Communication Systems MCQ Quiz in मल्याळम - Objective Question with Answer for Communication Systems - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

CONCEPT:

Coaxial cable:

• Coaxial cable is a type of copper cable specially built with a metal shield and other components engineered to block signal interference.
• It is primarily used by cable TV companies to connect their satellite antenna facilities to customer homes and businesses.
• Coaxial cables can be used to carry signals for internet connections, but internet signals run at higher frequencies than traditional analogue video.

EXPLANATION:

• Coaxial cable can carry both digital and analogue signal. Therefore option 3 is correct.
• Long-distance coaxial cable was used to connect radio and television networks.
• Coaxial cables are also used in local area network (LAN).
• Coaxial cables prevent the cable from electromagnetic waves from transmitting the signal.
• ​Fibre optics and household cable are also an example of coaxial cable.

CONCEPT:

Elements of a Communication System:

• Irrespective of the nature of the communication system, every communication system has three essential elements:

1. Transmitter
2. Medium or channel
3. Receiver

• In a communication system, the transmitter is located at one place, the receiver is located at some other place (far or near) separate from the transmitter and the channel is the physical medium that connects them.
• Depending upon the type of communication system, a channel may be in the form of wires or cables connecting the transmitter and the receiver or it may be wireless.
• The purpose of the transmitter is to convert the message signal produced by the source of information into a suitable form for transmission through the channel.
• If the output of the information source is a non-electrical signal like a voice signal, a transducer converts it to an electrical form before giving it as an input to the transmitter.
• When a transmitted signal propagates along the channel it may get distorted due to channel imperfection.
• Moreover, noise adds to the transmitted signal and the receiver receives a corrupted version of the transmitted signal.
• The receiver has the task of operating on the received signal. It reconstructs a recognizable form of the original message signal for delivering it to the user of information.
• There are two basic modes of communication:
  1. Point-to-point
  2. Broadcast

Point to point communication:

• In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver.
• A telephone call is an example of such a mode of communication.

Broadcast communication:

• In the broadcast mode, there are a large number of receivers corresponding to a single transmitter.
• Radio and television are examples of broadcast modes of communication.

EXPLANATION:

• We know that when a transmitted signal propagates along the channel it may get distorted due to channel imperfection. Hence, option 1 is correct.

Correct option is 3.

Concept:

In a communication system, the electromagnetic waves transmitted by the transmitter travels in three different modes to reach the receiver according to its frequency range.

1. Ground wave propagation or surface wave propagation (nearly 2 kHz to 2 MHZ)

2. Sky-wave propagation or ionospheric propagation (nearly 3 MHZ to 30 MHZ)

3. Space wave propagation (nearly 30 MHZ to 400 MHZ)

1. Ground wave propagation:

• If the electromagnetic waves transmitted by the transmitter antenna over the surface of the earth reach the receiver, then the propagation is called ground wave propagation.
• In this mode of transmitting and receiving antennas must be close to the earth's surface.
• During effective transmission through ground wave propagation mobe, electrical signals are attenuated over a distance. 

2. Sky-wave propagation:

• In the sky-wave propagation, the electromagnetic wave is radiated from the antenna, directed upwards at large angles gets reflected by the ionosphere back to the earth.
• The frequency range of EM waves in this mode of propagation is 3 to 30 MHZ.
• It is used for short-wave broadcast services medium and high frequencies are for long-distance radio communication.

3. Space wave propagation: 

• The process of sending and receiving information signals through space is called space wave communication.
• The EM waves above 30 MHZ frequency traveling from the transmitter to receiver in a straight line are used for line of sight communication (LOS).

Explanation:

Ground waves are not used for long-range communication because -

• As the ground wave passes over the surface of the earth, they are mostly absorbed by its surface this results in the weakening of the transmission signal.
• Due to such loss or attenuation of the signal, ground waves are restricted for long-range communication.
• The figure is given below shows the attenuation of the signal in ground wave propagation.

Hence, option-3 is correct.

