Basics of Communication System MCQ Quiz - Objective Question with Answer for Basics of Communication System - Download Free PDF

Output Waveform of a Variable Frequency Drive (VFD):

• A Variable Frequency Drive (VFD) is used to control the speed and torque of an electric motor by varying the frequency and voltage supplied to the motor.
• The VFD converts the fixed frequency AC power to variable frequency, which allows precise control of motor speed.

Pulse Width Modulation (PWM) Technique:

• VFDs commonly use Pulse Width Modulation (PWM) to generate the output waveform.
• In the PWM technique, a high-frequency square wave signal is modulated to approximate a sine wave.
• The width of the pulses is varied in a way that the average voltage over a cycle corresponds to the desired sine wave shape.
• By adjusting the pulse width, the VFD can effectively control the voltage and frequency supplied to the motor.

Advantages of PWM:

• High efficiency and low harmonic distortion.
• Precise control over motor speed and torque.
• Improved power factor and reduced energy consumption.

Conclusion:

• The output waveform of a VFD is a pulse width modulated sine wave (option 2), which allows for efficient and precise control of motor operation.
• This method ensures that the motor receives a waveform that closely approximates a pure sine wave while allowing for variable speed control.

Advantages of Using a High Frequency Carrier Wave:

• Signal Transmission Over Long Distances: High frequency carrier waves can be modulated with the signal information and transmitted over very long distances with less attenuation. This is because higher frequency waves have higher energy and can travel further before their energy dissipates.
• Reduced Power Dissipation: High frequency carrier waves dissipate less power compared to lower frequency waves. This is because they can be transmitted more efficiently with less loss of energy as heat, allowing for more effective power use.
• Reduced Antenna Height: The height of the transmitting antenna is inversely proportional to the frequency of the wave. Higher frequency waves require shorter antennas, making the design and construction of transmission systems more practical and cost-effective.

In summary, using a high frequency carrier wave provides multiple advantages such as efficient long-distance transmission, lower power dissipation, and reduced antenna height. Therefore, the correct option is All of the above.

The correct answer is: IEEE 802.11

Explanation:

The IEEE 802.11 specification is the standard that defines the protocols for implementing wireless local area network (WLAN) communications in the 2.4, 3.6, and 5 GHz frequency bands. It covers both the physical (PHY) layer and the data link layer (DLL) of the OSI model. The IEEE 802.11 standard is widely known as Wi-Fi, which is a trademark of the Wi-Fi Alliance, an association of companies that certifies products for interoperability.

Let's briefly explain the other options for clarity:

• IEEE 802.3 is the standard for Ethernet, a technology for wired LAN networking that specifies the physical and data link layers.
• IEEE 802.5 was the standard for Token Ring, a type of wired LAN networking technology. It has largely become obsolete, overtaken by faster Ethernet technologies.
• IEEE 802.2 specifies the Logical Link Control (LLC) layer, which is the upper sublayer of the data link layer in the OSI model. It is used in both IEEE 802.3 Ethernet and IEEE 802.11 Wi-Fi but is not by itself a specification for a wireless LAN.

Therefore, IEEE 802.11 is the correct specification that covers the requirements for a wireless LAN, addressing both the physical and data link layers of network architecture.

In communication, the message is the information that the communicator conveys to the audience.

Key Points

• It can be verbal or nonverbal, and it can be expressed in a variety of ways, such as through words, images, sounds, or gestures.
• The message is the core of communication, as it is the substance that the communicator aims to transmit to the audience.

Hint

• Action is the physical or verbal response of the audience to the message. 
• Behavior is the outward expression of a person's thoughts and feelings

Therefore, the correct answer is message. 

The correct option is 3

Concept:

In AM modulation, the modulation index 'or' modulation depth (m) is defined as a measure of the extent to which a carrier voltage is varied by the modulating signal.

It is one of the key parameters whose value determines if there is a distortion in the AM signal or not.

It is evaluated mathematically as:

\(μ=\frac{A_m}{A_c}\)

For three different values of the modulation index, we have different output waveforms:

Under Modulation (μ < 1):

Critical Modulation (μ = 1):

Over Modulation (μ > 1):

Observation:

• As the value of the modulation index increases, the carrier experiences a 180° phase reversal, which causes additional sidebands, and hence, the wave gets distorted.
• Such an overmodulated wave causes interference, which cannot be eliminated.

• Heterodyning is a signal processing technique that creates new frequencies by combining or mixing two frequencies
• Heterodyning is used to shift one frequency range into another frequency
• It is used in the process of modulation and demodulation
• Hence during the heterodyne process in the receiver, the modulation of the signal is not changed

Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in communication system when a transmitted signal propagates along channel it may get distorted due to channel imperfection also noise adds to transmitted signal.

Addition of noise in channel is most likely to affect signal recovery due to low signal strength cause of path loss.

• Wi-Fi is the wireless network system most commonly used in the homes to connect multiple electronic devices through the internet. An instrument called a router is needed to connect the several instruments through the internet.
• IEEE 802.11 specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN), Wi-Fi computer communication in various frequencies. 
• WiFi uses radio frequencies to send signals between devices. 
• WiFi works at a frequency of 2.4 GHz and 5 GHz. 

Modulation is a process of varying one or more properties of a carrier signal (High-frequency signal) with a modulating signal (Low-frequency signal). Hence, Modulation is the process of combining signal and radiofrequency.

