A trend of today's radio electronics
SOUND
Everything that we here is a sound. There are high-pitched sounds and low-pitched sounds. Sounds also vary in loudness from soft to loud. You take and hold one end of a rope and whip it up and down, waves from this end pass along the rope to the other end. The vibration of the rope generates a sound wave. The sound wave appears and the air compresses or expands. The forward and backward vibration of the rope forms a type of wave pattern. This is a sine wave.
A sine wave has peaks and valleys. We call a form of energy in motion a wave motion. The motion consists of several peaks and valleys. Sound is a form of wave. It represents a form of distribution of energy not only of sound waves but also of radio and light waves. We use the word "waves" also to represent alternating current (a.c.) and voltage.
It is difficult to detect the sound. Sometimes engineers amplify it before it with the help of different devices. They use a lot of various devices if they want to select a sound from an atmospheric noise.
ELECTRONIC ENGINEERING
Electronic engineering deals with the research, design, integration and application of circuits and devices that we use for transmission and processing of information.
Engineers in the field of electric and electronic engineering know all the aspects of electrical communications, from fundamental questions such as "What is information?" to the highly practical, such as the design of telephone systems. In their work they rely on various branches of advanced mathematics, such as linear systems, linear algebra, differential equations and probability theory. Engineers design, test, adjust and improve communication systems. Besides, they work on control systems that we use in automated manufacturing and in robotics. Due to engineer's work we have so many modern telephone systems, cellphones and digital cameras.
Major developments in the field of communications and control are the replacement of analogue systems with digital systems; instead of copper cables we use fibre optics. Digital systems offer far greater immunity to electrical noise. Fibre optics is likewise immune to interference. They also have great carrying capacity and are extremely light and inexpensive to manufacture.
TRANSISTORS
A small piece of the element germanium amplifies a speech signal about forty times. This process is a transistor effect. Due to the invention of such a device the transistor industry grows. Transistors are everywhere in homes, automobiles, and factories - even on the ocean floor and in outer space.
Transistors play a vital role in communication and information processing. Transistors improve or make possible the invention of telephone, the undersea cables, new central offices and radio transmission.
Transistors perform all the functions of vacuum tubes. They can amplify electrical signals. Transistor acts as oscillator. It controls and combines pulses of current. For practically every application they are less expensive, more reliable and smaller than vacuum tubes. Transistors also consume less power than vacuum tubes. These advantages of transistors greatly influence its wide application.
TELEPHONE
Today we can communicate with people who live far from us. A distance of few miles is not a limit for us now. It is possible due to the invention of a telephone. The construction of the first telephone is simple: a wire with a ground for the connection. The main parts are a transmitter and a receiver. Sound waves strike the diaphragm and make it to vibrate. The vibration of the diaphragm changes the magnetic field and induces electric waves of varying voltage and current. These waves pass to the distant telephone. There the changes that appear in the magnetic field make the diagram reproduce the original sound. That is how the first telephone works. But nowadays its construction changes greatly. It becomes more complex.
Engineers separate transmitters and receivers. They use auxiliary elements in the telephone's circuits for better transmission of speech. Then the invention of switchboard came, because engineers and scientists wanted to connect two of a large number of telephone sets. The advantage of a central switching office with a switchboard was very great for a while.
But now we have automatic telephone sets interconnections.
METERS
Engineers and scientists use many different meters for different purposes. The ohmmeters, the ammeters and wattmeter are the most common meters among them. We use the ohmmeter to measure the value of resistance. It consists of a milliammeter that we read in ohms, a battery and resistors. This meter is in parallel in the circuit and the circuit has no open when you want to measure its resistance. The readings on the scale show the value.
Engineers use the ammeter to measure the value of current. The circuit opens at one point. An engineer connects the terminals of the meter to the ammeter. He connects the positive terminal of the meter to the positive terminal of the source; the negative terminal of the meter - to the negative terminal of the source. The ammeter is in series in the circuit. The readings on the scale show the value of current.
Engineers use a wattmeter to measure the value of power. They connect it directly to the circuit. A wattmeter consists of two coils. The readings on its scale show the value of power.
RESISTORS
A resistor is one of the most common elements of a circuit. Engineers and scientists use resistors to reduce the value of current in the circuit, to produce IR voltage drop, and in this way to change the value of the voltage.
Current passes through a resistor and its temperature rises high. The higher the value of current the higher is the temperature of a resistor. Each resistor has a maximum temperature. It means that it can work up to these limits without a trouble. If the temperature rises higher the resistor gets open and opens the circuit.
The readings on its scale show the value of resistance in watt. The watt is the rate at which engineers obtain electrical energy when a current of one ampere passes at a potential difference of one volt.
