Communications - Chapter Notes, Class 12 Physics PDF Download

 Page 1


ABHA DHAMIJA PHYSICS CLASSES
H.No. 1282, Sector-7, KARNAL Ph.: 8950171870
* Communication : It is an act of transmission and reception of information.
* Elements of Communication System : The three necessary elements are :
*  Transmitter *   Communicatin Channel *  Receiver
* Block Diagram of Communication System :
* Terms used in Communication :
* Signal : It is a single valued function of time that carries information. It is usually in electrical form
suitable for transmission. The signal can be analog or digital.
* Transducer : It is a device that converts one form of energy to another.
e.g.: (1) A Photocell : Which coverts light energy into electrical energy.
(2) Microphone : Which converts sound energy into electrical energy.
(3) Loudspeakers : Which convert electrical energy to sound energy.
* Noise : It is the disturbance in the transmission and processing of message. This may be due to channel
imperfection or some source inside/outside the system
* Transmitter : It is an arrangement that converts the message singal to a suitabe form for transmission
and then transmit it through some suitable communication channel.
* Receiver : It is an arrangement that picks up the information signal and process it to reproduce the
message signals in suitable form.
* Attenuation : It is the loss of strength of signals during its propagation through communication channel.
* Amplification : It is process of increasing the strength of transmitted signal using some electronic
circuit. Amplification compensates attenuation.
* Range : The largest distance between transmitter and receiver upto where the signal is received in
proper strength.
* Band Width : It is the range of frequencies over which communication system works.
* Modulation : It is the phenomenon of super imposing a low frequency message signals on a high
frequency carrier wave called as modulated wave which is transmitted.
* Demodulation : It is the reverse of modulation. It is the phenomenon of retrieval (regaining) of information
from the modulated wave.
C O M M U N I C A T I O N S
S U B - T H 2 0 1 5 / X I I
T H - 1 5
Page 2


ABHA DHAMIJA PHYSICS CLASSES
H.No. 1282, Sector-7, KARNAL Ph.: 8950171870
* Communication : It is an act of transmission and reception of information.
* Elements of Communication System : The three necessary elements are :
*  Transmitter *   Communicatin Channel *  Receiver
* Block Diagram of Communication System :
* Terms used in Communication :
* Signal : It is a single valued function of time that carries information. It is usually in electrical form
suitable for transmission. The signal can be analog or digital.
* Transducer : It is a device that converts one form of energy to another.
e.g.: (1) A Photocell : Which coverts light energy into electrical energy.
(2) Microphone : Which converts sound energy into electrical energy.
(3) Loudspeakers : Which convert electrical energy to sound energy.
* Noise : It is the disturbance in the transmission and processing of message. This may be due to channel
imperfection or some source inside/outside the system
* Transmitter : It is an arrangement that converts the message singal to a suitabe form for transmission
and then transmit it through some suitable communication channel.
* Receiver : It is an arrangement that picks up the information signal and process it to reproduce the
message signals in suitable form.
* Attenuation : It is the loss of strength of signals during its propagation through communication channel.
* Amplification : It is process of increasing the strength of transmitted signal using some electronic
circuit. Amplification compensates attenuation.
* Range : The largest distance between transmitter and receiver upto where the signal is received in
proper strength.
* Band Width : It is the range of frequencies over which communication system works.
* Modulation : It is the phenomenon of super imposing a low frequency message signals on a high
frequency carrier wave called as modulated wave which is transmitted.
* Demodulation : It is the reverse of modulation. It is the phenomenon of retrieval (regaining) of information
from the modulated wave.
C O M M U N I C A T I O N S
S U B - T H 2 0 1 5 / X I I
T H - 1 5
2015 / [2]
* Repeaters : These are used between transmitter and receiver. Each repeater receives the transmitted
signal, amplifies it properly and then relay it to the next repeater.
* Message Signals : In communication system, the message signals are of 2 types :
(1)   Analog  signals (2)  Digital signal
(1) Analog Signals : In which voltage/current changes continuously with time. They are represented by
the equation, E = E
0
sin (wt + ?) where ? ?is the voltage and E
0
 is maximum voltage.
e.g.: Speech, music or any sound produced by a vibrating body.
(2) Digital Signals : There are discontinuous function of time, such signals are in the form of pulses. Each
pulse has two levels of current and voltage represented by 0 and 1 called as bits.
e.g.: *  Output of a digital computer.
