Fundamentals of Radio Communication - The Invention of Radio
On the 150th Anniversary of Tesla's birthday
By Petar Miličić, 9A6A, President of the Croatian Amateur Radio Association
Nikola Tesla (fig. 1), the great scientist, engineer, physicist, inventor and researcher was born at Smiljan (fig 2.), a small village near the town of Gospić in the central Croatian province Lika, on July 10, 1856. (In those days Croatia was a part of the Austro-Hungarian Monarchy.) His father Milutin was an Orthodox priest, while his mother Đuka did not have any formal education, but had a brilliant mind and Nikola was very attached to her. She taught Nikola legends and folk poetry where he showed an incredible memory. Being a dreamer with a poetic touch, as he matured Tesla added strict self-discipline and a desire for perfection to these earlier qualities. He started primary school at Smiljan (in German) and finished it in Gospić, together with a Junior High School (also in German). He had three sisters and one brother, who died young.
Fig. 1 Nikola Tesla in 1895 at the age of 39
He continued his education in Karlovac, another near-by town, where he finished a Senior High School (Gymnasium). There, he lived with his aunt, who never gave him enough food, so he was hungry all the time. Having finished the secondary school Tesla enrolled at the Technical University in Graz in 1877 where he studied physics and electricity for twenty hours a day, including Sundays, which greatly impaired his health. One day the students were shown the Z. Gramme's dynamo which could function also as an electric motor. The dynamo had great problems with huge sparks from the brushes. Tesla asked his professor if the dynamo could do away without brushes, and the professor answered him that it would be like making a perpetuum mobile - with a rotating magnetic field. Later in 1882, in Budapest, Tesla visualized the principle of a rotating magnetic field and conceived an induction motor which rotated without brushes - thus building the fundaments of his system of polyphase currents which eventually changed the world. (Tesla had a very sharp imagination and could hardly tell his mental pictures from reality.)
Fig. 2 Nikola Tesla birthplace – Tesla's Scientific Park – Smiljan, Croatia
In the same year 1882 Tesla went to work in Paris for the Continental Edison Company, and while on assignment in Strasbourg in 1883, he constructed, in after-work hours, his first induction motor. He immigrated to the USA in 1884 and started to work for Edison. In May 1885 George Westinghouse, head of the Westinghouse Electric Company in Pittsburgh, bought Tesla's patent rights of his polyphase system of alternating-current dynamos, transformers and motors. This transaction precipitated a titanic struggle between Edison's direct-current systems (where he had a lot of capital), and the Tesla-Westinghouse's alternating-current approach - which eventually won out. (During the campaign Edison used to electrocute dogs at public squares in order to show how dangerous the alternating current was.)
Tesla soon established his own laboratory where his inventive mind could be given free rein. He experimented with shadowgraphs similar to those that later were to be used by Wilhelm Rontgen when he discovered X-rays in 1895. Tesla's countless experiments included works on a carbon arc button lamp, on electrical resonance, and on various types of lighting. Westinghouse used Tesla's system to light the World's Columbian Exposition in Chicago in 1893. His success was a positive factor in winning him the contract to install the first power plant at Niagara Falls, which bore Tesla's name and patent numbers. The project brought electric power to the town of Buffalo, some 20 miles away - which could not be done with direct current.
Besides his polyphase system of producing and distributing eletrical power, Nikola Tesla's researches and patents were the first to establish the fundamentals of what we call radio communication today, irrespective of later developments and contributions by E. Branly, A.S. Popov, G. Marconi, Oliver Lodge, J.C. Bose, or John S. Stone. As early as 1893 in his well-known presentation "Light and other High-Frequency Phenomena" at the Franklin Institute in Philadelphia he suggested the use of high frequency electrical currents for a wireless transport of electric power, used resonant circuits and practically demonstrated how it worked.
In 1888, when George Westinghouse paid Tesla one million dollars for his patents of polyphase motors, Tesla decided to explore a completely new idea. Having read the works of Heinrich Hertz who in 1887 discovered the oscillating nature of electric sparks (which so produced radio waves and confirmed Maxwell's theory of light), Tesla decided to begin research of high frequencies - much higher than those he used for his motors. In his first experiments Tesla used a high frequency alternator of his own construction. He used a disc 75 cm in diameter with 384 poles centered inside an armature having 384 inductive coils. The disc was rotating up to 50 revolutions per second and produced a frequency of 9600 to 10000 Hz at 200 volts. Later Tesla made new alternators which could produce alternating currents up to 30000 Hz. With these machines Tesla could study the creation of high tensions by means of inductive coils. He also found that at these frequencies the removal of iron cores improved the work of the transformer which is called Tesla's transformer today. He was the first to use the cooked linseed oil to improve insulation between layers of wire under high voltage.
But Tesla was not satisfied with those alternators, because he wanted more power and higher frequencies. So he constructed a combination of a spark gap and a series resonant circuit connected to a high voltage transformer. When a spark jumped across the gap, the Leiden jar (being a capacitor) discharged through the coil - thus causing strong damped oscillations on the resonant frequency. This system is called Tesla’s coil (Fig 3).
