}</math>
| |
| *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 TE<sub>11</sub> 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 TE<sub>11</sub> 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
| |
| ::<math>f_c \approx {1 \over \pi ({D + d \over 2}) \sqrt{\mu \epsilon} }= {c \over \pi ({D + d \over 2}) \sqrt{\mu_r \epsilon_r} }</math>.
| |
| :Hence, the cable is single-mode from to d.c. up to this frequency, and might in practice be used up to 90%<ref>{{cite book|last=Kizer|first=George Maurice|title=Microwave communication|url=http://books.google.co.uk/books?id=T2fI766k2R0C&pg=PA312|year=1990|publisher=Iowa State University Press|isbn=978-0-8138-0026-4|page=312}}</ref> of this frequency.
| |
| *Peak Voltage. The peak voltage is set by the breakdown voltage of the insulator. One website<ref>{{cite web|url=http://www.rfcafe.com/references/electrical/coax.htm |title=Coaxial Cable Equations Formulas |publisher=RF Cafe |date= |accessdate=2012-01-25}}</ref> gives:
| |
| ::<math> V_p = 1150 \ S_\mathrm{mils} \ d_\mathrm{in} \ \log_{10}(D/d)</math>
| |
| ::: where
| |
| ::: ''S''<sub>mils</sub> is the insulator's breakdown voltage in volts per mil
| |
| ::: ''d''<sub>in</sub> is the inner diameter in inches
| |
| ::: The 1150 factor converts inches (diameter) to mils (radius) and log<sub>10</sub> to ln.
| |
| : The above expression may be rewritten<ref>See "field enhancement" discussion at http://www.microwaves101.com/encyclopedia/why50ohms.cfm</ref> as
| |
| ::<math> V_p = 0.5 \ S \ d \ \ln(D/d)</math>
| |
| ::: where
| |
| ::: ''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.<ref>{{cite web|url=http://www.microwaves101.com/encyclopedia/why50ohms.cfm|title=Why 50 Ohms? |publisher = Microwaves 101|date=2009-01-13|accessdate=2012-01-25}}</ref> 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.<ref>{{cite web|url= http://www.microwaves101.com/encyclopedia/coax_power.cfm|title=Coax power handling|publisher=Microwaves 101|date= 2008-09-14|accessdate=2012-01-25}}</ref>
| |
| | |
| 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 [[Cable television|CATV]], although many broadcast TV installations and CATV headends use 300 Ω folded [[dipole antenna]]s 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.<ref>{{cite web| url= http://www.microwaves101.com/encyclopedia/why50ohms.cfm |title=Why 50 Ohms? |publisher=Microwaves 101 |date= 2009-01-13 |accessdate=2012-01-25}}</ref> 50 Ω also works out well because it corresponds very closely to the drive impedance of a half-wave dipole in real environments, and provides an acceptable match to the drive impedance of a quarter-wave monopole, as well.
| |
| | |
| 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 (television)|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 its impedance.
| |
| | |
| ==Issues==
| |
| {{Unreferenced section|date=June 2009}}
| |
| | |
| ===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 [[electromagnetic interference|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 [[electronic noise|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. Practical cables must make compromises between shield efficacy, flexibility, and cost, such as the corrugated surface of 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.
| |
| | |
| ===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 (electricity)|ground loop]].
| |
| | |
| ===Noise===
| |
| 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 sometimes several 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.
| |
| | |
| ==Standards==
| |
| {{More footnotes|section|date=June 2009}}
| |
| 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 connector]]s.
| |
| | |
| A series of standard types of coaxial cable were specified for [[Army-Navy Equipment Code Designators|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 [[Defense Standard|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 [[electrical connector|connector]]s that fit the inner conductor, dielectric, and jacket dimensions of the old RG-series cables.