* Electronic transmission of dcoument to a distant place via telephone line i.e. fax.
* Communication by digital signal is better than analog signal as it maintain privacy and chances of adding
the disturbances is less.
* Communication Channel : It is a link through which information message signals is propagated from
source to the destination.
It is of 2 types :
(1)  Guided transmission medium (2)  Unguided transmission medium
* Guided Transmission Medium  is that in which there is point to point communication link from a
single transmitter to a singl receiver. e.g.: wirelines, cables and optical fibres.
* Unguided Transmission Medium  is that in which there is no point to point contact between transmitter
and a receiver. A large number of reeivers are connected to a single transmitter.
e.g.: Space communication and satellite communication.
* Antenna or Arial : Antenna is used for both transmission and reception. It is a metallic object that is
capable of radiating EM waves and receiving them. Antennas are of 2 types :
Page 3


ABHA DHAMIJA PHYSICS CLASSES
H.No. 1282, Sector-7, KARNAL Ph.: 8950171870
* Communication : It is an act of transmission and reception of information.
* Elements of Communication System : The three necessary elements are :
*  Transmitter *   Communicatin Channel *  Receiver
* Block Diagram of Communication System :
* Terms used in Communication :
* Signal : It is a single valued function of time that carries information. It is usually in electrical form
suitable for transmission. The signal can be analog or digital.
* Transducer : It is a device that converts one form of energy to another.
e.g.: (1) A Photocell : Which coverts light energy into electrical energy.
(2) Microphone : Which converts sound energy into electrical energy.
(3) Loudspeakers : Which convert electrical energy to sound energy.
* Noise : It is the disturbance in the transmission and processing of message. This may be due to channel
imperfection or some source inside/outside the system
* Transmitter : It is an arrangement that converts the message singal to a suitabe form for transmission
and then transmit it through some suitable communication channel.
* Receiver : It is an arrangement that picks up the information signal and process it to reproduce the
message signals in suitable form.
* Attenuation : It is the loss of strength of signals during its propagation through communication channel.
* Amplification : It is process of increasing the strength of transmitted signal using some electronic
circuit. Amplification compensates attenuation.
* Range : The largest distance between transmitter and receiver upto where the signal is received in
proper strength.
* Band Width : It is the range of frequencies over which communication system works.
* Modulation : It is the phenomenon of super imposing a low frequency message signals on a high
frequency carrier wave called as modulated wave which is transmitted.
* Demodulation : It is the reverse of modulation. It is the phenomenon of retrieval (regaining) of information
from the modulated wave.
C O M M U N I C A T I O N S
S U B - T H 2 0 1 5 / X I I
T H - 1 5
2015 / [2]
* Repeaters : These are used between transmitter and receiver. Each repeater receives the transmitted
signal, amplifies it properly and then relay it to the next repeater.
* Message Signals : In communication system, the message signals are of 2 types :
(1)   Analog  signals (2)  Digital signal
(1) Analog Signals : In which voltage/current changes continuously with time. They are represented by
the equation, E = E
0
sin (wt + ?) where ? ?is the voltage and E
0
 is maximum voltage.
e.g.: Speech, music or any sound produced by a vibrating body.
(2) Digital Signals : There are discontinuous function of time, such signals are in the form of pulses. Each
pulse has two levels of current and voltage represented by 0 and 1 called as bits.
e.g.: *  Output of a digital computer.
* Electronic transmission of dcoument to a distant place via telephone line i.e. fax.
* Communication by digital signal is better than analog signal as it maintain privacy and chances of adding
the disturbances is less.
* Communication Channel : It is a link through which information message signals is propagated from
source to the destination.
It is of 2 types :
(1)  Guided transmission medium (2)  Unguided transmission medium
* Guided Transmission Medium  is that in which there is point to point communication link from a
single transmitter to a singl receiver. e.g.: wirelines, cables and optical fibres.
* Unguided Transmission Medium  is that in which there is no point to point contact between transmitter
and a receiver. A large number of reeivers are connected to a single transmitter.
e.g.: Space communication and satellite communication.
* Antenna or Arial : Antenna is used for both transmission and reception. It is a metallic object that is
capable of radiating EM waves and receiving them. Antennas are of 2 types :
2015 / [3]
(a) Dipole Antenna : Which is used in transmission of radio waves in all directions.
(b) Dish Type Antenna : These antennas have a parabolic reflectors and they can transmit waves in a
particular direction. It is specially used for satellite communication.
