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| Text 3. The Elements of a System of Radio Communication
АРІЙ
Рецензенти: кафедра іноземних мов Київського Національного технічного університету
Редактор В. II. Авдієнко
Мансі Є. О., Гончарова Т. В. RADIO ENGINEERING and COMPUTING TECNIQUE (Радіотехніка і комп’ютерна техніка). Тексти до підручника з англійської мови для студентів і аспірантів немовних факультетів та студентів мовних факультетів, які вивчають англійську як другу іноземну мову у вищих навчальних закладах. — К. : Арій, 2008. — 80 с. ISBN 978-966-498-045-3. Тексти англійською мовою за фахом «Радіотехніка» і «Комп’ютерна техніка» дають можливість студентам і аспірантам не тільки збільшити свій лексичний запас з цих спеціальностей, але й підготуватися до іспиту з англійської мови. ISBN 978-966-498-045-3© Мансі Є.О., Гончарова Т. В., 2008 © «Видавництво “Арій”», 2008 © «Видавництво “Арій”», художнє оформлення, 200
Contents Radio Engineering Text 1. Electronics 5 Text 2. Electron Emission 6 Text 3. The Elements of a System of Radio Communication 9 Text 4.Propagation of Radio Waves of Different Frequencies 11 Text 5. Reception of Radio Signals 12 Text 6. Radio Receivers (I) 13 Text 7. Radio Receivers (II) 15 Text Oscillators 17 Text 9. Radio-Frequency Amplifiers 18 Text 10. General Classification of Amplifiers 18 Text 11. Detection ........................................................................................ 20 Text 12. The Telephones .......................................................................... 21 Text 13. Functions of Vacuum Tubes......................................................... 23 Text 14. Basic Tube Types......................................................................... 25 Text 15. Screen-Grid Tube......................................................................... 26 Text 16. Cathode-Ray Tube ................................... ………………………….28 Text 17. Magnetron 30 Text 18. Loudspeaker 32 Text 19. Handie-Talkie 33 Text 20. Fundamentals of Radar................................................................ 35 Text 21. Slant Range 36 Text 22. Bearing........................................................................................ 38 Text 23. Transistors, the Basic Mechanism................................................ 39 / Text 24. Radio Transmitters 41 Text 25. Transistor Radio Frequency Amplifiers 42 Text 26. The Televisor 43 Text 27. Antenna 46 Text 28. Amplifier 47 Text 29. Brief Analysis of the Television System 46 Text 30. Basic Structure of a Picture 49
Computing Technique Text 1. The Computer.......................................................... Text 2. Using the Computer................................................. Text 3. Peripheral Equipment.............................................. Text 4. Computers on Wheels.............................................. Text 5. Programming a Computer........................................ Text 6. The Robot’s Nervous System.................................... Text 7. Menu System........................................................... Text 8. Input, Process, Store, Output................................... Text 9. Input-Output System................................................ Text 10. Memory ................................................................. Text 11. Automatic Translator.............................................. Text 12. Universal Electronic Computer............................... Text 13. What Is a Digital Computer? .................................. Text 14. Digital Computers.................................................. Text 15. Analog Versus Digital Computers........................... Text 16. Age of Thinking Machines....................................... Text 17. General- and Special Purpose Computers .............. Text 18. Programming......................................................... Text 19. Types of Instructions.............................................. Text 20. Simple Hardware, Complicated Logic .................... Text 21. Machine Language and Language Structure........... Text 22. Video Terminals..................................................... Text 23. Mechanical and Electronic Calculating Machines
Radio Engineering Text 1. Electronics Electronics is the science of electronic phenomena, devices and systems. It describes and applies the flow of electrons emitted from solids or liquids passing through vacuum, gases or semiconductors. Electronics as a science studies the properties of electrons, the laws of their motion, the laws of the transformation of various kinds of energy through the media of electrons. The basic elements in electronics are the electron tube and the transistor. Although electronics is properly regarded as only a section of electrical technology, electronic techniques are applied in many fields, including industry, communication, defence and entertaining. Due to its versatility it becomes increasingly difficult to draw clear dividing lines between electronics and other branches of electronical technology. While physical electronics is the science of electronic processes, industrial electronics deals with the technology of