| |
| | |
| {| class="wikitable sortable" style="font-size:97%; text-align:center;"
| |
| |+Common Coaxial Cables
| |
| |-
| |
| !type
| |
| ![[Characteristic impedance|impedance]]<br />ohms
| |
| !core
| |
| !Dielectric Type
| |
| !Dielectric VF
| |
| !Dielectric in
| |
| !Dielectric mm
| |
| !OD in
| |
| !OD mm
| |
| !shields
| |
| ! style="width:250px;"|comments
| |
| !max attenuation @ 750 MHz dB/100 ft
| |
| |-
| |
| ![[RG-6]]/U
| |
| |75||1.0 mm ||PF || 0.75 ||0.185 ||4.7 ||0.270 ||6.86 ||double
| |
| |align="left"| Low loss at high frequency for [[cable television]], [[satellite television]] and [[cable modem]]s||5.65
| |
| |-
| |
| ![[RG-6]]/UQ
| |
| |75|| || PF || || || || 0.298 || 7.57 ||quad
| |
| |align="left"| This is "quad shield RG-6". It has four layers of [[Electromagnetic shielding|shielding]]; regular RG-6 has only one or two||5.65<ref>{{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg6_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-62
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |-
| |
| !RG-7
| |
| |75||1.30 mm ||PF || ||0.225 ||5.72 ||0.320 ||8.13 ||double
| |
| |align="left"| Low loss at high frequency for [[cable television]], [[satellite television]] and [[cable modem]]s||4.57
| |
| |-
| |
| !RG-8/U
| |
| |50||2.17 mm || PE || ||0.285 ||7.2 ||0.405 ||10.3 ||
| |
| |align="left"| [[Amateur radio]]; Thicknet ([[10BASE5]]) is similar
| |
| |5.967<ref name="LossCalculator" />
| |
| |-
| |
| !RG-8X
| |
| |50||1.0 mm || PF || 0.75 ||0.185 ||4.7 ||0.242 ||6.1 ||double
| |
| |align="left"| A thinner version, with the electrical characteristics of RG-8U in a diameter similar to RG-6.<ref>http://www.dxengineering.com/pdf/Belden%20RG8X%20Date%209258.pdf</ref>
| |
| |10.946<ref name="LossCalculator" />
| |
| |-
| |
| !RG-9/U
| |
| |51|| || PE || || || ||0.420 ||10.7 ||
| |
| |align="left"|
| |
| |-
| |
| !RG-11/U
| |
| |75||1.63 mm || PE || 0.66 ||0.285 ||7.2 ||0.412 ||10.5|| Dual/Triple/Quad
| |
| |align="left"| Used for long drops and underground conduit<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg11_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-11
| |
| |publisher= madaboutcable.com
| |
| }}</ref>||3.65
| |
| |-
| |
| !RG-56/U
| |
| |48||1.4859 mm || || || || || 0.308 || 7.82 || Dual braid shielded
| |
| |align="left"| Rated to 8000 volts, rubber dielectric
| |
| |-
| |
| ![[RG-58|RG-58/U]]
| |
| |50||0.81 mm || PE || 0.66 ||0.116 ||2.9 ||0.195 ||5.0 ||single
| |
| |align="left"| Used for radiocommunication and [[amateur radio]], thin Ethernet ([[10BASE2]]) and [[NIM]] electronics, Loss 1.056 dB/m @ 2.4 GHz. Common.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg58_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-58
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |13.104<ref name="LossCalculator" />
| |
| |-
| |
| ![[RG-59|RG-59/U]]
| |
| |75||0.64 mm || PE || 0.66 ||0.146 ||3.7 ||0.242 ||6.1 ||single
| |
| |align="left"| Used to carry [[baseband]] video in [[closed-circuit television]], previously used for cable television. In general, it has poor shielding but will carry an HQ HD signal or video over short distances.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg59_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-59
| |
| |publisher= madaboutcable.com
| |
| }}</ref>||9.708<ref name="LossCalculator" />
| |
| |-
| |
| !RG-59A/U
| |
| |75||0.762 mm || PF || 0.78 ||0.146 ||3.7 ||0.242 ||6.1 ||single
| |
| |align="left"| Similar physical characteristics as RG-59 and RG-59/U, but with a higher velocity factor.||8.9@700MHz<ref>
| |
| {{cite web
| |
| |url=http://www.febo.com/reference/cable_data.html
| |
| |title=Cable Velocity Factor and Loss Data
| |
| |publisher=febo.com
| |
| }}</ref>
| |
| |-
| |
| ![[3C-2V]]
| |
| |75||0.50 mm || PE || 0.85 || ||3.0 || ||5.4 ||single
| |
| |align="left"| Used to carry television, video observation systems, and other. PVC jacket.