A resistor can have constant value - this is a fixed resistor. The other resistor has different value in different cases. It is a rheostat. Engineers use it to change the resistance of circuits and in this way to vary the value of current.
ELECTRICAL CELL
Engineers use an electric cell to produce and supply electric energy. It consists of an electrolyte and two electrodes. We use electrodes as terminals. They connect the cell directly to the circuit - current passes through the terminals and the bulb lights.
Engineers connect the cells in series, parallel or in series-parallel. They want to increase the current capacity, they connect the cells in parallel. They connect the cells in series and increase the voltage output. A battery has a large current capacity and a large voltage output, this means that engineers connect its cells series-parallel.
When an engineer connects the cells in series, he connects the positive terminal of one cell to the negative terminal of the second cell, the positive terminal of the second cell - to the negative terminal of the third…and so on. Engineers connect together the cells' negative terminals and positive ones if they want to have the cells in parallel. In case a cell has a trouble it stops or operates badly. Engineer substitutes this cell by another one.
Measurements
Metric system is a decimal system of physical units. It got its name after its unit of length, the meter. The majority of countries adopts the metric system as the common system of weights and measures. The scientists all over the world use this system in their scientific work.
Weights and Measures
We measure length, capacity and weight and use standard units in these cases. The principal early standards of length were the palm or hand breadth, the foot and the cubit, which is the length from the elbow to the tip of the middle finger. Such standards were not accurate and definite. Only in modern time people adopted unchanging standards of measurement.
In the English-speaking world, the everyday units of linear measurement were traditionally the inch, foot, yard and mile. In Great Britain people defined these units of length in terms of the imperial standard yard, which was the distance between two lines on a bronze bar made in 1845.
In Britain scientists now also derive units of weight (ounces, pounds, and tons) from the metric standard — kilogram. This is a solid cylinder of platinum-iridium alloy maintained at constant temperature at Sevres, near Paris.
National standards laboratories in many countries maintain copies of this standard as exact as possible.
International System of Units is a system of measurement units based on the MKS (meter-kilogram-second) system. This international system is commonly referred to as SI.
At the Eleventh General Conference on Weights and Measures that took place in Paris in 1960 scientists defined standards for six base units and two supplementary units.
Length
The meter had its origin in the metric system. By international agreement the scientists defined the standard meter as the distance between two fine lines on a bar of platinum-iridium alloy. The 1960 conference redefined the meter as 1,650,763.73 wavelengths of the reddish-orange light that the isotope krypton-86 emitted. The scientists again redefined the meter in 1983 as the length of the path that light in a vacuum traveled during a time interval of 1/299,792,458 of a second.
Mass
When scientists created the metric system, they defined the kilogram as the mass of 1 cubic decimeter of pure water at the temperature of its maximum density or at 4.0 °C.
Time
For centuries, we measured time universally in terms of the rotation of the earth. The second is the basic unit of time. Scientists defined it as 1/86,400 of a mean solar day or one complete rotation of the earth on its axis in relation to the sun. They discovered, however, that the rotation of the earth was not constant enough to serve as the basis of the time standard. As a result, scientists redefined the second in 1967 in terms of the resonant frequency of the caesium atom, that is, the frequency at which this atom absorbs energy.
Temperature
The temperature scale is based on a fixed temperature, that of the triple point of water at which it's solid, liquid and gaseous. Scientists designate the freezing point of water as 273.15 K. It equals exactly 0° on the Celsius temperature scale. The Celsius scale, which is identical to the centigrade scale, gets its name from the name of the 18th-century Swedish astronomer Anders Celsius. He first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees. By international agreement, the term Celsius has officially replaced centigrade.
One feature of SI is that some units are too large for ordinary use and others too small. To compensate, scientists borrowed and expanded the prefixes for the metric system. Examples aremillimeter (mm), kilometer/hour (km/h),megawatt (MW), andpicofarad (pF). The prefixeshecto, deka, deci,and centi are used only rarely, and then usually with meter to express areas and volumes
high-pitched sounds - звуки высокой частоты
sine wave - синусоидальная волна
a.c. - переменный ток
atmospheric noise - атмосферные помехи
fibre optics - оптиковолоконные технологии
immunity - защищенность, невосприимчивость
carrying capacity - пропускная способность
processing -обработка
undersea - подводный
vacuum tube - электронная лампа
varying - меняющееся
auxiliary - вспомогательный
switchboard - коммутатор
made - сделанный
to be referred to as - называться
is based - основан
fixed - фиксированный
triple point - тройная точка
is divided -поделен
has officially replaced - официально заменил
Тексты для студентов-заочников группы (“РТ? 1к. 2с.)
