Invention of radio

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Contents 1 Hertz's radio work 2 Tesla's radio work 2.1 Tesla's arc-lamp patent 2.2 Tesla's work in New York 2.3 Tesla's results 2.4 Tesla's radio apparatus 2.5 Tesla's first two radio patents 2.5.1 Tesla's radio patents taken away & regranted 3 de Moura's radio work 4 Marconi's radio work 4.1 Marconi's early work 4.2 Marconi's patent 4.3 The Poldhu experiment 4.3.1 Doubt about the Poldhu result 5 Jagdish Chandra Bose's radio work 6 Court decision 7 Case for Marconi 8 Case against Marconi: priority 9 Case for Tesla 10 Case against Tesla 11 Timeline 12 Footnotes and citations

Many people men were involved in the invention of radio transmission of information as we know it today. Despite this, during its early development and long after wide acceptance, disputes persisted as to who could claim sole credit for this obvious boon to mankind. Much of this argument was and is driven by perceived profit or national pride, and so tends to consider such issues as 'the first practical...' (for a given value of 'practical'), or whether the development took place in the inventor's country of birth or not.

It is indisputable that Maxwell performed the theoretical physical research which correctly predicted the existence of radio (and all other electromagnetic) waves, and that Hertz was the experimental physicist who first created radio waves in a controlled manner. All other developments are greater or lesser engineering developments of this work, and so cannot be truly said to be 'inventions of radio', though many are certainly major developments in the field.

This Wikipedia entry covers the main arguments about attributions pertaining to the early development of radio. For the general history of radio, see History of radio.

[edit] Hertz's radio work

Between 1886 and 1888 in his classic UHF experiments, Heinrich Hertz had proved that the properties of radio waves were consistent with Maxwell’s electromagnetic theory. He demonstrated that radio radiation had all the properties of waves (now called Hertzian waves), and discovered that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.

Of the three basic forms of wireless aerial launching structures common at the time, the Hertz antenna was a center-fed half-wavelength vertical dipole. No ground connection was used. Hertz’s source and detector of radio waves might be regarded as a type of primitive radio transmitter and receiver good for true free space transmission (but the transmitter was not very good for actual use at the low frequency space waves that most early wireless systems used as it had no "ground" or earthing element). ^{[1] [2]}

Hertz used the damped oscillating currents in a dipole antenna, triggered by a high-voltage electrical spark discharge, as his source of radio waves. His detector in some experiments was another dipole antenna connected to a narrow spark gap. A small spark in this gap signified detection of the radio wave. When he added cylindrical reflectors behind his dipole antennas, Hertz could detect radio waves about 20 metres from the transmitter in his laboratory. He did not try to transmit further because he wanted to prove electromagnetic theory, not to develop wireless communications.

Hertz was uninterested in the practical importance of his experiments. He stated that "It's of no use whatsoever ... this is just an experiment that proves Maestro Maxwell was right - we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there." ^[3]

Asked about the ramifications of his discoveries, Hertz replied, "Nothing, I guess."

His discoveries would later be taken up by entrepreneurs looking to make their fortunes. Marconi's 1895 experiments followed Hertz's work (among others) by using a spark source in what became known as a spark-gap transmitter.

[edit] Tesla's radio work

[edit] Tesla's arc-lamp patent

Tesla was one of the first to patent a means to reliably produce radio frequencies. Tesla's U.S. Patent 447920 , "Method of Operating Arc-Lamps" (March 10, 1891), describes an alternator that produces high-frequency current for that time period, around 10,000 cycles per second (later to be known as hertz). His patentable innovation was to suppress the disagreeable sound of power-frequency harmonics produced by arc lamps operating on frequencies within the range of human hearing, but the frequency produced by the device was in the longwave broadcasting range (VLF band).

[edit] Tesla's work in New York

Around July of 1891, he established his New York laboratory and constructed various apparatus that produced between 15,000 to 18,000 cycles per second. At this location, he also lit vacuum tubes wirelessly (thus providing hard evidence for the potential of wireless transmissions).

[edit] Tesla's results

Transmission and radiation of radio frequency energy was a feature exhibited in the experiments by Tesla and was noted early on to be used for the telecommunication of information. ^[4][5]

In 1892, Tesla delivered a widely reported presentation before the Institution of Electrical Engineers of London in which he noted, among other things, that intelligence would be transmitted without wires. Later, a variety of Tesla's radio frequency systems were demonstrated during another widely known lecture, presented to meetings of the National Electric Light Association in St. Louis, Missouri and the Franklin Institute in Philadelphia. According to the IEEE, "the apparatus that he employed contained all the elements of spark and continuous wave that were incorporated into radio". ^[6]

In the beginning of 1895, Tesla could detect signals from the transmissions of his New York lab at West Point (50 miles away). ^[7] By early 1896, he attained devices that produced undamped (or continous) waves around 50,000 cycles per second^[8] and, between 1895 and 1898, Tesla continued his research into wireless transmission principles. After travelling to Colorado Springs (around 1899), Tesla lit a bank of incandescent bulbs wirelessly at very long distances during his experiments with the magnifying transmitter.