Fig. 3 Tesla’s coil – Tesla's Scientific Park, Smiljan, Croatia
He managed to produce frequencies of several megaherz and 100 000 volts. He could produce a spark 15 cm long. (His patent No. 568179 of 1896: "Method of and Apparatus for Producing Currents of High Frequency.)"
Between the years 1891 and 1893 Tesla held a series of lectures in America and in Europe where he presented his work with alternating currents. In those lectures he showed many of his basic devices needed for the wireless telegraphy, such as tuned resonant circuits (he said synchronized), inductive coils or simple and rotating spark gaps.
In his basic US patents Nos. 645576 and 649621 (System of Transmission of Electrical Energy and Apparatus for Transmission of Electrical Energy) which he filed in 1897 and which were issued in 1900, Tesla established the fundamentals of radio communication (fig 4.). Although his chief interest was in wireless transmission of electrical power, he also mentioned that his system could be used for the transmission of 'intelligible messages to great distances'. For other researchers wireless communication was a priority, but for Tesla it was a side effect. In Tesla’s fundamental requirements of radio communication the transmitter and the receiver had to be in electrical resonance. With this statement he solved the problem of a simultaneous and undisturbed work of several transmitters. So he gave four fundamental postulates for wireless communication:
Fig. 4. Apparatus for transmission electrical energy
1. For a wireless transmission high frequencies must be used, and the basic apparatus is a high frequency oscillator.
2. The system is based on four tuned circuits in resonance: two in the transmitter and two in the receiver.
3. All the circuits must be in resonance.
4. There are sensitive elements in the receiver which can detect high frequency currents.
Wireless transport of electric power
Why did Tesla need such high frequencies? Obviously, because he found out that through them he could get very high voltages more easily. And why did he need such high voltages? He speaks about 20 million volts. Having solved the problem of long distance transportation of electrical power by wires, Tesla was fascinated by the idea of transporting that same power without wires. In his patent No. 645 576 filed in 1897 he writes: ..."Thus it has been shown by William Crookes that all gasses behave as excellent insulators until rarefied to a point corresponding to a barometric pressure of about seventy-five millimeters... While this is true in every particular... I have found that neither the general behavior of the gasses nor the known relations between electrical conductivity and barometric pressure are in conformity with these observations... I have been led to the discovery of certain highly important and useful facts which have hitherto been unknown." Supposing that the electrical tension is high enough, Tesla concludes: "It becomes possible to transmit through easily accessible and only moderately rarefied strata of the atmosphere electrical energy not merely in insignificant quantities... but also in quantities suitable for industrial uses on a large scale up to practically any amount and, according to all the experimental evidence I have obtained, to any terrestrial distance." No doubt, Tesla had a magnificent vision of the Earth with its atmosphere as a huge Crooke’s tube glowing in the darkness of the Universe. Having described his main goal, a few pages later Tesla also mentions: "While the description here given contemplates chiefly a method and system of energy transmission to a distance through the natural media for industrial purposes, the principles which I have herein disclosed and 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..." Of course, the condition for this is that the transmitting and the receiving coils are "both connected to the ground and to an elevated terminal and adjusted so as to vibrate in synchronism..." Tesla was well aware that the ground can be used as a conductor, and also supposed that the Earth must have its own resonant frequency. In that case the wireless transport of energy would be much easier, Tesla reasoned (fig. 5.).
Fig. 5. Transmitting electrical energy through the natural mediums
Tesla noticed that it is possible to produce extremely high tensions if the secondary coil was large and with only one layer. He called them quarter wave coils, because the length of the wire in the secondary coil was equal to a quarter of the wavelength of the produced frequency. The primary coil had only few turns of thick wire and was placed at the bottom of the transformer. The lower part of the secondary was grounded, so the induced tension on the top was relevant to the ground, instead of "floating" as in his first experiments. By using conical secondary coils Tesla achieved tensions up to one million volts. As a capacitor to resonate the primary he used 32 Leiden jars connected in parallel - having a common capacity of about 40 nF. The inductance of the primary coil was "approximately ten thousand centimeters" (= 10 µH), so the resonant frequency was about 250 kHz (wavelength 1200 meters) as Tesla correctly reckoned. The applied voltage into the primary coil was 50 thousand volts from a Westinghouse transformer. As to the secondary coil, Tesla obviously had to rely on its self-capacitance and tune the primary to the natural resonating frequency of the secondary coil connected to the ground and the "elevated terminal" (i.e. antenna, a high metal rod with a ball above the building). The current in the primary coil was interrupted mechanically five thousand times per second.
