• A relatively simple oscillator, or spark producing radio transmitter, which was closely modeled after one designed by Righi, in turn similar to what Hertz had used;
• A wire or capacity area placed at a height above the ground;
• A coherer receiver, which was a modification of Edouard Branly's original device, with refinements to increase sensitivity and reliability;
• A telegraph key to operate the transmitter to send short and long pulses, corresponding to the dots - and - dashes of Morse code; and
• A telegraph register, activated by the coherer, which recorded the received Morse code dots and dashes onto a roll of paper tape.

Similar configurations using spark - gap transmitters plus coherer - receivers had been tried by others, but many were unable to achieve transmission ranges of more than a few hundred metres.

Marconi, just twenty years old, began his first experiments working on his own with the help of his butler Mignani. In the summer of 1894, he built a storm alarm made up of a battery, a coherer, and an electric bell, which went off if there was lightning. Soon after he was able to make a bell ring on the other side of the room by pushing a telegraphic button on a bench. One night in December, Guglielmo woke his mother up and invited her into his secret workshop and showed her the experiment he had created. The next day he also showed his father, who, when he was certain there were no wires, gave his son all of the money he had in his wallet so Guglielmo could buy more materials. In the summer of 1895 he moved his experimentation outdoors. After increasing the length of the transmitter and receiver antennas, and arranging them vertically, and positioning the antenna so that it touched the ground, the range increased significantly.Soon he was able to transmit signals over a hill, a distance of approximately 2.4 kilometres (1.5 mi). By this point he concluded that with additional funding and research, a device could become capable of spanning greater distances and would prove valuable both commercially and militarily.

Marconi wrote to the ministry of Post and Telegraphs, which at the time was under the direction of the honorable Pietro Lacava, explaining his wireless telegraph machine and asking for funding. He never received a response to his letter which was eventually dismissed by the minister who wrote "to the Longara" on the document, referring to the insane asylum on via della Lungara in Rome. In 1896, Marconi spoke with his family friend Carlo Gardini, the United States consulate in Bologna, about leaving Italy to go to England. Gardini wrote a letter to the Ambassador of Italy in London, Annibale Ferrero, explaining who Marconi was and about this extraordinary discoveries. In his response, ambassador Ferrero advised them not to reveal the results until after they had obtained the copyrights. He also encouraged him to come to England where he believed it would be easier to find the necessary funds to convert the findings from Marconi's experiment into a practical use. Finding little interest in his work in Italy, in early 1896 at the age of 21, Marconi traveled to London, accompanied by his mother, to seek support for his work; Marconi spoke fluent English in addition to Italian. While there, he gained the interest and support of William Preece, the Chief Electrical Engineer of the British Post Office. The apparatus that Marconi possessed at that time was strikingly similar to that of one in 1882 by A.E. Dolbear, of Tufts College, which used a spark coil generator and a carbon granular rectifier for reception. A plaque on the outside of BT Centre commemorates Marconi's first public transmission of wireless signals from that site. A series of demonstrations for the British government followed — by March 1897, Marconi had transmitted Morse code signals over a distance of about 6 kilometres (3.7 mi) across the Salisbury Plain. On 13 May 1897, Marconi sent the first ever wireless communication over open sea. It transversed the Bristol Channel from Lavernock Point (South Wales) to Flat Holm Island, a distance of 6 kilometres (3.7 mi). The message read "Are you ready". The receiving equipment was almost immediately relocated to Brean Down Fort on the Somerset coast, stretching the range to 16 kilometres (9.9 mi).

Impressed by these and other demonstrations, Preece introduced Marconi's ongoing work to the general public at two important London lectures: "Telegraphy without Wires", at the Toynbee Hall on 11 December 1896; and "Signaling through Space without Wires", given to the Royal Institution on 4 June 1897.