[edit] Tesla's radio apparatus

Tesla's aerial parameters consisted of a small (as to distribution of height) vertical high aspect-ratio quarterwave helical resonator, with a large capacitive top load, which was driven at the base by a regular power supply and suitable matching section. The aerial's opposing terminal was grounded. Tesla’s vertical structure could radiate as a common "hertzian" antenna, if driven in a certain fashion; but it would resonate if the driving circuitry was arranged properly. Some of the roughly hemispherical conductors that Tesla used had a capacitance comparable to that of a large radio antenna. The applied voltage caused an oscillating current to flow between the earth and the elevated conductor, as it does in a conventional low frequency radio transmitter with a vertical radio antenna and ground.

Tesla’s structure could also inject a large alternating current into the earth via the ground terminal. Tesla's discovery of great importance was the "groundwave" method. The method to produce surface waves was the consequence of adding a ground connection to the transmitter. Tesla said in 1893 that "One of the terminals of the source would be connected to Earth [as a electric ground connection ...] the other to an insulated body of large surface. ^[9] This method led to longer transmission ranges. Many AM stations use this same principle to boost reception of their signals. ^[10]

[edit] Tesla's first two radio patents

Nikola Tesla initially held the rights to radio. He had these patents:-

• Division of U.S. Patent 645576  "System of Transmission of Electrical Energy", March 20, 1900 (March 20, 1900; filed Sept. 2, 1897). In US645576, Tesla cited the well-known radiant energy phenomena and corrected previous errors in theory of behavior. Within this specification, Tesla declared, "The apparatus which I have shown will obviously have many other valuable uses - as, for instance, when it is desired to transmit intelligible messages to great distances [...]".
• U.S. Patent 649621 , "Apparatus for Transmission of Electrical Energy" (May 15, 1900; filed Feb. 19, 1900). In US649621, Tesla established a system which was composed of a transmitting coil (or conductor) arranged and excited to cause oscillations (or currents) to propagate via conduction through the natural medium from one point to another remote point therefrom and a receiver coil, or conductor, of the transmitted signals.

[edit] Tesla's radio patents taken away & regranted

Shortly after the turn of the 20th century, the US Patent Office reversed its decision on the priority of radio and awarded Marconi the patent for radio. Tesla was later re-granted a patent for the radio by the U.S. Supreme Court in 1943.

The consideration of patents, particularly in the US, is a political and profit-driven activity, and often subject to external pressure, including corrupt influence. It should not therefore be held to be an indicator to determine primacy in academic research.

[edit] de Moura's radio work

Father Landell de Moura, in the late 1800s, established the pioneering radio transmission experiment, with a transmitter located in downtown Sao Paulo and a receiver placed in one of its suburbs, some eight kilometers apart. Thus wireless communications commenced.[1]

[edit] Marconi's radio work

[edit] Marconi's early work

Guglielmo Marconi's proponents say that while on vacation in 1894 he read about the experiments which Hertz did in the 1880s. (Also, Hertz died in 1894). Marconi wondered if radio waves could be used for wireless communications.^[11]

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 further. He replaced Hertz’s vertical dipoles by a vertical wire topped by a metal sheet, with an opposing terminal connected to the ground. The Marconi antenna was a vertical quarter-wave monopole conductor, with no loading coil and no 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 for about a mile at the end of 1895. ^[12]

Marconi's reputation is largely based 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] 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" ^[13]). 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). ^{[14] [15] [16]} 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] Doubt about the Poldhu result

Marconi’s 1901 Poldhu to Newfoundland transmission claim has been attacked. ^[17] Critics have claimed that it is more likely that Marconi received stray atmospheric noise from atmospheric electricity in the 1901 experiment.^[18] The transmitting station in Poldhu, Cornwall used a spark-gap transmitter that 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 received was the morse letter 'S' - three dots. Dr Jack Belrose has recently contested this, however, based on theoretical work as well as a reenactment of the experiment; he believes that Marconi heard only random atmospheric noise and mistook it for the signal. There are Tesla supporters who agree with Jack Belrose that the Atlantic was not bridged in 1901, but most science historians agree that this was the first trans-atlantic radio transmission.

