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TABLE OF CONTENT

Unit 1 ..............................................................................................................1
Unit 2 ..............................................................................................................7
Unit 3 ..............................................................................................................11
Unit 4 ..............................................................................................................17
Unit 5 ..............................................................................................................22
Unit 6 ..............................................................................................................27
Grammar review .............................................................................................43


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UNIT 1
SEMICONDUCTORS
Reading
Task 1: Read this passage and find a sentence in which is similar in meaning to each of the

Reverse voltage

Forward current

following sentences

6.0 4.0 2.0
1.0 2.0

Reverse current

Forward voltage

Figure 1
If two crystals of semiconductor material, one of p-type and one of n-type are joined
together a pn junction is formed. This junction can be used as a rectifier and is known as a pn
junction diode.
Figure 1 illustrates what happens when a voltage is applied across a silicon pn junction
diode. The first quadrant of the graph shows the characteristics of the diode when the source is
connected with the positive to the p-side of the junction and the negative to the n-side. In the
other words, the diode is forward biased. With forward bias, the current at first increased slowly.
When the applied voltage reaches about 600 mV, the current rises rapidly. The diode is then a
good conductor. The current will continue to rise with increased voltage but eventually a point
will be reached where the diode is destroyed by heat.
The third quadrant shows the characteristics when the source is connected with the
positive the n- side and the negative to the p-side. When the diode is reverse biased, there is
almost no current flow. The junction is therefore a good rectifier it conducts well in one direction


2
and not all in the other. However, there is a small reverse leakage current, this leakage current
remains substantially constant until what is known as breakdown voltage (Vb) is reached. At this
point, there is a sharp increase in the reverse current. This sudden increase in current is called the
Zener effect.
Normal diodes are never operated in the breakdown region but Zener diode is designed to
make use of the breakdown phenomenon. Because any slight increase in voltage beyond the
breakdown point causes a large increase in current. Zener diodes are often used as a kind of
overspill to protect sensitive circuit from fluctuations in the power supply.
1. The positive of the source is connected to the p-side of the diode and the negative to the
n-side.
2. When a forward voltage is applied across the diode, there is, at first, only a slow rise in

current.
3. The diode allows current to flow freely
4. If a reverse voltage is applied to the diode, it conducts badly
5. There is almost no change in leakage current until the reverse voltage reaches
breakdown point.
Task 2: Meaning from context
Select a word from three alternatives given which is most similar in meaning to the word in
italics as it is used in the reading passage:
1. characteristics (line 5)

2. substantially (line 16)

a. typical behavior

a. almost

b. voltage figures

b. greatly

c. graph

c. hardly

3. sharp (line 17)

4. phenomenon (line 20)

a. slight

a. voltage

b. steep

b. effect

c. cutting

c. result


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5. fluctuations (line 22)
a. rises and falls
b. increases
c. failures

Task 3: Work in-group of three; complete this description of the current-voltage
characteristics of silicon diode. Use the reading passage and Figure 1 to help you.
At first, when a forward voltage is applied, …………………. When the forward voltage
has reached about 600 mV, …………………….. If the forward voltage is further
increased,…………………… .

…….………… only a very small leakage current flows.

When the breakdown voltage is reached ………………… After the breakdown point, any
further increase in reverse voltage causes ………………………
Task 4: Checking facts and ideas
Decide if these statements are true or false. Quote from the reading passage to support your
decisions.

1. The first quadrant of the graph shows the characteristics of the diode in forward bias.
2. For forward voltages over 600mV, the diode conducts well.
3. When the source is connected with the negative to the n-side and the positive to the pside, the diode is reverse biased.
4. When a reverse voltage is first applied, a diode conducts badly.
5. Zener diodes are never used beyond breakdown point.
Task 5: Writing description from graphs
This graph describes the characteristics of a tunnel diode. Use the information it contains to
complete the description below:


Forward current

4

Reverse voltage

P
1.
2
1.
0

0.2 0.1
0.

V
0.1 0.2 0.3 0.4 0.5 0.6

Reverse current

0.
2

Forward voltage

0.

