Communication System Chapter - Physics JEE Main

The communication system is a system model that describes a communication exchange between two stations, transmitter, and receiver. Signals or information passes from source to destination through a channel. It represents a way in which the signal uses it to move from a source toward its destination. To transmit signals in a communication system, it should first be processed by beginning from signal representation, to signal shaping until encoding and modulation. After the transmitted signal is prepared, it is passed to the transmission line of the channel. Due to signal crossing this media, it is faced with many impairments like noise, attenuation, and distortion.

The process of transferring the information between two points is called communication. The main elements needed to communicate are the transmitter to send the information, the medium to send the information and the receiver to receive the information on the other end. 

JEE Main Physics Chapters 2024 

Types of Communication Systems

Based on physical infrastructure:

Based on physical infrastructure there are two types of communication systems:

• Line communication systems: Uses the existing infrastructure of power lines to transfer data from one point to another point.

• Radio Communication systems: uses the infrastructure of radio waves to transfer the information from one point to another point.

There is a physical link, called a hardwire channel between the transmitter and the receiver inline communication systems. 

Based on Signal specifications:

Signal specifications that are used to decide the type of communication system are:

• Nature of the baseband or information signal: Baseband signals is a technology which can access the signals with very low frequency and also near zero frequency and based on the nature of the transmitted signal, the baseband signal can either be transmitted as it is without modulation or through a carrier signal with modulation.

Further, communication systems are divided into:

• Analog communication systems: The Analog system conveys the information from the audio, video and pictures between two points using the analogue signals. A sinusoidal signal is an example of an analogue communication system.

• Digital communication systems: Digital communication has become very important in the age of the internet. It is a physical exchange of information between two points discreetly. The information exchange happens through digital signals. 

• Baseband communication system: Baseband communication is the transfer of signals that are not amplified to higher frequencies. They help in transferring signals with near-zero frequency.

• Carrier communication system: Carrier communication systems transfer the information especially voice messages and calls by improving the frequency much higher than the actual rate. 

Out of four, a minimum of two types is needed to specify any communication system. Thus, two groups are formed consisting of each of the two types such that at least one of the types from each group is necessarily required to specify a communication system. These groups can be formed as:

• Analog/digital communication systems

• Baseband/carrier communication systems

To completely define any communication system, four out of the eight types are required. If any type is missing, then the description of the communication system will be incomplete.

Wireless and Wired Communication System

Wireless communication systems use radio waves, electromagnetic waves and infrared waves to communicate from one point to another point and the wire communication system uses wire, optical fibre which works on the phenomenon of total internal reflection to communicate from one point to another point. 

Wireless communication is further divided into satellite communication, ground wave communication, skywave and space wave communication. The satellite communication receives the signals from the earth and resends them back to another point on the earth with the help of a transponder. Wired communication is further divided into parallel wire, twisted wire, optical fibre and coaxial wired communication.

Elements of Communication System

The Channel that connects the transmitter and the receiver together consists of elements of communication.

1. Information Source: This can be defined as the source that produces the signal of the information which needs to be communicated from one location to the other.

2. Signal: This can be defined as the information which is in the electrical form and is suitable for the transmission.

3. Transmitter: It is the source device or an arrangement that converts one form of energy to the other. An electrical transducer converts Signal into suitable form for transmission through the channel or the physical variables such as pressure, force, temperature into corresponding electrical signal variations. 

4. Channel: The channel is the medium connecting the transmitter and the receiver is a physical medium. The channel can be in the following forms such as wires, cables or wireless.

5. Noise: When the transmitted signal propagates along the channel, it can get some distortion due to imperfection in the channel. Thus, the noise can be referred or defined as an unwanted signal that has a tendency to disturb the process of communication from the transmitter to the receiver.

6. Amplifier: It can be defined as the electronic circuit or electronic device that increases the amplitude or the strength of the transmitted signal whenever the signal strength becomes less than the required value of it for transmission, amplification is done anywhere in between transmitter and receiver.

7. Modulator: Since the original message or the signal cannot be transmitted over a large distance because of their low frequency and amplitude, thus they are superimposed with high frequency and amplitude and this wave is called carrier wave. This phenomenon of superimposing a message signal with a carrier wave is termed as modulation and the resultant wave is transmitted.

