Encyclopedia
This is longer information about some of the pioneers of development of
radio. For the main article, see
History of radio.
Marconi
After the 1880s Hertz experiments,
Guglielmo Marconi's proponents state that he read about the work while on vacation in 1894 . Marconi wondered if radio waves could be used for wireless communications. 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.
Marconi's reputation is based, in large measure, on this accomplishments in radio communications and the 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 .
Marconi's disclosed a two-circuit system for the transmission and reception of "Hertzian waves" . 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 . This was done by the careful determination of the size of the aerial plates.
In 1901, Marconi claimed to have received daytime transatlantic radio short wave frequency signals at a wavelength of 366 metres . 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.
Case against Marconi
By 1895, Marconi introduces 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. Marconi's later practical four tuned system was predated by N. Tesla, O. 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 . In addition, other prior work was conducted by others from which many of Marconi's devices and methods were derived. Marconi's
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, a distance of around a mile. In comparison, this was small when put against Tesla's early-1895 transmissions of up to 50 miles. Also of note is that Marconi’s 1901 Poldhu - Newfoundland transmission claim has been doubted. Critics have stated that it is more likely that Marconi received stray atmospheric noise from
atmospheric electricity in the 1901 experiment. 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 . 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 which agree with Jack Belrose that the 1901 bridging of the Atlantic never took place.
Tesla
Nikola Tesla initially held the rights to radio. He had , "
Apparatus for Transmission of Electrical Energy" , division of "
System of Transmission of Electrical Energy", March 20, 1900 . In US649621, Tesla established a system which was composed of a transmitting coil arranged and excited to cause oscillations 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. 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 [...]".
Vertical high aspect-ratio quarterwave helical resonator, possessing a large capacitive top load, which was driven at the base by a regular power supply and suitable matching section. This image is from one of
Tesla's patent.]]
Tesla's aerial parameters consisted of a small vertical high aspect-ratio quarterwave helical resonator, possessing 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 would resonate, though, if the driving circuitry was arranged properly. Some of the roughly hemispherical shaped 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,
not Marconi's, discovery of great importance was of the "groundwave" method. The method to produce surface waves was the consequence of adding a ground connection to the transmitter. Tesla stated, 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.
This method led to longer transmission ranges. Many AM stations use this same principle to boost reception of their signals.
It has also been noted that Tesla was one of the first to patent a means to reliably produce radio frequencies. Tesla's , "
Method of Operating Arc-Lamps" , describes an
alternator that produces high-frequency current for that time period, around 10,000 cycles per second . Though 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, the frequency produced by the device was in the
longwave broadcasting range . Around July of 1891, after becoming a naturalized citizen of the United States, 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 .
In the beginning of 1895, Tesla was able to detect signals from the transmissions of his New York lab at
West Point . By early 1896, he attained devices that produced
undamped waves around 50,000 cycles per second and, between 1895 and 1898, Tesla continued his research into wireless transmission principles. After travelling to Colorado Springs , Telsa lit a bank of incandescent bulbs wirelessly at very long distances during his experiments with the
magnifying transmitter.
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 fought to re-acquire his radio patent, but failed. 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 .
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 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."
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."
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."
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. 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".
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" and "
Experiments with Alternating Currents of High Potential and High Frequency" were reported on internationally. Tesla's 1893 presentation at the Franklin Institute was reported across America and throughout Europe. Tesla also did perform public demonstrations of actual and related work, such as the remote-controlled boat in 1898 . The remote-controlled boat contained "rotating coherers" that allowed secure communication between transmitter and receiver.
Tesla's system can produce a variety of waves propagation, pending the driving apparatus. Tesla believed that his wireless system would be better than most other radio systems because
transverse electromagnetic waves would decay as they travelled from the transmitter, making the signals uselessly weak at long distances. Tesla advanced that longitudinal electromagnetic waves 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 . 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.
Case against Tesla
It is a popular belief, or a misconception, that Tesla had a small influence on the development of radio. Tesla never did complete his "worldwide wireless system", primarily because of financial difficulties. Cost overruns prevented him from completing the
wireless station tower that he built in the early 1900s on Long Island, New York. Many
modern Marconi supporters dispute the relevancy of his demonstrations of the remote-controlled boat as well as his public lecture demonstrations.
Music group album
The band named "Tesla" has an album,
The Great Radio Controversy, which is titled after this controversy of the identity of the inventor of radio. The album inner sleeve recounts the story where the Serbian-American engineer Tesla is the true inventor of radio, while the Italian Marconi took the credit and is widely regarded with the title.
Jagdish Chandra Bose
Another pioneer of wireless communication was Prof
Jagdish Bose. In 1894, Bose ignited gunpowder and rang a bell at a distance using electromagnetic waves, replicating independently that communication signals can be sent without using wires. In 1896, the Daily Chronicle of England reported on his UHF experiments:
- "The inventor 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 closely related experiments but had recorded, in December 1895, that he was hoping for distant signalling with radio waves The wireless signalling experiment by Marconi on Salisbury Plain in England was not until May 1897. The 1895 public demonstration by Bose in Calcutta predates this experiment. Both of Bose's experiments, though, was well after Tesla's demonstration of radio communication in 1892 and 1893.
Bose, it has been noted, was not interested in the commercial applications of the experiment's transmitter. He did not attempt 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 Royal Society, London. Later, he received , "
Detector for electrical distrubances" , for a specific electromagntic receiver. While he is not known for greatly contributing to the development of commercial radio communication and did not file any patents for transmission, this doesn't discount that he does deserves recognition for contributing to the development of radio.
Heinrich Hertz
In his classic UHF experiments,
Heinrich Hertz had verified that the properties of radio waves were consistent with Maxwell’s electromagnetic theory. Of the three basic forms of wireless aerial launching structures common at the time, the Hertz antenna was a vertical dipole, center fed, half wavelength structure. 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 . 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 the detection of the radio wave. When he added cylindrical reflectors behind his dipole antennas, Hertz was able to detect radio waves about 20 metres from the transmitter in his laboratory. He did not try to extend this distance further because he was motivated by verifying electromagnetic theory, not by developing wireless communications. Hertz did not understand 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."
Asked about the ramifications of his discoveries, Hertz replied,
- "Nothing, I guess."
His discoveries would later be more fully understood by others. In Marconi's 1895 experiments, he followed Hertz's work by using a spark source in what became known as a
spark-gap transmitter.
Footnotes and citations
