Editing Spark-gap transmitter (section)

===First transatlantic radio transmission===
{{multiple image
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| header =
| image1= The Marconi Company first antenna system at Poldhu, Cornwall, December 1901.jpg
| caption1= Marconi's transmitting station at Poldhu, Cornwall, showing the original 400-wire vertical inverted cone aerial which collapsed
| width1= 225
| image2= The Marconi Company second antenna system at Poldhu, Cornwall.jpg
| caption2= The temporary antenna used in the transatlantic transmission, a fan-shaped 50-wire aerial.
| width2= 240
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}}
[[File:Marconi first transatlantic radio transmitter circuit - Poldhu 1901.png|thumb|upright=1.4|Circuit of Poldhu transmitter.<ref name="Fleming"/> Fleming's curious dual spark gap design was not used in subsequent transmitters.]]
[[File:Marconi Poldhu UK radio transmitter - made first transatlantic transmission 1901.jpg|thumb|View of Poldhu transmitter]]
Marconi decided in 1900 to attempt transatlantic communication, which would allow him to dominate Atlantic shipping and compete with [[submarine telegraph cable]]s.<ref name="Hong" />{{rp|p.60-61}}<ref name="Sarkar" />{{rp|p.387-392}} This would require a major scale-up in power, a risky gamble for his company. Up to that time his small induction coil transmitters had an input power of 100 - 200 watts, and the maximum range achieved was around 150 miles.<ref name="Hong" />{{rp|p.60-61}}<ref name="Fleming">{{cite book
| last1= Fleming
| first1= John Archibald
| title= The Principles of Electric Wave Telegraphy
| publisher= Longmans Green and Co.
| date= 1906
| location= London
| pages= 449–454
| url= https://archive.org/stream/cu31924074412739#page/n489/search/poldhu
}}</ref> To build the first high power transmitter, Marconi hired an expert in electric power engineering, Prof. [[John Ambrose Fleming]] of University College, London, who applied power engineering principles. Fleming designed a complicated inductively-coupled transmitter ''(see circuit)'' with two cascaded spark gaps ''(S1, S2)'' firing at different rates, and three resonant circuits, powered by a 25&nbsp;kW [[alternator]] ''(D)'' turned by a combustion engine.<ref name="Fleming"/><ref name="Hong" />{{rp|p.60-61}}<ref name="Belrose">{{cite conference
| last1= Belrose
| first1= John S.
| title= Fessenden and Marconi: Their differing technologies and transatlantic experiments during the first decade of this century
| conference= Proceedings of the 1995 International Conference on 100 Years of Radio
| pages= 32–34
| publisher= Institute of Engineering and Technology
| date= 5 September 1995
| location= London
| doi= 10.1049/cp:19950787
| issn= 0537-9989
| citeseerx= 10.1.1.205.7281
| s2cid= 218471926
}}</ref> The first spark gap and resonant circuit ''(S1, C1, T2)'' generated the high voltage to charge the capacitor ''(C2)'' powering the second spark gap and resonant circuit ''(S2, C2, T3)'', which generated the output.<ref name="Belrose"/> The spark rate was low, perhaps as low as 2 - 3 sparks per second.<ref name="Belrose"/> Fleming estimated the radiated power was around 10 - 12&nbsp;kW.<ref name="Fleming"/>

The transmitter was built in secrecy on the coast at [[Poldhu]], [[Cornwall]], UK.<ref name="Fleming"/><ref name="Hong" />{{rp|p.60-61}} Marconi was pressed for time because [[Nikola Tesla]] was building his own transatlantic radiotelegraphy transmitter on [[Long Island, New York]], in a bid to be first<ref name="Hong" />{{rp|p.286-288}} (this was the [[Wardenclyffe Tower]], which lost funding and was abandoned unfinished after Marconi's success). Marconi's original round 400-wire transmitting antenna collapsed in a storm 17 September 1901 and he hastily erected a temporary antenna consisting of 50 wires suspended in a fan shape from a cable between two 160 foot poles.<ref name="Fleming"/><ref name="Belrose"/><ref name="Hong" />{{rp|p.286-288}} The frequency used is not known precisely, as Marconi did not measure wavelength or frequency, but it was between 166 and 984&nbsp;kHz, probably around 500&nbsp;kHz.<ref name="Sarkar" />{{rp|p.387-392}} He received the signal on the coast of St. John's, [[Dominion of Newfoundland|Newfoundland]] using an untuned [[coherer]] [[radio receiver|receiver]] with a 400&nbsp;ft. wire antenna suspended from a [[kite]].<ref name="Sarkar" />{{rp|p.387-392}}<ref name="Fleming"/><ref name="Hong" />{{rp|p.286-288}} Marconi announced the first transatlantic radio transmission took place on 12 December 1901, from [[Poldhu]], [[Cornwall]] to [[Signal Hill, St. John's|Signal Hill, Newfoundland]], a distance of 2100&nbsp;miles (3400&nbsp;km).<ref name="Sarkar" />{{rp|p.387-392}}<ref name="Hong" />{{rp|p.286-288}}

Marconi's achievement received worldwide publicity, and was the final proof that radio was a practical communication technology. The scientific community at first doubted Marconi's report. Virtually all wireless experts besides Marconi believed that radio waves traveled in straight lines, so no one (including Marconi) understood how the waves had managed to propagate around the 300 mile high curve of the Earth between Britain and Newfoundland.<ref name="Gregersen"/> In 1902 [[Arthur Kennelly]] and [[Oliver Heaviside]] independently theorized that radio waves were reflected by a layer of [[ionization|ionized]] atoms in the upper atmosphere, enabling them to return to Earth beyond the horizon.<ref name="Gregersen"/> In 1924 [[Edward V. Appleton]] demonstrated the existence of this layer, now called the "[[Kennelly–Heaviside layer]]" or "E-layer", for which he received the 1947 [[Nobel Prize in Physics]].

Knowledgeable sources today doubt whether Marconi actually received this transmission.<ref name="Margolis">{{Cite news
| last= Margolis
| first= Laurie
| title= Faking the waves
| newspaper= The Guardian
| location= London
| date= 11 December 2001
| url= https://www.theguardian.com/education/2001/dec/11/highereducation.news
| access-date= 8 September 2018}}</ref><ref name="Belrose"/><ref name="Sarkar" />{{rp|p.387-392}} Ionospheric conditions should not have allowed the signal to be received during the daytime at that range. Marconi knew the Morse code signal to be transmitted was the letter 'S' (three dots).<ref name="Sarkar" />{{rp|p.387-392}} He and his assistant could have mistaken atmospheric [[radio noise]] ("static") in their earphones for the clicks of the transmitter.<ref name="Belrose"/><ref name="Sarkar" />{{rp|p.387-392}} Marconi made many subsequent transatlantic transmissions which clearly establish his priority, but reliable transatlantic communication was not achieved until 1907 with more powerful transmitters.<ref name="Belrose"/>