8. Receiver: It can be defined as the arrangement that finally extracts the message or information from the transmitted signal as the output at the of the channel and finally reproduces it in the suitable form as the original message signal is a receiver. Sometimes due to the noises and some other factors as well ,the corrupted version of the signal arrives at the receiver end. Thus the receiver has to reconstruct the signal into recognisable form of the original message for delivering it to the user. The signal at the receiver forms the output.

9. Demodulator: The function of the demodulator is exactly opposite to that of the process of modulation and this process of separation of the message signal from the carrier wave takes place in the device called demodulator. 

Understanding the Need for Modulation

In the realm of electronic communication, it is essential to understand the concept of modulation. Modulation is the process of varying the characteristics of a carrier signal in response to an information signal. There are two fundamental types of modulation:

• Amplitude Modulation (AM): In AM, the amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal. This process is mathematically represented as: 

$A(t)=A_c​ (1+k_a​ m(t))$

Where:

A(t) represents the instantaneous amplitude of the modulated signal.

$A_c$ is the amplitude of the carrier signal.

$k_a$ is the modulation index.

m(t) is the modulating signal.

• Frequency Modulation (FM): In FM, the frequency of the carrier wave is varied according to the instantaneous frequency of the modulating signal. This process is mathematically represented as:

$f(t)=f_c​ +k_f​ m(t)

Where:

f(t) represents the instantaneous frequency of the modulated signal.

$f_c$ is the carrier frequency.

$k_f$ is the modulation index for frequency modulation.

m(t) is the modulating signal.

Understand better the distinctions between Frequency and Amplitude modulation, including their various types and the advantages and disadvantages of each.

Bandwidth of Signals and Transmission Medium

The speech signal has a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication and for the frequencies being produced by the musical instruments, the audible range of the frequencies extends from 20 Hz to 20 kHz while video signals for transmission require about 4.2 MHz of bandwidth. A TV signal that contains both the voice and the picture is usually allocated bandwidth of 6 MHz for transmission. The commonly used medium for transmission are wire, free space and fibre optic cable.

The bandwidth of a modulated signal can be calculated using the following formula:

$B_{mod} = 2(f_{max} - f{min})$

Where:

$B_{mod}$​ - is the bandwidth of the modulated signal.

$f_{max}$ - is the maximum frequency component in the modulated signal.

$f_{min}$ - is the minimum frequency component in the modulated signal.

The Shannon-Hartley theorem provides a fundamental formula for calculating the channel capacity of Bandwith transmission:

$C=B log_2(1+SNR)$

Where:

C is the channel capacity (in bits per second).

B is the bandwidth of the channel (in Hertz).

SNR is the signal-to-noise ratio.

Propagation of Electromagnetic Waves

For the propagation or the transmission of electromagnetic waves over long distances, signals are radiated into space by using the devices called antennas. This radiated signal propagates as electromagnetic waves and the mode of propagation is generally influenced due to the earth and its atmosphere. Near the surface of the earth, electromagnetic waves propagate as surface waves. Surface wave propagation is generally useful up to a few MHz frequencies and the long-distance communication between the two points on the earth is achieved through reflection of electromagnetic waves by the ionosphere. Such waves are generally called sky waves. The propagation of the sky waves takes place up to frequency of about 30 MHz and above this value, the electromagnetic waves essentially propagate as space waves.

Did You Know?

• Communication Is Related To Every Human Activity.

• Communication in Organization Flows in Various Patterns.

• Communication Is Media or Channel Based

• There are around 250 billion emails sent every day. Around 80% of these are spam.

• Around 20 hours of video are uploaded to YouTube every minute. 

• Fiber optics are good because they use less energy and are better for the environment than electrical wires. They are also very resistant to weather. 

• The first telephone pole was built in 1876. 

• There are over 4 billion cell phones within the world and phones that are thrown away every year are over  100 million.

• The first cell phone was invented by a company called Motorola.

• Over 3.8 billion people use the internet, which is 40% of the world's population.

• The first smiley appeared in 1979, it first looked like this -) then three years later a colon was added to it and it took the form of :-) this.

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