Прочитайте текст и выполните задания. Radio Systems 1. Radio systems used for communications will ha...: ответ на тест 975822 - Английский язык

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Radio Systems
1. Radio systems used for communications will have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialized for different communications purposes. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate some property of the energy produced to impress a signal on it.
2. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space.
3. The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is «tuned» to respond preferentially to the desired signals, and reject undesired signals.
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Radio Systems
1. Radio systems used for communications will have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialized for different communications purposes. Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate some property of the energy produced to impress a signal on it.
2. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space.
3. The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is «tuned» to respond preferentially to the desired signals, and reject undesired signals.
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Why does a modulation system serve for in a transmitter?

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A Satellite Telephone
1. A satellite telephone, satellite phone, or satphone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. They provide similar functionality to terrestrial mobile telephones: voice, short messaging service and low-bandwidth Internet access are supported through most systems. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions. The mobile equipment, also known as a terminal, varies widely.
2. Early satellite phone handsets had a size and weight comparable to that of a late-1980s or early-1990s mobile phone, but usually with a large retractable antenna. More recent satellite phones are similar in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary smartphone. Satphones are popular on expeditions into remote areas where terrestrial cellular service is unavailable.
3. Since satellite phones are purpose-built for one particular network and cannot be switched to other networks, the price of handsets varies with network performance. If a satellite phone provider encounters trouble with its network, handset prices will fall, then increase once new satellites are launched. Similarly, handset prices will increase when calling rates are reduced.
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                                                           Family
1. The family, a basic social group united through bonds of kinship or marriage, has been present in all societies. Ideally, the family provides its members with protection, companionship, security, and socialization. The structure of the family and the needs that the family fulfils vary from society to society. The nuclear family – two adults and their children – is the main unit in some societies. In others, it is a subordinate part of an extended family, which also consists of grandparents and other relatives. A third family unit is the single-parent family, in which children live with an unmarried, divorced, or widowed mother or farther.
2. Historical studies have shown that family structure has been less changed by urbanization and industrialization than was once supposed. The nuclear family was the most prevalent pre-industrial unit and is still the basic unit of social organization. The modern family differs from earlier traditional forms, however, in its functions, composition, and life cycle and in the roles of husbands and wives.
3. The only function of the family that continues to survive all change is the provision of affection and emotional support by and to all its members, particularly infants and young children. Specialized institutions now perform many of the other functions that were once performed by the agrarian family: economic production, education, religion, and recreation. Jobs are usually separate from the family group; family members often work in different occupations and in locations away from the home. Education is provided by the state or by private groups. The family is still responsible for the socialization of children.
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                                                        Renaissance
1. Renaissance, literally «rebirth», is the period in European civilization immediately following the Middle Ages, traditionally held to have been characterized by a rise of interest in classical learning and values. The Renaissance also witnessed the discovery and exploration of new continents, the substitution of the Copernican for the Ptolemaic system of astronomy, the decline of the feudal system and the growth of commerce, and the invention or application of such potentially powerful innovations as paper, printing, the mariner’s compass,and gunpowder. To the scholars and thinkers of the day, however, it was primarily a time of the revival of classical learning and wisdom after a long period of cultural decline and stagnation.
2. The term Middle Ages was coined by scholars in the 15th century to designate the interval between the downfall of the classical world of Greece and Rome and its rediscovery at the beginning of their own century, a revival in which they felt they were participating. Indeed, the notion of a long period of cultural darkness had been expressed by Petrarch even earlier. Events at the end of the Middle Ages, particularly beginning in the 12th century, caused a series of social, political, and intellectual transformations that culminated in the Renaissance. These included the increasing failure of the Roman Catholic Church and the Holy Roman Empire to provide a stable and unifying framework for the organization of spiritual and material life, the rise in importance of city-states and national monarchies, the development of national languages, and the breakup of the old feudal structures.
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                                  Landmark Inventions of the Millennium
1. The last 1,000 years have produced an incredible number and variety of scientific and technological breakthroughs – but which of these were the most important? Narrowing a list of the thousands of inventions made since the year 1000 to the ten greatest requires some exact criteria. The qualifying inventions either provided radically new ways to do an important job, or they made possible tasks that were previously unimagined. Their impact was felt, if not right away then eventually, by a large portion of humanity. These developments have made possible significant new technological innovations and scientific discoveries. And finally, they have had an enduring effect on the world.
2. The inventions that meet these criteria, in chronological order, are the compass, the mechanical clock, the glass lens, the printing press, the steam engine, the telegraph, electric power, wireless communications, antibiotics, and the transistor. Missing from this list are many extremely significant technological advances, including the airplane, telephone, automobile, and computer. In many cases these inventions were omitted because they are based on earlier developments or breakthroughs.
3. In considering the ten most significant inventions of the past 1,000 years, a subtle distinction must be made: the difference between «invention» and «discovery» is not as clear as one might think. A discovery can be as simple as the observation of a previously unnoticed phenomenon, while an invention is a human-devised machine, tool, or apparatus that did not previously exist.
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