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Генина Моина Шульженко Информация и коммуникация 2011

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UNIT 1
Text 1. The Engineering Profession in the 21st century
1. Выучите следующие слова и выражения:
engineering [ˌenʤɪ'nɪərɪŋ] (adj) технический, инженерный;
(n) разработка и управление (о процессах, механизмах), инженерия
apply (to) [ə'plaɪ] применять к (чему-л.), использовать, употреблять для ч.-л.
expertise [ˌekspɜː'tiːz] человеческий опыт, знание дела; квалификация,
компетентность
related (to) [rɪ'leɪtɪd] (ppart) связанный, родственный
field область, сфера, поле деятельности
graduate ['grædjueɪt] (v) оканчивать (высшее учебное заведение);
['grædjuət] (n) выпускник учебного заведения (школы, университета)
career [kə'rɪə] карьера, занятие, профессия
pursue a career [pə'sjuː] делать / строить карьеру
degree [dɪ'griː] звание, учёная степень; диплом
a bachelor('s) degree ['bæʧ(ə)lə] степень бакалавра
a master('s) degree ['mɑːstə] степень магистра
guarantee [ˌgær(ə)n'tiː] (n) (of) гарантия, обязательство;
(v) давать гарантию; гарантировать, обеспечивать
vocation [və'keɪʃ(ə)n] призвание, профессия
emerge [ɪ'mɜːʤ] появляться, возникать
curriculum [kə'rɪkjələm] курс обучения, учебный план
challenging ['ʧælɪnʤɪŋ] сложный, требующий усилий; перспективный
complete [kəm'pliːt] (v) завершать, заканчивать, выполнять
2. Прочитайте и устно переведите текст:
In ‘Forefront’, a publication from the University of California at Berkeley
College of Engineering, Berkeley Chancellor Chang-Lin Tien, a mechanical
engineer, talks about the state of engineering education in a piece entitled
“Engineering for the Next Millennium”:
“We must reject the stereotype that engineers only do technical work. We
must apply our engineering expertise to related fields and bring other fields to bear
on our own. In the 21st century, America needs more politicians who are engineers.
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America needs more teachers who are engineers.”
From a cynic point of view, it sounds like the college is warning students that
they will have difficulty finding jobs as engineers after they graduate, so they had
better look into other areas for a successful career in case they do not find a job in
engineering.
The engineering profession is going through major changes as the cold war
becomes a memory, as government spending winds down, and as the economic
recovery from the recent recession continues to lag. In fact, there are some who say
that we have already seen the recovery, and what you see is what you get. The
result is that today’s economy may not change significantly for quite some time.
Many engineers today are pursuing careers outside of their fields, and engineering
jobs may never proliferate as they did, say, in the early 1980s. No longer is a
bachelor's degree in engineering a guarantee of an engineering job, either in
industry or for the government.
But for the long range, Chancellor Tien casts an interesting and certainly more
positive slant on engineering. He considers it not as limited vocation, but as a basic
education for the world of the future. It’s difficult to disagree with him that more
people with an engineering education are needed to spread out into such
professions as corporate management, teaching, and, as difficult as it is to say,
politics. And there’s always the strong chance that many engineering jobs will
emerge, and that many engineering graduates will practice as engineers.
Technology is the driving force behind more aspects of business with every
passing day, and the engineering curriculum is an excellent preparation for jobs
related to technology. The engineering curriculum also is one of the most
challenging of all college programs, and anyone who successfully completes it is
certainly someone who is prepared to handle almost any job. Perhaps it is time to
broaden the sights of engineering students and tell them they can take what they
have learned and apply it to another field.
3. Ознакомьтесь с дополнительными словами и выражениями:
forefront передняя часть; зд. предисловие
сhancellor ['ʧɑːns(ə)lə] ректор (в некоторых американских университетах)
bring to bear влиять, воздействовать
lag отставать, оставаться позади
proliferate [prə'lɪf(ə)reɪt] распространяться, быстро увеличиваться
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(в
количестве), разрастаться
for the long range зд. по большому счету
cast a slant (on) высказывать точку зрения (на), мнение о чем-либо
4. Ответьте на вопросы, используя информацию текста:
1. What is a wide-spread stereotype about engineers? 2. What teachers and
politicians are needed in the 21st century? 3. How can the Berkeley Chancellor's
words be interpreted? 4. Do engineers today find jobs exactly in their fields? 5.
How does the Berkeley Chancellor see engineering education of today? 6. Where
can engineers work in the modern world? 7. Why can a person who gets a degree
in engineering handle almost any job?
5. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Публикация; отвергать; с точки зрения; изучать, исследовать; постепенно
сходить на нет; спад; подъем (восстановление); отставать, оставаться позади;
трудно не согласиться; движущая сила; расширить поле зрения.
6. Переведите на русский язык следующие словосочетания:
Mechanical engineer, engineering education, engineering expertise,
engineering profession, engineering job, corporate management, government
spending, engineering graduate.
7. Переведите выделенные слова с английского на русский язык, исходя
из контекста:
1) суверенное state
твердое state вещества
скверное state вещей
высокая административная state
2) a piece разбитого стекла
написать a piece для газеты
оплачивать за piece
прекрасный piece искусства
3) to handle домашнее хозяйство
to handle с проблемой
тактично to handle с людьми
4) тяжелая industry
банковская industry
сельскохозйственное industry
похвалить за industry
5) электромагнитное field
field социальных услуг
field научных исследований
6) challenge на дуэль
решать challenges
преодолевать challenges
новый challenge для личного роста
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8. Вставьте пропущенные предлоги:
1. He wasn't lucky to find a job … engineering, so he had to pursue his career
… his field. 2. The engineering curriculum is an excellent preparation … any job
related … technology. 3. A bachelor's degree … engineering allows you to apply
your knowledge … another field like teaching, management or politics. 4. He
received a master's degree in engineering and now can work … a university, …
industry or … the government. 5. Engineering education is basic … the world of
the future.
9. Вспомните образование и случаи употребления The Past Simple Tense.
Преобразуйте следующие предложения в Past Simple (при
необходимости изменяя утвердительную форму на негативную, и
наоборот):
Пример: Today America needs more politicians who are engineers.
Earlier America didn't need so many politicians who were engineers.
1. Engineers don't do only technical work. 2. Many engineers build careers
outside of their field. 3. Engineering jobs don't proliferate today. 4. Nowadays
many people with an engineering education spread out into such professions as
corporate management, teaching and politics. 5. A bachelor's degree in engineering
does not guarantee an engineering job. 6. At present, an engineering profession is
not a limited vocation. 7. Graduates often have difficulty finding jobs as engineers.
8. Today's governments do not reduce their spending. 9. You can apply your
engineering expertise to almost any field.
Text 2. What Does an Engineer Do?
10. Выучите следующие слова и выражения:
design [dɪ'zaɪn] (n) проектирование, конструкция, конструирование;
(v) проектировать; конструировать, разрабатывать
maintain [meɪn'teɪn] обслуживать, содержать в исправности
process ['prəuses] обрабатывать (данные, информацию)
specialty ['speʃ(ə)ltɪ] = speciality специальность, специализация
specialize in [spe̱ ʃəlaɪz] специализировать(ся)
area ['ɛərɪə] область, сфера деятельность
require [rɪ'kwaɪə] требовать, нуждаться (в чём-либо)
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to meet requirements соответствовать / отвечать требованиям
certification [ˌsɜːtɪfɪ'keɪʃ(ə)n] свидетельство, сертификат, удостоверение;
аттестация, сертификация
refer (to) отсылать (к кому-либо / чему-либо), ссылаться, говорить, упоминать
set up устанавливать, ставить
operate приводить в движение, запускать, управлять
involve [ɪn'vɔlv] вовлекать, касаться, затрагивать; включать, содержать
focus (on) ['fəukəs] сосредоточивать (внимание), концентрироваться
skill умение; навык
11. Прочитайте и устно переведите текст:
Most of the technology that makes our lives better and more productive
depends on electricity and electrical devices. Electrical engineers are responsible
for designing and maintaining the electrical systems and components that make up
our modern technology. One example of the importance of electrical engineering
you encounter everyday is what engineers call signal processing. When a television
station or a cell phone sends out a signal, the transmitter and receiver have to be
able to process the radio signal, remove interference and deliver a clear and
understandable signal. Designing and integrating the electronic circuitry and
components to make this happen is a task for the electrical engineer. A variety of
industries rely heavily on electrical engineers, including radio and television
manufacturers and broadcasters, computer networking providers, power companies
and makers of electrical equipment and consumer products.
There are several specialties within the field of electrical engineering. These
include electrical power generation, signal processing for communications
systems, wireless communications, robotics, computer and control systems and
biomedical systems. An electrical engineer normally specializes in one of these
areas while in college and works to meet the educational and work experience
requirements for certification in that specialty.
Radio engineers may sometimes be referred to as broadcast technicians, radio
operators, or broadcast engineers; these titles often refer to a similar set of job
duties. Broadcast and sound engineering technicians and radio operators set up,
operate, and maintain a wide variety of electrical and electronic equipment
involved in almost any radio or television broadcast, concert, play, musical
recording, television show, or movie. Communication technicians are in charge of
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electronic communication equipment, such as telephone systems and computer
modems. They are also responsible for building and maintaining electronic circuits
and data networks. RF (Radio Frequency) engineers create schematics for cell
phones and broadcasting devices, set up new wireless Internet networks, and
maintain existing systems of communication.
A telecommunications engineer is a professional who designs complex
electronic communications and broadcasting systems. Many of the products and
services telecommunications engineers design are used by almost everyone on a
daily basis. This engineering discipline is not offered by many universities as a
bachelor’s degree program, but people who pursue this career often have at least a
bachelor’s degree in broadcast engineering, civil engineering, electronic
engineering, or computer engineering. Some educational programs offer a
bachelor’s degree in telecommunications engineering technology, or a master’s
degree that focuses on telecommunications. These programs typically include
technical,
management,
and
business
studies
because
designing
telecommunications systems require understanding all aspects of the design
process. These occupations often oversee design projects from conception to
completion. This includes overseeing staff, project financial budgets, and ensuring
telecommunications projects are completed on schedule.
Although required skills for these occupations can range extensively, many
radio and telecommunications engineers continue their education and training
throughout their career. As technology continues to advance, engineers usually
must learn new skills. Many join professional associations to learn about current
trends and find ways to improve their design techniques. Certifications, such as the
Professional Engineer or Project Management Professional certificates, as well as
joining professional groups and organizations, like the popular Institute for
Electrical and Electronics Engineers (IEEE), can also help electrical engineers of
various specializations advance their career and design capabilities.
12. Ознакомьтесь с дополнительными словами и выражениями:
encounter [ɪn'kauntə] встретиться, столкнуться
interference [ˌɪntə'fɪər(ə)ns] помехи
circuitry ['sɜːkɪtrɪ] схема (электрическая)
oversee наблюдать, следить за, надзирать
ensure гарантировать, застраховать
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schedule ['ʃedjuːl ]; ['skeʤuːl] график, программа, план
technique [tek'niːk] техника, технические приёмы, метод
Institute for Electrical and Electronics Engineers (IEEE) (pronounced “I-Triple-E”)
Институт инженеров по электротехнике и электронике
13. Ответьте на вопросы, используя информацию текста:
1. In what industries are electrical engineers employed? 2. What are the fields
of specialization of electrical engineering? 3. What are the other titles for a radio
engineer? 4. What do radio engineers normally do? 5. What are the responsibilities
of communication technicians? 6. What kind of work do RF engineers do? 7. Who
is a telecommunications engineer? 8. What are the requirements to become a
telecommunications engineer? 9. Why do the educational programs in
telecommunications engineering include not only technical but also management
and business studies? 10. Why do radio and telecommunications engineers
continue their education throughout their career? 11. How can engineers learn new
skills?
14. Найдите в тексте слова и выражения, эквивалентные следующим:
Электроприборы; быть ответственным за; сотовый телефон; передатчик;
приемник; исключать помехи; конструирование электронных цепей;
полагаться на; потребительские товары; называться; рабочие обязанности;
заведовать, отвечать за; ежедневно; гражданское строительство;
контролировать, следить за проектом; от идеи до полного завершения; точно,
вовремя; значительно варьироваться; на протяжении всей карьеры;
современные тенденции; развивать свою карьеру.
15. Переведите следующие группы существительных:
Signal processing, aerospace engineer, computer networking provider, power
company, employment prospects, communications field, signal processing,
electrical power generation, control system, data network, telecommunications
engineering technology, broadcast engineering, computer engineering, design
process, design technique.
16. Переведите выделенные слова, исходя из значений, приведенных в
скобках. Определите суффикс, с помощью которого образованs
выделенные слова. Назовите суффиксы и приставки производных
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глаголов, существительных, прилагательных, наречий.
transmit (передавать), transmitter (n), transmission (n)
receive (принимать), receiver (n)
manufacture (прозводить), manufacturer (n)
broadcast (транслировать), broadcaster (n), broadcasting (n)
consume (потреблять), consumer (n), consumption (n)
provide (снабжать, обеспечивать), provider (n), provision (n)
interfere (быть помехой, интерферировать), interference (n)
robot (робот), robotic (adj), robotics (n)
scheme (схема), schematic (adj), schematics (n)
complete (целый, завершенный), complete (v), completion (n), completely
(adv)
communicate (сообщать, общаться) communcator (n), communication (n),
communicative (adj)
special (особый, специальный), specialize (v), specialization (n)
recover (выздоравливать, восстанавливаться), recovery (n)
circuit (цепь, схема), circuitry (n)
prepare (готовить), preparation (n)
manage (управлять), management (n)
educate (образовывать, обучать), education (n), educational (adj)
technic (техника, прием), technical (adj), technically (adv), technician (n)
title (заголовок, название), entitle (v)
sure (уверенный), ensure (v)
17. Обратите внимание на разницу в значении слов electric и electrical:
electric – containing, producing, arising from, actuated by or carrying electricity
electrical – relating to, pertaining to, or associated with electricity but not
having its properties
Соедините следующие слова в пары со словами electric или electrical:
device, kettle, engineering, motor, conductivity, light, equipment
18. Вставьте пропущенные слова:
design, requiring, expertise, specialties, maintenance
1. Anything … the transmission of information across channels via wired or
unwired means utilises telecommunications engineering. 2. Engineering involves
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technical … and high level project management which can lead to careers in
technology development and business management. 3. The initial training of a
professional engineer usually includes a broad range of experience in design and
development, in providing a customer service, and in … and workshop practices.
4. The telecommunications engineer career is a fairly new development in
engineering … and has come about along with the growth of the
telecommunications industry. 5. Telecommunications engineers … , build and
manage systems that carry out the transmission, processing and storage of
information as electrical or optical signals.
19. Вставьте пропущенные предлоги:
1. Electrical engineers are responsible … designing and maintaining the
electrical systems and components. 2. Different industries rely … electrical
engineers. 3. Several specialties are … the field of electrical engineering. 4. An
electrical engineer specializes … electrical power generation, signal processing for
communications systems, wireless communications, robotics, computer and
control systems and biomedical systems. 5. Communication technicians are in
charge … electronic communication equipment and are also responsible …
building and maintaining electronic circuits and data networks.
20. Переведите на английский язык:
Современный радиоинженер должен обладать знаниями и умениями не
только в области классической радиотехники, но и хорошо ориентироваться в
информационных технологиях, системах телекоммуникаций и связи, в том
числе хорошо знать спутниковые и мобильные системы связи, пути и
направления развития радио- и телевещания и компьютерных технологий. Он
должен программировать на языках высокого уровня, знать один из
иностранных языков, владеть знаниями по менеджменту и экономике.
Благодаря отличной подготовке, выпускники инженерных специальностей
смогут найти работу не только в своей области, но и во многих других
сферах.
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UNIT 2
Text 1. Telecommunications Fundamentals
1. Выучите следующие слова и выражения:
essential [ɪ'sen(t)ʃ(ə)l] внутренне присущий, неотъемлемый; затрагивающий
concept ['kɔnsept] понятие
designate ['dezɪgneɪt] (v) указывать, обозначать, называть
designation [dezɪg'neɪʃ(ə)n] обозначение, знак, указание
magnitude ['mægnɪt(j)uːd ], [-ʧuːd] величина, размеры; значение
range [reɪnʤ] (v) колебаться, варьироваться
manifestation [mænɪfes'teɪʃ(ə)n] проявление
source [sɔːs] источник
transmitter [trænz'mɪtə], [træns-], [trɑːn-] передатчик
receiver [rɪ'siːvə] приёмное устройство, приёмник
medium [ 'miːdɪəm] (pl. mediums, media) средство
convert [ kən'vɜːt] (v) преобразовывать, превращать
distortion [dɪ'stɔːʃ(ə)n] искажение
integer ['ɪntɪʤə] целое число
broadcast ['brɔːdkɑːst] (n) радио- или телевещание, трансляция
(v) передавать по сети проводного вещания; использовать широковещательную передачу
broadcast communication циркулярная связь; широковещательная связь
point-to-point двухпунктовый, соединение типа «точка-точка»
point-to-point communication двухпунктовая связь; прямая связь;
коммуникации между двумя узлами
2. Прочитайте и устно переведите текст:
One way of understanding how telecommunications systems work and how
they are changing is to consider a number of essential concepts.