• EM waves of frequency above 30 MHZ can easily penetrate through the ionosphere and do not undergo reflection.  
• Extremely long-distance communication is also possible as radio waves can undergo multiple reflections between the earth and ionosphere.
• A single reflection helps the radio waves to travel about 4000km.
• The charged ions of the ionosphere provide a reflecting medium for reflection of radio waves or communication waves back to the earth's surface within the permitted frequency range.
• This phenomenon is called the total internal reflection of the EM wave.

Explanation:

Working function of a microphone

• There is a soft and very flexible diaphragm mounted at the front end of the microphone.
• And the coil is fixed with the diaphragm.
• A permanent magnet is placed at the center part of the coil which produces enough magnetic fields around the coil.
• When sound waves come and strike the flexible diaphragm, the diaphragm starts vibrating back and forth.
• The coil also moves with the diaphragm as it is fixed with it.
• As a result, an electrical current is induced in it and carried out to the amplifier.
• Microphones convert the sound energy into electrical energy
• A microphone takes sound waves or the variation in pressure of air as input and gives electrical signals as an output.

CONCEPT:

• The carrier wave may be continuous (sinusoidal) or in the form of pulses.
• A sinusoidal carrier wave can be represented as,

⇒ c(t) = Acsin (ωct + ϕ)

Where c(t) = signal strength (voltage or current), Ac = amplitude, ωc = angular frequency and ϕ = initial phase of the carrier wave

• During the process of modulation, any of the three parameters, viz Ac, ωc, and ϕ of the carrier wave can be controlled by the message or information signal.
• This results in three types of modulation:
  • Amplitude modulation (AM)
  • Frequency modulation (FM)
  • Phase modulation (PM)
• Similarly, the significant characteristics of a pulse are pulse amplitude, pulse duration or pulse width, and pulse position (denoting the time of rise or fall of the pulse amplitude).

Hence, different types of pulse modulation are:

• Pulse amplitude modulation (PAM)
• Pulse duration modulation (PDM) or pulse width modulation (PWM)
• Pulse position modulation (PPM)

EXPLANATION:

Mixing up of signals from different transmitters:

• Another important argument against transmitting baseband signals directly is more practical in nature.
• Suppose many people are talking at the same time or many transmitters are transmitting baseband information signals simultaneously.
• All these signals will get mixed up and there is no simple way to distinguish between them.
• This points out a possible solution by using communication at high frequencies and allotting a band of frequencies to each message signal for its transmission.
• The above arguments suggest that there is a need for translating the original low-frequency baseband message or information signal into a high-frequency wave before transmission such that the translated signal continues to possess the information contained in the original signal.
• In doing so, we take the help of a high-frequency signal, known as the carrier wave, and a process known as modulation which attaches information to it.

• We know that the significant characteristics of a pulse are pulse amplitude, pulse duration or pulse width, and pulse position (denoting the time of rise or fall of the pulse amplitude). Hence, option 4 is correct.

CONCEPT:

Elements of a Communication System:

• Irrespective of the nature of the communication system, every communication system has three essential elements:

1. Transmitter
2. Medium or channel
3. Receiver

• In a communication system, the transmitter is located at one place, the receiver is located at some other place (far or near) separate from the transmitter and the channel is the physical medium that connects them.
• Depending upon the type of communication system, a channel may be in the form of wires or cables connecting the transmitter and the receiver or it may be wireless.
• The purpose of the transmitter is to convert the message signal produced by the source of information into a suitable form for transmission through the channel.
• If the output of the information source is a non-electrical signal like a voice signal, a transducer converts it to an electrical form before giving it as an input to the transmitter.
• When a transmitted signal propagates along the channel it may get distorted due to channel imperfection.
• Moreover, noise adds to the transmitted signal and the receiver receives a corrupted version of the transmitted signal.
• The receiver has the task of operating on the received signal. It reconstructs a recognizable form of the original message signal for delivering it to the user of information.
• There are two basic modes of communication:
  1. Point-to-point
  2. Broadcast

Point to point communication:

• In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver.
• A telephone call is an example of such a mode of communication.

Broadcast communication:

• In the broadcast mode, there are a large number of receivers corresponding to a single transmitter.
• Radio and television are examples of broadcast modes of communication.

EXPLANATION:

• In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver.
• A telephone call is an example of such a mode of communication. Hence, option 1 is correct.

