LESSON
2
TELECOMMUNICATIONS.
WHAT IS IT AND HOW DOES IT
WORK?
I. Consider the
following
questions in
the group of
four. A
spokesperson will report
on your discussion
to the
whole group.
1. Why do you think telecommunications plays a vital role in our daily life?
2. Could you give us any examples of
telecommunications systems?
3. What kinds of telecommunications systems do you use?
4. Can you imagine your life without
them?
5. What can you
say about the further
development of telecommunications?
II.
Read the text below and
check
its comprehension.
Telecommunications:
what is it and how does
it work?
Telecommunications embraces all devices and systems that transmit elec-tronic signals across long distances. Telecommunications
allows people around the world to contact one another,
to access information instantly, and
to com-municate from remote areas. Telecommunications
usually involves a sender of
information and one or more
recipients linked by a technology,
such as a tele-phone system, that transmits information from one
place to another. Telecom-munications
devices convert different types of
information, such as
sound and video, into
electronic signals. The signals
can then be transmitted by means of
media such as telephone wires or radio waves. When a signal
reaches its des-tination, the
device on the receiving end
converts the electronic signal
back in-to an understandable message, such as sound over a telephone, moving ima-ges on a television, or words and pictures on a computer screen. Telecommu-nications enables people
to send and receive personal messages across
town, between countries, and
to and from outer space. It also
provides the key medi-um for news, data, information and entertainment.
Telecommunications messages can be sent in a variety of ways and by a wide range of devices. The
messages can be sent from one sender to a single receiver (point-to-point)
or from one sender to many receivers
(point-to-multi-point). Personal communications,
such as a telephone conversation between two
people
or a facsimile (fax) message (see Facsimile
Transmission),
usually involve point-to-point transmission. Point-to-multipoint
telecommunications, of-ten called
broadcasts, provide the basis for commercial radio and television programming.
How Telecommunications
Works
Telecommunications
begin with messages that are
converted into electronic signals. The signals are then
sent
over a medium to a receiver,
where
they are decoded back
into a form that the person
receiving a message can understand. There are
a variety of ways to create and
decode signals, and many different ways to transmit signals.
Creating
and Receiving
the
Signal
Devices such as the telegraph and telephone relay messages
by creating modulated electrical impulses,
or impulses that change in a systematic way. These impulses are then
sent by wires, radio waves,
or other media to a recei-ver that decodes the modulation. The
telegraph, the earliest method
of deliver-ing telecommunications, works by converting the contacts
(connections between
two conductors that permit a flow of
current) between a telegraph key and
a metal conductor into electrical impulses. These impulses are sent along a wire to a
receiver, which converts the impulses into short
and long bursts of sound or into dots and dashes on a simple printing device. Specific
sequences of dots and dashes represent letters of the
alphabet. In the early days of
the telegraph, these
sequences were decoded by telegraph
operators (see Morse code, Inter-national).
In this way, telegraph operators could transmit and receive letters that spelled words. Later versions of the telegraph could decipher letters and
numbers automatically. Telegraphs
have been largely replaced by other
forms of telecommunications, such as
fax machines and electronic mail (e-mail), but they are still used in some
parts of the world to send
messages.
The telephone uses
a diaphragm
(a small membrane) connected to a mag-net and a wire coil to convert
sound into electrical impulses. When
a person speaks into the telephone’s
microphone, sound waves created by the voice move the diaphragm,
which in turn creates electrical impulses that are sent along a telephone wire. The
receiver’s wire is connected to a speaker,
which converts the modulated electrical
impulses back into sound.
Broadcast radio and cellular radio telephones are
examples of devices that
create signals by modulating radio
waves. A
radio wave is one
type of electro-magnetic radiation, a
form of energy that travels in waves. Microwaves
are
also electromagnetic waves, but with shorter wavelengths and higher frequencies. In telecommunications, a transmitter creates and emits
radio waves. The
trans-mitter electronically encodes sound or other
information onto the radio waves by varying
either the amplitude (height) of the radio waves, or by varying the frequency (number) of the waves within an established
range (see Frequency Modulation).
A receiver (tuner) tuned to a specific frequency or range of frequ-encies will pick up the modulation added to
the
radio waves. A speaker connec-ted
to the
tuner converts the modulation back
into sound.
Broadcast television works in a similar fashion. A television
camera takes the light reflected
from a scene and converts it into an electronic
signal,
which is transmitted over high-frequency radio waves. A television set
contains a tuner that receives the signal and uses
that signal to modulate the
images seen on the picture tube. The picture
tube contains an electron gun
that
shoots electrons onto a
photo-sensitive
display screen. The
electrons illuminate the
screen whe-rever
they fall, thus creating moving pictures.