As the forward voltage is increased, the current (1).......................until point P is reached.
P is as known as the peak point. The peak voltage for a germanium tunnel diode is about (2)
............................ After P the current (3) ................. until V. V is known as the valley point.
From P to V the diode has a negative resistance. The forward voltage at V is about (4) ....…........
After the volley point, the current (5) ............…........... with increased voltage and the diode
behaves like a normal diode. When a reverse voltage is applied however, the reverse current
(6)........................... unlike normal diodes.

Further Reading
The transistor
During and after World War II, electronic equipment became so important and so
complex that a substitute for the vacuum tube was required for the continued growth of the field.
In a sense, the answer to the problem was found in the improvements in the use of crystals –
vacuum tubes were replaced by transistors consisting basically of silicon.
Silicon is one of the substances classes as a semiconductor. These substances have a
conductivity somewhere between good conductors like silver, copper, and aluminum, and
insulators like rubber, porcelain, and glass, which permit almost no movement of electrons at all.
Modern transistors are small pieces of semiconductor material such as silicon that have been
treated with impurities so that they possess free electrons at room temperature. Another material
used is a metal called germanium. Germanium, however, is very rare, whereas silicon is


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extremely common – it is the basic element in sand. Another element, selenium, is used in lightsensitive transistors. A number of chemical compounds have also been found suitable for use in
different types of transistors.
The transistor was developed at Bell Laboratories in 1948 by three American scientists, John
Bareen, Walter Brattain, and William Shockley. The transistors created as a result of their work
can perform most of the same tasks as vacuum tubes.
To make a transistor, controlled impurities are introduced into semiconductor material which has
been refined to a high degree of purity. Impurities such as arsenic, antimony, or phosphorous add
readily available electrons, creating an n type of treated or “doped”, semiconducting material.
The elements aluminum and boron, on the other hand, create tiny vacant spots, or holes, that tend
to capture the free electrons. This kind of doped semiconducting material is called the p type.
When n and p types of semiconductors are placed together, current flowing through them is
rectified because the electrons can flow only from n to p. In this way, the transistor is similar to
the diode vacuum tube, but unlike the diode, it has a three-part sandwich like structure. There are
three terminals, called the emitter, the collector, and the base. The base forms the middle part of
the sandwich. The first type of transistor developed for widespread use has an npn structure, the
base being made of p-type semiconductor. The other is called pnp. Depending upon how they are
connected in a circuit, the can perform a wide variety of functions, including those of amplifiers,
switches, and oscillators.
Transistors overcame most of the disadvantages of the vacuum tube. Since they were very small,
they could be packed closely together – observe the difference in size between a radio with tubes
and a transistor radio. They could take rough handling, seldom burned out, did not overheat,
required no warm-up time, and used less current. There were other electronic advantages – they
were inexpensive to manufacture and did not need nearly as much as wiring to connect them.
Transistors were first placed on boards or sheets of insulting materials and wired into a circuit.
Since then printed circuits have replaced complicated wiring systems in many cases. In printed
circuits, transistors are connected by thin lines of copper which aanre boned to the surface of an
insulator.
Task 1: Decide whether the following statements are true or false (T/F) by referring to the
information in the text. Then make the necessary changes so that the false statements
become true.

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1…. Transistor was developed due to the disadvantage of the vacuum tube.
2…. Silicon is a better conductor than aluminum.
3…. Arsenic is an impurity which creates an n type of semiconducting material by adding readily
available electrons.
4…. When n and p types of semiconductors are placed together, current can only flow through
them in on direction.
5…. The transistor performs a lot of functions no matter how they are connected in a circuit.
Task 2: Filling in the spaces of the following sentences with the appropriate words or
phrases, basing on the information in the text.
1. In the …………………… of treated semiconducting material, there are holes from which
electrons have been removed.
2. A transistor has three terminals: the one connected to the middle part of the “sandwich” is the
…………………… and the two outer parts are the ……………………… and the
…………………..
3. …………………….and ……………………… are two of the elements from which
transistors are made.
4. One arrangement of semiconductors in transistors is ………………….. and the other is
……………………..
5. …………………….. is one of the impurities that can create n type semiconducting material.
6. ……………………. is one of the impurities that can create p type semiconducting material.
7. Transistors perform a variety of functions including …………………… of amplifiers,
switches, and oscillators.