CAPACITOR
A capacitor is one of the main elements of a circuit. It is used to store electric energy. A capacitor stores electric energy provided that a voltage source is applied to it. The main parts of any capacitor are metal plate and insulators. Its function is to isolate the metal plate and in this way to prevent a short.
There are two common types of capacitors in use nowadays: a fixed capacitor and a variable one. The plates of a fixed capacitor can not be moved. For this reason its capacity does not change. The variable capacitor plates move, its capacity changes. The greater the distance between the plates, the less is the capacitor's capacity. The function of variable capacitors widely used is to vary the frequency in the circuit.
Fixed capacitors have insulators have insulators produced of paper, ceramics and other materials; variable capacitors have air insulators. Paper capacitors are used because of their advantage is their high capacity: it may be higher than 1,000 picofarad.
Besides, electrolyte capacitors are highly in use. They also have a very high capacity: it varies from o.5 to 2,000 micofarad. Their disadvantage is that they change their capacity when the temperature changes only at temperatures not lower than -40 degrees Celsius.
Common troubles in capacitors are an open and a short. A capacitor stops operating and does not store energy in case it has a trouble. It should be substituted by a new one.
A TREND OF TODAY'S RADIO ELECTRONICS
The reduction of radio instruments to miniature propositions is a major trend in modern radio electronics. The significance of this research has grown especially in connection with space communications. It is impossible to create a spaceship for lights over a long distance or to meet constantly increasing demand for satellites, to provide proper operation of portable computers and mobile phones without light, small and economical devices and apparatuses.
Almost any airplane carries nowadays a large amount of useful equipment for safety flight and its pilots use the great number of devices and sensors controlling different things. The reusable spaceship also carries a lot of equipment: a system for communication with the Earth, radars, life-supporting and experiments conducting systems, etc. And the further development in the field of airplane and spaceships design and construction will not leave much room for bulky equipment in the future.
Semiconductors and integrated circuits have helped to reduce the equipment size considerably. Having replaced the electronic valves semiconducting tools provide less size, weight and more reliability. They consume less power and are more durable. But it does not mean that radio valves were useless invention and they can no longer be developed. Taking into account hearing aids and pocket receivers we can be sure their development was impossible with the use of radio valves.
The emergence of new synthetic materials led to the size reduction of other parts of electronic instruments - resistors, condensers and transformers. For example, there is a wire with a cross section of just a few microns - 1/20 the thickness of a human hair. It can be used in miniature transformers and other elements of radio circuits. The development of micromodules - tiny ceramic plates with a metallized coating - has opened great possibilities for making miniature electronic instruments.
Semiconductors compressed into this plate are hundreds of times smaller than electronic valve. The component density of micromodules is very high and there are radio units with up to 70 parts within a cubic centimeter. A radio receiver assembled of micromodules does not weigh more than 60 grams.
Molecular electronics also opens new possibilities for the further radio electronics development. A crystalline lattice can be changed by proper substance added to semiconductors to obtain crystals with the required electrical properties. Germanium or silicon plates produced by the previously mentioned method will not operate as separate resistors or condensers, but as complete circuits - as generators or amplifiers. In these systems the assembly density will be higher as several thousand parts per a cubic centimeter.
It can be noted that in the nearest future superminiature elements will be developed like models of nerve cells of living organisms - neurons.
THE RADIO SYSTEM
Radiation through space is the basis of all radio communication, but means must be provided for generating the signal and receiving it at the receiving end. The transmitting station requires a means for generating the radio-frequency energy and this is done by converting direct current or low-frequency alternating current power into radio frequency by means of vacuum tubes and their associated circuits. The radio-frequency energy is fed into a radiating system, or antenna.
To transmit any message the information should be imposed upon the radio-frequency energy. In the case of radiotelephone operations it is done by varying the amplitude of the output in accordance with the voice frequencies of the operator picked up by microphone and amplified. Either by turning the output on and off to form the dots and dashes of the radio code that correspond to the letters of the words that the operator wishes to transmit. Thus the energy radiated from antenna serves as a carrier for the information.
At the receiving station transmitted energy (currents) is introduced into selective circuits which make it possible to select the desired signal out of all that exist in space. These currents are amplified by passing them through the suitable vacuum tube amplifiers that build up the energy level. But to make the signal audible it should be detected with the help of various radio devices.
The audio signal may be amplified after detection and made audible by feeding it into headphones or a loudspeaker.
