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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
TV. History of invention and production
Directory / The history of technology, technology, objects around us Television is a set of devices for transmitting a moving image and sound over a distance. In everyday life, it is also used to refer to organizations involved in the production and distribution of television programs. Together with broadcasting, it is the most massive means of disseminating information (political, cultural, scientific, educational or educational), as well as one of the main means of communication.
Television is, perhaps, one of the most remarkable inventions of the XNUMXth century and, along with the automobile, aircraft, computer, nuclear reactor, deserves the right to the epithets "greatest", "most important", "wonderful" and "incredible". It has now penetrated so deeply into all spheres of our existence, is so closely connected with the life of every person, that without a television screen it is already impossible to imagine either modern technology or modern civilization. Like any complex technical creation, television appeared and developed into a perfect system thanks to the efforts of many, many inventors. In a short chapter, of course, it is difficult to tell about everyone who, in one way or another, put their hands and minds into the creation of television technology. Therefore, we will focus only on the most important and significant moments in the history of its occurrence. Alexander Behn's copier telegraph, for which he received a patent in 1843, must be considered an early precursor of television. The basis of the sending and receiving devices here were wax-metal plates arranged in a special way. To make them, Ben took insulated wire, cut it into pieces 2 cm long and tightly stuffed them into a rectangular frame so that the wire segments were parallel to each other and their ends were located in two planes. Then he filled the frame with liquid sealing wax, cooled it and polished it on both sides until smooth dielectric surfaces with metallic inclusions were obtained.
Ben's apparatus was suitable for transferring images from metal plates or from metal types. If a metal cliché or typographic type was pressed against one of the sides of the metal-wax plate of the transmitting apparatus, then some of the wires were electrically closed to each other and received contact with the circuit section supplied to the type and to the current source. This contact also passed to the ends of the same wires on the opposite side of the plate. At the same time, a sheet of wet paper, previously impregnated with potassium and sodium salts, was applied to a similar plate of the receiving apparatus, which was able to change its color under the action of an electric current. The operation of the device consisted in the fact that at the same time at the transmitting and receiving stations they set in motion pendulums with contact feathers fixed on them, which slid along the polished surface of both plates (at the transmitting and receiving ends). Now consider what happened in the telegraph line at various positions of the contact pen. When the pen slid over the dielectric wax part of the plate and over the metal inclusions that had no contact with the protrusions of the clichés or letters of the font, then the circuit remained open, and no current was supplied to the line from the battery. Touching with a contact pen the end of the wire connected to the font, instantly closed the circuit, and the current flowed along the communication line to the receiving apparatus, causing the paper section to be colored. Having made the next oscillation, the pendulums were attracted by electromagnets and briefly stopped. During this time, the metal-wax plates were lowered by a clockwork to a small but equal distance down so that, with the next oscillation of the pendulum, the contact pen moved along the ends of the next row of wires. Thus, the relief image, pressed against the plate of the transmitting apparatus, point by point, line by line, was converted into elementary signals that arrived at the receiving point via a telegraph communication line. Here, due to the electrochemical action of the current, the image was developed on wet impregnated paper pressed against the plate of the receiving apparatus. This ingenious invention already contained three essential features of television systems: 1) the decomposition of the whole original into separate elements (points), which are transmitted one by one in strict sequence; 2) progressive scanning of the image; 3) synchronous movement of switching devices at the transmitting and receiving stations. Due to its complexity and high price, the copying telegraph was not used in practice, but its design was the first to solve the problem of electrically transmitting an image over a long distance. A similar Becuel apparatus, created in 1848, had a simpler device. A special paint that did not conduct electric current was used to write text or draw a picture on metal foil. Then this foil was wrapped around a cylinder, which rotated with the help of a clockwork. A single slider contact moved along the cylinder, connected by a wire to the same slider of the receiving apparatus. As the cylinder rotated at the departure station, the slider touched both the exposed and insulated foil surfaces. Depending on this, there was or was no electric current in the circuit, to which the chemically treated paper, laid on the cylinder in the receiver, reacted. A new era in the history of television began after the discovery of the photoelectric effect. First of all, the internal photoelectric effect was used, the essence of which was that some semiconductors, when illuminated, significantly changed their electrical resistance. The first to note this interesting ability of semiconductors was the Englishman Smith. In 1873, he reported on his experiments with crystalline selenium (discovered in 1817 by the Swedish chemist Berzelius). In these experiments, selenium strips were placed in sealed glass tubes with platinum inlets. The tubes were placed in a light-tight box with a lid. In the dark, the resistance of the selenium strips was quite high and remained very stable, but as soon as the lid of the box was removed, the conductivity increased by 15-100%. A simple movement of the hand over the tubes increased the resistance of selenium by 15-20%. (The explanation for this interesting phenomenon was found much later, when the quantum theory of light was created.
