Invention of radio

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This article covers the main arguments about who had what part in the early development of radio.

For the general history of radio, see History of radio.

Contents 1 Early wireless work 1.1 Scientific theory and verification 1.2 SLF and UHF experimentation 2 Tesla's work 2.1 Radio frequency generation 2.2 Continued research and patents 3 Popov's work 4 Bose's work 5 Guglielmo Marconi's work 5.1 Early years 5.2 The Poldhu experiment 6 Court decision 7 Case of priority 7.1 Case for Marconi 7.2 Case against Marconi 7.3 Case for Tesla 7.4 Case against Tesla 8 Timeline 9 See also 10 Notes 11 References

Within the timeline of radio, many people 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.

[edit] Early wireless work

[edit] Scientific theory and verification

James Clerk Maxwell performed the theoretical physical research that correctly predicted the existence of radio (and all other electromagnetic) waves. Heinrich Rudolf Hertz was the experimental physicist who created radio waves in a controlled laboratory manner. Neither Maxwell nor Hertz, though, devised systems for actual general use or described the application of the technology.

Developments, parallel to these individuals and after, are engineering investigations that lead to the 'invention of radio': the objects, processes, or techniques of information transception. Many individuals contributed to the art of wireless, in the air, earth, and water; this includes the precursory work in wireless telephony and wireless telegraphy

[edit] SLF and UHF experimentation

David E. Hughes, eight years before Hertz's experiments and nearly two decades before Guglielmo Marconi's demonstrations, induced electromagnetic waves in a signalling system. Hughes transmitted Morse code by an induction apparatus. In 1878, Hughes's induction transmission method utilized a "clockwork transmitter" to transmit signals. In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deployed a system of signalling on the Lehigh Valley Railroad. In 1892, Edison attained the wireless patent for this method using inductance (U.S. Patent 465,971 ).

From 1886 to 1888 inclusive 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, the Hertz antenna was a center-fed half-wavelength dipole (with the other forms being the Marconi antenna and Tesla antenna). Hertz’s setup for a source and detector of radio waves (archaically called Hertz waves in his honor) comprised a primitive radio system capable of transmitting and receiving space waves through free space.^[1] His transmitter was not at all efficient and was severely limited in power output. Its dipole antenna differed from the vertical quarter-wavelength antenna that was subsequently adopted by Marconi and others in that it was not grounded.^[2]

Hertz used the damped oscillating currents in a dipole antenna, triggered by a high-voltage electrical capacitive 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 seemed 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." Hertz also stated, "I do not think that the wireless waves I have discovered will have any practical application."^[3] Hertz died in 1894, so the art of radio was left to others to implement into a practical useful form. 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 work

[edit] Radio frequency generation

Nikola Tesla was one of the first to patent a means to reliably produce radio frequency currents. Tesla's U.S. Patent 447,920 , "Method of Operating Arc-Lamps" (March 10, 1891), describes an alternator that produced high-frequency current (for that time period), around 10,000 cycles per second. (The term cycles-per-second was later modified to "hertz.") His patentable innovation was suppression of the sound produced by arc lamps that were operated on alternating or pulsating current by using frequencies beyond the range of human hearing. The alternator produced frequencies in the Very Low Frequency (VLF) band.

[edit] Continued research and patents

Around July 1891, he established his New York laboratory and constructed various apparatuses 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). 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 intelligible messages could 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 late 1896 or early 1897 Tesla received wireless signals transmitted from the Houston St. lab in New York City to West Point, "a distance of about 30 miles." The transmitter consisted of an RF alternator and produced undamped (or continuous) waves in the neighborhood of 5,000 cycles per second. The receiver consisted of a powerful electromagnet, two large condensers, and a taut steel wire. The wire was placed within the magnetic field, and in conjunction with the condensers formed a tuned circuit.^[7][8] In 1899 Tesla established an "Experimental Station" in Colorado Springs where he continued his research into wireless transmission principles often using a form of electrical oscillator known as the magnifying transmitter.