[edit] Jagdish Chandra Bose's radio work

In November of 1894, the Indian physicist, Jagdish Chandra Bose, demonstrated publicly the use of radio waves in Calcutta, but he was not interested in patenting his work. ^[19] For more information see History of radio (more information)#Jagdish Chandra Bose.

In 1894, Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves, showing independently that communication signals can be sent without using wires. In 1896, the Daily Chronicle of England reported on his UHF experiments: "The inventor (J.C. Bose) has transmitted signals to a distance of nearly a mile and herein lies the first and obvious and exceedingly valuable application of this new theoretical marvel."

In Russia |Popov was performing similar experiments, but had recorded in December 1895 that he was hoping for distant signalling with radio waves. ^[20]

The 1895 public demonstration by Bose in Calcutta was before Marconi's wireless signalling experiment on Salisbury Plain in England in May 1897. ^{[21] [22]}

But Tesla demonstrated radio communication earlier, in 1892 and 1893.

Bose was not interested in the commercial applications of the experiment's transmitter. He did not try to file patent protection for sending signals. In 1899, Bose announced the development of a "iron-mercury-iron coherer with telephone detector" in a paper presented at the Royal Society, London. ^[23]

Later he received U.S. Patent 755840 , "Detector for electrical distrubances" (1904), for a specific electromagntic receiver. He is not known for greatly contributing to the development of commercial radio communication and did not file any patents for transmission, but he deserves recognition for contributing to the development of radio.

[edit] Court decision

In 1943 a lawsuit regarding Marconi's numerous other radio patents was resolved by the U.S. Supreme Court, who overturned most of these. At the time, the United States Army was involved in a patent infringement lawsuit with Marconi's company regarding radio, leading various observers to posit that the government nullified Marconi's other patents in order to moot any claims for compensation (as, it is speculated, the government's initial reversal to grant Marconi the patent right in order to nullify any claims Tesla had for compensation).

The court decision was based on the proven prior work conducted by others, such as by Tesla, Oliver Lodge, and John Stone Stone, from which some of Marconi patents (such as U.S. Patent 763772 ) stemmed. The U. S. Supreme Court stated that,

"The Tesla patent No. 645,576, applied for September 2, 1897 and allowed March 20, 1900, disclosed a four-circuit system, having two circuits each at transmitter and receiver, and recommended that all four circuits be tuned to the same frequency. [... He] recognized that his apparatus could, without change, be used for wireless communication, which is dependent upon the transmission of electrical energy." ^[24]

In making their decision, the court noted,

"Marconi's reputation as the man who first achieved successful radio transmission rests on his original patent, which became reissue No. 11,913, and which is not here [320 U.S. 1, 38] in question. That reputation, however well-deserved, does not entitle him to a patent for every later improvement which he claims in the radio field. Patent cases, like others, must be decided not by weighing the reputations of the litigations, but by careful study of the merits of their respective contentions and proofs." ^[25]

The court also stated that,

"It is well established that as between two inventors priority of invention will be awarded to the one who by satisfying proof can show that he first conceived of the invention." ^[26]

[edit] Case for Marconi

Marconi supporters have stated that Marconi was not aware of the works of Nikola Tesla in the United States. It is unlikely, though, that Marconi was unaware of Tesla's presentations. Both "On Light and Other High Frequency Phenomena" (Philadelphia/St. Louis; Franklin Institute in 1893) and "Experiments with Alternating Currents of High Potential and High Frequency" (London; 1892) were reported on internationally. Tesla's 1893 presentation at the Franklin Institute was reported across America (such as in the Century Magazine) and throughout Europe.^[27] Tesla also performed public demonstrations of actual and related work, such as the remote-controlled boat in 1898 (which was protected under U.S. Patent 613809 ). The remote-controlled boat contained "rotating coherers" that allowed secure communication between transmitter and receiver.

[edit] Case against Marconi: priority

By 1895, Marconi introduced to the public a device in London, asserting it was his invention. Despite Marconi's statements to the contrary, though, the apparatus resembles Tesla's descriptions in the widely translated articles. ^[28] Marconi's later practical four-tuned system was pre-dated by N. Tesla, Oliver Lodge, and J. S. Stone. Tesla was the first, though, to expound the principles of the four tuned system. The earlier two tuned systems were not practical for commercial activity (as found in the United States court case). In addition, other prior work was conducted by others (such as by Hertz and Bruan, but not excluding others) from which many of Marconi's devices and methods were derived. Marconi's U.S. Patent 676332  Apparatus for wireless telegraphy [1901], in which a more developed system was disclosed than in his earlier patents, was well after contributions made by other investigators.