Telegraphs, telephones, radio, and
televisions all work by modifying electronic signals, making the
signals imitate, or reproduce, the original
message. This form of
transmission is known as analog
transmission. Computers and other
types of electronic equipment, however, transmit digital information. Digital technolo-gies convert a message into electronic form
first by measuring different qualities of
the message, such as the pitch and volume
of a voice, many times. These measurements are then encoded into multiple series of
binary numbers, or 1s and 0s. Finally, digital technologies create
and send electrical impulses that correspond to the series of 1s
and 0s. Digital information can be
transmitted faster and more clearly
than analog signals, because the electrical impulses only need to correspond to two digits and not
to the full range of qualities
that compose the original message, such as the pitch and volume of a human voice. While digital transmissions can be sent over wires, cables or radio
waves, they
must be decoded by a digital receiver.
New digital telephones and televisions
are being developed to make
telecommunications more efficient.
Most personal computers communicate with each other and
with larger net-works, such as the Internet, by using the ordinary telephone
network.
Since the telephone network functions
by converting sound into electronic signals,
the computer must first convert its digital
data into sound. Computers
do this with a device called a modem,
which is short
for modulator/demodulator. A mo-dem converts the stream of 1s and 0s from a computer into an analog signal that can then be transmitted over the telephone network, as
a speaker’s voice would. The modem of the receiving computer demodulates the analog sound signal back into a digital form that
the computer can understand.
Transmitting the
Signal
Telecommunications systems deliver messages
using a number of different
transmission media, including
copper wires, fiber-optic
cables, communication satellites, and microwave radio. One
way to categorize telecommunications me-dia is to consider
whether or not
the media uses wires. Wire-based
(or wireline) telecommunications provide the initial link between most
telephones and the te-lephone network, and
are a reliable means for
transmitting messages. Telecom-munications without
wires, or
wireless communications, use technologies such
as cordless telephones, cellular
radio telephones, walkie-talkies, citizens
band (CB) radios, pagers, and
satellites. They offer
increased mobility and flexibility.
Wires and cables were the
original medium
for telecommunications and
are still the primary means for telephone connections. Wireline transmission evolved
from telegraph to telephone service and continues to provide the
majority of te-lecommunications
services. Wires connect telephones
together
within a home or business and also
connect these telephones to the nearest telephone
swit-ching facility.
Other wire line services employ
coaxial cable, which is used by
cable tele-vision to provide hundreds of
video channels to subscribers.
Much
of the con-tent transmitted by the coaxial
cable is sent by satellite to a central
location known as the
head end. Coaxial
cables flow from the head end throughout
a community to individual residences and
television sets.
Because signals wea-ken as
distance from the head end
increases, the coaxial cable network inclu-des amplifiers that process and
retransmit the television signals.
Fiber-optic
cables
are made of specially treated
glass that can transmit sig-nals in the form of pulsed beams of laser light. Fiber-optic cables carry many times more information than copper wires
and are able to transmit several
te-levision channels or thousands of
telephone conversations at the same
time. Fiber-optic technology is being used to replace copper wires in transoceanic cables and cables in other areas where large amounts of data are sent. New improvements promise cables that can
transmit millions of telephone
calls over a single fiber.
Wireless telecommunications use radio waves, sent through space from
one antenna to another, as the
medium for communication. Radio waves
are used for receiving AM and FM
radio and
for receiving television. Cordless telephones and wireless radio telephone services, such as cellular radio telephones and pagers, also use radio waves. Telephone
companies use microwaves to send signals over long
distances. Microwaves
use higher frequencies than
the radio waves used for AM, FM, or cellular telephone transmissions
and they can
trans-mit larger amounts of data more efficiently. Microwaves have
characteristics similar to those of light waves,
and transmit pencil-thin beams that can
be re-ceived using dish-shaped antennas. Such
narrow beams can be focused to a particular destination and provide
reliable transmissions over short distances on earth.
Even
higher and narrower beams
provide the high-capacity
links
to and from satellites. The high frequencies easily penetrate the ionosphere
and provide a high-quality signal.
Communications satellites
provide a means
of transmitting telecommunica-tions all over the globe, without the need for a network of wires
and cables. They orbit the earth at a
speed that allows them to stay above the same place on the earth at all times. This type of orbit is called
geostationary orbit. The satellites receive transmissions from earth and
transmit them back to numerous earth station receivers scattered within the
receiving coverage area of the satellite. This relay function makes it possible
for satellites to operate as "bent pipes," that is, wireless transfer
stations for point-to-point and point-to-multipoint transmissions.
Communications satellites are used by telephone and television companies to
transmit signals across great distances. Ship, airplane, and land navigators
also receive signals from satellites to determine geographic positions.
Telecommunications
Systems
Individual people, businesses, and
governments use many different types of telecommunications systems. Some
systems, like the telephone system, use a network of cables, wires, and
switching stations for point-to-point communication. Other systems, such as
radio and television, broadcast signals through space, which can be received by
anyone who has a device to receive them. Some systems make use of several types
of media to complete a transmission. For example, a telephone call may travel by
means of copper wire, fiber-optic cable, and radio waves as the call is sent
from sender to receiver. All telecommunications systems are constantly evolving
as telecommunications technology improves.