| |
| |-
| |
| !5C-2V
| |
| |75||0.80 mm || PE || 0.82 +/-2 || 0.181 ||4.6 || 0.256 ||6.5 ||double
| |
| |align="left"| Used for interior lines for monitoring system, CCTV feeder lines, wiring between the camera and control unit and video signal transmission. PVC jacket.
| |
| |-
| |
| ![[RG-60|RG-60/U]]
| |
| |50||1.024 mm || PE || ||||||0.425 ||10.8 ||single
| |
| |align="left"| Used for high-definition cable TV and high-speed cable Internet.
| |
| |-
| |
| !RG-62/U
| |
| |92|| || PF || 0.84 || || ||0.242 ||6.1 ||single
| |
| |align="left"| Used for [[ARCNET]] and automotive radio antennas.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg62_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-62
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |-
| |
| !RG-62A
| |
| |93|| || ASP || || || ||0.242 ||6.1 ||single
| |
| |align="left"| Used for [[NIM]] electronics
| |
| |-
| |
| !RG-63
| |
| |125|| 1.2mm || PE || || || || 0.405 || 10.29 || double braid
| |
| |align="left"| Used for aerospace || 4.6
| |
| |-
| |
| !RG-142
| |
| |50|| || || || || ||||4.95|| double||
| |
| |-
| |
| !RG-174/U
| |
| |50||7x0.16 mm || PE || 0.66 ||0.059 ||1.5 ||0.100 ||2.55 ||single
| |
| |align="left"| Common for [[Wi-Fi]] pigtails: more flexible but higher loss than RG58; used with [[LEMO]] 00 connectors in [[NIM]] electronics.
| |
| |23.565<ref name="LossCalculator" />
| |
| |-
| |
| !RG-178/U
| |
| |50||7×0.1 mm<br />(Ag-plated Cu-clad Steel) || PTFE || 0.69 ||0.033 ||0.84 ||0.071 ||1.8 ||single
| |
| |align="left"| Used for high-frequency signal transmission.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg178_milspec_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-178
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |42.7 @ 900 MHz<ref>
| |
| Caledonian.com - [http://www.caledonian-cables.net/Italy/product/Coaxial%20Cables/Mininature%20Coaxial%20Cables/RG178%20Mini-Coax.htm RG178 Mini-Coax]
| |
| </ref>
| |
| |-
| |
| !RG-179/U
| |
| |75||7×0.1 mm<br />(Ag-plated Cu) ||PTFE || 0.67 ||0.063 ||1.6 ||0.098 ||2.5 ||single
| |
| |align="left"|[[VGA]] RGBHV<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/audio_visual_cables/products/C07-R179AV5SL.html
| |
| |title=Coaxial Cable Specifications for 5 Core RG-179 (RGBHV)
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |-
| |
| !style=white-space:nowrap|RG-180B/U
| |
| |95||0.0120 in<br />(Ag-plated Cu-clad steel) ||PTFE || ||0.102 ||2.59 ||0.145 ||3.68 ||single Ag covered Cu
| |
| |align="left"|[[VGA]] RGBHV
| |
| |-
| |
| !RG-188A/U
| |
| |50||7×0.16 mm<br />(Ag-plated Cu-clad Steel) || PTFE || 0.70 ||0.06 ||1.52 ||0.1 ||2.54 ||single
| |
| |
| |
| |90 @ 900 MHz<ref>
| |
| [http://www.belden.com/techdatas/metric/83269.pdf Belden.com -]
| |
| </ref>
| |
| |-
| |
| !RG-213/U
| |
| |50||7×0.0296 in Cu|| PE || 0.66 ||0.285||7.2||0.405||10.3||single
| |
| |align="left"|For radiocommunication and [[amateur radio]], EMC test antenna cables. Typically lower loss than RG58. Common.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg213_coaxial_cable.html
| |
| |title=Coaxial Cable Specifications for RG-213
| |
| |publisher= madaboutcable.com