A basic item that appears throughout any communications description is the
prefix used in metric units for designating parameters such as length, speed, power
level, and information transfer rate. As a handy reference, the table below lists
standard prefixes, their symbols, and their magnitudes, which range in size from
1024 to 10-24. As an example, a distance of 2 X 10 -9 m (meters) (two times ten to the
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minus ninth power) = 2nm (nanometers). The three highest and lowest designations
are not especially common in communication systems (yet!), but are included in
the table for completeness.
Prefix
yotta
zetta
exa
peta
tera
giga
mega
kilo
deci
centi
milli
micro
nano
pico
femto
atto
zepto
yocto
Symbol
Decimal
Magnitude
Y
Z
E
P
T
G
M
k
d
c
m
μ
n
p
f
a
z
y
1,000,000,000,000,000,000,000,000
1,000,000,000,000,000,000,000
1,000,000,000,000,000,000
1,000,000,000,000,000
1,000,000,000,000
1,000,000,000
1,000,000
1,000
0.1
0.01
0.001
0.000001
0.000000001
0.000000000001
0.000000000000001
0.000000000000000001
0.000000000000000000001
0.000000000000000000000001
Septillion
Sextillion
Quintillion
Quadrillion
Trillion
Billion
Million
Thousand
Tenth
Hundredth
Thousandth
Millionth
Billionth
Trillionth
Quadrillionth
Quintillionth
Sextillionth
Septillionth
Multiple
1024
1021
1018
1015
1012
109
106
103
10-1
10-2
10-3
10-6
10-9
10-12
10-15
10-18
10-21
10-24
Some terms and concepts that are used in communications include:
information (the content, such as spoken words, an image, the measurement of a
physical unit, or values of bank accounts), a message (the physical manifestation of
the information produced by the source, ranging from a single number or symbol
to a long string of sentences), data (facts, concepts, or instructions presented as
some type of encoded entities used to convey the information – these include
arrays of integers, lines of text, video frames, digital images, etc.), signals
(understood as electromagnetic waves (in encoded electrical or optical formats)
used to transport the data over a physical medium).
The word 'telecommunication' was adapted from the French word
télécommunication, coined in 1904 by the French engineer and novelist Éd.
Estaunié. It is a compound of the Greek prefix tele-, meaning "far off", and the
Latin communicare, meaning "to share". Thus, telecommunication means literally
sharing (sending and receiving) information over distances.
A simple telecommunication system consists of three units that are always
present in some form: a) a transmitter that takes information and converts it to a
signal; b) a transmission medium, also called the “physical channel” that carries
the signal; c) a receiver that takes the signal from the channel and converts it back
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into usable information.
Every human being is equipped with a basic communication system. The
mouth (and vocal cords) is the transmitter, ears are the receivers, and air is the
transmission medium over which sound travels between mouth and ear. Between
the speaker and the listener (the receiver), there might be other devices that do or
do not introduce their own distortions of the original vocal signal (e.g. telephone,
ham radio, IP phone, etc.) Modern telecommunications include the use of such
devices as telegraphs, telephones, and teletypes, the exploitation of radio and
microwave communications, as well as fiber optics and their associated
electronics, plus the use of the orbiting satellites and the Internet.
Telecommunication over telephone lines is called point-to-point
communication because it is between one transmitter and one receiver.
Telecommunication through radio broadcasts is called broadcast communication
because it is between one powerful transmitter and numerous low-power but
sensitive radio receivers.
3. Ознакомьтесь с дополнительными словами и выражениями:
rate размер, уровень, скорость, частота, интенсивность
frame кадр
entity ['entɪtɪ] объект
coin создавать неологизмы, монета , выдумывать
compound ['kɔmpaund] целостное образование; смесь; сложное слово
4. Ответьте на вопросы, используя информацию текста:
1. What are some terms and concepts that are used in communications? 2.
What is understood as information, message, data and signals? 3. How are the
three units of a simple telecommunication system called? 4. What are the functions
of a transmitter and a receiver? 5. What are examples of communication systems?
6. Why is telecommunication over telephone lines called point-to-point
communication? 7. What does a broadcast communication system consist of?
5. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Основной элемент; варьироваться по размеру; множество целых чисел;
переносить данные; буквально; голосовые связки; голосовой сигнал;
искажения; оптическое волокно; связанный; чувствительный.
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6. Переведите на русский язык следующие словосочетания:
Power level; telecommunications systems; information transfer rate; video
frame; transmission medium; usable information; orbiting satellites; radio
broadcast; low-power radio receiver; microwave communications.
7. Вставьте пропущенные предлоги:
1. One way … understanding how telecommunications systems work and how
they are changing is to consider a number ... essential concepts. 2. Some
designations are not common … communications and are included … the table …
completeness. 3. Standard prefixes used … metric units … designating different
physical parameters range … size … 1024 … 10-24. 4. Telecommunication means
sending and receiving information … distances. 5. The word 'telecommunication'
was adapted … the French word télécommunication. 6. A simple
telecommuncation system consists … three units. 7. Every human being is
equipped … a basic communication system. 8. Telecommunication … telephone
lines is called point-to-point communication because it is … one transmitter and
one receiver.
8. Переведите предложения, обращая особое внимание на выделенные
слова:
Power
1. He did everything in his power to help me. 2. They have lost the power of
speech. 3. Nine is the second power of three. 4. It is necessary to disconnect the
power before attempting to repair electrical equipment.
Value
1. She valued the house at $1000. 2. His invention was of high practical value. 3.
What is the value of the prize?
Number
1. I gave him my number. 2. A small number of children do not play computer
games. 3. I decided not to invite the guests for a number of reasons. 4. Number
the pictures from one to five.
9. Подберите к следующим глаголам однокоренные существительные:
Describe, designate, introduce, transfer, equip, inform, distort, listen,
15
measure, refer, exploit.
10. Вспомните правила образования и употребления пассивного залога.
А. Найдите в тексте пять случаев употребления Passive Voice.
Переведите предложения.
Б. Преобразуйте в следующих предложениях формы
действительного залога в страдательный залог:
Пример: A transmission medium carries a signal.
A signal is carried by a transmission medium.
1. To understand how telecommuncations systems work we consider a
number of essential concepts. 2. We use a prefix in metric units to designate some
physical parameters such as length, speed and so on. 3. The table lists standard
prefixes, their symbols, and their magnitudes. 4. A message is a physical
manifestation of the information which the source produces. 5. We understand
signals as electromagnetic waves that we use to transport the data over a physical
medium. 6. A transmitter converts information to a signal. 7. A receiver then takes
the signal from the channel and converts it into usable information. 8. Today
modern telecommuncations not only use telegraphs and telephones but also exploit
radio systems and fiber optics.
Text 2. The Development of Telecommunications
11. Выучите следующие слова и выражения:
associate [ə'səuʃɪeɪt ], [ə'səusɪeɪt] связывать
encompass [ɪn'kʌmpəs ], [en-] охватывать
assume [ə's(j)uːm] принимать
release [rɪ'liːs] освобождать; выпускать
time-released [rɪ'liːzd] периодически выпускаемый
relay ['riːleɪ ], [riː'leɪ] (v) передавать; посылать
(n) смена; эстафета
relay fire = beacon ['biːk(ə)n] сигнальный огонь
in succession подряд
sophisticated [sə'fɪstɪkeɪtɪd] сложный, сложно устроенный
advent ['ædvənt] наступление (эпохи, события), прибытие, приход
heliograph ['hi lɪəugrɑːf] гелиограф
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core [kɔː] центр; сердцевина; глубинная часть; суть, сущность
expansion [ɪk'spæn(t)ʃ(ə)n ], [ek-] распространение, рост, развитие
tremendous [trɪ'mendəs] огромный, гигантский, громадный
12. Прочитайте и устно переведите текст:
While most people associate telecommunications with modern technologies,
the strict definition of the term encompasses primitive and even ancient forms of
telecommunication. Among these is the use of smoke signals as a kind of visual
telegraph. Puffs of smoke were time-released by smothering a fire with a blanket,
then quickly removing and replacing the blanket. Widely used by the American
Indians, smoke signals could communicate short messages over long distances,
assuming a clear line of sight.
At the same time, other visual signals have been in use since ancient times.
These were relay fires or beacons. Used foremostly in warfare, relay fires required
a handful of men posted along a range of hilltops, with the last man closest to the
area where troop movement was expected. When armies were spotted in the
distance, he would light a bonfire. The fire could be seen from a good distance
away by the next man in the relay, who would in turn light his own bonfire, and so
the fires were lit in succession along the range, creating an effective
telecommunications signal that travelled back over several miles in a relatively
short period of time. Finally, the last man in the relay would light a beacon to
signal his army below that the opponent was en-route.
The arrangement of a ship's flags and semaphores were other forms of
telecommunications. A semaphore was a mechanical device atop a tower with
paddle-like blades or flags. The device would be set in a specific position to
communicate information.
Throughout the 19th century, telecommunications devices became more
sophisticated with the advent of electricity, leading to telegraph, Morse code, and
signal lamps. A signal lamp, the optical version of the telegraph, is a powerful lamp
with shutters that block the light in long or short durations to translate to the dots
and dashes of Morse code. A heliograph is another optical telegraph -- a mirror
used to reflect light to mimic a signal lamp.
A revolution in wireless telecommunications began at the turn of the 19th20th centuries with pioneering developments in wireless radio communications by
Nikola Tesla, Guglielmo Marconi, and Alexander Popov. In the 20th century,
17
telecommunications reached beyond our planet. In June 1969, the world watched
and listened as astronauts walked on the moon. Twenty years later, in August 1989,
we would see pictures of Neptune arrive back from the Voyager 2 spacecraft,
riding radio waves that travelled over roughly three billion miles (4.8 billion km)
to reach us in a matter of a few hours.
Today, the core of modern communication is computer networks. All modern
aspects of the Public Switched Telephone Network (PSTN) are computercontrolled, and telephony increasingly runs over the Internet Protocol, although not
necessarily the public Internet. Computer networks, and the technologies needed to
connect and communicate through and between them, continue to drive computer
hardware, software, and peripherals industries. This expansion is mirrored by
growth in the numbers and types of users of networks from the researcher to the
home user.
Strides in telecommunications have changed the world immeasurably. People
now have multiple ways to see and hear what is occurring on the other side of the
world in real time. Satellite technology, television, the Internet and telephony keep
the globe connected in a humming buzz of interactive voices and pictures.
Telecommunications has come a long way from smoke signals and grown up from
a line telegraph via wireless radio messaging to e-mail, e-commerce, and elearning.
These steps are tremendous but we are just at the foothills of this change. The
future of telecommuncations has only begun.
13. Ознакомьтесь с дополнительными словами и выражениями:
puff [pʌf] облако дыма
smother ['smʌðə] гасить, тушить
foremostly['fɔːməustli] главным образом
warfare ['wɔːfɛə] война
troop [truːp] отряд, группа людей войска, армия
bonfire ['bɔnfa(ɪ)ə] костёр
be en-route [ɔn'ruːt] быть в пути
atop [ə'tɔp] на вершине
paddle ['pædl] весло
blade [bleɪd] лопасть
shutter ['ʃʌtə] задвижка, заслонка
dot [dɔt] точка
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dash [dæʃ] тире
stride [straɪd] шаг вперёд, продвижение, прогресс
pioneering [paɪə'nɪə(r)ɪŋ] новаторский, первопроходческий
Public Switched Telephone Network (PSTN) телефонная коммутируемая сеть
общего пользования
Internet Protocol = IP протокол Internet, протокол IP протокол сетевого уровня,
отвечающий за передачу и маршрутизацию сообщений между узлами
Internet
peripherals периферийное оборудование, устройство
14. Ответьте на вопросы, используя информацию текста:
1. What visual signals have been in use since ancient times? 2. How was the
communication with the help of fire organised? 3. What did the advent of
electricity lead to in telecommunications? 4. The core of modern communication
isn’t computer networks, is it? 5. What do the letters PSTN mean? 6. How is the
globe connected today?
15. Найдите в тексте слова и выражения, эквивалентные следующим:
Древний; при условии, что...; зажигать костер; наверху, на вершине;
система корабельных флагов; наступление (эпохи) электричества;
космический корабль; копировать, симулировать; исследователь; домашний
пользователь; у подножия.
16. Переведите следующие слова и словосочетания на русский язык:
Smoke signal; troop movement; Morse code; signal lamp; pioneering
developments; computer hardware; peripherals; line telegraph; e-commerce;
elearning.
17. Вставьте пропущенные предлоги:
1. Smoke signals were widely used … American Indians. … the same time,
other visual signals have been … use … ancient times. 2. Relay fires were lit …
succession and were an effective telecommuncations signal that travelled back ….
several miles … a short period of time. 3. … the 20th century, telecommuncations
reached … our planet. 4. Pictures of Neptune sent from the Voyager 2 spacecraft
travelled … four billion kilometers … just a few hours. 5. Today people can see
and hear what is happening … the other side of the world … real time.
19
18. Вставьте пропущенные слова:
flashing, signal, instructions, dashes, steady, acknowledge, relay, code
1. A communication relay is a station that … messages between various
points, so as to facilitate communications between units. 2. The idea of flashing
dots and … from a lantern was first put in to practice by Captain, later Vice
Admiral, Philip Colomb in 1867. 3. His original… , which the Navy used for seven
years, was not identical with Morse, but Morse code was eventually adopted with
the addition of several special signals. 4. … lights were the second generation of
signalling in the Royal Navy, after the flag signals. 5. In air traffic control towers,
... lamps are still used today, as a backup device in case of a complete failure of an
aircraft's radio. 6. Light signals can be red, green or white, and … or flashing. 7.
Messages are limited to a handful of basic … (e.g. "land", "stop" etc.); they are not
intended to be used for transmitting messages in Morse code. 8. Aircraft can ...
signals by rocking their wings or flashing their landing lights .
19. Вспомните функции модальных глаголов и особенности их перевода
на русский язык.
А. Найдите в тексте пять случаев употребления модальных
глаголов. Переведите предложения.
Б. Переведите следующие предложения на русский язык, обращая
особое внимание на перевод глагола “would”:
Greek hydraulic semaphore system involved identical containers on separate
hills; each container would be filled with water, and a vertical rod floated within it.
The rods were inscribed with various predetermined codes at various points along
its height. To send a message, the sending operator would use a torch to signal the
receiving operator; once the two were synchronized, they would simultaneously
open the spigots at the bottom of their containers. Water would drain out until the
water level reached the desired code, at which point the sender would lower his
torch, and the operators would simultaneously close their spigots. Thus the length
of time the sender's torch was visible could be correlated with specific
predetermined codes and messages.
20. Переведите письменно с английского языка на русский:
I know it is very difficult to imagine what life must have been like before
20
telephones, text messaging and emails. However, communication between people
living in separate cities or states was possible thanks in part to the telegraph
machine. The telegraph machine worked by sending a coded message on a wire
from one point to another. The most commonly used code was Morse code, which
gets its name from inventor Samuel Morse. Morse is credited with perfecting the
first telegraph machine in the 1830's. The codes were sent using electrical pulses.
20. Переведите письменно на английский язык по вариантам:
В.1. Связь имеет давнюю историю. К обмену новостями (информацией)
люди стремились во все времена. В доисторические времена люди
объяснялись с помощью условных знаков и жестов. Когда люди находились
на расстоянии друг от друга, они передавали свои сообщения криками. Еще
более эффективной была звуковая сигнализация с применением барабанов,
труб, колоколов. После изобретения пороха (gunpowder) в качестве
сигнальных средств использовали выстрелы из ружей и пушек. Для передачи
сообщений применялись также световые сигналы: факелы, костры.
В.2. В конце XVIII века появился оптический или семафорный телеграф.
В 1824 г. такая линия связала Петербург со Шлиссельбургом. В 1839 г. была
открыта самая протяженная в мире – 1200 км – линия оптического телеграфа
между Санкт-Петербургом и Варшавой. На ней было сооружено почти
полторы сотни башен для ретрансляции сигналов. В 30-x годах XVIII века
был изобретен электрический телеграф. 15 апреля 1855 г. открылась
телеграфная линия Петербург – Москва. В 1880-е годы в России начинает
развиваться телефонная связь.