The ability of a substance to conduct or not conduct current, as we know, depends on whether it contains free charged particles. In the normal state, there are no such charged particles in a selenium crystal. But when illuminated, photons of light knock out some of the electrons from selenium atoms. These electrons move freely between the nodes of the semiconductor crystal lattice in the same way as electrons in a metal. Thus, the semiconductor acquires the properties of a conductor and its resistance is significantly reduced.) Smith's discovery soon became widely used in television systems. It is known that each object becomes visible only if it is illuminated or if it is a source of light. Light or dark areas of the observed object or its image differ from each other by different intensity of light reflected or emitted by them. Television is just based on the fact that each object (if you do not take into account its color) can be considered as a combination of a large number of more or less light and dark points. From each of these points to the observer there is a light flux of different intensity - from light points it is stronger, from dark points it is weak. Therefore, if it were possible to create such a device that at the transmitting station converted the light signals of the image falling on it into the corresponding electrical impulses of different strengths, and at the receiving station again converted these impulses into light signals of different intensities, then the problem of transmitting an image over a distance would be generally allowed. After the discovery of the internal photoelectric effect, it became obvious that a selenium plate could serve as such a converting device. In 1878, the Portuguese physics professor Adriano de Paiva outlined the idea of a new device for transmitting images over wires in one of the scientific journals. De Paiva's transmitter was a camera obscura with a large selenium plate mounted on the back wall. Different sections of this plate had to change their resistance in different ways depending on the illumination. However, de Paiva admitted that he did not know how to perform the opposite action - to make the screen at the receiving station glow. In 1880, Paiva published the pamphlet "Electrical Telescope" - the first book in history specifically devoted to television. Here a further development of the idea set forth two years earlier has been given. So, the transmitted image was optically projected onto a plate of many selenium elements. The current from the battery was applied to a metal contact, which quickly moved across the plate. If a segment was brightly illuminated, its resistance was small and the current from it turned out to be stronger than that which was taken from a poorly lit segment. As a result, electrical signals of different strengths were transmitted through the wires. In the receiving device, the movement of this contact was synchronously repeated by an electric bulb moving behind a frosted glass, which burned either brightly or dimly depending on the strength of the current pulse (that is, on the illumination of each segment of the selenium plate). According to de Paiva, if it were possible to get a sufficiently fast movement of the contact and the light bulb, then the viewer, looking at the frosted glass, should have created a visual representation of the projected object. How to achieve this, de Paiva did not know. However, for its time it was a very interesting idea. In 1881, the French lawyer Constantine Senlek in the brochure "Telescope" described the design of a television device, consisting of two panels - transmitting and receiving - and from the same number of discharge bulbs. The image was projected onto a transmitting matrix of many selenium elements, as a result of which a current of a certain magnitude was taken from each of the cells, depending on its illumination. At the transmitting and receiving stations, there were mechanical switches connected to each other by an electrical wire, which operated completely synchronously. The transmitting switch was connected in series to all cells of the matrix at high speed (as if running around them line by line) and transmitted current from each of them to the receiving switch. As a result, bulbs on the receiving panel flashed, moreover, each burned more or less intensely, depending on the amount of current transmitted. Senleck built a working model of his telescope, but was unable to transmit anything on it except for a few luminous dots. The weak point of all early television systems was the mechanical switch. In fact, in order for the image of the image transmitted to him to be created on the retina of the observer's eye, about a dozen snapshots must be replaced on the screen of the receiving station in one second. That is, the image sweep (the time it takes to remove the signal from all cells of the transmitting selenium plate) should have taken about 0 seconds. The sweep with the help of a moving contact, invented by Ben, was clearly not suitable for this purpose. Several methods have been proposed to overcome this difficulty. Finally, in 1884, a young German student, Paul Nipkow, found a classical solution to the problem of unwrapping transmitted pictures. The main feature of Nipkow's device was a light-tight disk with tiny holes near the outer edge. The distances between the holes were the same, however, each subsequent one was shifted to the center of the disk by the value of the hole diameter.