Early on in his research Tesla used his high voltage resonance transformer—the Tesla coil—in radio-wave propagation experiments. The aerial consisted of a top-loaded electrical conductor that was connected to a high-voltage terminal of the transformer. The opposing high-voltage terminal was grounded. The secondary winding was driven by a primary circuit consisting of a few turns of heavy wire, a capacitor bank, a circuit controller, and a power supply transformer. The launching structure radiated as a common "Hertz wave" antenna. In Tesla's own words,

"The popular impression is that my wireless work was begun in 1893, but as a matter of fact I spent the two preceding years in investigations, employing forms of apparatus, some of which were almost like those of today. . . ."^[9]

After a while he began to favor another technique that he called the “disturbed charge of ground and air method.” Tesla's wireless system used the same basic apparatus, however instead of using electromagnetic space waves the energy is carried by the conduction of electrical currents through the earth and along with accompanying surface waves. In one form of the system the ‘return’ path closing the circuit is an electrical current flow established between two elevated terminals, one belonging to the transmitter and the other the receiver. These consist of conduction currents flowing through plasma and also electrostatic induction. Once again in Tesla's own words,

". . . It was clear to me from the very start that the successful consummation could only be brought about by a number of radical improvements. Suitable high frequency generators and electrical oscillators had first to be produced. The energy of these had to be transformed in effective transmitters and collected at a distance in proper receivers. Such a system would be manifestly circumscribed in its usefulness if all extraneous interference were not prevented and exclusiveness secured. In time, however, I recognized that devices of this kind, to be most effective and efficient, should be designed with due regard to the physical properties of this planet and the electrical conditions obtaining on the same. . ."^[10]

In other words, Tesla’s structure injected a large alternating current into the earth via the ground terminal. Tesla's discovery of importance was the "Surface wave" method. The production of surface waves as described by Arnold Sommerfeld and Jonathan Zenneck was partially the consequence of adding a deep 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.^[11]

A shallow buried ground plane or an elevated insulated counterpoise is commonly used in the construction of low and medium frequency 1/4-wavelength radio antennas. These lend to the development of the Norton Surface Wave. This method led to longer transmission ranges. Many AM stations use this same principle to boost reception of their signals.^[12] This also allows modern grounded AM 1/4 wavelength monopole antennas to be more practical in order to overcome the restrictions imposed upon designers by the large physical dimensions required for these structures.

Radio antennas radiate electromagnetic waves that can reach the receiver either by ground-wave propagation or by refraction from the ionosphere, known as sky-wave propagation. The ground-wave component is the portion of the radiated electromagnetic wave that propagates close to the earth's surface. It has both direct-wave and ground-reflected components, and under certain conditions a tropospheric ducting component. The direct-wave is limited only by the distance from the transmitter to the horizon plus a small distance added by atmospheric diffraction around the curvature of the earth. The ground-reflected portion of the radiated wave reaches the receiving antenna after being reflected from the earth's surface. A portion of the ground-wave energy radiated by the antenna may also be guided by the earth's surface as a ground-hugging surface wave.

Nikola Tesla's rights to radio were based upon these patents:

• Division of U.S. Patent 645,576  "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 649,621 , "Apparatus for Transmission of Electrical Energy" (May 15, 1900; filed February 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.

Shortly after the turn of the 20th century, the US Patent Office also awarded Marconi a patent for radio.

[edit] Popov's work

Beginning in the early 1890s, Alexander Stepanovich Popov conducted experiments along the lines of Hertz's research. In 1894 he built his first radio receiver, which contained a coherer. Further refined as a lightning detector, he presented it to the Russian Physical and Chemical Society on May 7, 1895 — the day has been celebrated in the Russian Federation as "Radio Day". The paper on his findings was published the same year (December 15 1895). Popov had recorded, at the end of 1895, that he was hoping for distant signaling with radio waves.^[13] In 1900, Popov stated (in front of the Congress of Russian Electrical Engineers),

"[...] the emission and reception of signals by Marconi by means of electric oscillations [was] nothing new. In America, the famous engineer Nikola Tesla carried the same experiments in 1893."^[14]

[edit] Bose's work

In November 1894, the Bengali Indian physicist, Jagdish Chandra Bose, demonstrated publicly the use of radio waves in Calcutta, but he was not interested in patenting his work.^[15] For more information see History of radio : 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." The 1895 public demonstration by Bose in Calcutta was before Marconi's wireless signalling experiment on Salisbury Plain in England in May 1897.^[16][17] Though Bose did this demonstration, Tesla had performed 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.^[18] Later he received U.S. Patent 755,840 , "Detector for electrical distrubances" (1904), for a specific electromagnetic receiver. Though he did not file any patents for transmission, he is recognized for contributing to the development of radio.