| |
| }}</ref>
| |
| |5.967<ref name="LossCalculator" />
| |
| |-
| |
| !RG-214/U
| |
| |50||7×0.0296 in ||PE || 0.66 ||0.285 ||7.2 ||0.425 ||10.8 ||double
| |
| |align="left"| Used for high-frequency signal transmission.<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg214_coaxial_cable.html
| |
| |publisher= madaboutcable.com
| |
| |title=Coaxial Cable Specifications for RG-214
| |
| }}</ref>
| |
| |6.702<ref name="LossCalculator" />
| |
| |-
| |
| !RG-218
| |
| |50||0.195 in Cu|| PE || 0.66 ||0.660 (0.680?) ||16.76 (17.27?) ||0.870 ||22 ||single
| |
| |align="left"|Large diameter, not very flexible, low loss (2.5dB/100' @ 400 MHz), 11kV dielectric withstand.
| |
| |2.834<ref name="LossCalculator" />
| |
| |-
| |
| !RG-223/U
| |
| |50||0.88 mm || PE || 0.66 ||0.0815 || 2.07 || 0.212 || 5.4 ||double
| |
| |align="left"|Silver-plated shields. [http://www.crownelectronics.com/Specs/RG-223-U.pdf Sample RG-223 Datasheet]
| |
| |11.461<ref name="LossCalculator" />
| |
| |-
| |
| !RG-316/U
| |
| |50||7x0.0067 in ||PTFE || 0.695 || 0.060 || 1.5 || 0.098 || 2.6 ||single
| |
| |align="left"|used with [[LEMO]] 00 connectors in [[NIM]] electronics<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg316_coaxial_cable.html
| |
| |publisher= madaboutcable.com
| |
| |title=Coaxial Cable Specifications for RG-316
| |
| }}</ref>
| |
| |22.452<ref name="LossCalculator" />
| |
| |-
| |
| !RG-400/U
| |
| |50|| 19x0.20mm || PTFE || || || 2.95 || || 4.95 || double
| |
| |align="left"|<ref>
| |
| {{cite web
| |
| |url=http://www.madaboutcable.com/cables/coaxial_cables/products/rg400_coaxial_cable.html
| |
| |publisher= madaboutcable.com
| |
| |title=Coaxial Cable Specifications for RG-400
| |
| }}</ref>
| |
| |12.566<ref name="LossCalculator" />
| |
| |-
| |
| !RG-402/U
| |
| |50|| 0.93 mm || PTFE || || || 3.0 || 0.1409 || 3.58 || single Silver Plated copper
| |
| |align="left"| semi-rigid
| |
| | 0.91dB/m@5GHz
| |
| |-
| |
| !RG-405/U
| |
| |50|| 0.51 mm || PTFE || || || 1.68 || 0.0865 || 2.20 || single Silver Plated copper clad steel
| |
| |align="left"| semi-rigid
| |
| | 1.51dB/m@5GHz
| |
| |-
| |
| !H155
| |
| |50|| 19 x 0.28 mm || || 0.79 || || || || 5.4 ||
| |
| |align="left"| lower loss at high frequency for radiocommunication and [[amateur radio]]
| |
| |-
| |
| !H500
| |
| |50|| || || 0.82 || || || || ||
| |
| |align="left"|low loss at high frequency for radiocommunication and [[amateur radio]]
| |
| |-
| |
| !LMR-100
| |
| |50|| || || || || || ||2.79||
| |
| |align="left"|low loss communications, 1.36 dB/meter @ 2.4 GHz
| |
| |20.725<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-195
| |
| |50|| || || || || || ||4.95||
| |
| |align="left"|low loss communications, 0.620 dB/meter @ 2.4 GHz
| |
| |10.125<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-200<br />HDF-200<br />CFD-200
| |
| |50||1.12 mm Cu ||PF || 0.83 ||0.116 ||2.95||0.195 ||4.95 ||
| |
| |align="left"|low loss communications, 0.554 dB/meter @ 2.4 GHz
| |
| |9.035<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-240
| |
| |50||1.42 mm Cu||PF||0.84||0.150||3.81||0.240||6.1||double
| |