21
UNIT 3
Text 1. Types of Signals
1. Выучите следующие слова и выражения:
convey [kən'veɪ] передавать
quantity ['kwɔntətɪ] количество; величина
spatial ['speɪʃ(ə)l] пространственный; cуществующий в пространстве
rate [reɪt] размер, уровень, скорость, частота, интенсивность
sampling ['sɑːmplɪŋ] [sæ̱m-] отбор образцов; дискретизация; сэмплирование
fluctuation [flʌkʧu'eɪʃ(ə)n ], [flʌktju'eɪʃ(ə)n] колебание
continuous непрерывный; длительный; постоянный
continuous time непрерывное время
discrete [dɪ'skriːt] дискретный; раздельный; лишённый непрерывности
discrete time дискретное время
scale [skeɪl] шкала
decimal ['desɪm(ə)l] десятичный
amplitude ['æmplɪt(j)uːd] амплитуда
frequency ['friːkwən(t)sɪ] частота
phase [feɪz] фаза
sequence ['siːkwən(t)s] последовательность; ряд; очерёдность
in sequence один за другим; последовательно
multiplex (adj) сложный; многочисленный, множественный
(n) уплотнение; объединение каналов; мультиплексная передача
modulate ['mɔdjəleɪt] модулировать; понижать частоту
baseband передача без модуляции
lowpass (сигнал) пропущенный через фильтр нижних частот
merge [mɜːʤ] сливать, соединять, объединять
train ряд, серия
pulse train последовательность импульсов
spectrum ['spektrəm] спектр, диапазон
bandwidth [bæ̱ndwɪdθ] полоса пропускания, ширина полосы пропускания
2. Прочитайте и устно переведите текст:
Communications via electronic means consist of the generation of signals that
22
contain or carry intelligent information and their processing at the receiver to
extract this information.
A signal is any kind of physical quantity that conveys information. The
examples of signals are audible speech (as it conveys the thoughts (information) of
one person to another through the physical medium of sound) or hand gestures
(conveying information by means of light). In the field of communications, a
signal is generally a relationship of a spatial parameter, such as amplitude, to time.
This relationship can be discrete or continuous. A continuous signal or a
continuous-time signal is one that has a value defined at every instant. A discrete
signal or a discrete-time signal is represented by a time series consisting of a
sequence of quantities. Discrete signals are usually received by acquiring values of
a continuous-time signal at constant or variable rate - this process is called
sampling, or by recording the number of events of a given kind over finite time
periods (for example, the ancient Egyptian records of the Nile's yearly floods or the
modern histograms of daily currency fluctuations).
An analog signal typically varies continuously over time, while digital signals
are present at discrete points in time. A well-known example of analog vs. digital is
that of clocks: analog being the type with pointers that slowly rotate around a
circular scale, and digital being the type with decimal number displays or a
"second-hand" that jerks rather than smoothly rotates. An analog clock is capable
of indicating every possible time of a day. In contrast, a digital clock is capable of
representing only a finite number of times (every tenth of a second, for example).
Most signals in nature are analog. Sound, noise, light, heat, and electronic
communication signals going through air (or space) are examples of analog
signals. The most fundamental analog signal is the periodic sine wave. Its three
main characteristics are its amplitude (the size of the waveform), frequency (the
number of cycles per second that the wave undergoes) and phase (the position of a
point in time (instant) on a waveform cycle, while a complete cycle is defined as
360 degrees of phase).
A common digital signal configuration is the binary waveform represented by
a sequence of two types of pulses of known shape. The information contained in a
digital signal is given by the particular sequence of the presence (a binary, or logic,
one) or absence (a binary zero) of these pulses. These are known as bits (this word
was derived from “binary digits”).
23
Fig. 1. Analog and digital signal
We commonly refer to the transmission of voice, music, video and data as
information signals as these intended signals contain what we want to
communicate. Information signals belong to baseband signals. A baseband signal,
or lowpass signal, is a signal at frequencies that are very near zero. This refers to
analog or digital data before they are merged with other signals (multiplexed) or
modulated. Information signals are at low frequencies, often less than 50 kHz.
There is another type of signal which is called a pulse train. Here the signal is
a train of impulses that last a long or a short time. The phase and amplitude of the
impulse determines how it is decoded. EKG is a good example of this type of
signal occurring in nature.
Two further common characteristics in communications are the frequency
spectrum (f) and the bandwidth (B) of a signal. The spectrum of a signal is the
range of frequencies that it contains. That is, the spectrum is the combination of all
the individual sine waves of different frequencies which make up that signal. The
bandwidth refers to the width of this spectrum. For example, if the spectrum of a
signal ranges from 2 kHz to 22 kHz, its bandwidth is fhigh - flow = 20 kHz.
3. Ознакомьтесь с дополнительными словами и выражениями:
intelligent [ɪn'telɪʤ(ə)nt] разумный
acquire [ə'kwaɪə] получать, приобретать
finite ['faɪnaɪt] ограниченный; конечный
сurrency ['kʌr(ə)n(t)sɪ ]; ['kɜːr(ə)nsɪ] валюта; средство денежного обращения
vs. (from versus) против
jerk [ʤɜːk] двигаться резкими толчками
smoothly ['smuːðlɪ] гладко; ровно; плавно
derive [dɪ'raɪv] получать, извлекать
24
4. Ответьте на вопросы, используя информацию текста:
1. What is a signal in general understanding and in communications? 2. Can
you give any examples of signals? 3. What's the difference between a continuous
and discrete signal? 4. What is sampling? 5. How can the difference between
analog and digital signals be explained? 6. What signals are typically met in
nature? 7. What are the three main characteristics of an analog signal? 8. How is a
digital signal represented? 9. What are bits? 10. What are baseband signals? 11.
What is a pulse train? 12. What is a frequency spectrum? 13. Does bandwidth
depend on the frequency spectrum?
5. Истинны или ложны следующие высказывания?
1. A signal that has a value not defined at every instant is continuous. 2. A
discrete signal is represented by a time series consisting of a sequence of
quantities. 3. A common digital signal configuration is the waveform represented
by a sequence of three types of pulses of known shape. 4. The information
contained in a digital signal is given by the particular sequence of the presence or
absence of the pulses. 5. Most signals in nature are discrete. 6. The periodic sine
wave is the most fundamental analog signal.
6. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Электронные средства; слышимая речь; посредством света; ежегодные
наводнения; ежедневные колебания валютного курса; с постоянной частотой;
гистограмма; круглый циферблат; форма волны; присутствие или отсутствие
импульса; уплотненный сигнал; модулированный сигнал; полоса частот.
7. Переведите на русский язык следующие словосочетания:
Intelligent information; finite time periods; decimal number display; periodic
sine wave; binary waveform; binary (logic) one; binary zero; binary digit;
baseband signal; frequency spectrum.
8. Вставьте пропущенные предлоги:
1. A signal can be treated as a relationship … an amplitude … time. 2. The
value … a continuous signal is defined … every instant. 3. A discrete signal or a
discrete-time signal is represented … a time series consisting ... a sequence of
quantities. 4. One way to receive dicrete signals is to acquire values … a
25
continuous-time signal … a constant or variable rate. 5. The information contained
… a digital signal is given by the particular sequence of the presence or absence of
pulses ... known shape. 6. An analog clock is capable … indicating every possible
time. 7. We commonly refer ... the transmission of voice, music, video and data as
information signals. 8. Frequency is the number of cycles … second that the wave
undergoes. 9. Analog or digital data are merged … other signals of higher
frequency. 10. Information signals belong … baseband signals.
9. Вставьте пропущенные cлова:
bandwidth, convey, analog , phase, digital, frequency
1. By controlling the … of the current, information can be transmitted to
another medium and presented on that medium. 2. Magnetic tape on a cassette …
information to the stereo which transmits it into electrical signals of specific
frequencies which in turn tell the speakers what noise to make. 3. … is the rate at
which the signal changes its relationship to time, expressed as degrees. 4. An …
signal is a kind of signal that is continuously variable, as opposed to having a
limited number of steps along its range. 5. The difference between the highest and
the lowest frequencies of a signal is … . 6. A … signal is a signal that changes
from one state to another in discrete steps.
10. Переведите выделенные слова с английского на русский язык, исходя
из контекста:
1) scale заработной платы
2) садиться на train
огромный scale
train верблюдов
двоичная scale
train импульсов
электронные scales
3) rate несчастных случаев
круговая scale
высокий rate от сделки
scales рыбы
rate повторения (импульсов)
Text 2. Signal Transmission
11. Выучите следующие слова и выражения:
transfer [træns'fɜ:] переносить, перемещать
amplify ['æmplɪfaɪ] усиливать
transduction [træns'dʌkʃn] преобразование
26
transducer [trænz'djuːsə ], [trɑːn-] преобразователь; датчик; приёмник
vary ['vɛərɪ] меняться, изменяться; отличаться
convert [kən'vɜːt] преобразовывать; превращать
AD converter аналого-цифровой преобразователь, АЦП
DA converter цифро-аналоговый преобразователь, ЦАП
shielding экранирование (способ защиты передающей среды от электромагнитных помех)
cable ['keɪbl] кабель
coaxial cable [ˌkəu'æksɪəl] коаксиальный кабель
twisted pair cable кабель с витыми жилами, скрученная пара
diminish [dɪ'mɪnɪʃ] уменьшаться, уменьшать
convey [kən'veɪ] передавать
transition [træn'zɪʃ(ə)n ],[ træn'sɪʒ(ə)n] перемещение, переход
digitization ['dɪʤɪtaɪzeɪʃ(ə)n] дискретизация, оцифровка, преобразование в
цифровую форму
quantization [ˌkwɔntaɪ'zeɪʃ(ə)n] квантование (преобразование непрерывной
информации в дискретную)
bounded ограниченный
guided направляемый
jacket оболочка (кабеля)
optical fiber (=fibre) [faɪbə] оптическое волокно; световод, светопровод
induce [ɪn'djuːs] вызывать; индуцировать
simplex односторонняя связь
half-duplex [hɑːf'djuːpleks] полудуплексная связь, поочерёдная двусторонняя
связь
full duplex дуплексная связь, одновременная двусторонняя связь, дуплекс
multiplex [mʌlti pleks] мультиплексная передача
12. Прочитайте и устно переведите текст:
As mentioned above, information can be transferred in two forms, analog and
digital. An analog format is that in which information is transmitted by modulating
a continuous transmission signal, such as amplifying a signal's strength or varying
its frequency to add or take away data. For example, telephones take sound
vibrations and turn them into electrical vibrations of the same shape before they are
transmitted over traditional telephone lines. The process of changing energy from
27
one form into another is called transduction. Some common examples of
transducers are a microphone which converts sound into an electrical signal, or an
antenna which converts electromagnetic waves into electric current and vice versa.
The main merit of an analog signal is its fine definition. However, its primary
disadvantage is that any system has noise – i.e., random unwanted variation
leading to signal loss and distortion. Electrically, these effects of noise can be
diminished by shielding, good connections, and several cable types such as coaxial
or twisted pair. Other methods of conveying an analog signal are to use modulation
or to change the phase of the base signal.
In contrast to analog communications, digital communications are the transfer
of discrete messages. These messages may be digital (when originating from a data
source, for example, a computer) or may start out as analog, being then converted
to digital for modulation, converted back to analog for radio frequency
transmission and, finally, converted to digital again. The conversion from the “real
world” analog signal to its discretized digital counterpart is called analog-to-digital
(AD) conversion. Analogously, a transition in the opposite direction is shorthanded
as DA conversion.
A digitization process carried out by an AD converter (ADC) is broken into
two stages. The first stage is sampling by which a continuous-time signal is
“reduced” to a discrete-time sequence. At the second stage, the ADC converts the
continuous range of values to the finite set of discrete values by rounding the input
values to the nearest integer numbers. This process known as quantization usually
results in deviations from the theoretically perfect reconstruction capabilities,
collectively referred to as distortion.
The type of a signal, analog or discrete, used for communications depends on
how far the signal has to travel and the medium it will have to pass through. In
telecommunications, transmission media are classified into two categories:
bounded, or guided media, and wireless, or unguided media. In both cases,
communication is in the form of electromagnetic waves.
Bounded media are physical links through which signals are confined to a
narrow path and energy waves are guided along a solid medium. Bounded media
are made up of an external conductor (usually copper) bounded by jacket material.
Three common types of bounded media are twisted pair cables, coaxial cables, and
optical fibers. Plain wires can be used, but they are generally unreliable in
screening out noise and are rarely considered.
28
Wireless transmission requires no physical means to define the path a
transmitted signal takes. Instead, the waves radiate by inducing a current in a
transmitting antenna and then travel through the air or free space. Examples of
these media include microwave, radio and satellite transmission.
Any transmission may be simplex, half-duplex, or full-duplex. In simplex
transmission, signals are transmitted in only one direction; one station is a
transmitter and the other is the receiver. In half-duplex operation, both stations may
transmit, but only one at a time. In full duplex operation, both stations may
transmit simultaneously. Telecommunications in which multiple transmitters and
multiple receivers have been designed to cooperate and to share the same physical
channel are called multiplex systems.
13. Ознакомьтесь с дополнительными словами и выражениями:
merit ['merɪt] достоинство
counterpart ['kauntəpɑ:t] дубликат, копия, двойник, аналог
confine ['kɔnfaɪn] (n) граница
(v) [kən'faɪn] ограничивать
shorthand стенография; условное обозначение
deviation [ˌdiːvɪ'eɪʃ(ə)n] отклонение
simultaneous [ˌsɪm(ə)l'teɪnɪəs] одновременный, синхронный
14. Ответьте на вопросы, используя информацию текста:
1. How is information transmitted in an analog format? 2. What is
transduction? 3. What transducers do you know? 4. What are the advantages and
disadvantages od analog transmission? 5. Are there any ways to reduce noise in
analog signal transmission? 6. What is AD conversion used for? 7. What does a
digitization process consist of? 8. What are bounded media? 9. How can wireless
transmission be described? 10. How are telecommuncations classified depending
on the number of transmitters and receivers and the direction of simultaneous
transmission?
15. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Усиливать сигнал; сообщение; изменять частоту; источник; выпадение
сигнала; уменьшать; экранирование; исходный сигнал; передача дискретных
сообщений; округлять исходные величины; целое число; оцифровка;
29
квантование; внешний проводник; обычные провода; отслеживать шум.
16. Переведите на русский язык следующие словосочетания:
Continuous transmission signal; sound vibrations; fine definition; random
unwanted variation; theoretically perfect reconstruction; bounded by jacket
material; simplex transmission; full-duplex operation; multiplex systems.
17. Вставьте пропущенные предлоги:
1. Information can be transferred … two forms. 2. Telephones take sound
vibrations and turn them … electrical vibrations … the same shape. 3. Noise in a
sommunications system is understood as random unwanted variation leading …
signal loss and distortion. 4. In contrast … analog communications, digital
communications are the transfer of discrete messages. 5. A digitization process
carried … by an AD converter is broken into two stages. 6. In bounded media
energy waves are guided … a solid medium. 7. In the half-duplex operation, both
stations may transmit, but only one ... a time.
18. Образуйте от данных слов
А) существительные: convert; vary; modulate; transfer; transit; define;
shield; capable;
B) глаголы: discrete; digit; class
C) прилагательные: currency, presence, frequency, absence
19. Продолжите части предложений в левой колонке частями из правой:
1) The main merit of an analog signal
a) is that any system has noise.
2) The process of changing energy
from one form into another
b) is its fine definition.
3) The primary disadvantage of
an analog signal
c) is that in which information is
transmitted by modulating a
continuous transmission signal.
4) An analog form
d) is called AD conversion.
5) The conversion from the
“real world” analog signal to its
discretized digital counterpart
e) is called transduction.
30
20. Переведите следующие предложения с английского языка на русский:
1. In order for any digital device to successfully interface with an analog signal,
that signal must be digitized by means of an analog-to-digital converter or ADC.
2. Any signal, in order to be processed by numerical computing devices, have to be
reduced to a sequence of discrete samples, and each sample must be represented
using a finite number of bits. 3. Bound transmission occurs when the
electromagnetic energy follows a path through a material like a copper cable or
fiber optic cable. This is by far the most common type of medium. 4. Unbound
media sometimes are referred to as wireless. This type of communication can
include radio waves, microwaves, and different forms of light.
21. Переведите письменно на английский язык:
Дискретные каналы служат для передачи импульсных сигналов. Такие
каналы обычно характеризуются скоростью передачи информации
(измеряемой в бит/сек) и верностью передачи. Дискретные каналы могут
быть также использованы для передачи аналоговых сигналов и, наоборот,
аналоговые каналы – для передачи импульсных сигналов. Для этого сигналы
преобразуются: аналоговые в импульсные (с помощью аналого-дискретных
(цифровых) преобразователей), а импульсные – в аналоговые (с помощью
дискретно- (цифро)-аналоговых преобразователей).