7

UNIT 2

PROPAGATION OF WAVES
Reading
A signal from a transmitter may be propagated in three ways: by ground waves, by space
waves and by sky waves. Ground waves travel round the surface of the earth for short distances.
As they travel, they lose energy. This loss of power, or attenuation, depends on the nature of the
surface. Attenuation also varies with the frequency of the signal; the higher the frequency, the
greater the ground wave attenuation. At frequencies above 20 MHz the range is reduced to the
line of sight.
Propagation by space waves applies mainly to very high frequencies. Part of the
transmitted signal travels in a direct line from transmitting antenna to receiving antenna. Partly
the signal is reflected from the ground. The higher the frequency, the greater the possible
ground_ wave reflection. The range of the space wave propagation is restricted to approximately
twice the direct optical path.
The range covered by ground waves and space waves is limited. Greater distances can be
achieved using sky waves. Sky wave propagation depends on the ionosphere.

B
A
Figure 2a
A signal transmitted from point A would not be received at B because of the curvature of
the earth if it were not for the ionosphere. This consists of a number of layers of ionized gas in
the upper atmosphere. If a transmission is directed towards these layers, it will be reflected back
to the earth as shown in Figure 2b.


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A

C

B
Figure 2b

The wave may then be reflected back from the earth to the ionosphere. Indeed it may be
carried right round the earth by successive reflections although it will lose power both in the
earth and in the ionosphere at each bounce. A receiver at point C, which is outside ground wave
range yet closer than B, will not receive the transmission.
The bending effect of the ionosphere depends on the frequency of the signal and the angle of
radiation. The higher the frequency the less the bending. At a certain frequency, signal will pass
straight through the layers and be lost in space. The smaller the angel of radiation, the greater the
distance, which can be covered in one reflection.
At any time there is a maximum usable frequency for transmissions from a given site over a
particular path. This frequency depends on the state of the ionosphere, which varies according to
many factors including the time of the day and the season of the year. The lower the frequency of
a transmission the greater the number of reflections needed to cover the required distance and
hence the weaker signal will be. For this reason, it is best to use a frequency as high as possible
without exceeding the maximum usable frequency as this will cover the required distance with
the smallest number of reflections and hence the least attenuation.
Task 1: Answer these questions about the passage.
1. List three types of propagation.
2. How do ground wave travel?
3. What is attenuation?
4. Name two factors, which affect the attenuation of ground waves?
5. What frequencies are propagated by space wave?
6. Name two ways in which space waves travel.
7. What range have space wave?
8. What controls sky wave propagation?


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9. What is the ionosphere?
10. How do sky waves cover great distances?
11. Name two factors, which determine the bending effect of the ionosphere.
12. What is the maximum usable frequency?
Task 3: Meaning from context
Select a word from the three alternatives given which is most similar in meaning to the word in
italics as it is used in the reading passage.
1. varies with ( line 4 )

3. This ( line 15 )

a. is proportional to

a. the ionosphere

b. is directly proportional to

b. the atmosphere

c. is inversely proportional to

c. transmission

2. approximately ( line 11 )

4. bounce ( line 20 )

a. nearly

a. reflection

b. over.

b. attenuation

c. around

c. receiving

Further reading
Radio waves from a transmitting aerial can travel in one or more of three different ways.
Surface or ground waves: This travels along the ground, following the curvature of the
earth's surface. Its range is limited mainly by the extent to which energy is absorbed from it by
the ground. Poor conductors, such as sand, absorb more strongly than water, and the higher the
frequency, the greater the absorption. The range is about 1500 km at low frequencies (long
waves).
Sky waves: It travels skywards and, if it is below a certain critical frequency (typically 30
MHz), is returned to earth by the ionosphere. This consists of layers of air molecules stretching
from about 80 km above the earth to 500 km. On striking the earth, the sky wave bounces back
to the ionosphere where it is again gradually refracted and returned earthwards as if by "
reflection ". This continues until it is completely attenuated.