Numerous additional demonstrations followed, and Marconi began to receive international attention. In July 1897, he carried out a series of tests at La Spezia in his home country, for the Italian government. A test for Lloyds between Ballycastle and Rathlin Island, Ireland, was conducted on 6 July 1898. The English channel was crossed on 27 March 1899, from Wimereux, France, to South Foreland Lighthouse, England, and in the autumn of 1899, the first demonstrations in the United States took place, with the reporting of the America's Cup international yacht races at New York.

Marconi sailed to the United States at the invitation of the New York Herald newspaper to cover the America's Cup races off Sandy Hook, NJ. The transmission was done aboard the SS Ponce, a passenger ship of the Porto Rico Line. Marconi left for England on 8 November 1899 on the American Line's SS St. Paul, and he and his assistants installed wireless equipment aboard during the voyage. On 15 November the St. Paul became the first ocean liner to report her imminent arrival by wireless when Marconi's Needles station contacted her sixty - six nautical miles off the English coast.

According to the Proceedings of the United States Naval Institute, the Marconi instruments were tested around 1899 and the tests concerning his wireless system found that the "[...] coherer, principle of which was discovered some twenty years ago, [was] the only electrical instrument or device contained in the apparatus that is at all new".

Around the turn of the century, Marconi began investigating the means to signal completely across the Atlantic, in order to compete with the transatlantic telegraph cables. Marconi established a wireless transmitting station at Marconi House, Rosslare Strand, Co. Wexford, in 1901 to act as a link between Poldhu in Cornwall and Clifden in Co. Galway. He soon made the announcement that on 12 December 1901, using a 152.4 metre (500 ft) kite supported antenna for reception, the message was received at Signal Hill in St John's, Newfoundland (now part of Canada), signals transmitted by the company's new high power station at Poldhu, Cornwall. The distance between the two points was about 3,500 kilometres (2,200 mi). Heralded as a great scientific advance, there was — and continues to be — some skepticism about this claim, partly because the signals had been heard faintly and sporadically. There was no independent confirmation of the reported reception, and the transmissions, consisting of the Morse code letter S sent repeatedly, were difficult to distinguish from atmospheric noise. (A detailed technical review of Marconi's early transatlantic work appears in John S. Belrose's work of 1995.) The Poldhu transmitter was a two - stage circuit. The first stage operated at lower voltage and provided the energy for the second stage to spark at a higher voltage. Nikola Tesla, a rival in transatlantic transmission, stated after being told of Marconi's reported transmission that "Marconi [... was] using seventeen of my patents."

Feeling challenged by skeptics, Marconi prepared a better organized and documented test. In February 1902, the SS Philadelphia sailed west from Great Britain with Marconi aboard, carefully recording signals sent daily from the Poldhu station. The test results produced coherer - tape reception up to 2,496 kilometres (1,551 mi), and audio reception up to 3,378 kilometres (2,099 mi). The maximum distances were achieved at night, and these tests were the first to show that for medium wave and long wave transmissions, radio signals travel much farther at night than in the day. During the daytime, signals had only been received up to about 1,125 kilometres (699 mi), less than half of the distance claimed earlier at Newfoundland, where the transmissions had also taken place during the day. Because of this, Marconi had not fully confirmed the Newfoundland claims, although he did prove that radio signals could be sent for hundreds of kilometres, despite some scientists' belief they were essentially limited to line - of - sight distances.

On 17 December 1902, a transmission from the Marconi station in Glace Bay, Nova Scotia, Canada, became the first radio message to cross the Atlantic from North America. In 1901, Marconi built a station near South Wellfleet, Massachusetts, that on January 18, 1903 sent a message of greetings from Theodore Roosevelt, the President of the United States, to King Edward VII of the United Kingdom, marking the first transatlantic radio transmission originating in the United States. This station also was one of the first to receive the distress signals coming from the RMS Titanic. However, consistent transatlantic signalling was difficult to establish.