| |align="left"|[[Amateur radio]], low loss replacement for RG-8X<ref>
| |
| {{cite web
| |
| |url=http://timesmicrowave.com/products/lmr/downloads/16-19.pdf
| |
| |title=Times Microwave LMR-240 Data Sheet
| |
| |accessdate=2011-10-26
| |
| }}</ref>
| |
| |6.877<ref name="LossCalculator">
| |
| {{cite web
| |
| |url=http://www.timesmicrowave.com/cgi-bin/calculate.pl
| |
| |title=Times Microwave Coax Loss Calculator
| |
| |accessdate=2011-10-26
| |
| }}</ref>
| |
| |-
| |
| !LMR-400<br />HDF-400<br />CFD-400<br />EMR-400
| |
| |50||2.74 mm<br />(Cu-clad Al)||PF || 0.85 ||0.285||7.24||0.405||10.29||
| |
| |align="left"|low loss communications, 0.223 dB/meter @ 2.4 GHz<ref>
| |
| {{cite web
| |
| |url=http://www.radioinc.com/oscmax/catalog/product_info.php?name=LMR%20400%20UltraFlex%20(RG-8)%20100%20ft%20pre-cut&products_id=1121
| |
| |title=Radio City Inc
| |
| }}</ref>
| |
| |3.544<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-600
| |
| |50||4.47 mm<br />(Cu-clad Al) ||PF || 0.87 ||0.455 ||11.56 ||0.590 ||14.99||
| |
| |align="left"|low loss communications, 0.144 dB/meter @ 2.4 GHz
| |
| |2.264<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-900
| |
| |50||6.65 mm<br />(BC tube) ||PF || 0.87 ||0.680 ||17.27 ||0.870 ||22.10 ||
| |
| |align="left"|low loss communications, 0.098 dB/meter @ 2.4 GHz
| |
| |1.537<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-1200
| |
| |50||8.86 mm<br />(BC tube) ||PF || 0.88 ||0.920 ||23.37 ||1.200 ||30.48 ||
| |
| |align="left"|low loss communications, 0.075 dB/meter @ 2.4 GHz
| |
| |1.143<ref name="LossCalculator" />
| |
| |-
| |
| !LMR-1700
| |
| |50||13.39 mm<br />(BC tube) ||PF || 0.89 ||1.350 ||34.29 ||1.670 ||42.42 ||
| |
| |align="left"|low loss communications, 0.056 dB/meter @ 2.4 GHz
| |
| |0.844<ref name="LossCalculator" />
| |
| |-
| |
| !QR-320
| |
| |75||1.80 mm ||PF || ||0.395||10.03 || || ||single
| |
| |align="left"| Low loss line, which replaced RG-11 in most applications||3.34
| |
| |-
| |
| !QR-540
| |
| |75||3.15 mm ||PF || ||0.610||15.49 || || ||single
| |
| |align="left"| Low loss hard line||1.85
| |
| |-
| |
| !QR-715
| |
| |75||4.22 mm ||PF || ||0.785||19.94 || || ||single
| |
| |align="left"| Low loss hard line||1.49
| |
| |-
| |
| !QR-860
| |
| |75||5.16 mm ||PF || ||0.960||24.38 || || ||single
| |
| |align="left"| Low loss hard line||1.24
| |
| |-
| |
| !QR-1125
| |
| |75||6.68 mm ||PF || ||1.225||31.12 || || ||single
| |
| |align="left"| Low loss hard line||1.01
| |
| |}
| |
| | |
| Dielectric Material Codes
| |
| * FPE is foamed polyethylene
| |
| * PE is solid [[polyethylene]]
| |
| * PF is polyethylene foam
| |
| * PTFE is [[polytetrafluoroethylene]];
| |
| * ASP is air space polyethylene<ref>{{cite web|url=http://www.rfcafe.com/references/electrical/coax-chart.htm |title=Coaxial Cable Specifications Cables Chart |publisher=RF Cafe |date= |accessdate=2012-01-25}}</ref>
| |
| | |
| VF is the Velocity Factor; it is determined by the effective <math>\epsilon_r</math> and <math>\mu_r</math><ref>{{cite web|url=http://www.microwaves101.com/encyclopedia/phasevelocity.cfm#velocityfactor |title=Phase Velocity |publisher=Microwaves 101 |date=2010-03-30 |accessdate=2012-01-25}}</ref>