Marconi’s late-1895 transmission of signals was for around a mile. This was small when put against Tesla's early-1895 transmissions of up to 50 miles.

[edit] Case for Tesla

Nikola Tesla at first held the rights to radio: see #Tesla's first two radio patents.

Tesla's system can produce a variety of wave propagations, pending the driving apparatus. Tesla believed that his wireless system would be better than most other radio systems because transverse electromagnetic waves (whose behavior depends on its wavelength) would decay as they travelled from the transmitter, making the signals uselessly weak at long distances. Tesla advanced that longitudinal electromagnetic waves (such as those that occur in waves in plasmas) through the medium would be used, as he theorized that they would be practically lossless. His devices can be driven to produce either transverse or longitudinal waves.

Besides his intention to transmit wireless signals of intelligence, he proposed to transmit electric power via electrical conduction through the Earth and the upper atmosphere, as well as in between them both (in the Earth-ionosphere region which is now known as a resonant cavity). This power transmission was to be done not by "hertzian waves", but through standing surface waves. Tesla’s proposed wireless transmitter utilized a resonant transformer to apply a very high voltage of high frequency between the earth and a large elevated conductor, as discussed earlier.

[edit] Case against Tesla

Tesla never completed his "worldwide wireless system", primarily because of financial difficulties. Cost overruns stopped him from completing the Wardenclyffe Tower (a "wireless station tower") that he built in the early 1900s in Shoreham on Long Island, New York. Many Marconi supporters dispute the relevance of Tesla demonstrations of the remote-controlled boat (with its internal rotating coherer) as well as Tesla's public lecture demonstrations^{[citation needed]}.

[edit] Timeline

• 1864: James Clerk Maxwell mathematically predicts the existence of radio waves.
• 1872: Mahlon Loomis and W. H. Ward (USA) file for U.S. Patents for a "wireless telegraph".
• 1885 - 1886: Heinrich Hertz proves the existence of radio waves.
• As a professor of physics at Karlsruhe Polytechnic, he produces electromagnetic waves in the laboratory and measures their wavelength and velocity. He shows that the nature of their reflection and refraction was the same as those of light, confirming that light waves are electromagnetic radiation obeying the Maxwell equations.
• 1887: Hertz publishes his research in the journal Annalen der Physik.
• 1890: Edouard Branly invents the coherer .
• 1892: Hertz publishes "Untersuchungen Ueber Die Ausbreitung Der Elektrischen Kraft” (“Investigations on the Propagation of Electrical Energy”).
• 1893: Tesla demonstrates "wireless telegraphy" at the Franklin Institute in Philadelphia and the National Electric Light Association, eight years after Hertz.
• 1894: Hertz dies, aged 37.
• 1894: Alexander Popov builds his first radio receiver in Russia. This was the first non-laboratory radio service.
• 1894: Oliver Lodge transmits radio signals at a meeting of the British Association for the Advancement of Science at Oxford University on August 14. One year before Marconi but one year after Tesla.
• 1894: Jagadish Chandra Bose uses electromagnetic waves to ignite gunpowder and ring a bell at a distance in November in Calcutta.
• 1895: Popov presents his radio receiver to the Russian Physical and Chemical Society on May 7. The paper on his findings was published December 15.
• 1895: Marconi transmits radio signals a distance of about a mile.
• 1897: Tesla applies for US patent for the four-tuned circuit.
• 1897: Marconi receives British patent for his work, establishes the world's first radio station on the Isle of Wight, England & forms the London company later to become the Marconi Wireless Telegraph Company
• 1897: Bose reports on his microwave radio experiments to the Royal Institute in London & speculates on the existence of electromagnetic radiation from the sun,
• 1898: Popov effects ship-to-shore communication over a distance of 6 miles
• 1898: Tesla publicly demonstrates his remote-controlled boat containing "rotating coherers" that allowed secure communication between transmitter and receiver.
• 1900: Popov supervises the construction of a radio station on Hogland island providing a two-way communication by wireless telegraphy between Russian navy base and crew of the battleship General-Admiral Apraksin.
• 1900: Tesla opens the Wardenclyffe Tower facility and advertised services
• 1901: Marconi receives the first trans-Atlantic radio signal on 12 December. The message received was three dots, the Morse code for the letter S.
• 1904: Bose receives patent for the use of a semi-conducting crystal as a detector of radio waves
• 1904: John Ambrose Fleming develops the "oscillation valve" or "kenotron". Later known as the diode.
• 1906: Lee De Forest invents the "audion", now known as the triode.
• 1906: Reginald Fessenden transmits the first audio radio broadcast on AM from Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing the song Silent Night on the violin and reading a passage from the Bible.
• 1909: Marconi wins the Nobel Prize in physics
• 1910: Lee de Forest, inventor of a type of vacuum tube called a triode, aired programs from New York's Metropolitan Opera House.
• 1920s: Hundreds of radio stations emerge in the USA
• 1922: The BBC begins broadcasting from London, on November 14.
• 1928: Julius Edgar Lilienfeld patents the transistor principle in Germany
• 1933: Edwin Armstrong patents FM (frequency modulation)
• 1947: William Shockley, John Bardeen and Walter Brattain succeeds in building the first practical point-contact transistor at Bell Labs on 22 December. This work followed from their war-time research into radar.
• 1956: Shockley, Bardeen and Brattain receive the Nobel Prize in Physics for the invention of the transistor.