Marconi began to build high-powered stations on both sides of the Atlantic to communicate with ships at sea, in competition with other inventors. In 1904 a commercial service was established to transmit nightly news summaries to subscribing ships, which could incorporate them into their on-board newspapers. A regular transatlantic radio - telegraph service was finally begun on 17 October 1907 between Clifden Ireland and Glace Bay, but even after this the company struggled for many years to provide reliable communication.

The two radio operators aboard the Titanic — Jack Phillips and Harold Bride — were not employed by the White Star Line, but by the Marconi International Marine Communication Company. Following the sinking of the ocean liner, survivors were rescued by the RMS Carpathia of the Cunard Line. Also employed by the Marconi Company was David Sarnoff, the only person to receive the names of survivors immediately after the disaster via wireless technology. Wireless communications were reportedly maintained for 72 hours between the Carpathia and Sarnoff, but Sarnoff's involvement has been questioned by some modern historians. When the Carpathia docked in New York, Marconi went aboard with a reporter from The New York Times to talk with Bride, the surviving operator. On 18 June 1912, Marconi gave evidence to the Court of Inquiry into the loss of the Titanic regarding the marine telegraphy's functions and the procedures for emergencies at sea. Britain's postmaster general summed up, referring to the Titanic disaster, "Those who have been saved, have been saved through one man, Mr. Marconi... and his marvelous invention."

Marconi's work built upon the discoveries of numerous other scientists and experimenters. His "two - circuit" equipment, consisting of a spark - gap transmitter plus a coherer - receiver, was similar to those used by other experimenters, and in particular to that employed by Oliver Lodge in a series of widely reported demonstrations in 1894. There were claims that Marconi was able to signal for greater distances than anyone else when using the spark - gap and coherer combination, but these have been disputed (notably by Tesla).

In 1900 Alexander Stepanovich Popov stated to the Congress of Russian Electrical Engineers that: "[...] 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."

When Marconi transmitted signals across the Atlantic on December 12, 1901, Tesla himself commented: "Marconi is a good fellow. Let him continue. He is using 17 of my patents."

The Fascist regime in Italy credited Marconi with the first improvised arrangement in the development of radio. There was controversy whether his contribution was sufficient to deserve patent protection, or if his devices were too close to the original ones developed by Hertz, Popov, Branley, Tesla, and Lodge to be patentable.

While Marconi did pioneering demonstrations for the time, his equipment was limited by being essentially untuned, which greatly restricted the number of spark - gap radio transmitters which could operate simultaneously in a geographical area without causing mutually disruptive interference. (Continuous - wave transmitters were naturally more selective and less prone to this deficiency). Marconi addressed this defect with a patent application for a much more sophisticated "four - circuit" design, which featured two tuned - circuits at both the transmitting and receiving antennas. This was issued as British patent number 7,777 on 26 April 1900. However, this patent came after significant earlier work had been done on electrical tuning by Nikola Tesla and Oliver Lodge. (As a defensive move, in 1911 the Marconi Company purchased the Lodge - Muirhead Syndicate, whose primary asset was Oliver Lodge's 1897 tuning patent. This followed a 1911 court case in which the Marconi company was ruled to have illegally used the techniques described under Lodge's tuning patent.) Thus, the "four - sevens" patent and its equivalents in other countries was the subject of numerous legal challenges, with rulings which varied by jurisdiction, from full validation of Marconi's tuning patent to complete nullification.

In 1943, a lawsuit regarding Marconi's numerous other radio patents was resolved in the United States. The court decision was based on the prior work conducted by others, including Nikola 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 2 September 1897 and allowed 20 March 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.

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 litigants, but by careful study of the merits of their respective contentions and proofs."

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."

The Supreme Court of the United States did not dispute Marconi's original British patent nor his reputation as the inventor of radio. The US Supreme Court stated that his original patent (which became reissue 11,913) was not being disputed.