CONCEPT:

Modulation: 

• The process of varying some characteristics such as amplitude, frequency, or phase of a carrier signal is varied in accordance with the instantaneous value of the low-frequency audio signal(or modulating signal) is known as Modulation.
  • In other words, in modulation, we use a high-frequency carrier wave to carry audio signals(message) to large distances.
  • Audio signals have low frequencies with a bandwidth of about 20 kHz only.
• Such low signals cannot be transmitted directly to large distances. That is why we need modulation of these audio signals because of following reasons:   

1. Practical height of Antenna: The height of the antenna should be comparable to the wavelength of the signal being transmitted.
   • Audio signals have low frequencies (or large wavelengths), so the height of the antenna should be very large(in kilometers) for the effective transmission of signals.
   • So to reduce this height and have a practical height, we need to increase the frequency of message signals, which is achieved by modulation.
2. Effective power radiation by Antenna: The power radiated by an antenna of length L is proportional to  \(\left(\dfrac{L}{\lambda}\right)^2\).  Because of low frequency(or high wavelength), the power radiated, and hence the range of transmission is very small. And in order to increase this power radiation, an increase in frequency is required. 
3. To Prevent intermixing of signals: Audio signals have a very small bandwidth(20Hz to 20kHz). Because of this message signals may get mixed up. 

EXPLANATION:

• Because of the low frequency of signals, the practical height of the antenna becomes very large, effective power radiation is very low and signals may intermix resulting in noises. Because of all these, we need modulation of signals.
• The correct answer is option (4) 

CONCEPT:

Attenuation:

• The loss of strength of a signal while propagating through a medium is known as attenuation.

Amplification:

• It is the process of increasing the amplitude (and consequently the strength) 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.

Modulation:

• The original low-frequency message or information signal cannot be transmitted to long distances.
• Therefore, at the transmitter, the information contained in the low-frequency message signal is superimposed on a high-frequency wave, which acts as a carrier of the information.
• This process is known as modulation.
• There are several types of modulation, abbreviated as AM, FM, and PM.

EXPLANATION:

• We know that amplification is the process of increasing the amplitude (and consequently the strength) of a signal using an electronic circuit called the amplifier. Hence, option 1 is correct.

Content:

GPS stands for Global Positioning System. It is a space-based satellite navigation system. It can provide location and time information in all weather conditions anywhere near the earth's surface. It can even provide information on objects that are not in Line of Sight. Because of this application, it is used in the military. It is controlled by the US government and anyone with GPS access can use it. 

Explanation:

The basic components of GPS are- 

1.Space Segment: This segment consists of 24 satellites that orbit around the Earth at a very high altitude (nearly 20,000 km).

2.Control Segment: This segment consists of five monitor stations and one Master control station which monitors the satellites revolving and check for any deviation from the normal working of satellites.

3.User Segment: This segment consists of the Users. Users can be both military and civil. There is no limit on the number of users that can use GPS.

The correct answer is option (3)

Concept:

1. Optical fibres can be used to transmit light and thus information over long distances. The electromagnetic spectrum is composed of visible and near-infrared light like that transmitted by fibre, and all other wavelengths used to transmit signals such as AM and FM radio and television.

For fibre optics with glass fibres, we use light in the infrared region which has wavelengths longer than visible light, typically around 850, 1300 and 1550 nm.

2. Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects.

Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz). X-band is a segment of the microwave radio region of the electromagnetic spectrum, within the frequency range 8–12 GHz.

3. Sonar is a system used for the detection of objects under water by emitting sound pulses and detecting or measuring their return after being reflected.

Ultrasonic waves (sounds having frequency greater than 20,000 Hz) are used in sonar because Ultrasonic waves can penetrate water to long distances (because of their high frequency and very short wavelength), but ordinary sound waves or infrasonic waves cannot penetrate water to such long distances.

4. A mobile phone receives microwave signals from a nearby phone (or transmitter) and sends microwave signals back. These short bursts of microwave radiation can transmit a lot of information in a very short time with frequencies between 300 MHz (1 m) and 300 GHz (1 mm).

Therefore, the correct matched pairs are