* Need of Modulation :
(1) Size of Antenna : Each Antenna should have a size comparable to that ? of the signal radiated by it.
( l = ?/4) l = length of Anteena.
For audio frequency (20,000 Hz), ? = c/f = 
8
4
3 10
2 10
?
?
 = 1.5 × 10
4 
m.
       length of Antenna ( l) = ?/4 = 
4
1.5 10
4
?
m = 3750 m = 3.75 km.
This length of antena is practically not possible.
          For radio waves, ? = c/f = 
8
6
3 10
10
?
 = 300 m.
l = ?/4 = 
300
4
 = 75 m.
This is reasonable. These calculations show that the length of antenna is reduced by the process of modulation.
(2) Power Radiated by Antenna : Power ? 
2
1
?
The range of transmission becomes more by using high frequency carrier waves.
Page 4


ABHA DHAMIJA PHYSICS CLASSES
H.No. 1282, Sector-7, KARNAL Ph.: 8950171870
* Communication : It is an act of transmission and reception of information.
* Elements of Communication System : The three necessary elements are :
*  Transmitter *   Communicatin Channel *  Receiver
* Block Diagram of Communication System :
* Terms used in Communication :
* Signal : It is a single valued function of time that carries information. It is usually in electrical form
suitable for transmission. The signal can be analog or digital.
* Transducer : It is a device that converts one form of energy to another.
e.g.: (1) A Photocell : Which coverts light energy into electrical energy.
(2) Microphone : Which converts sound energy into electrical energy.
(3) Loudspeakers : Which convert electrical energy to sound energy.
* Noise : It is the disturbance in the transmission and processing of message. This may be due to channel
imperfection or some source inside/outside the system
* Transmitter : It is an arrangement that converts the message singal to a suitabe form for transmission
and then transmit it through some suitable communication channel.
* Receiver : It is an arrangement that picks up the information signal and process it to reproduce the
message signals in suitable form.
* Attenuation : It is the loss of strength of signals during its propagation through communication channel.
* Amplification : It is process of increasing the strength of transmitted signal using some electronic
circuit. Amplification compensates attenuation.
* Range : The largest distance between transmitter and receiver upto where the signal is received in
proper strength.
* Band Width : It is the range of frequencies over which communication system works.
* Modulation : It is the phenomenon of super imposing a low frequency message signals on a high
frequency carrier wave called as modulated wave which is transmitted.
* Demodulation : It is the reverse of modulation. It is the phenomenon of retrieval (regaining) of information
from the modulated wave.
C O M M U N I C A T I O N S
S U B - T H 2 0 1 5 / X I I
T H - 1 5
2015 / [2]
* Repeaters : These are used between transmitter and receiver. Each repeater receives the transmitted
signal, amplifies it properly and then relay it to the next repeater.
* Message Signals : In communication system, the message signals are of 2 types :
(1)   Analog  signals (2)  Digital signal
(1) Analog Signals : In which voltage/current changes continuously with time. They are represented by
the equation, E = E
0
sin (wt + ?) where ? ?is the voltage and E
0
 is maximum voltage.
e.g.: Speech, music or any sound produced by a vibrating body.
(2) Digital Signals : There are discontinuous function of time, such signals are in the form of pulses. Each
pulse has two levels of current and voltage represented by 0 and 1 called as bits.
e.g.: *  Output of a digital computer.
* Electronic transmission of dcoument to a distant place via telephone line i.e. fax.
* Communication by digital signal is better than analog signal as it maintain privacy and chances of adding
the disturbances is less.
* Communication Channel : It is a link through which information message signals is propagated from
source to the destination.
It is of 2 types :
(1)  Guided transmission medium (2)  Unguided transmission medium
* Guided Transmission Medium  is that in which there is point to point communication link from a
single transmitter to a singl receiver. e.g.: wirelines, cables and optical fibres.
* Unguided Transmission Medium  is that in which there is no point to point contact between transmitter
and a receiver. A large number of reeivers are connected to a single transmitter.
e.g.: Space communication and satellite communication.
* Antenna or Arial : Antenna is used for both transmission and reception. It is a metallic object that is
capable of radiating EM waves and receiving them. Antennas are of 2 types :
2015 / [3]
(a) Dipole Antenna : Which is used in transmission of radio waves in all directions.
(b) Dish Type Antenna : These antennas have a parabolic reflectors and they can transmit waves in a
particular direction. It is specially used for satellite communication.
