Loading coil
The concept of loading coils was discovered by Oliver Heaviside in studying the problem of slow signalling speed of the first transatlantic telegraph cable in the 1860s.He concluded additional inductance was required to prevent amplitude and time delay distortion of the transmitted signal.A common application of loading coils is to improve the voice-frequency amplitude response characteristics of the twisted balanced pairs in a telephone cable.Due to narrower streets and higher cost of copper, European cables had thinner wires and used closer spacing.An antenna shorter than a quarter wavelength presents capacitive reactance to the transmission line [citation needed].[citation needed] Loading coils for powerful transmitters can have challenging design requirements, especially at low frequencies.To reduce power lost in dielectric losses, the coil is often suspended in air supported on thin ceramic strips.Expressing this in terms of number of coils per cutoff wavelength yields; where v is the velocity of propagation of the cable in question.then Campbell arrived at this expression by analogy with a mechanical line periodically loaded with weights described by Charles Godfrey in 1898 who obtained a similar result.[7] Heaviside immediately (1887) proposed several methods of increasing the inductance, including spacing the conductors further apart and loading the insulator with iron dust.Brittain attributes this to Heaviside's failure to provide engineering details on the size and spacing of the coils for particular cable parameters.[9] John S. Stone worked for the American Telephone & Telegraph Company (AT&T) and was the first to attempt to apply Heaviside's ideas to real telecommunications.[10] This cable of Stone's would increase the line inductance due to the iron content and had the potential to meet the Heaviside condition.Campbell was tasked with continuing the investigation into Stone's bimetallic cable, but soon abandoned it in favour of the loading coil.[13] The first telephone cable using loaded lines put into public service was between Jamaica Plain and West Newton in Boston on 18 May 1900.The cut-off phenomena of loading coils, an undesirable side-effect, can be exploited to produce a desirable filter frequency response.The confusion is easy to understand, Pupin himself claims that he first thought of the idea of loading coils while climbing a mountain in 1894,[19] although there is nothing from him published at that time.[20] Pupin's 1894 patent "loads" the line with capacitors rather than inductors, a scheme that has been criticised as being theoretically flawed[21] and never put into practice.[22] Consequently, only the capacitor is adding any significant impedance to the line and "the coils will not exercise any material influence on the results before noted".[24] Despite the legal disputes surrounding this invention, it is unquestionable that Campbell was the first to actually construct a telephone circuit using loading coils.When considering whether to allow Campbell to go ahead with the demonstration, their engineers had estimated that they stood to save $700,000 in new installation costs in New York and New Jersey alone.A further problem was that the material science of the time had difficulties sealing the joint between coil and cable against ingress of seawater.Krarup cable has iron wires continuously wound around the central copper conductor with adjacent turns in contact with each other.In c. 1915, Oliver E. Buckley, H. D. Arnold, and Elmen, all at Bell Labs, greatly improved transmission speeds by suggesting a method of constructing submarine communications cable using permalloy tape wrapped around the copper conductors.[44] Mu-metal has similar magnetic properties to permalloy but the addition of copper to the alloy increases the ductility and allows the metal to be drawn into wire.
inductorelectronic circuitinductanceradio antennasfeedlineresonantOliver Heavisidetransatlantic telegraph cableHeaviside conditionSubmarine communications cablesbalanced pairsMihajlo Pupinvoice-frequencytwisted balanced pairsbalancedtransformerscouplingattenuationcutoff frequencylow-pass filterlumpeddistributedwaveformscharacteristic impedanceaudio frequencypassbandcarrier systemsdigital subscriber linem-derived filterT-carrierlongwaveradiotelegraphantennasMonopoledipoleresonatorstransmission linestanding waveswavelengthresistanceelectrically shortcapacitive reactancestanding wave ratioinductive reactanceradiation resistanceskin effectLitz wireproximity effectdielectric lossesVariometersflexible AC transmission systemstatic VAR compensatorstatic synchronous series compensatorGeorge Ashley Campbellpropagation constantconstant k filterimage filter theorylow-passJoseph-Louis Lagrangethe development of filterstransmission linesoperational calculusdistortionimpedanceadmittanceprimary line coefficientsconductanceJohn S. StoneAmerican Telephone & Telegraph CompanyGeorge Campbellfrequency-division multiplexingMichael PupinSerbiansubmarine communication cablesdispersionSiemens and HalskeLake Constancecable shipsCarl Emil KrarupHelsingørHelsingborgmagnetic permeabilitypermalloyOliver E. BuckleyH. D. ArnoldBell Labssubmarine communications cableHorta (Azores)Mu-metalTelegraph Construction and Maintenance CompanyWestern Union Telegraph CoWestern Electric Companyco-axial cablerepeatersfibre-optic cableWorld War IIElectrical lengtheningAntenna tunerUnloaded phantomSarkar, Tapan KOliner, Arthur ASalazar-Palma, Magdalenapublic domain materialGeneral Services AdministrationMIL-STD-188TelecommunicationsHistoryBroadcastingCable protection systemCable TVData compressionDigital mediaInternet videoonline video platformsocial mediastreamingEdholm's lawInformation AgeInformation revolutionInternetMobile phoneSmartphoneOptical telecommunicationOptical telegraphyPhotophonePrepaid mobile phone