Elements Of Communication System
A communication system is the backbone of modern society, enabling the transfer of information from one point to another. It consists of various elements, each playing a critical role in ensuring that the message is accurately transmitted, received, and understood. Just like in a conversation between two people, where a clear voice and attentive listening are crucial, the elements of a communication system work together to ensure effective information exchange. In real life, this can be compared to a postal service, where the sender (transmitter) writes a letter, the postal service (medium) delivers it, and the recipient (receiver) reads and understands the message. Similarly, in technology-driven communication systems, the transmitter encodes the message, the channel carries it, and the receiver decodes it, making communication possible across vast distances.
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Basic elements of a Communication System
Information: The idea or message that is to be conveyed is known as information. The message may be an individual one or a set of messages.
Signal: A single-valued function of time ( that conveys the information ).
Transmitter: A device which makes an incoming message signal suitable for transmission through a channel and subsequent reception.
Transducer: A device that converts one form of energy into another.
Repeater: It is used to extend the range of the signal. Combination of the receiver and a transmitter.
Amplifier: It boosts the power of modulated signal.
Antenna: The signal is radiated in the space with the help of an antenna.
Noise: An unwanted signal that tends to disturb the transmission and processing of the message signal. The source of noise may be located within or outside the system.
Receiver: The device which extracts the desired message signal from the received signal at the channel output.
Amplification: It is the process of increasing the amplitude of a signal using an electronic circuit called the amplifier. Amplification is necessary to compensate for the attenuation of the signal in communication systems. The energy needed for additional signal strength is obtained from a DC power source. Amplification is done at a place between the source and the destination wherever signal strength becomes weaker than the required strength.
Attenuation: The loss of strength of a signal while propagating through a medium is known as attenuation.
Modulation: It is the process carried out at the transmitter in which the low-frequency message signal is superimposed on a high-frequency carrier signal.
Demodulation: The process of retrieval of information from the carrier wave at the receiver. Reverse process of modulation.
Bandwidth of Signals
The bandwidth of a signal is defined as the difference between the upper and lower frequencies of a signal generated. As seen from the representation below, the Bandwidth (B) of the signal is equal to the difference between the higher or upper frequency (fH) and the lower frequency (fL). It is measured in terms of Hertz(Hz) i.e. the unit of frequency.
For example, Whenever we tune into a radio we find various stations at varying particular frequencies. The bandwidth of FM radio is 200 KHz from 88.1 MHz to 101.1 MHz for most places. As you tune, the radio you find various stations at various frequencies.
For speech signals, a frequency range of 300 Hz to 3100 Hz is considered adequate. Therefore speech signal requires a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication. To transmit music, an approximate bandwidth of 20 kHz is required because of the high frequencies produced by the musical instruments. The audible range of frequencies extends from 20 Hz to 20 kHz. Video signals for the transmission of pictures require about 4.2 MHz of bandwidth. A TV signal contains both voice and picture and is usually allocated 6 MHz of bandwidth for transmission.
Bandwidth of Transmission Medium
A transmission medium is a material substance (solid, liquid, gas, or plasma) that can propagate energy waves. For example, the transmission medium for sounds is usually air, but solids and liquids may also act as transmission media for sound. The absence of a material medium in a vacuum may also constitute a transmission medium for electromagnetic waves such as light and radio waves. While material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance by absorption or by reflection or refraction at the interfaces between media.
Coaxial cable is a widely used wire medium, which offers a bandwidth of approximately 750 MHz. Such cables are normally operated below 18 GHz. Communication through free space using radio waves takes place over a very wide range of frequencies: from a few hundred kHz to a few GHz
Spectrum Allocations
A spectrum is a large bandwidth of frequencies. Cellular or digital methods use this bandwidth for communication. These allocations have arrived with the help of international plans and policies. Often they require an upgrade of existing systems and technologies.
For example: 4G communication is for cellular devices accessible. The upcoming years will see the introduction of the 5G spectrum as well. With such huge bandwidths, easy, reliable and ultra-fast data transmissions are possible regularly.
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Solved Examples Based On Elements Of Communication System
Example 1: In a radio communication system, a transmitter consists of
1)oscillator to generate a carrier wave
2)modulator
3)Amplifier
4)All of the above
Solution:
A device that makes an incoming message signal suitable for transmission through a channel and subsequent reception.
An oscillator is used to generate a carrier wave which carries the information during transmission
This carrier wave is modulated with the information during transmission
Furthermore, an amplifier is used to increase the power of the modulated signal so that it can transmit to long-range
The oscillator modulator and amplifier all are housed in the transmitter itself
Example 2: The physical size of the transmitter and receiver antenna in a communication system are :
1)Independent of both carrier and modulation frequency
2) Inversely proportional to carrier frequency
3)Inversely proportional to the modulation frequency
4) proportional to the carrier frequency
Solution:
Transmitter
A device which makes an incoming message signal suitable for transmission through a channel and subsequent reception.
Receiver
The device extracts the desired message signal from the received signal at the channel output.
Example 3: In a radio communication system, a receiver consists of
1)Filter
2)Amplifier
3)Demodulator
4)All of the above
Solution:
Receiver
The device extracts the desired message signal from the received signal at the channel output.
In a receiver, an electronic filter is housed which filters out the unwanted frequency signals and allows the specific frequency signals for further processing
The amplifier is used to increase the intensities of received signals and later these amplified signals are fed into the demodulator unit
In the demodulator, the carrier wave is removed and the desired information signal is sent to the transducer where it is converted into the desired form of energy.
Hence all of the above is present in a radio receiver
Example 4: What are the advantages of analogue communication systems over digital communication systems?
1)Less bandwidth communication
2)less power communication
3)less noise communication
4)All of the above
Analog Communication
Which make use of analogue signals.
where
e.g. Telegraphy, television broadcast, Radar etc.
Analogue communications system consumes more power to transmit the media as compared to digital communication systems.
Analog communication systems also suffer from poor signal-to-noise ratio (SNR) which means they are prone to more noise disturbance.
However, the bandwidth consumption for transmissions of media/information is less as compared to the digital communication system
Example 5: A signal $\mathbf{s}(\mathbf{t})=\frac{A_0}{2} \sin w t$ is fed to an amplifier. What may be the possible output of the amplifier from among the following waveforms?
1)
2)
3)
4)
Solution
Amplifiers are used in communication systems to increase the amplitude of signals. They don't change the frequency or phase of a signal.
Hence the correct option is (1)
Summary
A communication system contains different essential sections, which cooperate expeditiously to send the message. The master is the transmitter, the signal is the one who converts data into a suitable form for transmitting, and the message signal is the progenitor or alternatively, the information to be communicated. The transmission medium, that is, the channels through which the signals are transmitted, can be wired or wireless, and there lay the cable somewhere in between. The receiver is the one, which first records the given signal and, then, translates it into a comprehensible form for the users. Noise is an interference that can cause distortions in the signal because it occurs during its way of delivering the issues.
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