| |
| * 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.
| |
| | |
| [[File:RG-6 coaxial cable.png|thumb|right|200px|RG-6 Coaxial cable]]
| |
| [[File:RG-142 Coaxial cable.png|thumb|right|200px|RG-142 Coaxial cable]]
| |
| [[File:RG-405 semi-rigid coaxial cable.png|thumb|right|200px|RG-405 semi-rigid coaxial cable]]
| |
| | |
| ==Uses==
| |
| {{Unreferenced section|date=June 2009}}
| |
| Short coaxial cables are commonly used to connect home [[video]] equipment, in [[amateur radio|ham radio]] setups, and in [[NIM|measurement electronics]]. They used to be common for implementing [[computer network]]s, in particular [[Ethernet]], but [[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 network]]s, [[television network]]s, and [[L-carrier|Long Distance telephone]] networks though this has largely been superseded by later methods ([[fibre optics]], [[T-carrier|T1]]/[[E-carrier|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.
| |
| | |
| 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 [[Broadcasting|broadcast]] television and radio.
| |
| | |
| Coax cable is often used to carry data/signals from an [[antenna (radio)|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]].
| |
| | |
| ==Types==
| |
| | |
| ===Hard line===
| |
| [[File:Coaxialcableoneandfifthofan.jpg|thumb|right|200px|1-5/8" flexible line]]
| |
| 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 or gold 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. Since 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 (electronics)|antenna]] or aerial on a tower. Hard line may also be known by trademarked names such as Heliax (Andrew),<ref>
| |
| {{cite web
| |
| |url=http://www.commscope.com/andrew/eng/product/trans_line_sys/coaxial/wireless/1206774_13612.html
| |
| |title=Andrew Heliax
| |
| }}</ref> or Cablewave (RFS/Cablewave).<ref>
| |
| {{cite web
| |
| |url=http://www.rfsworld.com/
| |
| |title=Cablewave Radio Frequency Systems <http://www.rfsworld.com>
| |
| }}</ref> 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 [[Electric arc|arc]]ing. Gas-filled hardlines are usually used on high-power [[Radio frequency|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===
| |
| {{Main|Leaky feeder}}
| |
| '''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 (Andrew).<ref>{{cite web
| |
| |url= http://www.commscope.com/andrew/eng/product/trans_line_sys/coaxial/radiating/1206639_13611.html
| |
| |title=Andrew Radiax
| |
| }}</ref>
| |
| | |
| ===RG-6===
| |
| {{Main|RG-6}}
| |
| '''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 cable|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===
| |
| {{Main|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===
| |
| {{Main|Twinaxial cabling}}
| |
| '''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===
| |
| [[File:Semi-Rigid Coax.png|thumb|right|Semi-Rigid coax assembly]]
| |
| [[File:Semi-Rigid Coax Installed.jpg|thumb|right|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===
| |
| [[File:Exir Rigid line.png|thumb|right|200px|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.