The transfer of the image was to be carried out as follows. The lens projected a reduced real image of the object onto the disk. A selenium plate was placed on the other side of the disk. The disk was driven by an electric motor into a very fast rotation. At the same time, at each moment of time, the light hit the element only through one hole, which moved along an arcuate line. First, an upper hole passed between the image and the photosensitive plate, through which only the upper edge of the image was successively projected onto the photocell. When this hole went beyond the image frame, another one, located slightly lower, moved from the other edge of the frame and projected the next strip (or, as they began to say later, “line”) of the image onto the photocell. Thus, in one revolution of the disk, all sections of the image passed in turn in front of the photocell. (This process, called "progressive image scanning," is one of the central processes in the television system. The "Nipkow Disk" was the first simple device that allowed such a scan to be carried out. Over the next fifty years, it was an integral part of many television devices.) Further, the signals from each cell of the photocell were sequentially transmitted over the wire to the receiving station. Here, this current was supplied to a neon lamp, which, accordingly, burned either brighter or weaker, depending on the strength of the transmitted current. Between the observer and the lamp was placed the same perforated disk as on the transmitting station, which rotated with it in strict synchrony. At each moment of time, the viewer could observe luminous lines, the brightness of the elements of which was proportional to the brightness of the same elements on the transmitter disk. In general, Nipkow's device already contained all the main components of the so-called "mechanical" television. The early inventors of television intended to send electrical signals over wires, but as soon as radio began to develop, the idea arose that these signals could be transmitted using electromagnetic waves. This idea was first put forward by the 15-year-old Polish high school student Mieczyslaw Wolfke, who in 1898 filed a patent application for the first television device without wires. Wolfke's transmitter was the same as Nipkow's, only the signals from the photoelectric cell were transmitted here to the primary winding of the transformer, the secondary winding of which was connected to a Hertz vibrator, which emitted electromagnetic waves. In the receiver, current was applied to a neon lamp, and the image was projected in the same way as Nipkow's. Despite the successful resolution of the scanning problem, neither Nipkow nor his followers were able to transfer the images. Simple photocells, converting the brightness of the transmitted point into an electrical signal, gave very weak current pulses, which were lost in a more or less extended communication line. Although individual inventors were able to build working devices and transmit elementary images with their help, the technical means at their disposal did not allow them to take experiments outside the laboratory. The main obstacle to the further development of television was the lack of an essential element of communication - a signal amplifier. It wasn't until the invention of the vacuum tube that this obstacle was overcome. The development of television was also facilitated by new discoveries in the field of the photoelectric effect. In 1888, the Russian physicist Ulyanin discovered an interesting phenomenon - at the metal-selenium interface, when illuminated by the light of a source, an electric current began to be generated. Ulyanin hurried to use this property and made the first selenium photocell with a thin gold film, which produced a weak current in the light. (This effect is now widely used in technology, for example, in solar cells.) Recall that before that, only one manifestation of the light-sensitive properties of selenium was known - a change in resistance. Therefore, it was necessary to include a power source in the selenium photocell circuit - an external battery. Now the need for this has disappeared. The first practical television systems were created only in the 1923th century. In 