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The critical frequency varies with the time of day and the seasons. Sky waves of high
frequencies can travel thousands of kilometers but at VHF and above they usually pass through
the ionosphere into outer space.
Space waves: For VHF, UHF, and microwave signals, only the space wave, giving line
of sight transmission, is effective. A range up to 150 km is possible on earth is the transmitting
aerial is on high ground and there are no intervening obstacles such as hills, buildings, or trees.

Space waves are also used for satellite communications.
Fill in the table, which follow
Task 1: Read the following passage and fill in the blank with appropriate information
Surface waves

Sky waves

Space waves

Frequencies

..............................

..............................

..............................

Travels

..............................

...............................

..............................

Range

..............................

...............................

.............................

Difficulties

..............................

...............................

..............................


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UNIT 3
TRANSMISSION
Reading
We can only communicate information by radio waves by changing the wave in some ways.
This change is known as modulation. The simplest form of modulation is to turn the wave on or
off. This method was used in the early days of radio for telegraphic signals. The wave was
stopped and started to present the dots and dashes of the Morse code by means of a telegraph
key.
Speech and music produce audio frequencies, which cannot be transmitted directly. But
they can be used to modulate radio waves. The modulated radio wave is then transmitted. When it
is received, the wave is demodulated and the original audio- frequency signal is recovered. The
high frequency radio acts only to carry the audio - frequency signal and is called the carrier wave.
The audio - frequency signal is termed the modulating signal.
The wave has three quantities: amplitude, frequency and phase. Any of these quantities can
be modulated. The two commonest methods of modulation are amplitude modulation (AM) and
frequency modulation, (FM).

In amplitude modulation, the amplitude of the carrier wave is changed according to the
amplitude of the modulating signal. The frequency of the carrier is kept constant. Figure 3a
presents part of an audio - frequency signal, which might be generated by a microphone. Figure
3b represents a radio wave of much higher frequency. Figure 3c shows the same radio frequency
wave after it has been modulated by the audio - frequency signal in Figure 3a.

Figure 3a


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Figure 3b

Figure 3c
In frequency modulation, the amplitude of the carrier wave is kept constant, but the
frequency is varied in proportion to the amplitude of the modulating signal. Frequency
modulation has several advantages over amplitude modulation. The most notable is that
reception is less likely to be disturbed. This is because atmospheric disturbances and “noise "
generated in the receiver itself result in a change in the amplitude of the received signal.
However, changes in only the frequency would distort the modulated information.
In FM sound broadcasting, the limit of modulation is usually 75 kHz above and below the
frequency of the unmodulated carrier wave. In other words, FM broadcasts spread 75kHz either
side of the carrier frequency. This is one reason why FM stations broadcasts in the VHF band
(30- 300 MHz) where stations can be spaced more than several hundred kilohertz apart unlike
the medium frequency bands where spacing of only 9 to 10 kHz are common.
Task 1: Find the answers to these questions in the passage, which follows.
(Work as quickly as you can. Try to ignore information, which will not help you to answer these
questions)
1. What is modulation?
2. Which three quantities of a wave can be modulated?

3. Why is frequency modulation better than amplitude modulation?


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Task 2: Meaning from context
Select a word from the three alternatives given which is most similar in meaning to the
word in italics as it is used in the reading passage.
1. form (line 2)

3. these (line 11)

a. change

a. three quantities

b. communication

b. frequencies

c. method

c. methods

2. termed (line 10)

4. constant (line 15)

a. called

a. changed

b. modulated

b. unchanged

c. used

c. varied

Task 3: Checking facts and ideas
Decide if the statements are true or false. Quote from the reading passage to support your
decisions.
1. The first application of radio wave modulation was for telegraphic signals.
2. Phase modulation is commonly used.
3. In amplitude modulation, the frequency of the carrier wave is proportional to the amplitude
of the modulating signal.
4. FM reception is less likely to be disturbed than AM.
5. FM stations broadcast in the VHF band.
Task 4: Now read the passage carefully. Each of these sentences summarizes part of the
passage. Identify the lines summarized.
1. In fm the frequency of the carrier wave is modulated according to the amplitude of the
modulating signal. (lines...)
2. Audio frequencies cannot be transmitted. (line...)
3. The amplitude, frequency and phase of a wave can be modulated. (line...)
4. Fm broadcasts are in the VHF band partly because FM stations require greater spacing.
(line...)