31
UNIT 4
Text 1. Modulation
1. Выучите следующие слова и выражения:
detect [dɪ'tekt] замечать, обнаруживать
carrier signal сигнал-переносчик, сигнал несущей частоты
current ['kʌr(ə)nt ]; ['kɜːr(ə)nt] электрический ток
alternating current (AC) переменный ток
direct current (DC) постоянный ток
delay [dɪ'leɪ] задерживать, замедлять
pulse code modulation (PCM) импульсно-кодовая модуляция, ИКМ
pulse amplitude modulation (PAM) амплитудно-импульсная модуляция, АИМ
pulse duration modulation (PDM) широтно-импульсная модуляция, ШИМ
pulse position modulation (PPM) фазово-импульсная модуляция, ФИМ
sideband боковая полоса (частот)
single sideband (SSB) с одной боковой полосой, однополосный (о системе
передачи)
two-way radio одновременная двусторонняя радиосвязь
Phase Shift Keying (PSK) фазовая манипуляция
Quadrature Amplitude Modulation (QAM) квадратурная амплитудная
модуляция (используемая в высокоскоростных модемах техника
модуляции, сочетающая фазовую и амплитудную модуляцию)
2. Прочитайте и устно переведите текст:
One way to improve the transmission of a signal is modulation. Modulation is
the process of facilitating the transfer of information over a medium. For example,
sound transmission in air has limited range for the amount of power your lungs can
generate. To extend the range your voice can reach, we need to transmit it through
a medium other than air, such as a phone line or radio. The term modulation refers
to how information (voice in this case) is encoded so that it can be successfully
sent through a medium (wire or radio waves), and can later be detected by a
receiver.
There are two main reasons to blend data into a carrier signal. The first reason
is to reduce the wavelength for efficient transmission and reception (the optimum
32
antenna size is Ѕ or ј of a wavelength). A typical audio frequency of 3000 Hz will
have a wavelength of 100 km and would need an effective antenna length of 25
km! By comparison, a typical carrier for FM is 100 MHz, with a wavelength of 3
m, and could use an antenna only 80 cm long. The other reason is to allow
simultaneous use of the same channel, called multiplexing. If there were a group of
people transmitting signals between 20 Hz and 20 kHz the probability of one signal
interfering with another would be very high. With modulation, each unique signal
can be assigned a different carrier frequency (like radio stations) and still share the
same channel.
The process of modulation means taking either an analog or a digital signal
and turning it into an analog signal. The difference between a digital modulation
and analog modulation is the nature of the signal that is modulating the carrier. The
carrier is always analog - for most of radio and telecommunications today, it is
alternating current (AC) in a given range of frequencies.
Common modulation methods include: 1) amplitude modulation (AM), in
which the voltage applied to the carrier is varied over time; 2) frequency
modulation (FM), in which the frequency of the carrier waveform is varied in
small but meaningful amounts; 3) phase modulation (PM), in which the natural
flow of the alternating current waveform is delayed temporarily. These are
sometimes known as analog, or continuous wave modulation methods, to
distinguish them from pulse code modulation (PCM), which is used to encode both
digital and analog information in a binary way. The varieties of PCM include pulse
amplitude modulation (PAM), pulse duration modulation (PDM), and pulse
position modulation (PPM).
Radio and television broadcast stations typically use AM or FM. Most twoway radios use FM, although some employ a mode known as single sideband
(SSB).
More complex forms of modulation are Phase Shift Keying (PSK) and
Quadrature Amplitude Modulation (QAM). Optical signals are modulated by
applying an electromagnetic current to vary the intensity of a laser beam.
An electromagnetic carrier can be of any frequency depending on the medium
and the communications needs. Most media dictate what type of carrier (its
frequency, amplitude) can propagate through it and the type of distortions it will
suffer while travelling through it.
Anything that is wireless is analog – always. Wired signals can be digital or
33
analog. Communications inside a computer are examples of pure digital
communications, digital data over digital medium. LAN communications are
digital data over analog medium. The AM and FM radios are examples of analog
data over analog medium.
In general, when we talk about a digital system, we are usually talking about
digital information over an analog medium. However, there are exceptions. PCM,
for example, is a form of modulation where there is no carrier, so that makes a pure
digital system.
3. Ознакомьтесь с дополнительными словами и выражениями:
facilitate [fə'sɪlɪteɪt] облегчать; устранять трудности
lung [lʌŋ] (n) легкое
temporary ['temp(ə)r(ə)rɪ] временный
exception [ɪk'sepʃ(ə)n ], [ek-] исключение
LAN (local area network) локальная сеть
4. Ответьте на вопросы, используя информацию текста:
1. Why is it necessary to use modulation? 2. What does the term modulation
refer to? 3. What are two main reasons to blend data into a carrier signal? 4. Is it
possible not to use the analog carrier? 5. How is the process that allows
simultaneous use of the same channel called? 6. What kind of signals is modulated
by applying an electromagnetic current to vary the intensity of a laser beam?
5. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Ограниченная дальность; среда, отличная от воздуха; наложить
информацию; природа сигнала; данный диапазон; в зависимости от среды;
подвергаться искажениям.
6. Переведите на русский язык следующие словосочетания:
Sound transmission, a carrier signal, typical audio frequency, simultaneous
use, the probability of one signal interfering, a different carrier frequency,
continuous wave modulation methods, wired signals.
7. Вставьте пропущенные предлоги:
1. Modulation improves the transmission … a signal. 2. If we want to extend
34
the range our voice can reach, we transmit it … a medium other than air. 3. The
first reason to blend data … a carrier signal is to reduce the wavelength for
efficient transmission and reception. 4. AM, FM and PM are referred … as
analog, or continuous wave modulation methods to distinguish them … PCM. 5.
Examples of analog data … analog medium are the AM and FM radios.
8. Вставьте пропущенные слова:
modulation, digital, amplitude, carrier, modulate
1. To … is to impress the characteristics (intelligence) of one waveform onto a
second waveform by varying the amplitude, frequency, phase, or other
characteristics of the second waveform. 2. ... is the means whereby a signal of
some type is entered into and carried by an electronic signal carrier. 3. …
modulation describes a broadcast situation in which the level of voltage that is
carried over the medium vary noticeably over time. 4. A signal in a
communications channel modulated to carry analog or digital signal information is
called a …. 5. Communications inside a computer are examples of pure ...
communications.
Text 2. Multiplexing
9. Выучите следующие слова и выражения:
multiplexing мультиплексирование (разделение передачи информации между
двумя и более каналами); уплотнение (напр. линии связи); объединение
(напр. cигналов)
multiplexer мультиплексор; устройство объединения (каналов); канальный уплотнитель
channel ['ʧæn(ə)l] канал (ресурсы системы связи или системы вещания, выделяемые для передачи определённых данных)
subchannel подканал
enable [ɪ'neɪbl ], [en-] делать возможным; включать, запускать в работу
frequency-division multiplexing (FDM) частотное уплотнение
time-division multiplexing (TDM) временное уплотнение
subscriber [səb'skraɪbə] пользователь, абонент; подписчик
tune [t(j)uːn ], [ʧuːn] регулировать; настраивать; налаживать
access ['ækses] (n) доступ; (v) иметь доступ
35
wave-division multiplexing (WDM) уплотнение с разделением сигналов по
длине волны; спектральное уплотнение
slot выемка, бороздка; интервал времени
timeslot таймслот (часть мультиплексируемого канала, выделенная для
передачи одному подканалу)
route [ruːt] направлять (по определённому маршруту; электрический сигнал,
телефонный звонок и т. п. - по конкретной линии связи, сети)
Statistical Time Division Multiplexing (STDM) статистическое уплотнение (с
временным разделением сигнала)
statistical multiplexer статистический мультиплексор (устройство, объединяющее множество каналов в один за счет динамического выделения
промежутков времени (timeslot) для передачи данных каждому каналу по
мере его активности)
Space division multiplexing (SDM) пространственное разделение; пространственное уплотнение
phased-array antenna фазированная антенная решётка, ФАР
Code Division Multiplexing (CDM) кодовое разделение
code division multiple access (CDMA) множественный доступ с кодовым
разделением каналов
spread-spectrum technology метод передачи сигналов с расширенным
спектром
Universal Mobile Telecommunications System (UMTS) универсальная система
мобильной связи
3G (third-generation) третье поколение (беспроводной связи)
Global Positioning System (GPS) глобальная система навигации и опре-деления
положения
Time Division Multiple Access (TDMA) многостанционный [множественный]
доступ с временным разделением каналов, МДВР
Frequency-Division Multiple Access (FDMA) множественный доступ с
разделением частот
10. Прочитайте и устно переведите текст:
Apart from modulation, another method to increase the transmission speed
and convey more information is to divide the bandwidth of a signal carrier so that
more than one modulated signal can be sent on the same carrier. This is known as
36
multiplexing (or muxing). The aim is to reduce network costs by minimizing the
number of communications links needed between two points.
In multiplexing, the carrier is sometimes referred to as a channel and each
separate signal carried on it is called a subchannel. The device that puts the
separate signals on the carrier and takes them off of received transmissions is a
multiplexer, or a muxer.
Among various techniques that enable multiple channels to coexist on one
link the most common are FDM (frequency-division multiplexing) and TDM (time
-division multiplexing).
FDM is inherently an analog technology. It achieves the combining of several
digital signals into one medium by sending signals in several distinct frequency
ranges over that medium. Today's environment doesn't make great use of FDM, but
it is still used extensively in cable TV and radio. Only one cable reaches a
customer's home but the service provider can send multiple television channels or
signals simultaneously over that cable to all subscribers. Receivers must tune to the
appropriate frequency (channel) to access the desired signal. A variant technology,
called wavelength-division multiplexing (WDM) is used in optical
communications.
In digital transmission, signals are commonly multiplexed using TDM, in
which two or more signals are transferred simultaneously as sub-channels in one
communication channel, but are physically taking turns on the channel. The time
domain is divided into several recurrent timeslots of fixed length, one for each subchannel. A sample byte or data block of sub-channel 1 is transmitted during
timeslot 1, sub-channel 2 during timeslot 2, etc. A problem with TDM is that there
is a one-to-one correlation between each port and time slot, so if the device
attached to, for example, port 2 is out for the day, nobody else can make use of
time slot 2. Hence, there is a tendency to waste bandwidth when vacant slots occur
because of idle stations. However, this type of TDM is more efficient than standard
FDM because more subchannels can be derived.
Statistical Time Division Multiplexing (STDM) is an advanced version of
TDM in which both the address of the terminal and the data itself are transmitted
together for better routing. A statistical multiplexer, or a stat mux, has more
memory than other muxes, so if all the time slots are busy, excess data goes into a
buffer. If the buffer fills up, the additional access data gets lost, so it is important to
think about how much traffic to put through a stat mux in order to maintain
37
performance variables. Dynamically allocating the time slots enables you to make
the most efficient use of bandwidth.
Space division multiplexing (SDM) is nothing more than the provision of
multiple fixed bandwidth channels by multiple physical paths (i.e., pairs of wires
or optical fibers). A good example of SDM is the use of a 25-pair cable to carry the
conversations of 25 individual users from the customer's premises to the local
telephone company’s central office location. Wired space-division multiplexing is
typically not considered as multiplexing. In wireless communication, spacedivision multiplexing is achieved by multiple antenna elements forming a phased
array antenna. Different antennas make it possible for digital signal processing
techniques to separate different signals from each other.
Code Division Multiplexing (CDM) is a technique in which each channel
transmits its bits as a coded channel-specific sequence of pulses. One of the basic
concepts in data communication is the idea of multiple access allowing several
transmitters to send information simultaneously over a single communication
channel. To accomplish this CDM employs spread-spectrum technology and a
special coding scheme (where each transmitter is assigned a code). All channels,
each with a different code, can be transmitted on the same fiber and
asynchronously demultiplexed. CDM techniques as an access technology, namely
Code Division Multiple Access (CDMA), are used in Universal Mobile
Telecommunications System (UMTS) standard for the third generation (3G)
mobile communication. Another important application of the CDMA is the Global
Positioning System (GPS). Other widely used multiple access techniques are Time
Division Multiple Access (TDMA) and Frequency Division Multiple Access
(FDMA).
11. Ознакомьтесь с дополнительными словами и выражениями:
coexist [ˌkəuɪg'zɪst] сосуществовать
inherently [ɪn'her(ə)ntlɪ] в основе; внутренне; по существу
take turns делать что-л. поочерёдно, чередоваться, сменяться
recurrent [rɪkʌ̱rənt, AM -kɜ͟ːr-] повторяющийся периодически
excess [ɪk'ses ], [ek-] (n) чрезмерность; перевес;
(adj) избыточный; превышающий норму
buffer ['bʌfə] буфер
allocate ['æləkeɪt] назначать; распределять
38
premises ['preməsəz] здание с прилегающими постройками и участком земли
accomplish [ə'kɔmplɪʃ] совершать, выполнять
12. Ответьте на следующие вопросы:
1. What are the two methods to increase the transmission speed and convey
more information? 2. Are the words the carrier and the channel interchangeable in
multiplexing? 3. Name the most common techniques that enable multiple channels
to coexist on one link. 4. Where is FDM still extensively used? 5. How are STDM
and TDM connected? 6. What enables to use the bandwidth in case of STDM? 7.
How is space-division multiplexing achieved in wireless communication?
13. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Сокращать расходы на содержание коммуникационной сети,
многочисленные телеканалы, абонент, домен, порт, неработающая станция,
избыточные данные, схема кодирования; устанавливать код; асинхронно, не
совпадая
по
времени;
технология
подключения
(абонента)
к
коммуникационной сети; множественный (коллективный) доступ.
14. Переведите на русский язык следующие словосочетания:
Communications link; frequency range; service provider; one-to-one
correlation; waste bandwidth; performance variables; coded channel-specific
sequence of pulses; digital signal processing techniques; assign a code.
15. Вставьте пропущенные предлоги:
1. One of the basic concepts ... data communication is the idea of multiple
access allowing several transmitters to send information simultaneously ... a single
communication channel. 2.… various techniques that enable multiple channels to
be sent … one medium the most common are FDM and TDM. 3. FDM is still used
extensively … cable TV and radio. 4. Service providers can send multiple
television channels … only one cable … all subsribers. 5. To access a desired
channel you have to tune … the appropriate frequency. 6. With TDM, the time
domain is divided … several recurrent timeslots ... fixed length.
16. Вставьте пропущенные слова:
frequency, channel, code time, transmission, bandwidth, messages,
39
multiplexer
1. To maintain the integrity of each signal on the …, multiplexing can
separate the signals by time, space, or frequency. 2. The device used to combine
the signals is a …, and the separate signals are recovered at the end by a
demultiplexer. 3. Frequency-division multiplexing is a scheme in which numerous
signals are combined for … on a single communications line or channel. 4. With
time-division multiplexing, the whole … is assigned to each particular channel for
a fraction of the total transmission time. 5. Multiplexing may be used to make the
best use of an available physical channel by allowing many different … to use it. 6.
Frequency division multiple access (FDMA) puts each call on a separate …. 7.
Time division multiple access (TDMA) assigns each call a certain portion of … on
a designated frequency. 8. Code division multiple access (CDMA) gives a unique
… to each call and spreads it over the available frequencies.
17. Выполните письменный перевод текста на русский язык:
1. Multiplexing is also seen as you are travelling on a four lane road and
suddenly it gets narrower and turns to single lane, at this point the traffic police
will allow one car from each lane to drive through that narrow single lane, this is
what we called multiplexing. 2. CDMA, after digitizing data, spreads it out over
the entire available bandwidth. Multiple calls are overlaid on each other on the
channel, with each assigned a unique sequence code. CDMA is a form of spread
spectrum, which simply means that data is sent in small pieces over a number of
the discrete frequencies available for use at any time in the specified range.
18. Переведите письменно с русского на английский язык:
1. Мультиплексирование – технология разделения средств передачи
данных между группой использующих их объектов. В результате
мультиплексирования в одном физическом канале создается группа
логических
каналов.
Различают
временное
и
частотное
мультиплексирования. 2. Временное мультиплексирование – метод
мультиплексирования, при котором канал предоставляется всем системам по
очереди независимо от наличия у них данные для передачи. Временное
мультиплексирование предусматривает использование мультиплексора. 3.
Мультиплексирование
с
разделением
по
длине
–
способ
мультиплексирования, при котором свет с волнами разной длины передается
40
по одному световоду. Этот способ используется в оптоволоконных
технологиях. 4. Мультиплексор – устройство или программа, позволяющие
передавать по одной коммуникационной линии одновременно несколько
различных
потоков
данных.