1925, Charles Jenkins transmitted a still image by radio from Washington to Philadelphia and Boston, and in 12,5 he was able to transmit images of moving figures. Jenkins used a Nipkow disk to scan, and a vacuum tube amplifier to amplify the video signal. The receiver used a neon lamp, which the viewer looked through the holes of another Nipkow disk and saw points of different brightness, located in exactly the same order as in the transmitted image. To do this, the receiving disk rotated at the same speed as the transmitting disk, making 12 revolutions per second (in other words, 5 frames changed in front of the viewer in one second - sufficient speed to transmit movement). Later the speed was increased to 25 frames per second. Successful results were also achieved in England. In 1928, the Scotsman John Baird founded the first joint-stock television company in Europe and began experimental transmissions through a radio station located in London. His own company launched the production of the first mechanical televisions. The image in them was developed on 30 lines. The general public was initially enthusiastic about the new invention. Viewers were even tolerant of the fact that the image on their televisions often turned out to be dark, fuzzy and blurry. However, over the years the enthusiasm has waned. It turned out that it is generally impossible to get a good, clear image in mechanical television. (It is estimated that for this the Nipkow disk must have a scan of 600 lines with a hole diameter of about 0 mm. In this case, the diameter of the disk itself will reach 1 m. When rotating at the required speed, it will inevitably scatter under the action of centrifugal forces.) Although in many large cities (including Moscow and Leningrad) had their own television studios, and tens of thousands of people had televisions at home, mechanical television was not widely used and eventually gave way to electronic television everywhere, which will now be discussed. The era of electronic television began with the invention of the cathode ray tube. The prototype of the electron tube was a gas-discharge lamp invented in 1856 by the German glassblower Geisler, who learned how to fuse platinum electrodes into a glass bulb and created the first gas-filled tubes. Now gas-discharge lamps are widespread everywhere, and their device is well known: two electrodes are placed on both sides of a glass tube filled with some kind of gas. When voltage is applied to these electrodes from a strong current source, an electric field is created between them. In this field, gas molecules are ionized (lose their electrons) and turn into charged particles. As a result, an electrical discharge occurs through the tube, under the influence of which the gas begins to glow brightly. This phenomenon immediately interested many scientists. Among them was the Bonn professor Plücker, for whom Geisler specially manufactured sealed tubes with various mixtures of gases. In 1858, Plücker noticed that when an electric current was passed, the glass near the cathode glowed somehow in a special way, not like in the rest of the lamp. Having studied this effect, Plücker came to the conclusion that some kind of radiation arises near the cathode during an electric discharge, which he called "cathode". In 1869, the German physicist Gittorf discovered that cathode rays can be deflected by a magnetic field. In 1879, the English physicist William Crookes conducted a fundamental study of cathode rays and came to the conclusion that a stream of some particles is emitted from the surface of the cathode when it is heated. (In 1897, the English physicist Thomson proved that cathode rays are a stream of charged particles - electrons.) For his experiments, Crookes created a special tube, which was the first cathode ray tube in history.
Incidentally, Crookes discovered that certain substances (they were called phosphors) begin to glow when bombarded with cathode rays. In 1894, Lenard found that the luminescence of phosphors is the stronger, the stronger the cathode current. In 1895, a professor at the University of Strasbourg, Karl Brown, based on the Crookes tube, created a cathode (electronic) oscilloscope tube designed to study various electric currents.