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5. The carrier wave is demodulated by the receiver and the audio - frequency signal
recovered. (line...)
6. No information can be communicated by radio waves without modulating them. (line... )
7. In AM, the amplitude of the carrier wave is modulated according to the amplitude of the
modulating signal. (line...)
8. Stopping and starting the wave is the simplest method of modulation. (line...)
9. Fm is better than AM because there is less interference. (line... )
10. Audio frequencies can be used to modulate high frequency radio waves, which can then
act as carriers of the audio - frequency signal.

Further reading
Radio frequency (AF) waves are used to carry audio frequency (AF) waves over long
distances through the air. The audio signals can be combined with the RF carrier wave in such a
way that it varies the amplitude of the carrier. This gives an amplitude - modulated (AM) carrier
wave (see Figure 3d).

AF signal

RF carrier

Modulated RF carrier

Figure 3d
If frequency-modulated (FM) wave, the audio signal is combined with the RF carrier
wave to vary the frequency of the carrier (see Figure 3e).

AF signal


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RF carrier

FM carrier
Figure 3e
The block diagram of a radio is shown in Figure 3f below. The turner selects the required
RF wave from those picked up by the aerial. The selected RF wave is amplified and passed to the
detector, which separates the audio modulation from the RM carrier wave. The audio frequency
amplifier amplifies the audio signal to make it strong enough to drive the loudspeaker.
aerial
Amplified
Modulated

Amplified AF

Modulated

AF

RF carrier

RF tuner

Loud speaker
RF

Detector or

AF

AF power

Amplifier

Demodulato
r

amplifier

amplifier

Figure 3f
Turner
A typical radio turner circuit consists of an inductor and capacitor connected in parallel
(see Figure 3g). The size of the aerial inductance coil can be kept small by winding it on a ferrite
rod core.

Aerial

C

Figure 3g


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The RF waves fed to the turner cause the circuit to oscillate. The impedance of the circuit
is smallest and the oscillation is greatest at a particular frequency known as the resonant
frequency. This frequency is determined by the values of the inductance and the capacitance. By
using a variable capacitor, the circuit can be tuned to the required radio frequency, and selected

RF wave passed on to the RF amplifier.


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UNIT 4
SWITCHING
Reading
Task 1. Read the following TEXT. As you read, complete Figure 4a.
On the march 10th 1876, in Boston USA, Alexander Graham Bell spoke the first
recognizable words over that was certainly his most famous invention, the telephone. “Mr
Watson, come here. I want you” he called out to an astonished assistant.
It quickly became necessary to link up people using the new invention. This was done
through the telephone exchange. In the first simple exchanges, all calls were handled manually
by the operator. Using the switchboard in front of her, she plugged the line of the subscriber
calling her into the line of the subscriber being asked for.
The idea of an automatic exchange was soon suggested. In 1892, three years after
patenting his ideas, Almon B.Strowger saw his system installed at La Porte, Indiana. Strowger,
an undertaker from Kansas City, found his business was becoming less and less profitable
because the operator always connected calls intended for him to other undertakers.
Strowger’s automatic exchange underwent several modifications over the next fifty years,
but the principle has remained the same ever since. It is known as the “step-by-step” system and
there are still thousands of Strowger exchanges in service throughout the world today.
The next generation of exchanges was first developed in Sweden. Crossbar exchanges as
they are called, consist of a series of vertically and horizontally crossed bars. For the first time a
common control system was used. This made crossbar exchanges cheaper than Strowger, for
each selector could now carry up to ten calls. They were not as noisy as Strowger, either. These
exchanges are electromechanically operated using electromagnets.
In 1948, the invention of the transistor at Bell Telephone Laboratories led to a revolution
in electronics and to the creation of semi-electronic telephone exchanges.

