Communication System

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Communication is the whole process of transmission and reception of information and elements of communication system comprises transmitter, communication channel and receiver, etc even all small elements contributing to the process of communication in other words the system which basically describes the information exchange between two points. And this process of transmission and reception of information is called communication. 


Modes of communication

  • In the Point to Point Mode of Communication the communication takes place over a provided link between a transmitter signal and the receiver. Eg.Telephone

  • Broadcast Mode of Communication: In this mode there are a large number of receiver’s signals corresponding to a transmitter signal. Radio and television are examples of broadcast mode of communication.

  • Analog Mode of Transmission: In an analogue mode of transmission the message is physical quantity that varies with time usually in a smooth and continuous fashion.

  • Digital Mode of Transmission: In this mode of transmission the digital message is an ordered sequence of symbols selected from a finite set of discrete elements.


Elements of Communication System

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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. 


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.


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.

FAQ (Frequently Asked Questions)

Q1. What are three types of Modulation?

Ans. Three different types of Modulation are:

i. Amplitude Modulation (AM): In this process the amplitude of the signal wave is changed by impressing or superimposing it on a high-frequency carrier wave, keeping its frequency constant.

ii. Frequency Modulation (FM): Frequency modulation is the technique in which the frequency of the message signal is changed or varied by modulating with a carrier wave. 

iii. Phase Modulation (PM): In this the phase of the carrier wave changes the phase of the signal wave. The phase shift after the modulation is dependent on the frequency of the carrier wave as well. 

Q2. What are Repeaters?

Ans. Repeaters are placed at different locations in between the transmitter and receiver. Thus a repeater is a device which receives the transmitted signal, amplifies it and sends it to the next repeater without distorting the original signal.

Q3. Explain Attenuation

Ans. Attenuation is the problem caused by the medium when the signal propagates for the longer distance through a medium and depending upon the length of the medium the initial power decreases. The loss in this initial power is directly proportional to the length of the medium in which it is travelling.