In Brown's tube, the cathode was covered with a diaphragm - a screen with a small hole, as a result of which not a wide beam was emitted from the cathode, as in Crookes' experiments, but a narrow beam. A coil was placed outside the glass flask, to which the current under study was applied. This current, passing through the coil, created an alternating magnetic field around, which deflected the cathode ray in the vertical plane. A glass plate coated on the cathode side with a phosphor served as a screen. The beam passed through the diaphragm and created a small luminous spot on the screen. Under the action of a deflecting magnetic field, the beam began to oscillate and drew a vertical line on the screen, which marked the maximum and minimum values of the current under study. With the help of a mirror, this luminous line was cast onto an external screen. Somewhat later, in 1902, the Russian scientist Petrovsky improved the Brown tube by proposing to use a second coil to deflect the electron beam also in the horizontal plane. Now, by giving the appropriate signals, it was possible to make the beam go around the entire screen. In 1903, the German physicist Wenelt made another improvement - he introduced a negatively charged cylindrical electrode into the tube. By changing the strength of the charge on this electrode, it was possible to increase or decrease the electron flow from the cathode, making the dot on the screen either brighter or dim. In 1907, Leonid Mandelstam proposed to use two systems of deflecting plates to which a sawtooth voltage was applied to control the beam in the Brown tube. Thanks to this, the electron beam began to draw on the screen the so-called raster - luminous lines that were located one under the other from the top edge of the screen to the very bottom. It happened in the following way. On the path of the electron beam, two vertically arranged plates were placed in the tube, to which, as already mentioned, an alternating sawtooth voltage was applied, created by a special generator. When this voltage was equal to 0, the electron beam occupied some initial position on the screen. Then, after the positive plate began to charge at a certain rate, the electrons were deflected towards it and the end of the beam moved across the screen. This movement continued until the voltage of the positive plate reached its maximum. After that, the voltage rapidly decreased, and the electron beam quickly returned to its original position. Then everything was repeated from the beginning. At the same time, the beam oscillated in the vertical plane. The second pair of plates was intended for vertical deflection. It is easy to see that if the frequency of the sawtooth voltage applied to the vertical plates was 10 times greater than that applied to the horizontal ones, then in the time corresponding to one frame, the beam managed to form 10 lines. Instead of an alternating electric field, it was possible to use an alternating magnetic field created by two coils. All these discoveries and inventions laid the fundamental foundations of electronic television. The first to propose the use of a cathode ray tube for television transmission was the Russian physicist Boris Rosing. In 1907, he received a patent for a method for electrically transmitting images over a distance.
For progressive scanning of the image, Rosing used two mirror drums, which were polyhedral prisms with flat mirrors. Each mirror was slightly inclined to the axis of the prism, and the angle of inclination increased uniformly from mirror to mirror. When the drums rotated, the light rays coming from different elements of the transmitted image were reflected sequentially by mirror faces and alternately (line by line) fell on the photocell. The current from the photocell was transferred to the capacitor plates. Depending on the magnitude of the supplied current, a greater or lesser number of electrons passed between them, which made it possible to change the brightness of the illumination of the corresponding points of the luminescent screen. (The electric field inside the capacitor, when the signal voltage changed, deflected the beam vertically, as a result of which the number of electrons that hit the screen through the hole in the diaphragm changed.)
Thus, the tube replaced at once two nodes of the previous mechanical systems of the spreading device (for example, the Nipkow disk) and a light source (for example, a gas lamp). Two mutually perpendicular coils controlled the movement of the beam in such a way that it drew a raster (it started moving from the upper left corner of the screen and ended in the right corner, then quickly returned to the left edge, went down a little and scanned the second line). The movement of the beam and the rotation of the mirror drums were strictly synchronized with each other, so that the passage of each projected face past the photocell corresponded to the passage of one line of the projecting beam. The beam took about 0 seconds to pass through the entire screen. Due to this, the pattern of the beam was perceived by the eye as an integral image. After long and persistent experiments with his imperfect apparatus, Rosing managed to get the first image - a brightly illuminated grating - on the screen of his receiver. This image consisted of four stripes. When one of the lattice holes was closed, the corresponding strip on the screen disappeared. The TV could transmit the image of simple geometric shapes, as well as the movement of the hand. Messages about Rosing's invention were published in technical journals in the United States, Japan and Germany and had a great influence on the further development of television. Although Rosing is credited as the founder of electronic television, his television system was not yet completely electronic - filming and image transmission were carried out using a mechanical device - mirror drums. Only the receiving tube was electronic in his system, in the device of which one can already see many features of a black-and-white TV. The next step was to create a cathode ray transmitting tube, the operation of which is based on an external photoelectric effect. The external photoelectric effect was discovered in 1887 by Heinrich Hertz and studied in depth the following year by the Russian physicist Alexander Stoletov. The essence of this phenomenon lies in the fact that under the action of light, electrons are knocked out from the surface of a charged plate. The ejected electrons form a cloud that is attracted to the positive electrode, forming an electric current in a vacuum or rarefied gas. This principle is based on the work of a photocell, created in 1906 by the German scientist Dember. The cathode and anode are placed in a glass flask from which air is pumped out. K - cathode coated with a photosensitive substance (preferably cesium); A - the anode, which is a metal mesh and does not interfere with the passage of light to the anode; C - light source; E - battery. Light falling on the photocathode of the photocell releases electrons from it, which rush to the positively charged anode. Decreasing or increasing illumination of the photocathode increases or decreases the current in its circuit accordingly. In 1911, the English engineer Alain Swinton proposed a project for a television device in which a cathode ray tube was used not only as a receiver, but also as a transmitter. At the heart of the transmitting Swinton tube is a Crookes tube, to the cathode of which a negative voltage of 100000 volts was applied relative to the anode. A narrow beam of electrons passed through the hole in the anode C and hit the screen I, describing a raster on it with the help of deflecting coils E. The screen consisted of miniature rubidium metal cubes isolated from each other. On the opposite side, an image was projected through the grid L and the compartment with sodium vapor onto the screen I. Light from each of its points fell on a separate rubidium cube of the screen, which acted as an independent photocell, and knocked out electrons from its surface. In accordance with the laws of the external photoelectric effect, these electrons were the greater, the more intense the action of light turned out to be.