The old mechanical and electromechanical exchanges have now begun to disappear, and
since the 1970s they have started to be replaced by exchanges built around electronic
components. The latest digital switching centers have several advantages over other types of
exchange, for they provide: a substantial reduction in equipment cost; a larger reduction in


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equipment size; shorter procurement times; shorter installation and commissioning times; greater
reliability and reduced running costs; new services for the customer; and new facilities for the
administration
1880

1892

1940s

1948

1970s

…(1)..system

…(2)…system

…(3)…system

…(4)…system

…(5)…system

…………

………..

.…….

Main characteristics of the systems
First,

simple ……..

exchanges.
Connections
manually
established
Figure 4a
Task 2. Answer the following questions:
a. Who invented the telephone? When and where?
b. What did the first operators do?
c. Why did Strowger invent the automatic telephone exchange?
d. What is a “crossbar” system?
e. What advantages does crossbar offer over Strowger?
f. What important development took place in 1948?
g. What are mechanical and electromechanical exchanges being replaced by?

Further Reading
Task 1. Read the following passage about electronic exchange. As you read complete Figure
4b
Classification

Electromechanical exchange

Digital exchange

Transmission type

Analogue transmission

Digital
switching

transmission

and


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Installation

a……..

b………

Maintenance

High maintenance cost

Lower maintenance cost

c…..

d……

Crossed lines

g…..

e……..

h……

Technical comments

rigidity

of

design

wrong i…….

numbers

j…….

f……

k….higher

evolutionary

potential
l……..
Figure 4b
Most of the world’s telephone traffic is still handled by exchanges of electromechanical
design, each with thousands of wear-prone exposed moving parts. Analogue exchanges of this
type are costly to install and maintain, and are subject to familiar faults such as crossed lines,
noise and wrong numbers.
Many of the world’s telecommunications administrations have explored other, digital,
solutions. They are designing networks that offer: a much higher quality of service than before,
using the latest microchip technology with few or no moving parts; less interference than
previously; lower installation and maintenance costs; and much faster connection speed for calls
and fewer wrong numbers than in the past
The main characteristics of a digital exchange are:
1. Integrated Digital Transmission and Switching
Speech and other signals are digitally encoded and a common method of time division
multiplexing is used in both transmission and switching equipment. The main advantage of this
system is that the transmission loss encountered by speech becomes more or less independent of
both distance and the number of exchanges through which a call is routed.
2. Stored Program Control (SPC) is the application of data processing and computer
techniques to an exchange, thus providing a powerful, flexible method of controlling the
operation of the exchange.


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3. Common Channel Signaling (CCS) uses just one (go and return) pair of signaling channels,
not directly associated with the traffic circuits, for performing all the signaling functions of an
entire route which may contain several hundred traffic circuits.
4. Microelectronics technology is the application of solid- state semiconductor technology to
provide components, which range in function from a signal active element (e.g. transistor) to

large scale integrated circuits. Use of this technology offers small physical size and reliability
together with automated design, manufacture and testing. The components are fixed onto printed
circuit boards, and if there is a fault the defective printed circuit board can be taken out and
replaced by another in a matter of seconds.
Task 2.
a. Match each of the headings with one set of functions.
1. stored program control

a. the application of solid -state semiconductors to

2. common channel signaling

provide greater reliability small size and automated

3. integrated digital transmission and design
switching

b. the application of data-programming techniques

4. microelectronics technology

to an exchange, providing greater control and
flexibility in the operative of an exchange
c. the use of one pair of channels not directly
associated with the traffic circuits, to perform all
signaling functions on a complete route
d. speech and other signals are digitally encoded and
a common method of time division multiplexing is
used.