design, construction and application of electronic devices. The industrial applications of electronics include control gauging, counting and measuring, speed regulations, and many others. The invention of electronic device is known to have become a new important phase in the development of electrical engineering. It considerably enlarges the application of electrical energy for various industrial purposes. The invention of the vacuum tube made radiobroadcasting possible and later on — telecasting. The researches in the field of electronics gave us radar devices, computers, tape recorders, betatron and a lot of medical tools. Semiconductor devices which have replaced electron tubes reduce the size of instruments. A great advance in electronics is considered to be connected with the appearance of the transistor. The use of the transistor is likely to be the first step in miniaturization of electronic devices and has increased the range of their application. The introduction of the transistor in 1948 is supposed to be the beginning of the evolution of microelectronics which led in the late 1970s to the development of large-scale integrated (LSI) circuits. Now hundreds of circuits can be packed on to one square inch and there seems to be no limit to it. The technology of so-called molecular epitaxy is the best proof of this suggestion. Electronics is evident to have made a great contribution to automation. It has extended the range of automatic control in large-scale industrial operations and made the processing of information rapid. Electronic computers have provided the basis for the construction of automatic lines, automatic units, shops and whole plants, tools with programmed control, robots and manipulators. The steering of big ships, jet planes, interplanetary rockets is controlled by electronic devices. Radio-electronic systems ensure reliable communication with space stations at distances amounting to scores of millions of kilometres. Hundreds of electronic devices perform various tasks on board every satellite and spaceship. Electronics has penetrated into all the spheres of human activity from household appliances to artificial intelligence and search of outerspace civilizations. Such advantages of electronic devices as microscopic size, high speed, low cost and reliability are likely to have no competitor. No wonder electronic technology is the most dynamic technology of the present industrial age. Electronics is sure to make still greater progress in the nearest future and help humanity gain new victories in science and engineering. Notes
Text 2. Electron Emission There is little doubt that wireless, radio, and television are among the greatest miracles of modern science. Travelling with the speed of light, code signals, the human voice and music can be heard around the world within the very second they are produced in the broadcastingstudio. Through television, world events can be observed in full colour at the same moment they occur hundreds of miles away. The more we learn of the fundamental principles of radio and its operation the more amazing does their reality become. The heart of a tube is the source of electrons. Every vacuum tube depends for its action upon a stream of electrons that acts as a carrier of current. As necessary as the stream of electrons is the electrode that emits them. Whatever the nature of the tube and the arrangement of electrodes, an emitting electrode cannot be dispensed with. Even in cold-cathode tubes, one of the electrodes is treated with a low-work-function material to facilitate the production of some electrons that will initiate the action. In general, the excellence of performance of a given tube depends upon the efficiency with which free electrons are produced. When the emission fails, the tube is useless. We infer correctly then, that the subject of electron emission is worthy of considerable study. The types of electronic emission may be listed as follows: 1. Thermionic, or primary, emission. 2. Secondary emission. 3. Photoelectric emission. 4. Field emission. Thermionic Emission. The velocity of electrons and atoms, as they move about within the confines of the material they comprise, is dependent on the temperature. At a temperature of absolute zero all molecular activity is supposed to cease. As the temperature is increased, the activity of electrons and atoms increases until a point is reached where the electrons have sufficient velocity to enable them to break through the potential barrier of the material. This evaporation of electrons from the body of a solid at high temperature is known as thermionic emission. The emission or evaporation of electrons takes place at lower temperature than does that of atoms. The mass of electrons being smaller, it reaches the higher velocities necessary for evaporation at low temperatures than does the heavier atom. The temperature becoming high enough for the atoms to evaporate, the material or solid that they compose rapidly disintegrates. Secondary Emission. One knows to a high degree of certainty that being accelerated to a sufficiently high velocity an electron may have enough kinetic energy imparted to it to knock one or more electrons