As long as no voltage was applied to the cube, the ejected electrons were near the screen. But when the electron beam, which ran around all the cubes one after the other, hit one of them, it received a negative charge. Then the electrons knocked out by the light from the surface of the cube rushed to the grid L, which, consequently, at each moment of time had a charge corresponding to some point of the screen. This charge was removed from the grid and then transmitted as a video signal to a receiving tube, the device of which was based on the same principles as that of Rosing. The electron beam of the receiving tube was synchronized with the beam of the transmitting tube, and its intensity at each point directly depended on the strength of the video signal being sent. Swinton did not create a practical television installation, but in his project we already see those basic elements that later entered the design of all subsequent generations of transmitting tubes: a double-sided mosaic of many individual photocells with an external photoelectric effect, a collector in the form of a grid L and deflecting coils E. The next step in the development of television was taken only in the 20s. In 1923, Vladimir Zworykin (in his student years, Zworykin was one of Rosing's students and actively helped him in creating the first television; in 1917 he emigrated to the United States, where he worked until his death) patented a fully electronic television system with a transmitting and receiving electronic beam tubes.
In the transmitting tube, Zworykin used a three-layer double-sided target. The tube consisted of a signal plate 4 - a thin aluminum film (transparent to electrons), coated on one side with an aluminum oxide dielectric 3, on which a light-sensitive layer 2 was deposited, which has an external photoelectric effect. Grid 1 was installed next to this layer. A positive (relative to the grid) voltage was applied to the aluminum film. The image was projected onto this layer through the grid 1. On the other side of the aluminum film, the electron beam 5 from the electron projector 6 created a raster. The signal was taken from the load RN in the grid circuit. The transmission tube mosaic contained many individual photocells. This tube also did not become a working model, but in 1929 Zworykin developed a high-vacuum receiving cathode-ray tube, which he called a kinescope, which was later used in the first televisions. Thus, the receiving cathode ray tube was already created in the early 30s. With transmission tubes, the situation was more complicated. All the electronic tubes proposed by the inventors by the end of the 20s had one significant drawback - they had a very low light sensitivity. The video signal taken from them was so weak that it could not provide not only a good, but also any satisfactory image. The low photosensitivity was rightly explained by the inefficient use of the light flux. Indeed, suppose that a photosensitive mosaic plate is divided into 10 thousand cells, and the electron beam goes around them all in 0 s. This means that when the transmitted image was discharged, the light acted on each individual photocell for only 1/1 of a second. If it were possible to use the energy of the light flux, which was wasted uselessly during the remaining 100000/99999 seconds, the sensitivity of the television system would have to increase significantly. One of the first to try to solve this problem was the American engineer Charles Jenkins, already known to us. In 1928, he proposed a device for accumulating charge in a television tube. The essence of Jenkins' idea was that a capacitor C was connected to each photocell of the photosensitive panel. Light fell on the photocell, and the resulting current charged the capacitor during the entire time the frame was transmitted. Then, with the help of a commutator, the capacitors were alternately discharged through the load RN, from which the signal was taken, that is, Jenkins intended to use the discharge current as a video signal. Jenkins' idea was very fruitful, but it needed further refinement. First of all, I had to think about where and how to place tens, or even hundreds of thousands of small capacitors (after all, each individual cell of the screen had to have its own capacitor), then it was necessary to create a switch that could discharge all these capacitors with the necessary speed and synchronism. capacitors. No mechanical device could cope with this task. Therefore, the role of the switch began to be entrusted to the same electron beam. Over the next five