[edit] Footnotes and citations

1. ^ Gary L. Peterson, "Comparing the Hertz-wave and Tesla wireless system". Feed Line No. 9 Article
2. ^ Hertz wave
3. ^ Eugenii Katz, "Heinrich Rudolf Hertz". Biographies of Famous Electrochemists and Physicists Contributed to Understanding of Electricity, Biosensors & Bioelectronics.
4. ^ "On Light and Other High Frequency Phenomena". Delivered before the Franklin Institute, Philadelphia, February 1893, and before the National Electric Light Association, St. Louis, March 1893.
5. ^ "Experiments with Alternating Currents of High Potential and High Frequency". Delivered before the Institution of Electrical Engineers, London, February 1892.
6. ^ "Nikola Tesla, 1856 - 1943". IEEE History Center, IEEE, 2003.
7. ^ PBS: Marconi and Tesla: Who invented radio? (ed. this is noted as having been accomplished in Leland's book concerning Tesla's "Work with Alternating Currents" [see general information section])
8. ^ Covered in Leland's book concerning Tesla's "Work with Alternating Currents".
9. ^ "On Light and Other High Frequency Phenomena". Delivered before the Franklin Institute, Philadelphia, February 1893, and before the National Electric Light Association, St. Louis, March 1893.
10. ^ "Why AM Radio Stations Must Reduce Power, Change Operations, or Cease Operations at Night". fcc.gov.
11. ^ 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.)
12. ^ Marconi's Three; Transatlantic Radio Stations In Cape Breton.
13. ^ Marconi, "Wireless Telegraphic Communication: Nobel Lecture, December 11, 1909." Nobel Lectures. Physics 1901-1921. Amsterdam: Elsevier Publishing Company, 1967: 196-222.
14. ^ Henry M. Bradford, "Marconi in Newfoundland: The 1901 Transatlantic Radio Experiment".
15. ^ Henry M. Bradford, "Did Marconi Receive Transatlantic Radio Signals in 1901? - Part 1". Wolfville, N.S..
16. ^ Henry M. Bradford, "Did Marconi Receive Transatlantic Radio Signals in 1901? Part 2, Conclusion: The Trans-Atlantic Experiments". Wolfville, N.S..
17. ^ 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)
18. ^ "Marconi's Error: The First Transatlantic Wireless Telegraphy in 1901"
19. ^ "Jagadish Chandra Bose". ieee-virtual-museum.org.
20. ^ D.T. Emerson, "The work of Jagadis Chandra Bose: 100 years of mm-wave research". National Radio Astronomy Observatory, February 1998.
21. ^ "The Work of Jagdish Chandra Bose: 100 years of mm-wave research". tuc.nrao.edu.
22. ^ "Jagadish Chandra Bose", ieee-virtual-museum.org.
23. ^ Bondyopadhyay, Probir K., "Sir J. C. Bose's Diode Detector Received Marconi's First Transatlantic Wireless Signal Of December 1901 (The "Italian Navy Coherer" Scandal Revisited)". Proc. IEEE, Vol. 86, No. 1, January 1988.
24. ^ U.S. Supreme Court, "Marconi Wireless Telegraph co. of America v. United States". 320 U.S. 1. Nos. 369, 373. Argued April 9-12, 1943. Decided June 21, 1943.
25. ^ Wireless Telegraph co. of America v. United States.
26. ^ Wireless Telegraph co. of America v. United States.
27. ^ Ljubo Vujovi, "Tesla Biography; Nikola Tesla, The genius who lit the world". Teslasociety.com.
28. ^ P.J.Papadopoulos, "Nikola Tesla; The Guglielmo Marconi Case, Who is the True Inventor of Radio?"