* Need of Modulation :
(1) Size of Antenna : Each Antenna should have a size comparable to that ? of the signal radiated by it.
( l = ?/4) l = length of Anteena.
For audio frequency (20,000 Hz), ? = c/f = 
8
4
3 10
2 10
?
?
 = 1.5 × 10
4 
m.
       length of Antenna ( l) = ?/4 = 
4
1.5 10
4
?
m = 3750 m = 3.75 km.
This length of antena is practically not possible.
          For radio waves, ? = c/f = 
8
6
3 10
10
?
 = 300 m.
l = ?/4 = 
300
4
 = 75 m.
This is reasonable. These calculations show that the length of antenna is reduced by the process of modulation.
(2) Power Radiated by Antenna : Power ? 
2
1
?
The range of transmission becomes more by using high frequency carrier waves.
2015 / [4]
(3) Mixing up of Signals from Different Transmissions : It a receiver is connected to more than one
transmitter, then the mixing of signals takes place. The possible solution is to communicate at high frequency
and alotting a band of frequencies to each transmission so that there is no mixing.
Types of Modulation :
* Amplitude Modulation : In amplitude modulation, the amplitude of carrier is varied in accordance
with the amplitude of audio frequency modulating signals.
Let the modulating signals is represented by the equation m(t) = A
m
 sin W
m
t.
Let the equation of the carrier is : c(t) = A
c
 sin W
c
t
In amplitude modulation, the amplitude of modulated wave will be.
Page 5


ABHA DHAMIJA PHYSICS CLASSES
H.No. 1282, Sector-7, KARNAL Ph.: 8950171870
* Communication : It is an act of transmission and reception of information.
* Elements of Communication System : The three necessary elements are :
*  Transmitter *   Communicatin Channel *  Receiver
* Block Diagram of Communication System :
* Terms used in Communication :
* Signal : It is a single valued function of time that carries information. It is usually in electrical form
suitable for transmission. The signal can be analog or digital.
* Transducer : It is a device that converts one form of energy to another.
e.g.: (1) A Photocell : Which coverts light energy into electrical energy.
(2) Microphone : Which converts sound energy into electrical energy.
(3) Loudspeakers : Which convert electrical energy to sound energy.
* Noise : It is the disturbance in the transmission and processing of message. This may be due to channel
imperfection or some source inside/outside the system
* Transmitter : It is an arrangement that converts the message singal to a suitabe form for transmission
and then transmit it through some suitable communication channel.
* Receiver : It is an arrangement that picks up the information signal and process it to reproduce the
message signals in suitable form.
* Attenuation : It is the loss of strength of signals during its propagation through communication channel.
* Amplification : It is process of increasing the strength of transmitted signal using some electronic
circuit. Amplification compensates attenuation.
* Range : The largest distance between transmitter and receiver upto where the signal is received in
proper strength.
* Band Width : It is the range of frequencies over which communication system works.
* Modulation : It is the phenomenon of super imposing a low frequency message signals on a high
frequency carrier wave called as modulated wave which is transmitted.
* Demodulation : It is the reverse of modulation. It is the phenomenon of retrieval (regaining) of information
from the modulated wave.
C O M M U N I C A T I O N S
S U B - T H 2 0 1 5 / X I I
T H - 1 5
2015 / [2]
* Repeaters : These are used between transmitter and receiver. Each repeater receives the transmitted
signal, amplifies it properly and then relay it to the next repeater.
* Message Signals : In communication system, the message signals are of 2 types :
(1)   Analog  signals (2)  Digital signal
(1) Analog Signals : In which voltage/current changes continuously with time. They are represented by
the equation, E = E
0
sin (wt + ?) where ? ?is the voltage and E
0
 is maximum voltage.
e.g.: Speech, music or any sound produced by a vibrating body.
(2) Digital Signals : There are discontinuous function of time, such signals are in the form of pulses. Each
pulse has two levels of current and voltage represented by 0 and 1 called as bits.
e.g.: *  Output of a digital computer.
* Electronic transmission of dcoument to a distant place via telephone line i.e. fax.
* Communication by digital signal is better than analog signal as it maintain privacy and chances of adding
the disturbances is less.
* Communication Channel : It is a link through which information message signals is propagated from
source to the destination.
It is of 2 types :
(1)  Guided transmission medium (2)  Unguided transmission medium
* Guided Transmission Medium  is that in which there is point to point communication link from a
single transmitter to a singl receiver. e.g.: wirelines, cables and optical fibres.