out of any material it comes in contact with, either a metal conductor or an insulator. A positively charged electrode situated near the source of these “secondary” electrons will collect them. Inactual tubes the secondary electrons may be attracted back to the electrode they come from, as from the plate, or they may be collected by another electrode which is positively charged. In many tubes these secondary electrons give rise to undesirable effects, design steps being taken to reduce their number and to control their movements. In a few tubes, such as electron multipliers, the desired operation is based on the principle of secondary emission. Photoelectric Emission. When light of proper wavelength is allowed to fall upon certain metals, electrons are released from the surface of the metal as a result of the energy imparted by the light. Here, then, is another electron source. Such sources are used in phototubes and in certain types of television camera tubes. Field emission occurs at cold surfaces under the influence of extremely strong fields. All types of emission are most effective in vacuum. If the emission did occur in air, the emitted electrons would not get very far through the relatively dense surrounding atmosphere. Most metals would burn up in air at the temperatures to which they must be raised to emit satisfactorily. Notes
Text 3. The Elements of a System of Radio Communication Radio Waves Electrical energy that has escaped into free space exists in the form of electromagnetic waves. These waves, which are commonly called radio waves, travel with the velocity of light and consist of magnetic and electrostatic fields at right angles to each other and also at right angles to the direction of travel. One half of the electrical energy contained in the wave exists in the form of electrostatic energy, while the remaining half is in the form of magnetic energy. The essential properties of a radio wave are the frequency, intensity, direction of travel, and plane of polarization. The radio waves produced by an alternating current will vary in intensity with the frequency of the current and will therefore be alternately positive and negative. ^ The distance occupied by one complete cycle of such an alternating wave is equal to the velocity of the wave divided by the number of cycles that are sent out each second and is called the wave length. The relation between wave length X in meters and frequency / in cycles per second is therefore λ= The quantity 300 000 000 is the velocity of light in meters per second. The frequency is ordinarily expressed in kilocycles, abbreviated KC; or in megacycles, abbreviated MC. A low-frequency wave has a long wave length while a high frequency corresponds to a short wave length. The strength of a radio wave is measured in terms of the voltage stress produced in space by the electrostatic field of the wave and is usually expressed in microvolts stress per meter. Since the actual stress produced at any point by an alternating wave varies sinusoidally from instant to instant, it is customary to consider the intensity of such a wave to be the effective value of the stress, which is 0.707 times the maximum stress in the atmosphere during the cycle. The strength of the wave measured in terms of microvolts per meter of stress in space is exactly the same voltage that the magnetic flux of the wave induces in a conductor 1 meter long when sweeping across this conductor with the velocity of light. Thus the strength of a wave is not only the dielectric stress produced in space by the electrostatic field, but it also represents the voltage that the magnetic field of the wave will induce in cutting across a conductor. In fact, the voltage stress produced by the wave can be considered as resulting from the movement of the magnetic flux of the same wave. The minimum field strength required to give satisfactory reception of a wave depends upon a number of factors, such as frequency, type of signal involved, and amount of interference present. Under some conditions radio waves having signal strengths as low as 0.1 (xy per meter are usable. Occasionally signal strengths as great as 5,000 to 30,000 |iy per meter are required to ensure entirely satisfactory reception at all times. In most cases the weakest useful signal strength lies somewhere between these extremes. A plane parallel to the mutually perpendicular lines of electrostatic and electromagnetic flux is called the wave front. The wave always travels in a direction at right angles to the wave front, but whether it goes forward or backward depends upon the relative direction of the lines of electromagnetic and electrostatic flux. If the direction of either the magnetic or electrostatic flux is reversed, the direction of travel is reversed; but reversing both sets of flux has no effect. The direction of the electrostatic lines of flux is called the direction of polarization of the wave. If the electrostatic flux lines are vertical the wave is vertically polarized; when the electrostatic flux lines are horizontal and the electromagnetic flux lines are vertical, the wave is horizontally polarized. Notes
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