Download COMMUNICATION SYSTEMS (5marks)

COMMUNICATION SYSTEMS
(5marks)
The setup used to transmit information from one
point to another is called as communication
system
PARTS OF COMMUNICATION SYSTEM
• Transmitter
#Transmits the message through the communication channel.
#converts the message from the source into a suitable form.
• Communication channel (Transmission medium)
#Medium or the physical path that connects a transmitter and the
receiver.
#Carries the modulated signal from transmitter to the receiver.
• Receiver
#Receives the signal and converts back into its original form.
TRANSMITTER
• A setup which transmits the message from source to the
receiving end through the communication channel.
MAIN FUNCTION :# Modify the signal into a suitable form.
# Transmit the signal through the channel.
BASIC COMPONENTS:#Message signal generator
# Modulator
#Antenna
SCHAMATIC DIAGRAMS
• TRANSMITTER
Antenna
Microphone
Transducer
MODULATOR
AMPLIFIER
Converts the signal into
required form
Increases the strength
of the signal
Transmits
modulated
& amplified
signal into
the
medium
RECEIVER
• A set up that receives the transmitted signals and converts
them back into their original form.
MAIN FUNCTION :#Receives the selected signal through antenna.
#Amplifies it
# Converts it into required form.
BASIC COMPONENTS:# Antenna
#Tuner circuit
#Demodulator
# Audio amplifier
Schematic diagram
• RECEIVER
Antenna
Receives the
modulated &
amplified
signal from
the medium
Microphone
TUNABLE
AMPLIFIER
Tunes the receiver
to selected station
&boosts up the
signal from desired
station
DEMODULATOR
Retrieves back
the original signal
from the
modulated signal
AUDIO
AMPLIFIER
Amplifies the
required
audio signal
Transducer
BLOCK DIAGRAM OF
COMMUNICATION SYSTEM
Information
source
Message signal
Transmitter
Transmitted
signal
Channel
Noise
Received
signal
Receiver
Message signal
User of
information
Terms to remember:1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Transducer
Signal
Noise
Transmitter
Receiver
Attenuation
Amplification
Range
Bandwidth
Baseband
Modulation
Demodulation
Repeater
TYPES OF COMMUNICATION SYSTEMS
According to
the nature of
information
source
1. Speech
transmission
2. Audio visual
transmission
3. Facsimile
(FAX)
According to
the mode of
Transmission
1.Analog
communication
2. Digital
communication
According to
the method
of
transmission
1.Line communication
a)Two wire line
communication
b)Coaxial cable
c) Optical fiber cable
2. Space
communication
a) Ground wave
communication
b)Space or
tropospheric wave
communication
c)Sky wave or
ionospheric wave
communication
According to
the type of
modulation
A) Sinusoidal carrier
waves
1)Amplitude modulation
2)Frequency modulation
3)Phase modulation
A) Pulsed carrier waves
1)Pulse amplitude
modulation
2)Pulse time modulation
3)Pulse code modulation
MODULATION
• The process by which some characteristic, usually an
amplitude, Frequency or phase angle of high frequency
carrier wave is varied in accordance with the instantaneous
value of low frequency audio signal , called the modulating
signal
• Need of modulation
1. To have a practical length of antenna
length of antenna ≈ ʎ/4
1. To have effective power radiation by antenna
Power radiated α (1/ʎ)²
1. For frequency multiplexing
Allows all signals to be received by the antenna
1. To convert a wide band signal into narrow band
Allows more stations to be placed in the same band
CONTINIOUS WAVE MODULATION
1. Carrier wave is a sine wave.
2. Mainly used in analog transmission.
3. Types are:a)Amplitude modulation (Amplitude of carrier
wave is a function of audio or base signal)
b) Frequency modulation (Frequency of carrier
wave is a function of audio or base signal)
c) Phase modulation (Phase of carrier wave is a
function of audio or base signal)
Amplitude modulation
• Amplitude of the carrier wave changes as per the
frequency of modulating signal.
• Frequency of AM wave is equal to the frequency of
unmodulated carrier wave.
• Amplitude of carrier wave is a function of audio or
base signal.
• Bandwidth = twice the frequency of modulating signal
Modulation factor = Change in amplitude of carrier wave
Amplitude of original carrier wave
= Am /Ac
Percentage modulation = µ
µ = (Amax
-Amin)/ (Amax + Amin) x 100%
AMPLITUDE MODULATION
ADVANTAGES
1) Easier method for
transmitting and
receiving audio signals
2)Requires low carrier
frequencies (.5MHz –
20 MHz)
3)More area can be
covered by transmitter.
4)Requires simple and
cheaper transmitters
and receivers.
DISADVANTAGES
1)Suffers from large
amount of noise.
2)Quality of audio signal is
poor.
3)Low efficiency as the
information is
contained only in the
side bands.
FREQUENCY MODULATION
• The frequency of modulated signal is a
function of base (audio) signal.
• Amplitude of modulated signal remains same
as the carrier wave
• The amount of frequency deviation is
proportional to the instantaneous value of
amplitude of the modulating signal.
• The rate of frequency deviation is equal to
the modulating frequency.
FREQUENCY MODULATION
ADVANTAGES
• Highly efficient as all of the
transmitted power is useful.
• Less prone to noise
• No limit for depth of
modulation
• Gives high fidelity (hi-fi)
reception as more number
of useful sidebands are
present
DISADVANTAGES
• BW = 2 ( no of significant
sidebands ) x modulating
frequency. Hence more
channel width is needed.
• FM transmitters and
receivers are more complex
and costly.
• FM reception is limited to
line of sight. Hence less area
is covered.
PROPAGATION OF
ELECTROMAGNETIC WAVES
GROUND WAVE PROPAGATION
• Radio wave travels directly
from one point to another
following the surface of the
earth
• Transmitting and receiving
antennas are close to the
earth’s surface.
• Energy is partially absorbed by
the earth’s surface hence
more attenuation.
• Not suitable for long distance
communication & higher
frequencies.
• Range 500kHz to 1500kHz
• Less affected by atmospheric
conditions
SPACE WAVE PROPAGATION
• Radio wave travels directly
from transmitter to the
receiver following the line
of sight communication
• Transmitting and receiving
antennas are placed as high
as possible from the earth’s
surface.
• Range is limited by earth’s
curvature and the distance
between transmitting and
receiving antenna.
• Range 100 MHz -220 MHz
SKY WAVE OR IONOSPERIC PROPAGATION
• A radio wave directed towards the sky and
reflected by the ionosphere towards the desired
location of the earth is called as sky wave
propagation.
• Due to change (gradual decrease) of refractive
index of earth’s atmosphere, the EM wave bends
at critical angle and sent back to the ground
station.
• Range 2 MHz to 20 MHz.
• Highly affected by atmospheric conditions.