* Unguided Transmission Medium  is that in which there is no point to point contact between transmitter
and a receiver. A large number of reeivers are connected to a single transmitter.
e.g.: Space communication and satellite communication.
* Antenna or Arial : Antenna is used for both transmission and reception. It is a metallic object that is
capable of radiating EM waves and receiving them. Antennas are of 2 types :
2015 / [3]
(a) Dipole Antenna : Which is used in transmission of radio waves in all directions.
(b) Dish Type Antenna : These antennas have a parabolic reflectors and they can transmit waves in a
particular direction. It is specially used for satellite communication.
* Need of Modulation :
(1) Size of Antenna : Each Antenna should have a size comparable to that ? of the signal radiated by it.
( l = ?/4) l = length of Anteena.
For audio frequency (20,000 Hz), ? = c/f = 
8
4
3 10
2 10
?
?
 = 1.5 × 10
4 
m.
       length of Antenna ( l) = ?/4 = 
4
1.5 10
4
?
m = 3750 m = 3.75 km.
This length of antena is practically not possible.
          For radio waves, ? = c/f = 
8
6
3 10
10
?
 = 300 m.
l = ?/4 = 
300
4
 = 75 m.
This is reasonable. These calculations show that the length of antenna is reduced by the process of modulation.
(2) Power Radiated by Antenna : Power ? 
2
1
?
The range of transmission becomes more by using high frequency carrier waves.
2015 / [4]
(3) Mixing up of Signals from Different Transmissions : It a receiver is connected to more than one
transmitter, then the mixing of signals takes place. The possible solution is to communicate at high frequency
and alotting a band of frequencies to each transmission so that there is no mixing.
Types of Modulation :
* Amplitude Modulation : In amplitude modulation, the amplitude of carrier is varied in accordance
with the amplitude of audio frequency modulating signals.
Let the modulating signals is represented by the equation m(t) = A
m
 sin W
m
t.
Let the equation of the carrier is : c(t) = A
c
 sin W
c
t
In amplitude modulation, the amplitude of modulated wave will be.
2015 / [5]
* Ac + Am sin w mt and its angular frequency wc remains unchanged.
? the equation of amplitude modulated wave will be,
Amplitude y(t) = (A
c
 + A
m
 sin W
m
t) sin W
c
t
Modulated wave y(t) = A
c
 sin W
c
t + A
m
 sin W
m
t sin W
c
t
Multiply and divide by A
c
 the second term.
y(t) = A
c
 sin W
c
t + 
m c
c
A A
A
?
sin W W
m
t sin W
c
t
Modulation index ( ?) = 
m
c
A
A
 < 1
y(t) = A
c
 sin W
c
t + ?A
c
 sin W
m
t sin W
c
t
Multiply and divide second term by 2
y(t) = A
c
 sin W
c
t + 
c
A
2
?
2 sin W W
m
t sin W
c
t.
Using Property : 2 sin A sin B = cos (A – B) – cos (A + B)
y(t) = A
c
 sin W
c
t + 
c
A
2
?
 [cos (W
c
 – W W
m
)t – cos (W
c
 + W
m
)t]
This is equation of amplitude modulated wave.
L.S.B U.S.B
W
Band width = (W
c
 + W
m
) – (W
c
 – W
m
) = 2 W
m
.
Therefore for an amplitude modulated wave, band width is twice the frequency of modulating signal. Different
radio stations would not interfere with each other when their carrier wave frequencies are so widely separated
that their side bands do not overlap.
* Production of Amplitude Modulated Wave :
Let the modulating wave is, m(t) = A
m
 sin W
m
t
Let the carrier wave is, c(t) = A
c
 sin W
c
t
When the modulating signals is added to the carrier wave, then the signal produced is.
x(t) = A
m
 sin W
m
t + A
c
 sin W
c
t
This signals is passed through a square law device (which is a transistor) so that the equation becomes.
y(t) = x(t) + x
2
(t). (parabolic equation)
y(t) = [A
m
 sin W
m
t + A
c
 sin W
c
t] + [A
m
 sin W
m
t + A
c
 sin W
c
t]
2
y(t) = A
m
 sin W
m
t + A
c
 sin W
c
t + A
m
2
sin
2
 W
m
t + A
c
2
sin
2 
W
c
t + 2 A
c
 A
m
 sin W
m
t sin W
c
t