years, several variants of transmitting tubes using the principle of charge accumulation were proposed in different countries, but all these projects were not implemented. Vladimir Zworykin was lucky to overcome numerous obstacles successfully. In 1933, at a convention of the Society of Radio Engineers in Chicago, he announced that his decade-long effort to build a working television tube had been a complete success. Zworykin began this work in the Westinghouse laboratory, and completed it at the Radio Corporation of America, where he had at his disposal a well-equipped laboratory and a large group of experienced engineers. After many experiments, Zworykin, with the help of the chemist Izig, found a very simple method for manufacturing a mosaic light-sensitive target with storage capacitors. It happened in the following way. A mica plate measuring 10 by 10 cm was taken and a thin layer of silver was applied to one of its sides. After that, the plate was placed in an oven. A thin silver layer, when heated, acquired the ability to curl into granules. Thus, several million granules isolated from each other were formed on a mica plate. Then cesium was applied onto the silver layer, which, like selenium, had an increased sensitivity to light. On the opposite side, the mica plate was covered with a continuous metal layer. This layer, as it were, served as a second capacitor plate in relation to silver granules with a light-sensitive cesium layer. As a result, each of the million miniature photocells served at the same time as a miniature capacitor. This tube Zworykin gave the name iconoscope.
The work of the iconoscope proceeded as follows. The glass spherical cylinder was supplied with a cigar-shaped cylindrical process, in which an electronic searchlight was placed. The ball contained a target mounted obliquely to the axis of the process. This target, as already mentioned, consisted of a mica plate, on one side of which a metal signal layer was deposited, and on the other, a photosensitive mosaic consisting of many photocells isolated from each other (5). Part of the surface of the glass ball tube tube was made flat, parallel to the target. An image was projected onto the mosaic through it, so that the axis of the objective was perpendicular to the plane of the target (this excluded any distortion). Next to the mosaic, a grid (1) was placed in front of the photosensitive layer, on which a positive charge relative to the anode (3) was applied (the anode was grounded, and a large negative potential was created on the thermal cathode (4). The electron beam (2) passed through the grid and created a raster on the mosaic. The signal was taken from the signal plate (6) and applied to the resistance RN, and then to the amplifying lamp (7). The electron beam, running through the photomosaic, discharged successively all its sections. As a result, electrical impulses (video signals) were generated that were proportional to the illumination of the mosaic areas. These pulses were amplified and fed to a radio transmitter. In the future, the iconoscope was significantly improved. The ball was replaced by a cylinder with a branch for an electronic searchlight. Instead of a grid that distorted the signal, they began to use a collector (8) in the form of a metal ring. The photoelectrons emitted by the mosaic were collected on the inner surface of the cylinder. The target consisted of a mosaic of photocells - a photosensitive layer (2), a mica dielectric plate (3) and a metal film as a signal plate (4). The iconoscope was the last link in the chain of inventions that led to the creation of electronic television. But due to the depression that then gripped the United States, the television network here took shape only a few years later. Meanwhile, in 1934, a group of Soviet engineers led by Boris Krusser also created an iconoscope. In England, television broadcasting on equipment developed by Marconi and EMI began in 1936. That same year, the NBC broadcaster began regular television broadcasts in New York City. Television broadcasting began in Germany and the USSR in 1938.
In December 1936, the RCA laboratory demonstrated the first television set suitable for practical use. In April 1939, RCA introduced the first television set for general sale. It was shown at the New York World's Fair. This TV was produced in four versions - three consoles and one desktop, which had a 5-inch screen and was known as the RCA TT-5. All models were housed in handmade walnut cabinets. Author: Ryzhov K.V.
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