RADIO
Radio is a system of communication employing electromagnetic waves propagated through space. Because of their varying characteristics, radio waves of different lengths are employed for different purposes and are usually identified by their frequency. The shortest waves have the highest frequency, or number of cycles per second; the longest waves have the lowest frequency, or fewest cycles per second. In honor of the German radio pioneer Heinrich Hertz, his name has been given to the cycle per second (hertz, Hz); 1 kilohertz (kHz) is 1000 cycles per sec, 1 megahertz (MHz) is 1 million cycles per sec, and 1 gigahertz (GHz) is 1 billion cycles per sec. Radio waves range from a few kilohertz to several gigahertz. Waves of visible light are much shorter. In a vacuum, all electromagnetic waves travel at a uniform speed of about 300,000 km (about 186,000 mi) per second.
Radio waves are used not only in radiobroadcasting but in wireless telegraphy, telephone transmission, television, radar, navigational systems, and space communication. In the atmosphere, the physical characteristics of the air cause slight variations in velocity, which are sources of error in such radio-communications systems as radar. Also, storms or electrical disturbances produce anomalous phenomena in the propagation of radio waves.
WAVES IN RADIO ELECTONICS
Wave motion is a mechanism by which energy is conveyed from one place to another in mechanically propagated waves without the transference of matter. At any point along the path of transmission a periodic displacement, or oscillation, occurs about a neutral position. The oscillation may be of air molecules, as in the case of sound traveling through the atmosphere; of water molecules, as in waves occurring on the surface of the ocean; or of portions of a rope or a wire spring. In each of these cases the particles of matter oscillate about their own equilibrium position and only the energy moves continuously in one direction. Such waves are called mechanical because the energy is transmitted through a material medium, without a mass movement of the medium itself. The only form of wave motion that requires no material medium for transmission is the electromagnetic wave; in this case the displacement is of electric and magnetic fields of force in space.
Because electromagnetic waves in a uniform atmosphere travel in straight lines and because the earth's surface is approximately spherical, long-distance radio communication is made possible by the reflection of radio waves from the ionosphere. Radio waves shorter than about 10 m (about 33 ft) in wavelength—designated as very high, ultrahigh, and superhigh frequencies (VHF, UHF, and SHF)—are usually not reflected by the ionosphere; thus, in normal practice, such very short waves are received only within line-of-sight distances. Wavelengths shorter than a few centimeters are absorbed by water droplets or clouds; those shorter than 1.5 cm (0.6 in) may be absorbed selectively by the water vapor present in a clear atmosphere.
A typical radio-communication system has two main components, a transmitter and a receiver. The transmitter generates electrical oscillations at a radio frequency called the carrier frequency. Either the amplitude or the frequency itself may be modulated to vary the carrier wave. An amplitude-modulated signal consists of the carrier frequency plus two sidebands resulting from the modulation. Frequency modulation produces more than one pair of sidebands for each modulation frequency. These produce the complex variations that emerge as speech or other sound in radiobroadcasting, and in the alterations of light and darkness in television broadcasting.
Transmitter
Essential components of a radio transmitter include an oscillation generator, an amplifier and a transducer. The first component is used for converting commercial electric power into oscillations of a predetermined radio frequency. Amplifiers are employed for increasing the intensity of these oscillations while retaining the desired frequency. And finally a transducer is applied for converting the information to be transmitted into a varying electrical voltage proportional to each successive instantaneous intensity. For sound transmission a microphone is the transducer; for picture transmission the transducer is a photoelectric device.
Other important components of the radio transmitter are the modulator, which uses these proportionate voltages to control the variations in the oscillation intensity or the instantaneous frequency of the carrier, and the antenna, which radiates a similarly modulated carrier wave. Every antenna has some directional properties. This means that it radiates more energy in some directions than in others. But the antenna can be modified so that the radiation pattern varies from a comparatively narrow beam to a comparatively even distribution in all directions. The latter type of radiation is employed in broadcasting.
The particular method of designing and arranging the various components depends on the effects desired. The principal criteria of a radio in a commercial or military airplane, for example, are lightweight and intelligibility. Cost is a secondary consideration, and fidelity of reproduction is entirely unimportant. In a commercial broadcasting station, on the other hand, size and weight are of comparatively little importance, cost is of some importance and fidelity is of the utmost importance, particularly for FM stations. Rigid control of frequency is an absolute necessity. In the U.S., for example, a typical commercial station broadcasting on 1000 kHz is assigned a bandwidth of 10 kHz by the Federal Communications Commission. But this width may be used only for modulation. The carrier frequency itself must be kept precisely at 1000 kHz, for a deviation of one-hundredth of 1 percent would cause serious interference with even distant stations on the same frequency.
reusable spaceship — космический корабль многократного применения
bulky - громоздкий, занимающий много места
hearing aid - слуховой аппарат
Тексты для студентов-заочников группы (“РТ” 2к. 3с.)