User:Anthony Appleyard/Marconi's role in the history of radio
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- This is a longer description of Guglielmo Marconi's role in the history of radio. For the main article, see History of radio.
[edit] Marconi's early work
After the 1880s Hertz experiments, Guglielmo Marconi's proponents state that he read about the work while on vacation in 1894 (which was the same year Hertz died). Marconi wondered if radio waves could be used for wireless communications. [1] Marconi’s early apparatus was a development of Hertz’s laboratory apparatus into a system designed for communications purposes. At first he used a transmitter to ring a bell in a receiver in his attic laboratory. He then moved his experiments out-of-doors on the family estate near Bologna, Italy, to communicate over larger distances. He replaced Hertz’s vertical dipoles by a vertical wire topped by a metal sheet, together with an opposing terminal that had a ground connection. The Marconi antenna was a vertical quarterwave monopole conductor, with no loading coil nor capacitive top load, and base driven by a regular power supply with a suitable matching section. Marconi replaced the spark gap in his receiver by the metal powder coherer, a detector developed by Edouard Branly and other experimenters. Marconi transmitted radio signals a distance of about a mile at the end of 1895. [2]
Marconi's reputation is based, in large measure, on these accomplishments in radio communications and commercializing a practical system. His demonstrations of the use of radio for wireless communications, equipping ships with life saving wireless communications, establishing the first transatlantic radio service, and building the first stations for the British short wave service, have marked his place in history. Marconi and his company were not alone in the field; his principal competition came from German scientists whose work would become the basis for the Telefunken company (which Nikola Tesla assisted in building).
[edit] Case against Marconi: priority
- For Marconi's dispute with Tesla over priority, see Radio priority controversy.
[edit] Marconi's patent
Marconi's U.S. Patent 586193 (July 13, 1897) (and the reissued U.S. Patent RE11913 ) disclosed a two-circuit system for the transmission and reception of "Hertzian waves" (though he would later acknowledge that in the early wireless systems the "waves do not propagate in the same manner as free radiation from a classical Hertzian oscillator, but glide along the surface of the Earth" [3]). The transmitter was an antenna circuit, with an aerial plate and a ground plate, and a spark gap. Induced signals in the circuit were caused to discharge through a spark gap, producing oscillations which were radiated. The receiver contained an antenna circuit, an aerial plate and a ground plate, and a coherer. Marconi's apparatus was to be resonant (commonly called by various researcheres at the time "syntonic"). This was done by the careful determination of the size of the aerial plates.
[edit] The Poldhu experiment
In 1901, Marconi claimed to have received daytime transatlantic radio short wave (HF) frequency signals at a wavelength of 366 metres (820 kHz). [4] [5] [6] The early spark transmitters may have been broadly tuned and the Poldhu transmitter may have radiated sufficient energy in that part of the spectrum for a transatlantic transmission, if Marconi was using an untuned receiver when he claimed to have received the transatlantic signal at Newfoundland in 1901. When he used a tuned receiver aboard the SS Philadelphia in 1902, he could only receive a daytime signal from Poldhu, a distance of 700 miles, less than half the distance from Poldhu to Newfoundland. At night the signals were reported to have been received several times further, and his successful transatlantic transmissions from Glace Bay, Nova Scotia in 1902 were made at night. Marconi would later found the Marconi Company and would jointly receive the 1909 Nobel Prize in Physics with Karl Ferdinand Braun.
[edit] Case against Marconi: Poldhu
Marconi’s 1901 Poldhu - Newfoundland transmission claim has been doubted. [7] Critics have stated that it is more likely that Marconi received stray atmospheric noise from atmospheric electricity in the 1901 experiment.[8] The transmitting station in Poldhu, Cornwall used a spark-gap transmitter that, at best, could produce a signal just below the medium frequncy and with high power levels (a maximum time-averaged power of 35 kilowatts, but with a peak pulse power of megawatts). The message reportedly received was three dots. Dr Jack Belrose has recently contested this, however, based on theoretical work as well as an actual reenactment of the experiment; he believes that Marconi heard only random atmospheric noise and mistook it for the signal. There are engineers who agree with Jack Belrose that the 1901 bridging of the Atlantic never took place. If it did take place then it should be possible to tune in to VOCM Radio, Newfoundland, at around 4PM in December in Britain.... or BBC Radio going the other way. VOCM is on a frequency near to that used by Marconi. It has only ever been heard in Britain after midnight and nowhere near strong enough to be detected by Marconi's very crude and insensitive receiver.
[edit] Footnotes and citations
- ^ Henry M. Bradford, "Marconi's Three; Transatlantic Radio Stations In Cape Breton". Read before the Royal Nova Scotia Historical Society, 31 January 1896. (ed. the site is reproduced with permission from the Royal Nova Scotia Historical Society Journal, Volume 1, 1998.)
- ^ Marconi's Three; Transatlantic Radio Stations In Cape Breton.
- ^ Marconi, "Wireless Telegraphic Communication: Nobel Lecture, December 11, 1909." Nobel Lectures. Physics 1901-1921. Amsterdam: Elsevier Publishing Company, 1967: 196-222.
- ^ Henry M. Bradford, "Marconi in Newfoundland: The 1901 Transatlantic Radio Experiment".
- ^ Henry M. Bradford, "Did Marconi Receive Transatlantic Radio Signals in 1901? - Part 1". Wolfville, N.S..
- ^ Henry M. Bradford, "Did Marconi Receive Transatlantic Radio Signals in 1901? Part 2, Conclusion: The Trans-Atlantic Experiments". Wolfville, N.S..
- ^ John S. Belrose, "Fessenden and Marconi; Their Differing Technologies and Transatlantic Experiments During the First Decade of this Century", International Conference on 100 Years of Radio, 5-7 September, 1995, (PDF file; ed. accessed April 14, 2006)
- ^ "Marconi's Error: The First Transatlantic Wireless Telegraphy in 1901"