5.Статистическое
временное
мультиплексирование – метод мультиплексирования, при котором канал
представляется, по очереди только тем системам, которым способны
немедленно начать передачу данных. Статистическое временное
мультиплексирование предусматривает использование мультиплексора. 6.
Частотное мультиплексирование – метод мультиплексирования, при котором
полоса пропускания физического канала делится на ряд узких частотных
полос.
41
UNIT 5
Text 1. Frequency and Phase Modulation
1. Выучите следующие слова и выражения:
amount [ə'maunt] величина, количество
wide-band FM (WBFM) широкополосная частотная модуляция
narrow band FM (NBFM) узкополосная частотная модуляция, УЧМ
application[ˌæplɪ'keɪʃ(ə)n]
применение,
использование,
употребление,
приложение, применимость
resilience [rɪ'zɪlɪən(t)s] устойчивость(к внешним воздействиям), упругость
amplification[ˌæmplɪfɪ'keɪʃ(ə)n] усиление
linear ['lɪnɪə] линейный
2. Прочитайте и устно переведите текст:
The modulation techniques can be broadly divided into two basic categories:
amplitude modulation and angle modulation. The angle modulation can be further
divided into two more categories: frequency and phase modulations.
The basic principle behind frequency modulation (FM) is that the amplitude
of an analog baseband signal can be represented by a slightly different frequency
of the carrier. This is a method of impressing data onto an alternating-current (AC)
wave by varying the instantaneous frequency of the wave.
Fig. 2. Frequency Modulation
When the audio signal is modulated onto the radio frequency carrier, the new
radio frequency signal moves up and down in frequency. The amount by which the
signal moves up and down is known as the deviation and is normally quoted as the
42
number of kilohertz deviation. As an example the signal may have a deviation of
±3 kHz. In this case the carrier is made to move up and down by 3 kHz.
Broadcast stations in the VHF portion of the frequency spectrum between 88.5
and 108 MHz use large values of deviation, typically ±75 kHz. This is known as
wide-band FM (WBFM). These signals are capable of supporting high quality
transmissions, but occupy a large amount of bandwidth. Usually 200 kHz is
allowed for each wide-band FM transmission. For communications purposes less
bandwidth is used. Narrow band FM (NBFM) often uses deviation figures of
around ±3 kHz. It is narrow band FM that is typically used for two-way radio
communication applications. Having a narrower band it is not able to provide the
high quality of the wideband transmissions, but this is not needed for applications
such as mobile radio communication.
There are several advantages of frequency modulation.
One particular advantage of frequency modulation is its resilience to signal
level variations. The modulation is carried only as variations in frequency. This
means that any signal level variations will not affect the audio output, provided
that the signal does not fall to a level where the receiver cannot cope. As a result
this makes FM ideal for mobile radio communication applications including more
general two-way radio communication or portable applications where signal levels
are likely to vary considerably. The other advantage of FM is its resilience to noise
and interference. It is for this reason that FM is used for high quality broadcast
transmissions.
Another advantage of frequency modulation is associated with the
transmitters. It is possible to apply the modulation to a low power stage of the
transmitter, and it is not necessary to use a linear form of amplification to increase
the power level of the signal to its final value.
It is possible to use non-linear RF amplifiers to amplify FM signals in a
transmitter and these are more efficient than the linear ones required for signals
with any amplitude variations. This means that for a given power output, less
battery power is required and this makes the use of FM more viable for portable
two-way radio applications.
Phase modulation is similar in practice to FM. When the instantaneous phase
of a carrier is varied, the instantaneous frequency changes as well, and vice versa.
But PM tends to require more complex receiving hardware and there can be
ambiguity problems in determining whether, for example, the signal has changed
43
phase by +180° or -180°. Although PM is used for some analog transmissions, it is
far more widely used as a digital form of modulation where it switches between
different phases. This is known as phase shift keying, PSK, and there are many
flavours of this.
Fig
.3.
Phase
Modula
tion
3.
Озна
комьтесь с дополнительными словами и выражениями:
instantaneous [ˌɪnstən'teɪnɪəs] мгновенный
quote [kwəut] ссылаться
VHF (very high frequency) ультракороткие волны (УКВ)
output вывод, итог, результат
cope (with) [kəup] справиться; выдержать, совладать
portable ['pɔːtəbl] портативный, переносный
viable ['vaɪəbl] жизнеспособный
ambiguity [ˌæmbɪ'gjuːɪtɪ] неопределенность, неясность
flavour ['fleɪvə] зд. особенность
4. Ответьте на вопросы, используя информацию текста:
1. What is the basic princile of frequency modulation? 2. What is understood
as deviation? 3. For what purposes WBFM and NBFM are used? 4. What are the
advantages of frequency modulation? 5. What are the distinctions between linear
and non-linear amplification? 6. Are there any disadvantages of phase modulation?
7. Where is phase modulation mostly used?
5. Прочитайте предложения и определите истинны они или ложны:
1. Frequency modulation consists in impressing data onto an AC wave by
varying the frequency of the wave. 2. Deviation is a spontaneous process of
sending the wave in the wrong direction. 3. Wide-band is used for high-quality
transmissions, like FM broadcasting stations, while narrow-band is used for speech
44
and data. 4. FM is highly influenced by different types of noise and interference. 5.
For FM signals amlification low battery power can be used. 6. Phase modulation is
mostly used for analog transmissions.
6. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Угловая модуляция; индуцировать, размещать (данные); величина
отклонения; устойчивость сопротивляемость; при условии, что...;
двусторонняя радиосвязь; усиление (сигнала); неопределенность.
7. Переведите на русский язык следующие словосочетания:
Alternating-current wae; signal level variations; audio output; portable
applications; high quality bradcast transmissions; receiving hardware.
8. Вставьте пропущенные слова:
amplitude, broadcasts, carrier, narrowband, bandwidth
1. The … form is used for voice communications in commercial and amateur
radio. 2. Frequency modulation requires a wider … than amplitude modulation by
an equivalent modulating signal. 3. Frequency modulation (FM) is a technique
used to mix (encode) an information-carrying signal onto a much higher sine wave
… frequency . 4.Wideband FM (W-FM) requires a wider signal bandwidth than …
modulation by an equivalent modulating signal. 5. Since the amplitude is kept
constant, FM modulation is a low-noise process and provides a high quality
modulation technique which is used for music and speech in hi-fidelity ....
9. Вставьте пропущенные предлоги:
1. When a signal is modulated … the radio frequency carrier, the new radio
frequency signal moves up and down … frequency. 2. Wide-band signals are
capable … supporting high-quality transmissions. 3. One of the advantages of FM
is its resilience … noise and interference. 4. Another advantage of FM is associated
… the transmitters. 5. It is possible to apply FM … a lower power stage of
transmitters and use non-linear RF amplifiers.
10. Переведите предложения с английского языка на русский:
1. It is possible to use efficient RF amplifiers with frequency modulated
signals. 2. The spectrum of an FM wave consists of a carrier wave with a series of
pairs of sidebands. 3. Ionospheric refraction doesn't appreciably affect FM or TV
45
signals because of their higher frequency. 4. The unmodulated frequency of a FM
signal is called its center frequency. 5. The amount of "swing" in the transmitter's
frequency in any direction above or below the center frequency is called its
deviation. 6. The total frequency space occupied by a FM signal is twice its
deviation. 7. FM is often encountered by the general public in the form of FM
radio broadcasting, which supports high fidelity sound and stereophonic
reproduction.
11. Переведите текст с русского языка на английский
Вид модуляции, при которой частота сигнала несущей изменяется в
соответствии с аналоговым информационным сигналом. Наиболее
распространенный вид модуляции радиосвязи в КВ (SW) и УКВ диапазонах.
По сравнению с АМ менее подвержен зашумлению и помехам. Есть два
подвида – узкая и широкая частотная модуляция. Все известные приемники
способны принимать оба подвида.
Text 2. Amplitude Modulation
12. Выучите следующие слова и выражения:
accurately ['ækjərətlɪ] точно, безошибочно, аккуратно
interfere [ˌɪntə'fɪə] 1. интерферировать, пересекаться , скрещиваться
2) (interfere with) служить препятствием, мешать, быть помехой
superimpose [ˌs(j)uːp(ə)rɪm'pəuz] (on) накладывать (одно на другое)
sum [sʌm] сумма, количество, величина, итог, совокупность.
reference ['ref(ə)r(ə)n(t)s] справка; справочная информация
predominant [prɪ'dɔmɪnənt] господствующий, преобладающий
vestigial sideband signal [ves'tɪʤɪəl] сигнал с частично подавленной боковой
полосой
13. Прочитайте и устно переведите текст:
Amplitude modulation (AM) is one of the earliest and easiest radio
modulation techniques. In this case the radio frequency signal has a representation
of the data (a sound wave) superimposed in it.
F
ig.
4.
46
Amplitude Modulation
In AM, the carrier itself does not fluctuate in amplitude. It is found that when
a carrier is amplitude modulated, the modulating data appears in the form of signal
components at frequencies slightly higher and lower than that of the main carrier.
These components are called sidebands. The sideband power accounts for the
variations in the overall amplitude of the signal. To see how this happens, let’s take
the example of a carrier on a frequency of 1 MHz which is modulated by a steady
tone of 1 kHz.
The process of modulating a carrier is exactly the same as mixing two signals
together, and as a result both sum and difference frequencies are produced.
Therefore when a tone of 1 kHz is mixed with a carrier of 1 MHz, a "sum"
frequency is produced at 1 MHz + 1 kHz (upper sideband), and a difference
frequency is produced at 1 MHz - 1 kHz (lower sideband).
Amplitude modulation is inefficient in terms of power usage and much of it is
wasted. At least two-thirds of the power is concentrated in the carrier signal, which
carries no useful information (beyond the fact that a signal is present); the
remaining power is split between two identical sidebands, though only one of these
is needed since they contain identical information.
A variant of amplitude modulation when only one sideband is transmitted is
called single-sideband transmission (SSB). In this case, the modulated signal
contains only one sideband and no carrier. The information can be demodulated
only if the carrier is used as a reference. This is normally accomplished by
generating a wave in the receiver at the carrier frequency. Since the sidebands are
mirror images, the choice which sideband to use is a matter of convention.
The problem is that the more of the sideband you filter out, the more
distortion you get from the detected waveform. So there is a practical limit to how
much you can reduce the bandwidth of the signal. It's about 50% reduction of one
sideband. SSB modulation is used for long-distance telephony (such as in the
amateur radio bands) and telegraphy over land and submarine cables.
An alternative technique used for signal power reduction is to remove the
remaining carrier signal from the AM signal; the signal produced is a doublesideband suppressed carrier (DSSC) signal. A compromise between the DSBSC
modulation and the SSB modulation is known as Vestigial Side Band (VSB)
modulation. VSB is used in television transmission to save RF spectrum space. If
the carrier signal is not completely removed, the signal is called a double-sideband
47
reduced carrier (DSRC) signal.
However, as there now are more efficient and convenient methods of
modulating a signal, the use of AM is declining.
14. Ознакомьтесь с дополнительными словами и выражениями:
medium frequency средняя частота
frequency divider делитель частоты
picture transmission телевидение, передача телевизионных изображений
to superimpose one image on another накладывать изображения одно на другое
15. Ответьте на вопросы, используя информацию текста:
1. What are main reasons to blend data into a carrier signal? 2. Is this form of
modulation is a very efficient way to send information? 3. Why is the power
required relatively large? 4. Is it possible to demodulate the signal if the carrier
isn’t used as a reference? 5. Why is it impossible to filter out the whole sideband?
6. How is the transmission with only one sideband called? 7. What is the reason to
remove the remaining carrier signal from the AM signal? 8. Where is SSB used?
16. Вставьте пропущенные слова:
amplitude, transmit, bandwidth, frequency, tuning, envelope, carrier, modulate
1. Amplitude modulation (AM) is a method used … a signal. 2. In the case of
an analog signal to be sent, the … of the radio wave is modulated to be directly
proportional to the value of the analog signal at the time. 3. Amplitude modulation
typically produces a modulated output signal that has twice … of the modulating
signal. 4. The working principles of AM radio is as follows: a … wave introduces
an alternating positive and negative electrical voltage in the receiving antenna. 5.
An AM receiver is capable of picking up the radio waves … from a radio station
and transforming them into audible signals suitable to the human ear. 6. Because
the carrier … is significantly greater than the modulating frequency it is possible to
use a capacitor to smooth or filter the waveform to remove the carrier. 7. Several
stations may be transmitting different signals simultaneously, and therefore the AM
receiver must be capable of focusing on the specific station of your choice ( this is
referred to as “… ”). 8. The … , or boundary, of the amplitude modulated signal
embeds the information bearing signal.
48
17. Заполните пропуски предлогами:
1. Signals … low carrier frequencies require very large antennas. 2. The
length … the antenna has an inverse relationship with the transmission frequency.
3. The original sound can later be detected … a radio receiver. 4. Let’s take the
example of a carrier … a frequency of 1 MHz which is modulated … a steady tone
of 1 kHz. 5. One signal can interfere with another. 6. The information can be
demodulated only by generating a wave … the receiver at the carrier frequency. 7.
The problem is that the more of the sideband you filter … , the more distortion you
get …the detected waveform.
18. Переведите следующие предложения на русский язык:
1. Amplitude modulation is the modulation method used in the AM radio
broadcast band. 2. In this system the intensity, or amplitude, of the carrier wave
varies in accordance with the modulating signal. 3. Amplitude modulation is not
efficient in terms of its power usage. 4. If the modulated carrier is rectified and the
carrier frequency filtered out, the modulating signal can be recovered. 5. Singlesideband signals are very efficient in their use of the frequency spectrum when
compared to standard amplitude modulation (AM) signals. 6. If part of one
sideband and all of the other remain, it is called vestigial sideband, used mostly
with television broadcasting, which would otherwise take up an unacceptable
amount of bandwidth. 7. Nowadays, amplitude modulation is used for audio
broadcasting on the long, medium and short wave bands, and for two way radio
communication at VHF for aircrafts. 8. Amplitude modulation is prone to high
levels of noise because most noise is amplitude based and obviously AM detectors
are sensitive to it. 9. When two signals are modulated, they are said to “beat” with
each other, creating additional frequencies called “beat frequencies”. 10.
Unfortunately, amplitude modulation is subject to static interference from such
things as household appliances – and especially from thunderstorms. 11. AM radio
waves can end up hundreds and even thousands of miles away from where they
started, and interfere with all other stations on the same frequency because of
ionospheric refraction. 12. Nowadays, amplitude modulation is used for audio
broadcasting on the long, medium and short wave bands, and for two way radio
communication at VHF for aircrafts. 13. The envelope of the carrier can be seen to
change in line with the modulating signal.
49
19. Письменно переведите с английского языка на русский:
The working principles of АМ radio is as follows: a carrier wave introduces
an alternating positive and negative electrical voltage in the receiving antenna.
Modulating the wave causes the amplitude of these electrical voltages to be greater
or smaller but in equal and opposite amounts. The receiver uses a diode to remove
either the positive or negative part of the electrical signal, leaving a signal which
when filtered and amplified produces an audible sound. Because the carrier
frequency is significantly greater than the modulating frequency it is possible to
use a capacitor to smooth or filter the waveform to remove the carrier.
20. Письменно переведите предложения с русского языка на английский:
1. Модуляция – это процесс, при котором высокочастотная волна
используется для переноса низкочастотной волны. 2. В системах с
амплитудной модуляцией (АМ) модулирующая волна изменяет амплитуду
высокочастотной несущей волны. 3. Полезная информация полностью
содержится в каждой из двух областей боковых частот. 4. Сигнал с
амплитудной модуляцией, когда для уменьшения занимаемой им полосы
частично подавляют одну из боковых полосy называется АМ с частично
подавленной боковой полосой и такие сигналы используют, например, для
передачи телевидения. 5. Модуляция с одной боковой полосой дает
возможность использовать всю мощность передающей аппаратуры для
передачи только полезного сигнала и увеличить дальность связи
(communication range ).