The case was resolved in the U.S. Supreme Court by overturning most of Marconi's patents. At the time, the United States Army was involved in a patent infringement lawsuit with Marconi's company regarding radio, leading observers to posit that the government nullified Marconi's other patents to render moot 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). In contrast to the United States system, Mr. Justice Parker of the British High Court of Justice upheld Marconi's "four - sevens" tuning patent. These proceedings made up only a part of a long series of legal struggles, as major corporations jostled for advantage in a new and important industry.

The 1895 public demonstrations by J.C. Bose in Calcutta regarding radio transmission were conducted before Marconi's wireless signaling experiments on Salisbury Plain in England in May 1897. 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." Marconi, while being fully aware of Bose's prior work in this area, nonetheless claimed exclusive patent rights.

Over the years, the Marconi companies gained a reputation for being technically conservative, in particular by continuing to use inefficient spark - transmitter technology, which could only be used for radiotelegraph operations, long after it was apparent that the future of radio communication lay with continuous - wave transmissions, which were more efficient and could be used for audio transmissions. Somewhat belatedly, the company did begin significant work with continuous - wave equipment beginning in 1915, after the introduction of the oscillating vacuum tube (valve). In 1920, employing a vacuum tube transmitter, the Chelmsford Marconi factory was the location for the first entertainment radio broadcasts in the United Kingdom — one of these featured Dame Nellie Melba. In 1922 regular entertainment broadcasts commenced from the Marconi Research Centre at Writtle.

In 1914 Marconi was made a Senator in the Italian Senate and appointed Honorary Knight Grand Cross of the Royal Victorian Order in the UK. During World War I, Italy joined the Allied side of the conflict, and Marconi was placed in charge of the Italian military's radio service. He attained the rank of lieutenant in the Italian Army and of commander in the Italian Navy. In 1924, he was made a marquess by King Victor Emmanuel III.

Marconi joined the Italian Fascist party in 1923. In 1930, Italian dictator Benito Mussolini appointed him President of the Royal Academy of Italy, which made Marconi a member of the Fascist Grand Council.

Marconi died in Rome in 1937 at age 63 following a series of heart attacks, and Italy held a state funeral for him. As a tribute, all radio stations throughout the world observed two minutes of silence. His remains are housed in the Villa Griffone at Sasso Marconi, Emilia - Romagna, which assumed that name in his honour in 1938.

Marconi had a brother, Alfonso, and a stepbrother, Luigi. On 16 March 1905, Marconi married the Hon. Beatrice O'Brien (1882 – 1976), a daughter of Edward Donough O'Brien, 14th Baron Inchiquin. They had three daughters, Degna (1908 – 1998), Gioia (1916 – 1996), and Lucia (born and died 1906), and a son, Giulio, 2nd Marchese Marconi (1910 – 1971). The Marconis divorced in 1924, and, at Marconi's request, the marriage was annulled on 27 April 1927, so he could remarry. Beatrice Marconi married on 3 March 1924, as her second husband, Liborio Marignoli, Marchese di Montecorona, and had further issue, a daughter, Flaminia.

On 12 June 1927 (religious 15 June), Marconi married Maria Cristina Bezzi - Scali (1900 — 1994), only daughter of Francesco, Count Bezzi - Scali. Fascist dictator Benito Mussolini was Marconi's best man at the wedding. They had one daughter, Maria Elettra Elena Anna (born 1930), who married Prince Carlo Giovannelli (born 1942) in 1966; they later divorced.

For unexplained reasons, Marconi left his entire fortune to his second wife and their only child, and nothing to the children of his first marriage.

Later in life, Marconi was an active Italian Fascist and an apologist for their ideology and actions such as the attack by Italian forces in Ethiopia.

Marconi wanted to personally introduce in 1931 the first radio broadcast of a Pope, Pius XI, announcing at the microphone: "With the help of God, who places so many mysterious forces of nature at man's disposal, I have been able to prepare this instrument which will give to the faithful of the entire world the joy of listening to the voice of the Holy Father".