| |
| [[File:Exir Rigid line parts.png|thumb|right|200px|Rigid line parts]]
| |
| Rigid line is produced in a number of different sizes:
| |
| {| class="wikitable"
| |
| |-
| |
| ! !! Outer conductor !! !! Inner conductor !!
| |
| |-
| |
| ! Size !! Outer diameter (not flanged) !! Inner diameter !! Outer diameter !! Inner diameter
| |
| |-
| |
| | 7/8" || 22.2 mm || 20 mm || 8.7 mm || 7.4 mm
| |
| |-
| |
| | 1 5/8" || 41.3 mm || 38.8 mm || 16.9 mm || 15.0 mm
| |
| |-
| |
| | 3 1/8" || 79.4 mm || 76.9 mm || 33.4 mm || 42.6 mm
| |
| |-
| |
| | 4 1/2" || 106 mm || 103 mm || 44.8 mm || 42.8 mm
| |
| |-
| |
| | 6 1/8" || 155.6 mm || 151.9 mm || 66.0 mm || 64.0 mm
| |
| |}
| |
| | |
| ==Interference and troubleshooting==
| |
| {{Unreferenced section|date=June 2009}}
| |
| 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.
| |
| | |
| ==History==
| |
| *1880 — Coaxial cable patented in [[England]] by [[Oliver Heaviside]], patent no. 1,407.<ref>[[Google Book Search]] - [http://books.google.com/books?id=e9wEntQmA0IC&pg=PA29&lpg=PA29&dq=coaxial+cable+Oliver+Heaviside&source=bl&ots=f0kQnzwRQA&sig=CirRGTNdKXxb9n--KVrrt5sXIIA&hl=en Oliver Heaviside By Paul J. Nahin]</ref>
| |
| *1884 — [[Siemens & Halske]] patent coaxial cable in [[Germany]] (Patent No. 28,978, 27 March 1884).<ref>{{cite book|last=Feldenkirchen|first=Wilfried|title=Werner von Siemens - Inventor and International Entrepreneur|year=1994|isbn=0-8142-0658-1}}</ref>
| |
| *1894 — [[Oliver Lodge]] demonstrates waveguide transmission at the [[Royal Institution]].
| |
| *1894 — [[Nikola Tesla]] Patent of an electrical conductor. An early example of the coaxial cable <ref>{{US patent|514167}}</ref>
| |
| *1929 — First modern coaxial cable patented by [[Lloyd Espenschied]] and [[Herman Affel]] of [[AT&T (1885-2005)|AT&T's]] [[Bell Labs|Bell Telephone Laboratories]].<ref>{{US patent|1835031}}</ref>
| |
| *1936 — First [[Closed-circuit television|closed circuit]] transmission of [[television|TV]] pictures on coaxial cable, from the [[1936 Summer Olympics]] in Berlin to [[Leipzig]].<ref>earlytelevision.org - [http://www.earlytelevision.org/1936_olympics.html Early Electronic Television - The 1936 Berlin Olympics]</ref>
| |
| *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.<ref>The worldwide history of telecommunications By Anton A. Huurdeman - [http://books.google.com/books?id=SnjGRDVIUL4C&lpg=PA334&dq=1936%20underwater%20coaxial%20cable%20Apollo%20Bay&pg=PA334#v=onepage&q&f=false Copper-Line Transmission]</ref>
| |
| *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.<ref>"[http://www.time.com/time/magazine/article/0,9171,757144-1,00.html Coaxial Debut]," ''[[Time (magazine)|Time]]'', Dec. 14, 1936.</ref><ref>[[Boing Boing]] - [http://gadgets.boingboing.net/2009/04/17/gallery-an-illustrat.html Gallery: An illustrated history of the transoceanic cable]</ref>