50
UNIT 6
Text 1. Transmission Media
1. Выучите следующие слова и выражения:
degrade [dɪ'greɪd] ухудшать (качество), портить, вызывать деградацию
degradation [ˌdegrə'deɪʃ(ə)n] ослабление; упадок, деградация
signal degradation деградация сигнала
propagate ['prɔpəgeɪt] распространяться
emission [ɪ'mɪʃ(ə)n ], [iː-] эмиссия, излучение
attenuation [ətenju'eɪʃ(ə)n] затухание, ослабление
devise [dɪ'vaɪz] разрабатывать, продумывать (планы, идеи); изобретать
dissipation [dɪsɪ'peɪʃ(ə)n] рассеяние, рассеивание
plot график; план; диаграмма
loss затухание
ease [i:z] лёгкость, простота
installation [ɪnstə'leɪʃ(ə)n] установление ;установка; сборка;
maintenance ['meɪnt(ə)nən(t)s] содержание и техническое обслуживание, уход;
текущий ремонт
availability [əveɪlə'bɪlətɪ] возможность использования
radiate [reɪdieɪt] излучать(ся)
2. Прочитайте и устно переведите текст:
Every telecommunications system involves the transmission of an
information-bearing electromagnetic signal through a physical medium that
separates the transmitter from the receiver. All transmitted signals are to some
extent degraded by the environment through which they propagate. Signal
degradation generally falls into three types: noise, distortion, and attenuation
(reduction in power). Noise is the presence of random, unpredictable, and
undesirable electromagnetic emissions that can mask the intended information
signal. Distortion is any undesired change in the amplitude or phase of any
component of an information signal that causes a change in the overall waveform
of the signal. Both noise and distortion are commonly introduced by all
transmission media, and they both result in errors in reception.
Various modulating and encoding schemes have been devised to provide
51
protection against the errors caused by channel distortion and channel noise.
However, even powerful signals suffer some degree of attenuation as they pass
through the transmission medium. The principal cause of power loss is dissipation,
the conversion of part of the electromagnetic energy to another form of energy
such as heat. In communications media, channel attenuation is typically expressed
in decibels (dB) per unit distance. Attenuation of zero decibels means that the
signal is passed without loss; three decibels means that the power of the signal
decreases by one-half. The plot of channel attenuation as the signal frequency is
varied is known as the attenuation spectrum, while the average attenuation over the
entire frequency range of a transmitted signal is defined as the attenuation
coefficient.
Channel attenuation is an important factor in the use of each transmission
medium. Along with noise and distortion, it can influence the choice of one
medium over another. Transmission efficiency which is generally viewed as the
amount of signal degradation created by the use of a particular transmission
medium, is the most important factor to consider when choosing transmission
media. Though cost, ease of installation and maintenance, and availability, also
count.
As it has been previously noted, modern telecommunications systems employ
three main transmission media: wire, radio, and optical.
In wire transmission an information-bearing electromagnetic wave is guided
along a wire conductor to a receiver. Propagation of the wave is always
accompanied by a flow of electric current through the conductor. Since all practical
conductor materials are characterized by some electrical resistance, part of the
electric current is always lost by conversion to heat, which is radiated from the
wire. This dissipative loss leads to attenuation of the electromagnetic signal, and
the amount of attenuation increases linearly with increasing distance between the
transmitter and the receiver.
Optical communication employs a beam of modulated monochromatic light to
carry information from transmitter to receiver. The light spectrum spans a
tremendous range in the electromagnetic spectrum, extending from the region of
10 terahertz (104 gigahertz) to 1 million terahertz (109 gigahertz). This frequency
range essentially covers the spectrum from far infrared (0.3-mm wavelength)
through all visible light to near ultraviolet (0.0003-mm wavelength). Propagating
at such high frequencies, optical wavelengths are naturally suited for high-rate
52
broadband telecommunication. For example, amplitude modulation of an optical
carrier at the near-infrared frequency of 300 terahertz by as little as 1 percent yields
a transmission bandwidth that exceeds the highest available coaxial cable
bandwidth by a factor of 1,000 or more.
In radio transmission a radiating antenna is used to convert a time-varying
electric current into an electromagnetic wave or field, which freely propagates
through a nonconducting medium such as air or space. In a broadcast radio
channel, an omnidirectional antenna radiates a transmitted signal over a wide
service area. In a point-to-point radio channel, a directional transmitting antenna is
used to focus the wave into a narrow beam, which is directed toward a single
receiver site. In either case the transmitted electromagnetic wave is picked up by a
remote receiving antenna and reconverted to an electric current.
3. Ознакомьтесь с дополнительными словами и выражениями:
random ['rændəm] случайный, произвольный
span отмерять, охватывать
yield [jiːld] давать результат, приводить (к чему-либо)
essentially [ɪ'senʃ(ə)lɪ] по существу, существенно; в высшей степени;
чрезвычайно
directional antenna направленная антенна
omnidirectional antenna ненаправленная антенна
4. Ответьте на следующие вопросы:
1. How many types does signal degradation fall into? 2. What do noise and
distortion result in? 3. Give the definition of dissipation. 4. What are the factors to
consider when choosing transmission media? 5. What main transmission media do
modern telecommunications systems employ? 6. Why are noise and distortion
undesirable in signals? 7. In wire transmission an information-bearing
electromagnetic wave isn’t guided along a wire conductor to a receiver, is it?
5. Прочитайте предложения и определите истинны они или ложны:
1. The degradation of signals is caused by the environment through which they
propagate. 2. Attenuation does not influence signal reception. 3. The choice of
transmission medium depends purely upon its cost and availability. 4. Optical
media use a rather narrow range in electromagnetic spectrum. 5. Radio
53
transmission doesn't require any conductiong medium.
6. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Приводить к ошибкам; уменьшаться наполовину; эффективность
передачи сигнала; простота установки и обслуживания; проводящий
материал; преобразование в тепло; электрический ток; электрическое
споротивление;
монохроматический
свет;
удаленный;
заново
преобразовывать.
7. Переведите на русский язык следующие словосочетания:
Information-bearing electromagnetic signal; intended information signal;
channel attenuation; attenuation spectrum; dissipative loss; high-rate broadband
telecommunication; far-infrared and near-infrared frequency; point-to-point radio
channel.
8. Вставьте пропущенные слова:
attenuation, dissipation, conversion, plot, degrade, noise
1. All transmitted signals are to some extent … by the environment through
which they propagate. 2. Reduction in power is called … . 3. … is any undesired
change in the amplitude or phase of any component of an information signal that
causes a change in the overall waveform of the signal. 4. The … of channel
attenuation as the signal frequency is varied is known as the attenuation spectrum.
5. … and distortion are commonly introduced by all transmission media. 6. Since
all practical conductor materials are characterized by some electrical resistance,
part of the electric current is always lost by … to heat.
9. Вставьте пропущенные предлоги:
1. All transmitted signals are degraded by the environment … which they
propagate. 2. The principal cause … power loss is dissipation. 3. A radiating
antenna converts a time-varying electric current … an electromagnetic wave or
field. 4. Signal degradation generally falls … three types: noise, distortion, and
attenuation . 5. Propagation of the wave is always accompanied … a flow of
electric current through the conductor. 6. Optical wavelengths are naturally suited
… high-rate broadband telecommunication. 7. Both noise and distortion are
54
commonly introduced … all transmission media, and they both result in errors in
reception.
Text 2. Wire Media Types
10. Выучите следующие слова и выражения:
bundled связанный
hard-drawn холоднотянутый
tensile corrosion ['ten(t)saɪl] [kə'rəuʒ(ə)n] коррозия из-за растяжения
insulate ['ɪnsjəleɪt] изолировать
crosstalk взаимное влияние каналов
foil фольга
jacket оболочка
shield [ʃiː ld] экран, оплётка
shielded twisted pair (STP) экранированная витая пара (два перевитых
вокруг друг друга изолированных медных провода с экранирующей
оплёткой)
unshielded twisted pair (UTP) неэкранированная витая пара
impedance [ɪm'piːd(ə)n(t)s] полное сопротивление, импеданс
twist [twɪst] скрутка
axis ['æksɪs] ось
strand [strænd] жила, полоса
solid conductor одножильный провод
stranded conductor многожильный провод; многожильный кабель
skin-effect скин-эффект, поверхностный эффект
dissipation factor коэффициент рассеяния
braid оплетка
flame retardant [rɪˈtɑːd(ə)nt] огнезащитный
attenuation constant коэффициент затухания
11. Прочитайте и устно переведите текст:
Most modern wire transmission is conducted through the metallic-pair circuit,
in which a bundled pair of conductors is used to provide a forward current path and
a return current path. The most common conductor is hard-drawn copper wire,
55
which has the benefits of low electrical resistance, high tensile strength, and high
resistance to corrosion. The basic types of wire media found in
telecommunications are twisted pair cables and coaxial cables.
Twisted pair cabling was initially used as the main connector in telephone
communication. It consists of two separate, insulated copper wires twisted together
at specific intervals to help block crosstalk interference.
The most commonly used form of twisted pair is unshielded twisted pair
(UTP). It is just two insulated wires twisted together. Data communication cables
and normal telephone cables are of this type. Shielded twisted pair (STP) differs
from UTP in that it has a foil jacket that helps prevent crosstalk and noise from
outside source. In data communications there is a cable type called FTP (foil
shielded pairs) which consists of four twisted pair inside one common shield (made
of aluminium foil).
The impedance of a cable is actually a function of the spacing of the
conductors, so separating the conductors significantly changes the cable impedance
at that point.
When many twisted pairs are put together to form a multi-pair cable,
individual conductors are twisted into pairs with varying twists to minimize
crosstalk. Specified color combinations are used to provide pair identification.
The coaxial cable is a flexible transmission line and typically is used to
connect two electronic instruments together.
A coaxial cable consists of two conductors separated by a dielectric material.
The center conductor and the outer conductor, or shield, are configured in such a
way that they form concentric cylinders with a common axis (hence co-axial).
The center conductor may be made of various materials and constructions.
Most common constructions are solid or stranded conductors. Solid conductors are
used in permanent, infrequently handled or low flex applications and stranded
conductors used in flexible cable applications. Common materials include copper,
tinned or silver plated copper, copper clad steel and copper clad aluminum. Plated
copper is used to aid in solderability of connectors or to minimize corrosion
effects. Because of a phenomenon known as skin-effect, copper clad materials may
be used in higher frequency applications.
Insulation, or dielectric materials, are used to provide separation between the
conductors. It is desirable that the material has stable electrical characteristics
(dielectric constant and dissipation factor) across a broad frequency range. The
56
most common materials used are polyethylene (PE), polypropylene (PP),
fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE).
The outer conductor is typically made from a number of smaller aluminum or
copper conductors combined together. These conductors are woven together to
form a braid around the dielectric core. For higher frequency applications, a second
braid or aluminum foil tapes are often added to improve attenuation and shield
effectiveness.
The jacket material serves as a protective covering from the environment and
may also serve to add in the overall flame retardant properties of the cable. Typical
materials include polyvinyl chloride (PVC), PE, FEP and polyvinylidene fluoride
(PVDF).
An optical cable is one of the easiest ways to connect your devices together to
transfer a digital sound signal. Also known as SPDIF or Toslink, an optical cable
consists of a fibre optic that transfers light rather than an electrical signal as a
digital coaxial cable would. There are many different types of cable available, and
which one you choose really depends on what you will be using the cable for.
12. Ознакомьтесь с дополнительными словами и выражениями:
spacing ['speɪsɪŋ] расстояние, интервал
flexible ['fleksəbl] гибкий
outer ['autə] внешний, наружный
handle ['hændl] обращаться с чем-либо
tin[tɪn] олово
weave (woven; woven) переплетать, вплетать
plated покрытый тонким слоем
clad steel плакированная сталь (плакирование - нанесение на поверхность
металлических листов, проволоки и др.)
solderability [səuldərə'bɪlɪtɪ] паяемость, пригодность к пайке
polyethylene [pɔlɪ'eθɪliːn] полиэтилен (PE)
polypropylene [pɔlɪ'prəupɪliːn] полипропилен (PP)
polytetrafluoroethylene [pɒlɪtɛtrəflʊərəʊ'ɛθɪliːn] политетрафторэтилен, тефлон
13. Ответьте на вопросы по тексту:
1. What kind of cabling was initially used as the main connector in telephone
communication? 2. How is the form of twisted pair with just two insulated wires
57
twisted together called? 3. What is the difference between STP and UTP? 4. What
is the way to minimize crosstalk? 5. Is it possible to identify pairs in a multi-pair
cable? 6. Where are solid and stranded conductors used?
14. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Цепь, образуемая парой металлических проводников; преимущество;
прямой ток; обратный ток (ток отражённой волны); предотвращать
перекрестное взаимовлияние каналов; оболочка из фольги; кабель с плохой
гибкостью; диэлектрическая постоянная (диэлектрическая проницаемость):
15. Переведите на русский язык следующие словосочетания:
Data communication cables, multi-pair cable; minimize crosstalk; dielectric
material; concentric cylinder; solid conductor; stranded conductor; aluminum foil
tape; flame retardant properties; digital sound signal.
16. Вставьте пропущенные слова:
jacket, coaxial, rate, crosstalk, impedance, shield, twisted
1. A … cable has a solid copper or copper-clad-steel centre conductor
surrounded by a non-conductive dielectric insulating material. 2. The dielectric is
surrounded by foil … and/or copper braid/s which form the outer conductor and
also shield against electromagnetic interference (EMI). 3. The outer
conductor/shield is encased in a PVC… . 4. Twisted pair cable consists of a pair of
insulated wires … together. 5. Cable twisting helps to reduce noise pickup from
outside sources and … on multi-pair cables. 6. When cable is twisted at constant
twist … over the length of the cable, a cable with well defined characteristic
impedance is formed. 7. Characteristic … of twisted pair is determined by the size
and spacing of the conductors and the type of dielectric used between them.
17. Вставьте пропущенные предлоги:
1. Most modern wire transmission is conducted … the metallic-pair circuit. 2.
The jacket material serves as a protective covering … the environment. 3. A
coaxial cable consists … two conductors separated by a dielectric material. 4.
When many twisted pairs are put together to form a multi-pair cable, individual
conductors are twisted … pairs with varying twists. 5. Twisted pair cabling
consists of two separate, insulated copper wires twisted together … specific
58
intervals.
18. Подберите к словам ниже однокоренные слова указанной части речи:
A) существительные: devise, define, propagate, identify, connect, improve,
attenuate, add, configure, resist, radiate
B) прилагательные: environment, optics, protection, availability, dissipation
C) глаголы: reception, reduction, degradation, conversion
19. Сделайте письменный перевод текста:
Losses are incorporated into the transmission-line model with the addition of
a distributed resistance in series with the inductor and a distributed conductance in
parallel with the capacitor. Additional distributed circuit elements can be
incorporated into the model in order to describe additional effects. For example,
the linear capacitors could be replaced with reverse-biased varactor diodes and the
propagation of nonlinear solitons could be studied.
A transmission line transmits energy (electric power, acoustic waves or
electromagnetic waves) from one point to another as efficiently as possible with
minimum energy loss. Energy can be directed through a regular electric wire but
with enormous losses.
20. Переведите текст на английский язык:
Существует большое количество типов коаксиальных кабелей,
используемых в сетях различного типа – телефонных, телевизионных и
компьютерных. Не так давно коаксиальный кабель был самым
распространенным типом кабеля. Это объяснялось двумя причинами. Вопервых, он был относительно недорогим, легким, гибким и удобным в
применении. А во-вторых, широкая популярность коаксиального кабеля
привела к тому, что он стал безопасным и простым в установке. Самый
простой коаксиальный кабель состоит из медной жилы (core), изоляции, ее
окружающей, экрана в виде металлической оплетки и внешней оболочки.
Если кабель, кроме металлической оплетки, имеет и слой фольги, он
называется кабелем с двойной экранизацией. При наличии сильных помех
можно воспользоваться кабелем с учетверенной экранизацией. Он состоит из
двойного слоя фольги и двойного слоя металлической оплетки.
59
UNIT 7
Text 1. Fiber Optics
1. Выучите следующие слова и выражения:
be subject (to) ['sʌbʤɪktˌtuː] быть подверженным (чему-либо)
reflection [rɪ'flekʃ(ə)n] отражение
boundary ['baund(ə)rɪ] граница
eliminate [ɪ'lɪmɪneɪt ], [ə-] устранять, исключать
cladding ['klædɪŋ] оболочка
layer ['leɪə] слой
bundle ['bʌndl] пучок
multi-mode fiber многомодовый волоконно-оптический кабель
single-mode fiber одномодовое оптоволокно
core [kɔː] стержень, сердечник
coating оболочка
covering покрытие; внешняя оболочка
2. Прочитайте и устно переведите текст:
Fiber optics (or “optical fibre”) refers to the medium and the technology
associated with the transmission of information as light impulses along a strand of
glass or plastic. A fiber-optic strand carries much more information than a
conventional copper wire and is far less subject to electromagnetic interference
(EMI). Optical fibers of very pure glass are able to carry light over long distances
ranging from a few inches or centimeters to more than 100 miles (160 km) with
little dimming, owing to it they can be used to illuminate and observe hard-toreach places.