In the middle of these exciting experiments, on March 13, 1895, a disaster hit Tesla when his laboratory in the South Fifth Avenue in New York burned down to the ground - together with all the documents, drawings, diaries and equipment. Before that Tesla had announced that he had a complete system of wireless communication ready, and a prototype of the transmitter, but that disaster stopped him. Tesla reckoned that tensions of 20 to 50 million volts could activate the lower layers of the atmosphere so that they would become good conductors of electricity. He hoped that such tensions could carry useful electrical power to about ten kilometers, because at such voltages only a small current is needed. (In the same year G. Marconi began his experiments with wireless communication.) Recovering from the disaster, in 1897 Tesla began to build a huge transmitting and receiving station at Colorado Springs where he successfully experimented with voltages of 10 to 12 million volts (Fig. 6). His signals could be detected at more than 1000 kilometers. There he also experimented with two different frequencies where he could use only one - at his choice - by means of resonant circuits: He called that method "individualization", today we say "selectivity" (Fig. 7.).
Fig. 6. Tesla’s antenna – Tesla's Scientific Park, Smiljan, Croatia
In September 1896 in his patent No. 613 808 Tesla describes a model of a boat "directed and controlled from distance" by wireless signals. Tesla called it "telautomaton" - we call it radio-control today. The patent officer did not believe his papers, so Tesla had to demonstrate his invention practically. The boat had "start-stop" and progressive "left-straight-right" commands, although he used only one resonant frequency, i.e. one channel. He achieved that with sophisticated electro-mechanical multifunctional devices. In the text Tesla emphasized the importance of the quality of the resonant coil in the boat's receiver which must have "the highest possible induction and at the same time the least possible resistance" (Q = XL/R) - in order to avoid interference from other disturbing signals. Today this sounds self-evident, but in those days Tesla hardly had any precedent in radio theory. To get a useful signal Tesla made a coherer of his own. He calls it "sensitive device". All the metal particles in it were processed in acid and were of equal dimension - and, instead of being tapped, the coherer was turned upside-down after each activation. The whole apparatus had to be 100% reliable, because if you transmit information, you will lose only one letter, but here you could lose the whole ship - Tesla says.
Fig. 7. System of signaling
Encouraged by successful experiments at Colorado Springs, in 1900 Tesla started building his life project - a huge radio station called Wardenclyffe Tower in Long island (Fig. 8). He planned it to be the World Center of sending information and wireless electrical energy. However, the project was never finished because Tesla's sponsor - a banker John P. Morgan (who invested over 75000 dollars in the project) - stopped financing him in 1903. Allegedly, Morgan said: "I do not know if Tesla is a genius or a lunatic, but I do not wish to offer free energy to whoever wants it." The tower was eventually dismantled.
Fig. 8. Wardenclyffe Tower in Long Island
Being in his fifties Tesla lost his laboratory and his name slowly faded away. Let us mention that at the beginning of the 20th century wireless communication had a very fast progress. Many radio amateurs gave their contribution to the field of radio communication. As early as 1924 the Croatian radio amateurs established Radio Club Zagreb - the first radio club in the south-east Europe. In 1926 they installed Radio Zagreb, the first commercial broadcasting station in this part of Europe, only thirty years after Tesla's discoveries and patents. This year (2006), celebrating the 80th anniversary of that event,Radio Zagreb (The Voice of Croatia - Glas Hrvatske) has started broadcasting the first digital DRM program on 594 kHz.
Tesla died in his 87th year on January 7, 1943 in his room on the 33rd floor of the Newyorker Hotel in New York - practically penniless. During his life he was afraid of bacteria - so he never shook hands. Faithful to his celibacy he never touched a woman, either. Perfectly aware of his extraordinary mental abilities Tesla dedicated his life to the benefit of the mankind - as much as he could in the given circumstances. Having elegantly solved the problem of brushless generators, motors and long distance transportation of electrical energy, we can say that he has also laid the fundamentals of radio as a by-product, working on a project which he thought was more important and which probably belongs to the far future.
The US Supreme Court
In September 1943, six years after Marconi's death and eight months after Tesla died, the Supreme Court of the USA decided "that Marconi's basic patents were 'anticipated' and therefore were invalid". What really happened? The Marconi Wireless Telegraph Corporation of America had sued the US government for patent infringement to the US Court of Claims - claiming a recompensation of 6 million dollars from the US government. The Marconi Corporation asserted that during the First World War the US government infringed four US patents owned by the Corporation, two of them belonging to Marconi himself, one to Oliver Lodge and one to Ambrose Fleming. In its 1935 decision the Court of Claims decided that the radio equipment used by the US government had not infringed on the Marconi US patents Nos. 763772 and 11913 (reissued). In its 1943 decision the Supreme Court declared the most part of Marconi's patents invalid, stating that his work had been anticipated by John Stone (patent No. 714756) and Oliver Lodge (patent No. 609154). The Supreme Court also examined Tesla's patent No. 645576 and found out that Tesla had used the four tuned circuits before Marconi. After such judgments the Marconi Corporation settled all the claims for 34000 $. But the consequences of those court decisions are bigger than that sum and are still arousing the question "Who was the first?"
Today, 150 years after Tesla's birth, in the SI system of units "tesla" is the unit for magnetic flux density: 1 Tesla = 1 weber/m2. So Tesla has entered into the immortal family of Volta, Ohm, Ampere, Watt, Hertz - and a few others.