| |
| *1936 — Coaxial cable laid by the [[General Post Office]] (now [[British Telecom|BT]]) between [[London]] and [[Birmingham]], providing 40 telephone channels.<ref>[[Google Book Search|Google books]] - [http://books.google.com/books?id=DL73f4vFeEwC&pg=PA819&dq=coaxial+cable+London+and+Birmingham&ei=WKk1SqnfGaSUywSE1v39BQ Broadcast engineer's reference book By Edwin Paul J. Tozer]</ref><ref>Radio-electronics.com - [http://www.radio-electronics.com/info/antennas/coax/rf-coaxial-feeder-cable.php Coaxial feeder or RF coax cable]</ref>
| |
| *1941 — First commercial use in USA by AT&T, between [[Minneapolis]], Minnesota and Stevens Point, Wisconsin. L1 system with capacity of one TV channel or 480 telephone circuits.
| |
| *1956 — First transatlantic coaxial cable laid, [[TAT-1]].<ref>Atlantic-cable.com - [http://atlantic-cable.com/Souvenirs/1956TAT-1/ 1956 TAT-1 Silver Commemorative Dish]</ref><ref>[[Google Book Search|Google books]] - [http://books.google.com/books?id=SnjGRDVIUL4C&pg=PA470&dq=1956+TAT-1&as_brr=3&ei=M7w_SpHECp3KMYrL9ZUF The worldwide history of telecommunications By Anton A. Huurdeman]</ref>
| |
| | |
| == See also ==
| |
| * [[Transmission line]]
| |
| * [[Radio frequency power transmission]]
| |
| * [[L-carrier]]
| |
| * [[Balanced pair]]
| |
| * [[Shielded cable]]
| |
| * [[Triaxial cable]]
| |
| * [[Twinaxial cabling]]
| |
| | |
| == References ==
| |
| {{reflist|colwidth=30em}}
| |
| | |
| ==External links==
| |
| *''RF transmission lines and fittings.'' Military Standardization Handbook MIL-HDBK-216, U.S. Department of Defense, 4 January 1962. [http://combatindex.com/mil_docs/pdf/Hopper/MIL-HDBK/CI-216-MH-8403-5993.pdf]
| |
| *[http://www.dscc.dla.mil/Programs/MilSpec/ListDocs.asp?BasicDoc=MIL-HDBK-216 ''Withdrawal Notice for MIL-HDBK-216 2001'']
| |
| *''Cables, radio frequency, flexible and rigid.'' Details Specification MIL-DTL-17H, 19 August 2005 (superseding MIL-C-17G, 9 March 1990). [http://www.dscc.dla.mil/Programs/MilSpec/ListDocs.asp?BasicDoc=MIL-DTL-17]
| |
| *''Radio-frequency cables'', International Standard [[International Electrotechnical Commission|IEC]] 60096.
| |
| *''Coaxial communication cables'', International Standard [[International Electrotechnical Commission|IEC]] 61196.
| |
| *''Coaxial cables'', [[British Standard]] BS EN 50117
| |
| *H. P. Westman et al., (ed), ''Reference Data for Radio Engineers, Fifth Edition'', 1968, Howard W. Sams and Co., no ISBN, Library of Congress Card No. 43-14665
| |
| | |
| {{Commons category|Coaxial cables}}
| |
| {{RF connectors}}
| |
| {{Telecommunications}}
| |
| | |
| {{DEFAULTSORT:Coaxial Cable}}
| |
| [[Category:Signal cables]]
| |
| [[Category:Antennas (radio)]]
| |
| [[Category:Television terminology]]
| |