Editing Reginald Fessenden (section)

===Audio transmissions===
Fessenden had a very early interest in the possibility of making audio radio transmissions, in contrast to the early spark-gap transmissions that could only transmit Morse code messages. As early as 1891, he had investigated sending alternating currents of varying frequencies along telegraph lines, in order to create a multiplex telegraph system.<ref>[https://babel.hathitrust.org/cgi/pt?id=njp.32101048865586&view=1up&seq=280 "Sine Form Curves of Alternating E.&nbsp;M.&nbsp;F."] (letter from Reginald Fessenden), ''The Electrical World'', September 15, 1894, p. 264.</ref> He would later apply the knowledge gained about tuning and resonance from his alternating current electrical work to the higher frequency currents used in radio, in order to develop the concept of [[continuous wave|continuous-wave]] radio signals.<ref>Fessenden, Helen (1940), [https://babel.hathitrust.org/cgi/pt?id=uc1.b4540711&view=1up&seq=74 pp. 60–61, 76].</ref>

Fessenden's basic approach was disclosed in U.S. Patent 706,737, which he applied for on May 29, 1901, and was issued the next year. It called for the use of a high-speed alternator (referred to as "an alternating-current dynamo") that generated "pure sine waves" and produced "a continuous train of radiant waves of substantially uniform strength", or, in modern terminology, a continuous-wave (CW) transmitter.<ref>{{patent|US|706737|patent: "Wireless Telegraphy"}}, submitted May 29, 1901, and issued August 12, 1902, to Reginald Fessenden.</ref> The idea of using continuous-wave radio signals was in direct conflict with the current orthodoxy that the abrupt "whiplash" effect produced by large electrical sparks was needed in order to create adequately strong signals. [[John Ambrose Fleming]], a Marconi associate, was particularly dismissive in his book ''The Principles of Electric Wave Telegraphy'', a detailed review of the state of the art as he saw it that was published in 1906. Reviewing Fessenden's patent, he wrote that "The creation of an electric wave seems to involve a certain suddenness in the beginning of the oscillations, and an alternator giving a simple sine-curve would not be likely to produce the required effect..."<ref>[https://babel.hathitrust.org/cgi/pt?id=wu.89059298398&view=1up&seq=557 ''The Principles of Electric Wave Telegraphy''] by J. A. Fleming, 1906 edition, p. 511.</ref> (In view of Fessenden's ultimate success, this statement disappeared from the book's 1916 edition.) Fessenden's next step, taken from standard wire-telephone practice, was to insert a simple [[carbon microphone]] into the transmission line, which was used to modulate the [[carrier wave]] signal for audio transmissions, or, again using modern terms, used to produce [[amplitude modulation|amplitude modulated]] (AM) radio signals.<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=149 "Figure 9"], "Experiments and Results in Wireless Telephony" (part II) by John Grant, ''The American Telephone Journal'', February 2, 1907, p. 70.</ref>

Fessenden began his research on audio transmissions while still on Cobb Island. Because he did not yet have a continuous-wave transmitter, initially he worked with an experimental "high-frequency spark" transmitter, taking advantage of the fact that the higher the spark rate, the closer a spark-gap transmission comes to producing continuous waves. He later reported that, on December 23, 1900, he successfully transmitted speech over a distance of about 1.6 kilometers (one mile), saying; “One, two, three, four. Is It snowing where you are, Mr. Thiessen? If so, telegraph back and let me know”, which appears to have been the first successful audio transmission using radio signals.<ref name="experiments">"Experiments and Results in Wireless Telephony" by John Grant, ''The American Telephone Journal''. [https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=111 Part I]: January 26, 1907, pp. 49–51; [https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=147 Part II]: February 2, 1907, pp. 68–70, 79–80.</ref><ref>[https://www.thestar.com/news/canada/2020/12/23/the-canadian-father-of-radio-broadcasting.html The Canadian Father of Radio Broadcasting – Toronto Star]</ref> However, at this time the sound was far too distorted to be commercially practical, although as a test this did show that with further refinements it would become possible to effectively transmit sounds by radio.<ref>Aitken (1985), p. 61.</ref> 

For a time Fessenden continued working with more sophisticated high-frequency spark transmitters, including versions that used compressed air, which began to take on some of the characteristics of [[arc converter|arc-transmitters]] patented by [[Valdemar Poulsen]].<ref>Aitken (1985), p. 62.</ref> Fessenden unsuccessfully attempted to sell this form of radiotelephone, later noting: "In 1904, with a 20,000 frequency spark and compressed nitrogen gap, such good results were obtained that a demonstration was given to a number of electrical engineers, who signed affidavits that they considered the articulation as commercially good over twenty-five miles, and the sets were advertised for sale..."<ref name=FESS>{{cite web|url=https://ewh.ieee.org/reg/7/millennium/radio/radio_wireless.html |author=Fessenden, Reginald A. |title=Inventing the Wireless Telephone and the Future |publisher=[[IEEE]] |access-date=2014-02-09}}</ref> (In a 1908 review, he conceded that with this approach "The transmission was, however, still not absolutely perfect.")<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015068171985&view=1up&seq=585 "Wireless Telephony"] by Reginald A. Fessenden, ''Transactions of the American Institute of Electrical Engineers'', Vol. XXVII (1908), Part 1, pp. 553–629.</ref>