Line Communication PPT Physics Class 12

 Page 1


Line Communication
1. Two Wire Transmission Lines                                                               
- Parallel Wire Line                                                                                              
- Twisted Pair Wires                                                                           
- Coaxial Line
2. Equivalent Circuit of a Transmission Line
3. Velocity Factor in a Line
4. Losses in a Line
5. Cable System
6. Optic Fibre System & Components of Fibre Optic
Equipment
7. Optical Fibre – Types of Optical Fibre
8. Principle of Optic Fibre
9. Important Aspects – Numerical Aperture, Attenuation and 
Dispersion
10. Advantages and Disadvantages of Optic Fibres
Page 2


Line Communication
1. Two Wire Transmission Lines                                                               
- Parallel Wire Line                                                                                              
- Twisted Pair Wires                                                                           
- Coaxial Line
2. Equivalent Circuit of a Transmission Line
3. Velocity Factor in a Line
4. Losses in a Line
5. Cable System
6. Optic Fibre System & Components of Fibre Optic
Equipment
7. Optical Fibre – Types of Optical Fibre
8. Principle of Optic Fibre
9. Important Aspects – Numerical Aperture, Attenuation and 
Dispersion
10. Advantages and Disadvantages of Optic Fibres
Line Communication:
The simplest and the oldest mode of communication from point-to-point in 
contact through transmission lines or wires is called ‘line communication’.
The main line communication channels are:
(i) Two wire transmission lines
(ii) Coaxial cables
(iii)Optical fibres
Two Wire Transmission Lines:
The most commonly used two wire lines are:
(a) Parallel wire line    (b) Twisted pair of wires and    (c) Coaxial line
Parallel Wire Line:
Insulation
It is also known as balanced line.  It resembles a ribbon.  It 
is commonly used to connect an antenna with the TV 
receiver.  It suffers from interferences and losses.
If the conductor separation is nearly equal to half wave 
length of the operating frequency of the signal, the system 
of wires may start radiating the signal.
Parallel wire lines are not suitable for microwaves.
Conductors
Page 3


Line Communication
1. Two Wire Transmission Lines                                                               
- Parallel Wire Line                                                                                              
- Twisted Pair Wires                                                                           
- Coaxial Line
2. Equivalent Circuit of a Transmission Line
3. Velocity Factor in a Line
4. Losses in a Line
5. Cable System
6. Optic Fibre System & Components of Fibre Optic
Equipment
7. Optical Fibre – Types of Optical Fibre
8. Principle of Optic Fibre
9. Important Aspects – Numerical Aperture, Attenuation and 
Dispersion
10. Advantages and Disadvantages of Optic Fibres
Line Communication:
The simplest and the oldest mode of communication from point-to-point in 
contact through transmission lines or wires is called ‘line communication’.
The main line communication channels are:
(i) Two wire transmission lines
(ii) Coaxial cables
(iii)Optical fibres
Two Wire Transmission Lines:
The most commonly used two wire lines are:
(a) Parallel wire line    (b) Twisted pair of wires and    (c) Coaxial line
Parallel Wire Line:
Insulation
It is also known as balanced line.  It resembles a ribbon.  It 
is commonly used to connect an antenna with the TV 
receiver.  It suffers from interferences and losses.
If the conductor separation is nearly equal to half wave 
length of the operating frequency of the signal, the system 
of wires may start radiating the signal.
Parallel wire lines are not suitable for microwaves.
Conductors
Twisted Pair of Wires:
A twisted pair of wires consists of two insulated copper wires twisted around 
each other at regular intervals.
If the wires run parallel without twisting, then the electrical interference will 
be more for the wire close to the source of noise than the wire away from the 
source of noise.  As a result of this, a distorted signal is available at the 
receiving end.
So, to minimize the electrical interference, two wires are twisted around each 
other.
Twisted pair wires are used to connect telephone systems.  Usually many 
twisted pairs parallel to each other are grouped in the form of a bundle which 
is encased in a protective sheath.
In case of twisted pair wires, signals having frequency range 100 Hz to 5 MHz
are transmitted.
Outer Insulation Protective shield 
(Wire mesh)
Twisted pairs
Page 4