Fiber optics is based on the optical phenomenon known as total internal
reflection. With the simplest form of optical fiber, light entering one end of the
fiber strikes the boundary of the fiber and is reflected inward. The light travels
through the fiber in a succession of zigzag reflections until it exits from the other
end of the fiber. Other forms of optical fibers are designed in such a way that the
zigzagging of the light is greatly reduced or virtually eliminated.
The fiber optic strand is constructed in several layers. Most optical fibers
made today consist of at least two parts: a core through which the light is
60
transmitted and a protective coating – called cladding (either glass or plastic) – that
surrounds the core and helps prevent light from leaking from the core. The
cladding bends or reflects inward the light rays that strike its inside surface. The
core, coating and covering are collectively referred to as a “strand”. Fiber strand
sizes are always referred to in terms of the diameter of the core. Some individual
fibers are thinner than human hair and measure less than 0.00015 inch (0.004 mm)
in diameter. A detector, such as a photosensitive device or the human eye, receives
the light at the other end of the fiber.
Fig.5. Optical fibers
Fiber strands are typically bundled within a cable. Optical fiber bundles are
either coherent or incoherent. In a coherent bundle, the fibers are arranged so that
images, as well as illumination, can be transmitted. In incoherent bundles, the
fibers are not arranged in any particular way and can transmit only illumination.
There are two basic types of optical fibers: single-mode fibers and multi-mode
fibers. Single mode fibers are designed for the transmission of a single ray as a
carrier and are used for high-speed signal transmission over long distances. They
have much smaller cores than multi-mode fibers, and they accept light only along
the axis of the fibers. Tiny lasers send light directly into the fiber. Multi-mode
fibers are designed to carry multiple light rays. They have much larger core
diameter compared to those of single-mode fibers, and they accept light from a
variety of angles. Multi-mode fibers use more types of light sources and cheaper
connectors than single-mode fibers. They are mostly used for communication over
shorter distances.
The first studies of fiber optics were made in the late 1800s, but practical
development did not begin until the early 1950s. The development of fiber optics
was spurred by the introduction of lasers in the early 1960s and by the production
of the first optical fibers of very pure glass in 1970. The commercial use of fiber
61
optics, especially in communications systems, developed rapidly in the 1980s.
Today the uses of optical fibers are numerous. Almost all telephone longdistance (cross country) lines are now fiber optic. Fiber-optic cables are also the
common medium whenever people talk about the cable TV system or the Internet.
In medicine, optical fibers enable physicians to look and work inside the body
through tiny incisions without having to perform surgery. They are used for
endoscopes - instruments for viewing the interior of hollow organs in the body.
They can also be used for insertion into blood vessels to give a quick, accurate
analysis of blood chemistry.
In scientific research and in manufacturing, fiber optic devices carry light to
and from hazardous areas, vacuum chambers, and confined spaces within
machines. Some instruments use optical-fiber coils as a sensing device; so optical
fibers are used to measure temperature, pressure, acceleration, and voltage in
industries.
3. Ознакомьтесь с дополнительными словами и выражениями:
dimming уменьшение силы света
virtually ['vɜːʧuəlɪ ], ['vɜːtjuəlɪ] фактически, практически
leak просачиваться
spur [spɜː] стимулировать
incision [ɪn'sɪʒ(ə)n] разрез
surgery ['sɜːʤ(ə)rɪ] хирургия
confined space закрытое пространство
acceleration [əkˌselə'reɪʃ(ə)n] ускорение
4. Ответьте на вопросы, используя информацию текста:
1. What does the term fiber optics refer to? 2. Why is it possible to use
optical fibers to illuminate and observe hard-to-reach places? 3. How does the light
travel through the fiber? 4. Where is a protective coating situated? 5. What is the
difference between coherent and incoherent bundles? 6. How many types of optical
fibers exist and what is the difference between them? 7. How are optical fibers
used?
5. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Обычный провод; труднодоступные места; полное внутреннее
отражение; устранять; отражать внутрь; светочувствительный; кровеносный
62
сосуд; химический состав крови; измерительное устройство (датчик).
6. Переведите на русский язык следующие слова и словосочетания:
Light impulse; pure glass; zigzag reflections; telephone long-distance (cross
country) lines; physician; vacuum chamber.
7. Вставьте пропущенные слова:
bundles, core, coating, strands, mode
1. Fiber-optic lines are … of optically pure glass as thin as a human hair that
carry digital information over long distances. 2. Optical fibers come in two types:
single-… fibers and multi- … fibers. 3. Thin glass center of the fiber where the
light travels is called the …. 4. To protect the fiber from damage and moisture the
plastic … is necessary. 5. Hundreds or thousands of optical fibers are arranged in
… in optical cables.
8. Вставьте пропущенные предлоги:
1. A fiber-optic strand is not much subject ... electromagnetic interference. 2.
Owing … fiber-optic strand properties, the information sent … a strand of glass
can reach most remote places. 3. Optical fibers consist ... two parts: a core and a
protective coating. 4. A detector receives the light ... the other end of the fiber. 5.
The first studies of fiber optics were made ... the late 1800s, but practical
development did not begin ... the early 1950s.
9. Составьте предложения, подбирая к левой части соответствующее
продолжение:
1. Optical fibers of very pure glass
2. Other forms of optical fibers
3. Fiber strand sizes
4. Fiber strands
5. In incoherent bundles, the fibers
6. Single mode fibers
a. are typically bundled within a cable.
b. are designed for the transmission of a
single ray as a carrier
c. are able to carry light over long distances
d. are designed in such a way that the
zigzagging of the light is greatly
reduced or virtually eliminated.
e. are not arranged in any particular way
f. are always referred to in terms of the
diameter of the core.
63
10. Переведите текст на английский язык:
Структура оптоволоконного кабеля очень проста и похожа на структуру
коаксиального электрического кабеля, только вместо центрального медного
провода здесь используется тонкое (диаметром порядка 1-10 мкм)
стекловолокно, а вместо внутренней изоляции – стеклянная или пластиковая
оболочка, не позволяющая свету выходить за пределы стекловолокна. В
данном случае мы имеем дело с режимом так называемого полного
внутреннего отражения света от границы двух веществ с разными
коэффициентами преломления (у стеклянной оболочки коэффициент
преломления значительно ниже, чем у центрального волокна).
Металлическая оплетка кабеля обычно отсутствует, так как экранирование от
внешних электромагнитных помех здесь не требуется, однако иногда ее всетаки применяют для механической защиты от окружающей среды .
Text 2. Wireless Media
11. Выучите следующие слова и выражения:
comprise [kəm'praɪz] включать; заключать в себе, содержать ,составлять
destination[ˌdestɪ'neɪʃ(ə)n] назначение, место назначения
curvature ['kɜːvəʧə] кривизна
repeater повторитель, промежуточная станция; промежуточный усилитель
(линии связи)
transponder [tran'spɒndə, trɑːn-] ретранслятор
cease [siːs] переставать (делать что-л.), прекращать
geosynchronous [ˌdʒiːə(ʊ)'sɪŋkrənəs] геосинхронный
geostationary [ dʒiːə(ʊ)ˈsteɪʃ(ə)n(ə)ri] геостационарный
overlap [ˌəuvə'læp] частично перекрывать; заходить один за другой
'footprint' зона обслуживания (в спутниковой связи)
option ['ɔpʃ(ə)n] выбор, альтернатива, (возможный) вариант
diffuse [dɪ'fjuːs] (adj) разбросанный, распространённый, рассеянный
[dɪ'fjuːz] (v) рассеивать
12. Прочитайте и устно переведите текст:
Unlike wired transmission media wireless
64
transmission
relies
on
electromagnetic waves. These waves require no physical medium, they radiate by
including a current in a transmitting antenna and then travel through the air or free
space using infrared, radio, or microwave signals.
To understand wireless technology, a basic understanding of the radio
frequency (RF) spectrum is required. The RF spectrum is a part of the
electromagnetic spectrum in which a variety of commonly used devices (including
television, AM and FM radios, microwave radios, cell phones, and others) operate.
The electromagnetic spectrum has been used for communications for over 100
years, and it comprises an infinite number of frequencies, from AM radio at 1 MHz
to the cellular/PCS band at 2 GHz.
Frequencies are measured in cycles per second, or Hertz, which are inversely
related to wavelength. At low frequencies wavelengths are long, while at higher
frequencies wavelengths are very short. Given an equal power level, the longer the
wavelength, the greater the distance the signal can travel. Whereas low-frequency
signals (such as AM radio) can be transmitted for hundreds of miles, highfrequency signals (such as infrared) can travel only a few feet.
Radio waves are easy to generate and are omnidirectional, but have low
transmission rates. Also, depending on their frequency, radio waves either cannot
travel very far, or are absorbed by the earth. In some cases, though, High
Frequency (HF) waves are reflected back to earth by the ionosphere (a layer of the
atmosphere).
Microwaves are high frequency radio waves that travel in straight lines
through the air. Microwave links are widely used to provide communication when
it is impractical or too expensive to install physical transmission media. With
microwave transmission, a source can be directly focused on its destination
without interfering with neighboring transmissions. Because they travel in straight
lines, though, the curvature of the earth can interfere with the microwave
transmitters; the solution to this is the addition of repeaters between the source and
destination to redirect the data path. Microwaves are used for long distance
communication, cellular phones, garage door openers, and much more.
Satellite transmission is microwave transmission in which one of the stations
is a satellite orbiting the earth. A microwave beam is transmitted to the satellite
from the ground. This beam is received and retransmitted (relayed) to the
predetermined destination. The receiver and transmitter in satellites is known as
transponder.
65
A satellite operates in specific frequency ranges. Bands are grouped in pairs
such as 4/6 GHz, where the number refers to downlink / uplink frequencies.
Normally there are many microwave bands assigned by letter: P, L, C, X, K, Q, V,
and W. Most of the bands have a subband such as Ku, Ka, Kt, Kp, Ce, Cz, etc. The
optimum frequency range for satellite transmission is in the range 1 to 10 GHz.
As a satellite moves across the sky, communication is possible for only a short
time: as it drops below the horizon, communication ceases until it later appears
above the other horizon. To always provide communications, modern
telecommunication satellites are positioned approximately 22,300 miles (over
35,888 km) above the equator and arrange a satellite's velocity synchronous with
the earth's rotation. This is called geostationary, or geosynchronous orbit. Only
three satellites are needed to provide coverage of the entire earth with small
overlapping areas.
Another wireless telecommunications technology is the low-earth orbit (LEO)
satellite system, where satellites communicate directly with handheld telephones
on the Earth. Because these satellites are relatively low (less than 900 miles (or
1450 km) above), they move across the sky quite rapidly, so sophisticated ground
equipment must be used to track a satellite, increasing the cost of the system.
Satellites in this orbital range have a very small 'footprint', so lots of them are
required to enable world wide communication (35 or more).
Infrared light is used for close-range communication, such as remote controls
or a computer mouse, because it does not pass through objects well. This is also a
plus because infrared communications in one room do not interfere with the
infrared communications in another room. Infrared communication is more secure
than other options, such as radio, but it cannot be used outside due to interference
by the Sun.
Lasers are also used for wireless communications. It is a relatively low cost
way to connect two buildings' LANs, but it has drawbacks: it is difficult to target
on the destination's receiver because the beam is so small. Laser light also diffuses
easily in poor atmospheric conditions, such as rain, fog, or intense heat.
13. Ознакомьтесь с дополнительными словами и выражениями:
ionosphere [aɪ'ɔnəsfɪə] ионосфера (верхние слои атмосферы, от 50-80 км)
horizon [hə'raɪz(ə)n] горизонт
target ['tɑːgɪt] предназначать
66
PCS (personal communications service) служба персональной связи
whereas [(h)wɛə'ræz] тогда как; несмотря на то, что
14. Ответьте на следующие вопросы:
1. What is the difference between wired transmission media and wireless
transmission? 2. How are frequencies measured? 3. What is the relation between
the wavelength of a signal and the distance it can travel? 4. Is it difficult to
generate radio waves? 5. When are microwave links used? 6. How do radio waves
propagate? 7. What drawbacks do lasers have? 8. What are the main features of
communication with the help of satellites?
15. Найдите в тексте слова и выражения, эквивалентные данным ниже:
Находиться в обратном отношении к ч-л.; микроволновая связь;
распространяться по прямой линии; нисходящая линия связи (пересылка
данных со спутника на наземную станцию); передача информации с
наземной станции на спутник (линия связи Земля - космос); низкая
околоземная орбита; безопасный; нацеливаться.
16. Переведите на русский язык следующие слова и словосочетания:
Wireless technology; low transmission rate; data path; garage door openers;
position; coverage; handheld telephones; sophisticated ground equipment; closerange communication; remote control; computer mouse; poor atmospheric
conditions.
17. Устно изложите данный ниже текст по-английски. Затем переведите
этот текст на русский язык.
Transmission of waves take place in the EM spectrum. The carrier frequency
of the data is expressed in cycles per second called hertz (Hz). Low frequency
signals can travel for long distances through many obstacles but can not carry a
high bandwidth of date while high frequency signals can travel for shorter
distances through few obstacles and carry a narrow bandwidth. Also the noise
effect on the signal is inversely proportional to the power of the radio transmitter.
The three broad categories of wireless media are:
1. Radio transmission within the range of 10 Khz to 1 Ghz. It is broken into
many bands including AM, FM, and VHF bands.
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2. Microwave transmission is presented by terrestrial and satellite media. Terrestrial media are used to link networks over long distances but the two microwave
towers must have a line of sight between them. The frequency is usually 4-6GHz
or 21-23GHz. Speed is often 1-10Mbps.
A satellite orbits at 22,300 miles above the earth which is an altitude that will
cause it to stay in a fixed position relative to the rotation of the earth. This is called
a geosynchronous orbit. A station on the ground will send and receive signals from
the satellite. The transmission frequency is normally 11-14GHz with a transmission
speed in the range of 1-10Mbps.
3. Infared transmission is just below the visible range of light between
100Ghz and 1000Thz. A light emitting diode (LED) or laser is used to transmit the
signal. The signal cannot travel through objects. Light may interfere with the
signal.
18. Письменно переведите тексты на английский язык по вариантам:
В.1. Коммуникационный спутник – это специальный беспроводной
приемо-передатчик, принимающий радиоволны из одного места и
передающий их в другое, который запускается с помощью ракеты и
закрепляется на околоземной орбите. Спутники используются для передачи
данных через сети широкого спектра действия, прогнозирования погоды,
телевещания, непрофессионального общения посредством радиоустройств,
доступа в Интернет и спутниковой навигации.
Прием и передача данных осуществляется посредством транспондера
(приемо-передающего тракта). Один транспондер на спутнике может
одновременно управлять примерно 5000 голосовых каналов и каналов
передачи данных. Стандартный спутник имеет 32 транспондера.
В.2. Основным применением микроволн, распространяющихся у
поверхности Земли, является связь на большие расстояния. Микроволны
представляют собой альтернативу коаксиальному кабелю и оптоволокну.
Микроволновые линии передачи требуют значительно меньшего числа
усилителей и повторителей, чем линии на основе коаксиальных кабелей,
передающих сигналы на то же расстояние. Однако в микроволновых линиях
связи необходимо обеспечивать прямую видимость. Микроволны
применяются для передачи как голоса, так и телевизионного сигнала.
Другим распространенным применением микроволн является
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обеспечение коротких двухточечных каналов связи между зданиями. Эти
каналы используются в кабельном телевидении или в качестве линий связи
между локальными сетями.
69
ADDITIONAL TEXTS
Communication Technician Job
People who need to troubleshoot a computer or have their telephone systems
repaired often turn to a communication technician. Communication technicians
install and maintain electronic communication equipment. They are also
responsible for building and maintaining electronic circuits and data networks.
Humans rely very heavily upon complex communication networks.
Communication technicians are needed to maintain and repair all of the devices
within these networks. They must be able to properly utilize diagnostic and
measuring tools to test, alter, and repair any equipment necessary.
A communication technician might be responsible for working on cellular
phones, wireless Internet services, two-way radios, handheld computers, and other
electronic equipment. A technician may also work on important law enforcement
or military devices, such as vehicle location equipment or marine radios. Satellite
systems and their related equipment are also included.
To become a communication technician, a person should be very familiar with
digital radio technology, cellular systems, and electronics in general. He or she will
need good reading skills to be able to read work orders depicting equipment needs.
Good communication skills are also necessary to be able to converse with
equipment operators and clients in order to assess problems and equipment needs.
Sometimes schematic drawings and other written materials are needed in order to
locate and rectify problems.
When wireless communications break down, a field communication
technician is typically dispatched to repair the damage. This may happen on a work
site or wireless network relay sites. Much of the work of a communication
technician is not emergency, however, but standard maintenance. Many
corporations and other users of wireless networks hire communication techs in
order to maintain their systems periodically.