Telegraph
Telegraph services use both
wireline and wireless media
for transmissions. Soon after the introduction of the
telegraph in 1844, telegraph wires
spanned the country. Telegraph
companies maintained a system of wires and offices located in numerous cities.
A message sent by telegraph was called a tele-gram. Telegrams were printed
on paper and delivered to the receiving party by the telegraph company. With
the invention of the radio in the early 1900s, telegraph signals could also be
sent by radio waves. Wireless telegraphy made it practical for oceangoing ships
as well as aircraft to stay in constant contact with land-based stations.
Telephone
The telephone network also uses both wireline and wireless methods to
deliver voice communications between people, and data communications between
computers and people or other computers. The
part of the telephone
network that currently serves individual residences and many businesses
operates in an analog mode and relays electronic signals that are continuous, like the human voice. Digital
transmission is now used in some sections of the telephone network that send
large amounts of calls over long distances. However, since the rest of the
telephone system is still analog, these digital signals must be converted back
to analog before they reach users. The telephone network is stable and
reliable, because it uses its own wire system that is powered by low-voltage
direct current from the telephone company. Telephone networks modulate voice
communications over these wires. A complex system of network switches maintains
the telephone links between callers. Telephone networks also use microwave
relay stations to send calls from place to place on the ground.
Comprehension Check Up
1. What
do telecommunications mean? 2. What is telecommunications used
for? 3. How can telecommunications messages be sent?
4.
How does the tele-graph relay
messages? 5. How does the telephone create
signals? 6. What wa-ves are used in telecommunications? 7.
How does
broadcast television
work? 8. Can you explain the difference between analog and
digital transmission?
9. What makes telecommunications more efficient? 10. What devices convert
digits into sound? 11.
What kinds of transmission media do you know? 12. What
do you know about applying wires and cables? 13. Where are coaxial cables employed? 14. What are the advantages of
fiber-optic cables? 15. What is the difference between using radio waves and microwaves? 16. What have you learnt about communications satellites?
III.
Choose the best answer.
1. The
word frequency means …
a) a message;
b) telegraph; c) a number of repetitions; d) media.
2. The word microwave
refers to…
a) a beam; b) a very short wave; c) a very long wave; d) wavelength.
3. The
best
explanation of the word network
might be …
a) connected system; b) broadcast;
c) matrix; d) complex system of lines that cross.
4. The
word diaphragm implies
…
a) a magnet;
b) a wire coil; c) a microphone; d) a
small membrane.
5. The
word head end
means …
a) a central location; b) individual residence; c) analog transmission; d) an amplifier.
6. The
word data implies
…
a) a season; b) the day of a month; c) a
number; d) facts, things certainly known.
7. The
best explanation of the word satellite might
be …
a) a planet moving round another planet; b) an artificial object put in
space; c) a person, state depending
upon taking the lead from another; d) a walkie-talkie.
8. The
word broadcasts
refers to …
a) bursts of sounds; b) point-to-point
telecommunications; c) moving
picture; d) point-to-multipoint
telecommunications.
9. The
word subscriber means …
a) a painter; b) a person who subscribes word combination;
c) a speaker; d) a person who sings.
10. The
verb to convert information implies
…
a) to receive information; b) to send
information; c) to change from one form into another; d) to
apply
information.
11. The
word message refers to …
a) a letter; b) a piece of news or a request, send to smb; c) an error; d) a connection.
12. The word wire
implies …
a) telephone; b)
pipeline; c) wavelength; d) metal
drawn out into the form of
a thread.
13. The word transmission means …
a) travelling; b) smth. transmitted
or being transmitted; c) change; d) trans-lation.
14. The verb to
encode refers to
…
a) to send signals over long
distances; b) to focus on a particular
destina-tion; c) to operate in high frequencies; d) to put (a
message) into code.
IV.
Use the
right verb from those given below.
to create, to contain,
to replace, to employ, to decode to transmit, to emit, to deliver, to allow, to
involve, to travel to communicate, to provide.
1. Telecommunication systems … messages using a number of different transmission media. 2.
Wireline transmission … the majority of telecommuni-cation services. 3. A
transmitter … and … radio waves. 4. The picture tube … an electron gun. 5.
Computers … digital information. 6. Telegraphs
… by fax machines and e-mail. 7. Some
wireline services … coaxial
cable. 8. Tele-communications usually … a sender of information and one or more recipi-ents linked by
a technology, transmitting information from one place to another.
V.
Are the following statements True or False?
1. Nowadays Telegraphs are widely
used in all parts of the world. 2. Tele-communications allows people around the world
to contact one another and to access information instantly. 3. Fiber-optic
cables carry less information than copper wires can. 4. Computers and other types of electronic equipment transmit
analog information. 5. Telephone
companies use microwaves to send signals over long distances. 6.
Computers convert their data into sound with a device called a memory.
VI.
Divide
the text into paragraphs.
VII.
Express the main idea of
each
paragraph
in one sentence.
VIII.
Summarize the
text and be ready to retell it.
IX.
Tell us about the advantages and disadvantages of
using telecommu-nications.