ĐIỆN tử VIỄN THÔNG DTVT2 nhom4 bai6 txt khotailieu

Radio
D8-DTVT2
Group 4 :
Ngô Đắc Quân
Lê Văn Hoạch
Phùng Thế Quảng
Phạm Thị Minh Phượng
Nguyễn Thị Phương
Nguyễn Nhật Thư
Nguyễn Tuấn Anh


Task 1: Turning in
Study this diagram. Name five things, other than radio which make
use of electromagnetic waves.
Short wavelength
Long wavelength
Low frequency
High frequency
Visible light

Task 2: Reading Information transfer
Proagation of radio waves
Radio waves from a transmitting aerial can travel in one or more of three different
ways.
Surface or ground wave
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 1500km at low
frequencies (long waves).

Table 1
Frequencies
Travels
Range
Difficulties

Task 3: Work in pairs

Surface wave
Low Frequency
Along the ground
1500 km
Absorption by the ground


Sky wave
It travels skywards and, if it is below a certain critical frequency (typically
300MHz), is returned to earth by the ionosphere. This consists of layers of air
molecules stretching from about 80km above the earth to 500km. On striking the
earth, the sky wave bounces back to the ionosphere where it is again gradually
refracted and returned earthwards as it by ‘reflection’. This continues until it is
completely attenuated.
The critical frequency varies with the time of day and the seasons. Sky waves of
high frequencies can travel thousands of kilometres but at VHF and above the
usually pass through the ionosphere into outer space.
Space wave
For VHF, UHF, and microwave signals, only the space wave, giving line of sight
transmission, is effective. A range of up to 150km is possible on earth if the
transmitting aerial is on high ground and there are on intervening obstacles such
as hills, buildings, or trees. Space waves are aslo used for satellite

communications

Frequencies
Travels
Range
Difficulties

Sky wave

Space wave

below 300MHz
Skywards and returned to
earth by the ionosphere

VHF, UHF

Thousans km
attenuated by refraction

line of sight transmission
150km
hills, buildings, or trees

Task 4: With the help of Table 1 and 2, label the diagram using these
labels:
1-a transmitting aerial
2-e surface wave

3-d space wave
4-c sky wave
5-b receiving aerial

Task 5: Link these pairs of actions. Use short ways when this is
possible.
1, When the switch is closed, current flows through the primary of the
Transformer
2, On striking, The radar signal is reflected
3, When discharging quickly, A cell may become hot
4, On receiving signals from the remote control, the TV follows your instructions.
5, On receiving the reflected signal, the signal is compared with the transmitted
signal.
6,When choosing a course in electronics, you think carefully about your future.
7, On striking a high building, microwave signals are deflected.
8, When making a recording, you should ensure the recording levels are
satisfactory.
9, On detecting an intruder, the alarm triggers an audible warning.
10,On pressing remote control button, the television set changes channel.

Task 6: Speaking practice

Task 7: Word study Word formation
Verb
Noun (component)

Noun (property)

Absorb
Attenuate

Communicate
Conduct

Absorption
Attenuation
Communucation
Conductivity

Absorber
Attenuator
Communicator
Conductor


Induct
Modulate
Reflect
Resist

Inductor
Modulator
Reflector
Resistor

Induction
Modulation
Reflection
Resistance

Task 9: Technical Reading

1 : AF

audio frequency

2 : RF

Radio frequency

3 : AM

Amplitude modulated

4: FM

Frequency modulated

Task 10: Identify the waves. Use these terms:
a : RF carier
b: AF signal
c: AM carrier
d: FM carrier

Task 11: Explain what happens at each stage in this flowchart,
which shows how a radio works. The first and last stage are done for
you.
Component

Function

Aerial

Receiver weak RF signals

RF tuner

Modulater Rf carrier


RF amplifier

Amplifier RF wave

Detector

Detect RF signal

AF amplifier

Amplifier AF signal

Loudspeaker

Convert the audio signal into sound

Task 12:.
Radio waves are very popular in today's life. It was used extensively in the field of
communication today. Here are all described block diagram of a simple radio
receiver.
Diagram includes seven components. Aerial is receiving antenna, receiver RF
carrier is modulated and put into an amplifier. Audio signal is separated from the

carrier and into the audio signal amplifier and power amplifier signal. audio signal
after amplification was converted and emitted speakers.