Need for Modulation:

• It is needed in order to match the characteristics of the input signal to that of channel characteristics.
• Low-frequency signals can be multiplexed with high-frequency signals to travel long distances.
• Wireless transmission of low pass signal is made possible due to modulation.
• Practically realization of antenna size can be achieved.
• Some modulation technique reduces the effect of noise on the signal.

The AM, FM, and PM output waveforms are as shown:

In Frequency modulation, the frequency of the carrier is varied according to the amplitude of the message signal and the amplitude of the carrier remains constant.

Concept:

The total transmitted power for an AM system is given by:

\({P_t} = {P_c}\left( {1 + \frac{{{μ^2}}}{2}} \right)\)

Pc = Carrier Power

μ = Modulation Index

The above expression can be expanded to get:

\({P_t} = {P_c} + P_c\frac{{{μ^2}}}{2}\)

The total power is the sum of the carrier power and the sideband power, i.e.

\({P_s} = P_c\frac{{{μ^2}}}{2}\)

Calculation:

Given: P_c = 1000 W and μ = 0.8.

We can write:

\({P_s} = P_c\frac{{{μ^2}}}{2}\)

\(= 1000 \times \frac{0.8^2}{2}\)

\(P_s=320~W\)

The total sideband power = 320 W

power in upper sideband + power in lower side band = 320 W

power in upper sideband = power in lower sideband = 160 W

Explanation:

Shadowing is a type of large-scale fading in wireless communication.

• Shadowing is caused by obstacles between the transmitter and receiver that attenuate signal power through absorption, reflection, scattering, and diffraction. When the attenuation is strong, the signal is blocked.
• Received power variation due to path loss occurs over long distances (100–1000 m), whereas variation due to shadowing occurs over distances that are proportional to the length of the obstructing object (10–100 m in outdoor environments and less in indoor environments). Since variations in received power due to path loss and shadowing occur over relatively large distances, these variations are sometimes referred to as large-scale propagation effects.
• Large scale fading, or shadowing is fading that occurs on several meters or more; it reflects conditions that may vary as one turns a corner, moves behind a large building, or enters a building.

Additional InformationFading is a significant part of any wireless communication design and is important to model and predict accurately. There are two very different types of fading: small scale fading and large scale fading (or shadowing). Small scale fading is often handled in a wireless system with diversity schemes. Large scale shadowing, on the other hand, is very dependent on location with respect to obstacles; its modeling often consists in predicting the likelihood of outage.

Concept:

• The process of superimposing a message signal with a carrier wave is known as modulation.
• In modulation, the message signal is used to modify the characteristics of the carrier wave, such as its amplitude, frequency or phase, in order to carry information.
• The resulting modulated wave can then be transmitted through a communication channel, such as a radio frequency transmission system, where it can be received and demodulated to recover the original message signal.
• Modulation is a key technique used in many forms of communication, including radio, television, and digital communications.

Additional Information Need for Modulation:

1. It is needed in order to match the characteristics of the input signal to that of channel characteristics.

2. Multiplexing is made possible due to modulation.

3. Wireless transmission of low-pass signal is made possible due to modulation.

4. Practically realization antenna size can be achieved

5. Some modulation technique reduces the effect of noise on the signal.

Important PointsThe AM, FM, and PM output waveforms are as shown:

Concept:

• Forward or downlink channels are used to transmit data from the base station to mobile devices.
• Reverse or uplink channels are the channels used to transmit data from cell phones to base stations.
• The forward control channel and the reverse control channel are responsible for call initiation and service requests.
• During a call, a user's call may be moved from one base station to another. The term "handoff" refers to the method of exchange.

MODEM:

• Modem stands for Modulator-demodulator.
• It converts the analog signals from the transmission wires into digital signals which can be read by the computer devices (modulation).
• Then conversion of digital signal into analog and extracting out the useful information (demodulation) takes place.

​Important Points

Multiplexers:

• A multiplexer is a combinational circuit.
• A multiplexer is Many to one data selector.
• A multiplexer selects one of the many data available at its input depending on the bits on the select line.
• For 2n inputs, there are n select lines that determine, which input is to be connected to the output.

Gateway: A gateway is networking hardware used in telecommunications for telecommunications networks that allows data to flow from one discrete network to another.

Serial Port: An asynchronous port on the computer used to connect a serial device to the computer and capable of transmitting one bit at a time.

The correct option is  (B), (A), (D), (C), (E)"

Important Points

This sequence of elements represents Aristotle's model of communication, also known as the "Aristotelian model" or the "Rhetorical Triangle." According to Aristotle, effective communication involves the following five elements:

1. Speaker: The person responsible for delivering the message
2. Speech: The message itself, including the words, tone, and delivery style used by the speaker
3. Occasion: The context in which the message is being delivered, including the purpose, audience, and setting
4. Audience: The individuals or groups to whom the message is directed
5. Effect: The impact that the message has on the audience, including the attitudes, beliefs, and behaviors that it elicits

In this model, the speaker and speech are the central elements of communication, with the occasion and audience serving as the context in which the message is delivered, and the effect representing the outcome of the communication process. According to Aristotle, effective communication requires the speaker to carefully consider all of these elements and tailor their message to the particular audience and occasion in order to maximize its impact.

Additional Information

The Aristotle model of communication is a linear model with a focus on public speaking. The Aristotle model of communication was developed by the Greek philosopher and orator Aristotle, who proposed the linear model to demonstrate the importance of the speaker and their audience during communication.

It comprises three key elements:

• Ethos (the speaker’s degree of credibility or authority),
• Pathos (the ability of the speaker to form an emotional bond with the audience), 
• Logos (the literal meaning of the word logos is logic).
• "Rhetorical Triangle.
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