Line Communication
1. Two Wire Transmission Lines                                                               
- Parallel Wire Line                                                                                              
- Twisted Pair Wires                                                                           
- Coaxial Line
2. Equivalent Circuit of a Transmission Line
3. Velocity Factor in a Line
4. Losses in a Line
5. Cable System
6. Optic Fibre System & Components of Fibre Optic
Equipment
7. Optical Fibre – Types of Optical Fibre
8. Principle of Optic Fibre
9. Important Aspects – Numerical Aperture, Attenuation and 
Dispersion
10. Advantages and Disadvantages of Optic Fibres
Line Communication:
The simplest and the oldest mode of communication from point-to-point in 
contact through transmission lines or wires is called ‘line communication’.
The main line communication channels are:
(i) Two wire transmission lines
(ii) Coaxial cables
(iii)Optical fibres
Two Wire Transmission Lines:
The most commonly used two wire lines are:
(a) Parallel wire line    (b) Twisted pair of wires and    (c) Coaxial line
Parallel Wire Line:
Insulation
It is also known as balanced line.  It resembles a ribbon.  It 
is commonly used to connect an antenna with the TV 
receiver.  It suffers from interferences and losses.
If the conductor separation is nearly equal to half wave 
length of the operating frequency of the signal, the system 
of wires may start radiating the signal.
Parallel wire lines are not suitable for microwaves.
Conductors
Twisted Pair of Wires:
A twisted pair of wires consists of two insulated copper wires twisted around 
each other at regular intervals.
If the wires run parallel without twisting, then the electrical interference will 
be more for the wire close to the source of noise than the wire away from the 
source of noise.  As a result of this, a distorted signal is available at the 
receiving end.
So, to minimize the electrical interference, two wires are twisted around each 
other.
Twisted pair wires are used to connect telephone systems.  Usually many 
twisted pairs parallel to each other are grouped in the form of a bundle which 
is encased in a protective sheath.
In case of twisted pair wires, signals having frequency range 100 Hz to 5 MHz
are transmitted.
Outer Insulation Protective shield 
(Wire mesh)
Twisted pairs
Advantages:
(i) The signals can travel several kilometers without any amplification in a 
telephone system when twisted pair wires are used.
(ii) Both analogue and digital signals can be transmitted.
(iii)It is a cheap mode of communication.
Disadvantages:
(i) The signal becomes weak when it travels a very large distance through a 
twisted pair of wires.  As a result, transmission becomes faulty.
(ii) Telephone lines run overhead, so they can be broken during storm, etc.
Coaxial Line:
It is also called unbalanced line.  Such a line resembles a rounded cable.  
It is commonly used by TV Cable operators.
Outer Insulation
Conductor - II   
in mesh form
Conductor - I
Inner Insulation
Page 5


Line Communication
1. Two Wire Transmission Lines                                                               
- Parallel Wire Line                                                                                              
- Twisted Pair Wires                                                                           
- Coaxial Line
2. Equivalent Circuit of a Transmission Line
3. Velocity Factor in a Line
4. Losses in a Line
5. Cable System
6. Optic Fibre System & Components of Fibre Optic
Equipment
7. Optical Fibre – Types of Optical Fibre
8. Principle of Optic Fibre
9. Important Aspects – Numerical Aperture, Attenuation and 
Dispersion
10. Advantages and Disadvantages of Optic Fibres
Line Communication:
The simplest and the oldest mode of communication from point-to-point in 
contact through transmission lines or wires is called ‘line communication’.
The main line communication channels are:
(i) Two wire transmission lines
(ii) Coaxial cables
(iii)Optical fibres
Two Wire Transmission Lines:
The most commonly used two wire lines are:
(a) Parallel wire line    (b) Twisted pair of wires and    (c) Coaxial line
Parallel Wire Line:
Insulation
It is also known as balanced line.  It resembles a ribbon.  It 
is commonly used to connect an antenna with the TV 
receiver.  It suffers from interferences and losses.
If the conductor separation is nearly equal to half wave 
length of the operating frequency of the signal, the system 
of wires may start radiating the signal.
Parallel wire lines are not suitable for microwaves.
Conductors
Twisted Pair of Wires:
A twisted pair of wires consists of two insulated copper wires twisted around 
each other at regular intervals.
If the wires run parallel without twisting, then the electrical interference will 
be more for the wire close to the source of noise than the wire away from the 
source of noise.  As a result of this, a distorted signal is available at the 
receiving end.
So, to minimize the electrical interference, two wires are twisted around each 
other.
Twisted pair wires are used to connect telephone systems.  Usually many 
twisted pairs parallel to each other are grouped in the form of a bundle which 
is encased in a protective sheath.
In case of twisted pair wires, signals having frequency range 100 Hz to 5 MHz
are transmitted.
Outer Insulation Protective shield 
(Wire mesh)
Twisted pairs
Advantages:
(i) The signals can travel several kilometers without any amplification in a 
telephone system when twisted pair wires are used.
(ii) Both analogue and digital signals can be transmitted.
(iii)It is a cheap mode of communication.
Disadvantages:
(i) The signal becomes weak when it travels a very large distance through a 
twisted pair of wires.  As a result, transmission becomes faulty.
(ii) Telephone lines run overhead, so they can be broken during storm, etc.
Coaxial Line:
It is also called unbalanced line.  Such a line resembles a rounded cable.  
It is commonly used by TV Cable operators.
Outer Insulation
Conductor - II   
in mesh form
Conductor - I
Inner Insulation
The inner and outer conductors are separated with the help of low 
dielectric. The common insulations are Polyethylene and Teflon.  
Coaxial cables can be gas filled also.  To reduce flash over between the 
conductor handling high power, nitrogen gas is used in the cable.  Dry air 
can also be used under high pressure to avoid moisture in the cable.
These cables can find wide application for frequencies between 1 GHz and 
20 GHz.
Advantages:
(i) Coaxial cable is well protected than an ordinary twisted pair of wires, so 
communication through cables is more efficient than through the twisted 
pairs.
(ii) The speed of transmission of signals is more than that of twisted pairs.
(iii)Electrical signals of higher frequencies (100 kHz to 500 kHZ) are 
transmitted through the cables than through the twisted pair wires.
It is also used to interconnect transmitter and an earthed antenna.  Such 
cables are shielded i.e. outer conductor surrounds the insulated inner wire 
and the outer conductor is always earthed.
These cables do not suffer from radiation problems and be used for 
microwave and UHF region.