Editing Loading coil (section)

===Michael Pupin===
[[File:Pupin coil.png|thumb|left|Pupin's design of loading coil]]
[[Mihajlo Idvorski Pupin|Michael Pupin]], inventor and [[Serbia]]n immigrant to the US, also played a part in the story of loading coils. Pupin filed a rival patent to the one of Campbell's.<ref>Pupin, M, ''Art of Reducing Attenuation of Electrical Waves and Apparatus Therefor'', US patent 0 652 230, filed 14 December 1899, issued 19 June 1900.</ref> This patent of Pupin's dates from 1899. There is an earlier patent<ref>Pupin, M, ''Apparatus for Telegraphic of Telephonic Transmission'', US patent 0 519 346, filed 14 December 1893, issued 8 May 1894.</ref> (1894, filed December 1893) which is sometimes cited as Pupin's loading coil patent but is, in fact, something different. 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,<ref>Pupin, M I, ''From Immigrant to Inventor'', pp. 330-331, Charles Schribner & Sons, 1924.</ref> although there is nothing from him published at that time.<ref>Brittain, p. 46</ref>

Pupin's 1894 patent "loads" the line with capacitors rather than inductors, a scheme that has been criticised as being theoretically flawed<ref>Brittain, p. 46, quoting a contemporary criticism in ''Electrical Review'' and experiments by the [[General Post Office|GPO]] showing that the scheme does not work.</ref> and never put into practice. To add to the confusion, one variant of the capacitor scheme proposed by Pupin does indeed have coils. However, these are not intended to compensate the line in any way. They are there merely to restore DC continuity to the line so that it may be tested with standard equipment. Pupin states that the inductance is to be so large that it blocks all AC signals above 50&nbsp;Hz.<ref>Pupin, 1894, p. 5 lines 75-83</ref> 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".<ref>Pupin, 1894, p. 5 lines 123-125</ref>
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