Many communications techs work in stores, repair shops, or service centers.
At these locations, they fix wireless communications devices usually brought in by
customers. They may also help advise customers about replacement parts and other
devices they may be interested in purchasing or upgrading.
Large telecommunications companies typically employ many communication
70
technicians. In this field, they are responsible for both addressing the needs of the
telecommunications companies themselves as well as the customers using their
services. Such careers may also include duties in sales, purchasing office
equipment, and executing office administration.
Formal training in electronics is generally preferred in a communications
technician. This can be acquired through community and technical colleges, as
well as universities. Many communications technicians receive their training and
experience while serving in the armed forces.
The Future of Telecommunications
It is impossible today to imagine our world without telecommunications. It's a
common sight now to see people walking down the street talking into a mobile
phone or hands-free headset. But what we have today is just an intermediate step.
In modern laboratories, there are some developments that introduce more
sophisticated devices. For example, something you can put in your shirt that will
pick up your voice so that you don't need earphones or a microphone. These
electronic devices will probably be of nano variety, which means they will be
assembled at the molecular or even atomic level, but they will operate like
microphones and earphones in today's mobile devices. In fact, you could have fulltime connectivity through your shirt or your wallet. Some people will have a strong
reaction against this. They will refuse to be connected this way because they will
see it as a kind of dependence. But other people, like some smart people in, say, the
City of London will be very happy to have a dress that is both beautiful and that
can also connect them to whomever they want to stay in touch with.
Nanotechnology will have a tremendous impact because it facilitates full
flexibility of use. When you look at the history of communications, it is the
development of many different devices. First there was a telephone in a fixed
position, then television, then mobile phone, then the Internet, and so on.
Delivering these services to the customer was complex, and the customer had to be
more or less of an engineer to manage them all. For people who are not technically
inclined, it can become a kind of nightmare. So the dream is that all the points of
access will be merged into a pocket-size device or even a nano-chip in your
clothing, and with that, you can hear music, you can call up a movie on the TV
screen, you can play games – you can do whatever you want.
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Even more impressive is what will happen in your house. You will have a
screen on the wall that will be like a TV screen but won't be dedicated to a single
use, like television. Its applications will be flexible and you will have a small
device that will let you select how you use it. When you are working, you can use
it for computing or the Internet. When you are relaxing, you can watch TV or a
movie or some other form of entertainment. Or you can be in touch with your
friends. Your TV set can be connected to the Internet now, but it's a secondary
usage. The new screen will be neutral and you will manage the way you use it with
a device that fits in your pocket.
Telecommunications will also have a considerable influence on businesses
and industry. No one can run a company now without being on the Internet. A lot
of small businesses that used to only sell locally are now selling internationally,
thanks to telecommunications. In fact, there are some start-up businesses that begin
on the international level, and once they are established there, they begin selling
locally. In the global digital village, your market can come from anywhere. This
represents a massive shift in the world economy, and it is going to continue
evolving as new technologies are introduced. The revenues in telecommunications
drive to the highest of all businesses. Companies will need to keep adjusting to
accommodate these changes and the ones that do this best are the ones that will
succeed. Flexibility and innovation will be key.
Signal Processing
The intentional operation on a signal produced by one process, an “input
signal”, to produce a new signal, an “output signal”, is generally referred to as
signal processing. It is an area of electrical engineering and applied mathematics
that deals not only with operations on, but also analysis of signals, in either
discrete or continuous time, to perform useful operations on those signals. Signals
of interest can include sound, images, time-varying measurement values and sensor
data, for example biological data such as electrocardiograms, control system
signals, telecommunication transmission signals such as radio signals, and many
others.
The analysis of signals and the automation of repetitive tasks of recognition
are ubiquitous in several applications such as bioengineering, biometrics, industrial
inspection, agroindustry, artificial vision, bioacoustics and seismology.
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Professionals in those areas need advanced data and signal analysis techniques to
understand better the nature of their objects of study and the interactions between
the variables involved in their corresponding processes. In addition, pattern
recognition techniques are able to provide them with advanced and reliable
methods to automate classification or identification procedures as well as to assist
them in complex decisions such as diagnoses and forecasts.
The topic can be easily illustrated by examples.
 A time-varying voltage waveform is produced by a human speaking into a
microphone or telephone. This signal might be modulated for transmission, then it
might be digitized and coded for transmission on a digital link. Noise in the digital
link can cause errors in reconstructed bits, the bits can be used to reconstruct the
original signal within some fidelity. All of these operations on signals can be
considered as signal processing, although the name is most commonly used for
manmade operations such as modulation, digitization, and coding, rather thatn the
natural possibly unaviodable changes such as the addition of thermal noise or other
changes out of control.
 For digital speech communications at very low bit rates, speech is
sometimes converted into a model consisting of a simple linear filter and an input
process. The idea is that the parameters describing the model can be communicated
with fewer bits than can the original signal, but the receiver can synthesize the
human voice at the other end using the model so that it sounds very much like the
original signal. A system of this typr is called a vocoder.
 Signals including image data transmitted from remote spacecraft are
virtually buried in noise added to them on route and in the front end amplifiers of
the receivers used to retrieve the signals. By suitably preparing the signals prior to
transmission, by suitable filtering of the received signal plus niose, and by suitable
decision or estimation rukes, high quality images are transmitted through this very
poor channel.
 Signals produced by biomedical measuring devices can display specific
behavior when a patient suddenly changes for the worse. Signal processing
systems can look for these changes and warn medical personnel when suspicious
behavior occurs.
 Images produced by laser cameras inside elderly North Atlantic pipelines
can be automatically analyzed to locate possible anomalies indicating corrosion by
looking for locally distinct random behavior.
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How Modems Work
The purpose of a modulator is to modulate (vary) the carrier properties, while
a demodulator detects the modulation on the carrier wave and recovers the original
waveform at the destination.
Today we don't have all-digital or all-analog networks; we have a mix of the
two. Therefore, at various points in a network, it is necessary to convert between
the two signal types. To infuse digital data onto transmission facilities and vice
versa a two-way computer conversation, the MOdulator and DEModulator are
combined into a single device called a 'modem'.
To understand better how modems work, think of how you use the telephone.
You don't just pick up the receiver and start talking. You have to go through a
series of quite orderly steps: you have to lift the receiver, wait for the dialing tone,
dial each number so it's recognized, wait for the sound of the ringing at the other
end, listen for the other person's voice, say hello, and then alternate your speech
with theirs. If there's no answer, you have to know when to replace the receiver and
hang up the call.
Modems have to behave exactly the same way, exchanging information in a
very 'orderly' conversation. If you've used a dialup modem, you'll have noticed that
your modem opens the line, dials the number, waits for the other modem to reply,
and ''handshakes'', before any real data can be sent or received. If there's no reply,
it'll hang up the line and tell you there's a problem. ''Handshaking'' is the initial part
of the conversation where two modems agree the speed at which they will talk to
one another. If you have a very fast modem but your ISP has only a slow one, the
two devices will be forced to communicate at the slower speed.
Every dialup modem works according to a particular international standard (a
number prefaced by a capital letter V) – and this tells you how quickly it sends and
receives data in bits (binary digits) per second (usually abbreviated bps). The older
standards, such as V.22 (1200 bps), assumed the connection between two
computers was mostly analog; newer standards like V.90 (56,000 bps) achieve
higher speeds by assuming the connection is at least partly digital.
When sending information, the modulation process involves the conversion of
the digital computer signals (high and low, or logic 1 and 0 states) to analog audiofrequency tones. Digital highs are converted to a tone having a certain constant
74
pitch; digital lows are converted to a tone having a different constant pitch. These
states alternate so rapidly that, if you listen to the output of a computer modem, it
sounds like a hiss, a screech, or roar. At the other end of your modem connection,
the computer attached to its modem reverses this process. The receiving modem
demodulates the various tones into digital signals and sends them to the receiving
computer. Actually, the process is a bit more complicated than sending and
receiving signals in one direction and then another. Modems simultaneously send
and receive signals in small chunks. The modems can tell incoming from outgoing
data signals by the type of standard tones they use.
Depending upon how your computer is configured and your preferences, you
can choose between several modem types.
External modems have their own power supply and connect with a cable to a
computer's serial port. The advantages of external modems are that they do not
drain any power from the computer, you can turn off the modem to break an online
connection quickly without powering down the computer and you can monitor
your modem's connection activity by watching the status lights.
Internal modems, usually installed in the computer you buy, are activated
when you run a communication programme and are turned off when you exit the
programme, which is especially useful for novice users. The major disadvantage
with internal modems is their location: when you want to replace an internal
modem, you have to go inside the computer case to make the switch.
PC Card modems, designed for portable computers and fit into the PC card
slot on notebook and handheld computers. Except for their size, PC Card modems
are like a combination of external and internal modems. The cards are powered by
the computer, which is fine unless the computer is battery-operated: running a PC
Card modem drastically decreases the life of your batteries.
Wireless modems transmit the data signals through the air instead of by using
a cable. They sometimes are called a radiofrequency modem. This type of modem
is designed to work with cellular technology, and wireless local area networks.
Wireless modems are not yet perfected, but the technology is rapidly improving.
Digital Modulation Techniques
Like analog modulation, digital modulation alters a transmittable signal
according to the information in a message signal. However, in this case, the
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message signal is a discrete-time signal that can assume finitely many values.
Amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift
keying (PSK) are basic digital modulation schemes.
ASK refers to a type of amplitude modulation that assigns bit values to
discrete amplitude levels. The carrier signal is then modulated among the members
of a set of discrete values to transmit information.
FSK is a frequency modulation scheme in which digital information is
transmitted through discrete frequency changes of a carrier wave. The simplest
FSK is binary FSK (BFSK). BFSK literally implies using a couple of discrete
frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is
called the mark frequency and the "0" is called the space frequency.
PSK uses a finite number of phases, each assigned a unique pattern of binary
bits. Usually, PSK systems are designed so that the carrier can assume only two
different phase angles and each change of phase carries one bit of information, that
is, the bit rate equals the modulation rate. If the number of recognizable phase
angles is increased to four, then 2 bits of information can be encoded into each
signal element; likewise, eight phase angles can encode 3 bits in each signal
element. Although any number of phases may be used, two common PSK
variations are "binary phase-shift keying" (BPSK) which uses two phases, and
"quadrature phase-shift keying" (QPSK) which uses four phases.
In practical systems the signal is separated into the set of independent
components: I (In-phase) and Q (Quadrature). These components are orthogonal
and do not interfere with each other. This may be considered as follows: the
inphase component will be the real value of the signal and the out of phase
component will be 900 phase shift version of the signal. A simple way to view this
is by defining a signal as a vector. The signal can be expressed in polar form as a
magnitude and a phase. The phase is relative to a reference signal (the carrier), the
magnitude is either an absolute or relative value. On a polar diagram, the I axis lies
on the zero degree phase reference, and the Q axis is rotated by 90 degrees. The
speed at which the vector rotates around the circle is the frequency of the sine
wave.
76
I-Q representations are typically used in digital communications where the
amplitude, phase, frequency, or a combination of two of these characteristics, is
modulated (varied) to transmit the information signal. I-Q representation provides
an effective way to visualize and measure the quality of modulation.
Amplitude and phase can be modulated simultaneously and separately, but
this is difficult to generate, and especially difficult to detect. This can be improved
by combining ASK and PSK. This combined modulation technique is known as
Quadrature Amplitude Modulation (QAM). QAM is the encoding of information
into a carrier wave by variation of the amplitude of both the carrier wave and a
'quadrature' carrier that is 90° out of phase with the main carrier in accordance with
two input signals. What this actually means is that the amplitude and the phase of
the carrier wave are simultaneously changed according to the information you want
to transmit.
Each of these techniques has a number of variations. Generally speaking,
digital modulation has many advantages over the analog modulation. It provides
more information capacity, compatibility with digital data services, higher data
security, better quality communications, and quicker system availability. Because
of this digital modulation finds more and more applications in both wired and
wireless transmissions.
The Evolution of Telephone Cable
When Alexander Graham Bell invented the telephone over 100 years ago the
telephone lines were separate lines that connected pairs of telephones. To connect
private telephones with the central interconnection facility telephone lines were
needed.
The first telephone lines were single grounded wires made of iron or steel,
placed on telephone poles or attached to racks on rooftops. Those lines were
inherently noisy. Phosphor bronze wires and compound copper steel wires were
made in attempts to decrease the noise in the lines. The benefits of using copper
conducting wire were not available until Thomas Doolittle developed the process
for hard drawn copper wire in 1877. This wire was strong enough for overhead
wires and copper took over the telephone wire market.
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Early telephone cables with several wires relied upon the technology used in
the manufacture of telegraph cables. Gutta percha and various rubber compounds
were used for insulating and water proofing the telegraph and early telephone
cables. Telephone cables were employed for aerial, underwater and underground.
By 1887 all of the newly manufactured cables were metallic circuit cables. Some
of the cables contained up to 100 copper wires. They were insulated with cotton,
cotton impregnated with paraffin, gutta percha or a rubber compound, and then
wrapped in lead.
There was a large demand for telephone cables as they were needed to replace
the large number of aerial wires in the cities. In the 1880's the major telephone
cable concerns were noise elimination, waterproofing and fitting more wires in
each cable. The technique of wrapping the conducting wires in lead was developed
to eliminate electromagnetic noise in the lines. Other insulating techniques, such as
covering the insulated wires with tin foil and using additional insulating layers,
were employed. Techniques for impregnating the lead tubes after the conducting
wires were drawn through with melted paraffin, resin, or high test illuminating oil
were used to protect the insulation from moisture. By the late 1890's telephone and
electric power cables were laid underground in conduits made of creosoted wood.
Then the multiple duct vitrified clay conduit became the main type of underground
construction used. A separate square hole was provided for each cable, and when
more ducts were required sections of conduit could be added.
The general complaints of the poor voice transmission over the telephone
cables were still present. There were two major improvements made to telephone
cable in the late 1880's. The first was the issuance of a specification for a standard
telephone cable, which outlined a metallic circuit or twisted pair cable. The wires
were made of copper and covered with at least two layers of cotton and sheathed in
a 97% lead, 3% tin alloy pipe. The spaces in the core and between the core and the
pipe were filled with an insulating material. A two inch diameter cable could
contain up to 52 pairs of wires. The second improvement was the development of
paper insulated dry core cable, where the lead tin alloy sheathing now provided
adequate water proofing. By 1891 dry core paper insulated cable was the standard.
The size of the conductor and the electrostatic capacity requirement were further
reduced and greatly decreased the noise in the lines.
Improvements were continually being made to the telephone cable. Some of
them were made possible because of the improvements made in other areas of
78
telephony such as transmitters, receivers, coils and switchboard circuits. The next
major step was loading of the telephone lines. Loading the telephone cables
increased transmission efficiencies. In 1912 a new 1% antimony, 99% lead alloy
was developed for cable sheaths. This material was more economical than the lead
tin alloy pipes, it had good tensile strength, corrosion resistance, and the
mechanical properties necessary for aerial and underground cables. Another
improvement was the invention of the repeater, which amplified voice signals.
Carrier systems or multiplexing enabled a single pair of wires to be used for
multiple calls.
The end of the 19th and the beginning of the 20th centuries were a time of
change and rapid expansion in the telephone industry. The telephone went from
being a novelty item that only a few could afford, to what most consider a
necessity today. Some of the more recent improvements are the use of plastic
insulation and the development of coaxial cable which occurred during World War
II. Up to 600 conversations could be transmitted over two coaxial cables. Today
most of the improvements in telephone cables have centered around sending more
information at a faster rate over the same wires. One area of interest is in the
development of ADSL or asymmetrical digital subscriber line. Telephone cable has
come a long way since 1877, and the technology is still being improved.
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СОДЕРЖАНИЕ
UNIT 1
Text 1. The Engineering Profession in the 21st century..................... ...3
Text 2. What Does an Engineer Do?......................................................6
UNIT 2
Text 1. Telecommunications Fundamentals..........................................12
Text 2. The Development of Telecommunications................................16
UNIT 3
Text 1. Types of Signals........................................................................22
Text 2. Signal Transmission..................................................................26
UNIT 4
Text 1. Modulation................................................................................32
Text 2. Multiplexing.............................................................................35
UNIT 5
Text 1. Frequency and Phase Modulation.............................................42
Text 2. Amplitude Modulation.............................................................46
UNIT 6
Text 1. Transmission Media..................................................................51
Text 2. Wire Media Types.....................................................................55
UNIT 7
Text 1. Fiber Optics...............................................................................60
Text 2. Wireless Media.........................................................................64
ADDITIONAL TEXTS...............................................................................69
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