[edit] Guglielmo Marconi's work

[edit] Early years

Guglielmo Marconi's proponents say that while he was on vacation in 1894 he read about the experiments that Hertz did in the 1880s, and about Nikola Tesla's work in the just-published book Inventions, Researches and Writings of Nikola Tesla. It was at this time that Marconi began to understand that radio waves could be used for wireless communications.^[19]

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 dipole with a vertical wire topped by a metal sheet, with an opposing terminal connected to the ground. On the receiver side, Marconi replaced the spark gap with a 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.^[20]

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).

Marconi's U.S. Patent 586,193  (July 13, 1897) (and the reissued U.S. Patent RE11,913 ) 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"^[21]). 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 frequency signals at a wavelength of 366 metres (820 kHz).^[22][23][24] 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.

Marconi’s 1901 Poldhu to Newfoundland transmission claim has been attacked.^[25] Critics have claimed that it is more likely that Marconi received stray atmospheric noise from atmospheric electricity in the 1901 experiment.^[26] The transmitting station in Poldhu, Cornwall used a spark-gap transmitter that could produce a signal just below the medium frequency 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 various science historians who agree with Jack Belrose (in addition to being bolstered by Tesla supporters) that the Atlantic was not bridged in 1901, but other science historians have taken the position that this was the first trans-atlantic radio transmission.

[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 763,772 ) 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."^[27]

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."^[28]

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."^[29]

[edit] Case of priority

[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 impossible,^[30] 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.^[31] 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 613,809 ). The remote-controlled boat contained "rotating coherers" that allowed secure communication between transmitter and receiver.

[edit] Case against Marconi

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.^[32] 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 676,332  Apparatus for wireless telegraphy [1901], in which a more intricate system was disclosed than in his earlier patents, was filed 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 was first to hold the rights to radio:

• U.S. Patent 645,576 , "System of Transmission of Electrical Energy", March 20, 1900 (March 20, 1900; filed Sept. 2, 1897).
• U.S. Patent 649,621 , "Apparatus for Transmission of Electrical Energy" (May 15, 1900; filed February 19, 1900).

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 their 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.

There is also the relevance of Tesla demonstrations of the remote-controlled boat (with its internal rotating coherer) as well as Tesla's public lecture demonstrations. 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.

[edit] Timeline

Main article: Timeline of radio

The identity of the original inventor of radio, at the time called wireless telegraphy, is contentious. The key invention for the beginning of "wireless transmission of data using the entire frequency spectrum" has been attributed to various inventors and researchers. Below is a selection of pertinent events and individuals related to the development of radio.

[edit] See also

• Category:Radio pioneers
• Category:Radio people

[edit] Notes

[edit] References

• "Marconi Wireless Tel. Co. v. United States, 320 U.S. 1 (U.S. 1943)", 320 U.S. 1, 63 S. Ct. 1393, 87 L. Ed. 1731 Argued April 9,12, 1943. Decided June 21, 1943. http://caselaw.lp.findlaw.com/scripts/printer_friendly.pl?page=us/320/1.html
• Anderson, L.I., "Priority in the Invention of Radio: Tesla vs. Marconi", Antique Wireless Association Monograph No. 4, March, 1980.
• Anderson, L.I., "John Stone Stone on Nikola Tesla's Priority in Radio and Continuous-Wave Radiofrequency Apparatus", The A.W.A. (Antique Wireless Association) Review, Vol. 1, 1986, pp. 18-41.
• Howeth, Captian H.S. History of Communications – Electronics in the United States Navy, published 1963, GPO, 657 pages. Free online public domain US government published book.
• Wunsch, A.D., "Misreading the Supreme Court,” Antenna, Volume 11 No. 1, November 1998, Society for the History of Technology http://www.mercurians.org/nov98/misreading.html
• Brand, W.E., "Rereading the Supreme Court: Tesla's Invention of Radio", Antenna, Volume 11 No. 2, May 1998, Society for the History of Technology http://www.mercurians.org/may99/rereading.html

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