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b. Match the following terms with a suitable explanation
1. an electromechanical exchange

a. a call is incorrectly routed

a. a digital exchange

b. a system in which a varying electrical current

b. a wrong number

transmits the caller’s voice pattern

c. a crossed line

c. an exchange which uses microchip technology

d. analogue transmission

d. the cost of a telephone call

e. call charges

e. during a telephone conversation, you hear another
conversation at the same time
f. a switching centre, the design of which is based on
thousands of moving parts

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UNIT 5
RADIO COMMUNICATIONS
Reading
Task 1. Read the following description on certain types of radio communications. As you
read, fill in Figures 5a, 5b, 5c.
Communicating by radio is a method of sending or receiving sounds, pictures and data
through the air by means of electro-magnetic waves.
We use the airwaves for many purposes: broadcasting most of out local and national
radio and TV stations, in our mobile radio and telephone services, and to communicate on a
global scale through distant satellites, which act as a kind of reflector in the sky, redirecting the
information we send up to them.

Type of communication : a…….
Purpose

:b…….

Earth
Fig 5a
Another important use of this means of communicating is shipping. A ship that is in
difficulty can call the nearest coast station, giving details of its situation and, if necessary, ask for
help. We call this “ship –to- shore” radio. Radio can ensure greater safety in navigation (for
example, to want of bad weather or of hazards in the shipping lanes) and it enables large amounts
of information to be sent over land or water without the support of several hundred kilometres of
wires and cables. Radio networks can, therefore, be cheaper to install but often have fewer

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circuits than cable links. Radar systems also enable air traffic controllers to follow and guide the
light paths of planes from take-off to landing.
Radio-paging systems enable us to be contacted even though we do not have a telephone
within easy reach. It is a way of letting us know that something important has just happened and
that we must act quickly. The system works through a pager or ‘bleeper’, a small receiver about
the size of a packet of cigarettes, which you can keep in your pocket. When people want to
contact you, they simply pick up the nearest telephone, dial your personal paging number free of
charge, and wherever you are in the coverage area, your pager will bleep. (You must, however,
be love, not below ground lever, for the signal will not get through if you are underground). The
bleeping informs you that someone is calling you. You can identify up to four callers on some
types of equipment. The most modern type of radio-pager displays the number of the telephone
the caller is ringing from. The main advantage of radio-paging is that you can be contacted
wherever you are, even though you may be a long way from a telephone set.

Type of communication : c…….

Type of communication : e…….

Purpose

Purpose

:d…….
Fig 5b

:f…….
Fig 5c

Many companies which have personnel on business trips have found that radio-paging

improves their competitive position and allows them to be more responsive to a lot of their
customers’ needs. It also increases company efficiency by cutting out many unnecessary and
expensive journeys that are sometimes made by salesman. This saves time and fuel costs.


24
Doctors can be contacted immediately and return to their surgery or hospital, thus possibly
saving the life of a very sick patient.
Task 2. Answer the following questions:
a. How does the text define radio communications?
b. What examples does the text give of radio communications?
i. ship-to-shore radio

ii. …..etc

c. Why can radio networks be cheaper to install?
d. What equipment does the radio-paging user need?
e. Where does the user keep this equipment?
f. Where must you do not go if you wish to be contacted by radio-paging?
g. How can companies benefit from radio-paging? (give three ways)
h. Why do many doctors carry a bleeper?

Further Reading
Task 1. Read the description of the Nordic Mobile Telefone System (NMT). As you read,
complete Figure 6d
Description of System
The NMT system is made up of the following component parts: MTX (Mobile
Telephone Exchange) is the brain of the system and is technically the most complicated part.
The MTXs form the interface between the NMT system and fixed telephone network. Whereas
signalling and other system components of NMT are the same in all Nordic countries, their

telephone networks differ in some respects. One of the functions of the exchanges is therefore to
compensate for these differences.
The Base Stations are intermediary links without switching function between the wire and radio
transmission. There will be about 1,000 base stations when the system is developed to full
capacity.
The Mobile Stations i.e. the subscriber equipment, will be available in various forms.e.g…
vehicle-borne, portable or of coin-box type. A mobile station is owned or leased by the
subscriber and must be type-approved by the Administrations.