Elements of Communication System ( Analog Communications ) MCQs – Analog Communications MCQs
Latest Analog Communications MCQs
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Analog Communications MCQs – Elements of Communication System ( Analog Communications ) MCQs
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Source of Information
1. FM stands for ________
a) Frequency Modulation
b) Frequency Modulator
c) Frequent Frequent Multiplier
d) Frequency Mixer
Answer: a
Explanation: FM stands for Frequency Modulation. It is the encoding of information on a carrier wave by varying its frequency with respect to the instantaneous amplitude of the message signal. Rest other options are the components used in the process of frequency modulation.
2. Why a sinusoidal signal is considered analog?
a) It moves in both positive and negative direction
b) It is positive for one half cycle
c) It is negative for one half cycle
d) It has an infinite number of amplitudes in the range of values of the independent variable
Answer: d
Explanation: A sinusoidal wave is an analog signal. An analog electrical signal is a signal with infinite number of amplitudes in the range of values of independent variable. Analog signals can take on any value in the continuous interval.
3. The minimum height of antenna required for transmission in terms of ʎ is ________
a) 3ʎ⁄2
b) ʎ⁄4
c) 2ʎ
d) ʎ
Answer: b
Explanation: For effective transmission, height of antenna should be one-forth of ʎ.
(H = ʎ⁄4 where ʎ = c⁄f). The reason for maintaining antenna height to ʎ/4 is for matching impedance. It means that the antenna is atleast 1/4th above ground level.
4. What do you understand by the term analog communication?
a) A method in which one of the properties of a carrier signal varies in proportion to an instantaneous value of modulation signal
b) A way for data and computer communication
c) A numerical coded communication
d) A suitable method for long distance communication
Answer: a
Explanation: Analog communication means that information is transmitted in the form of a continuous signal through the process of modulation. Rests of the options are applicable for digital communication, where coding is applied.
5. What is Demodulation?
a) Process of varying one or more properties of a periodic waveform
b) Recovering information from a modulated signal
c) Process of mixing a signal with a sinusoid to produce a new signal
d) Involvement of noise
Answer: b
Explanation: Demodulation is the process of recovering information from a modulated carrier wave while it is modulation in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. A modem can perform both functions.
6. Data transmitted for a given amount of time is called ________
a) Noise
b) Power
c) Frequency
d) Bandwidth
Answer: d
Explanation: A Demodulation is a process of recovering the information signal from a modulated carrier wave, in which properties of a periodic waveform is varied. A modulator is a device that performs modulation while the demodulator performs demodulation. The process of mixing a signal with a sinusoid to produce a new signal is done by a mixer.
7. If Output can be represented as linear combination of input then ________
a) The system is linear
b) The system is causal
c) The system is non causal
d) The system is time invariant
Answer: a
Explanation: The input signal is divided into sub-components, where each sub-component is processed individually and reunited. The result is tested for additivity and homogeneity and if it satisfies both, then the system is said to be linear. It also follows superposition property.
8. Amplitude Modulation suffers from ________
a) Side-band Suppression
b) IntraPulse Modulation
c) Cross Modulation
d) Carrier Suppression
Answer: c
Explanation: Cross modulation generally occurs in receivers receiving an AM signal in the presence of other strong AM signal. The modulation from the strong signal cross modulates and appears on the weaker signal being received.
9. Medium which sends information from source to receiver is called ________
a) Transmitter
b) Transducer
c) Loudspeaker
d) Channel
Answer: d
Explanation: Channel is the medium through which information is transmitted. Transmitter is used to process the electrical signal through different aspects. The transducer is used to convert a message signal to an electrical signal. Loudspeaker is a type of Transducer.
10. Telephones send information through wires in form of ________
a) radio signals
b) electrical signal
c) electromagnetic waves
d) microwaves
Answer: b
Explanation: A telephone converts sound waves into electrical signals which are suitable for transmission over long distances, where it is converted to sound waves again, through a transducer. The essential components of a telephone are a microphone which acts as a transmitter and an earphone which acts as a receiver.
11. Cell phones sent information in form of ________
a) microwaves
b) electrical signals
c) infrared Waves
d) radio waves
Answer: d
Explanation: Cell phones transmit information in form of radio waves to communicate with each other. Radio waves are transmitted in all directions by the cell phone, and they travel at the speed of light in air or vacuum.
12. The ability of receivers to select the wanted signals among various incoming signal is called ________
a) Selectivity
b) Fidelity
c) Sensitivity
d) Modulation
Answer: a
Explanation: The ability of receiver to select wanted signal from various incoming signals is called selectivity. It rejects the other signals at closely lying frequencies. Sensitivity is the ability of the receiver to amplify weak signals. Fidelity is the feature of receiver to reproduce all modulating frequencies equally. While modulation is the process of varying one or more properties of carrier signal with respect to the modulating signal.
13. Which device is used for tuning the receiver according to incoming signal (especially in TV)?
a) Low pass filter
b) High pass filter
c) Zener diode
d) Varacter diode
Answer: d
Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in Voltage Controlled Oscillators (VCOs) and RF Filters for tuning the receiver to the incoming signal or different stations.
Transmitter
1. Modulation is done in ________
a) Receiver
b) Transducer
c) Between transmitter and radio receiver
d) Transmitter
Answer: d
Explanation: Transmitter modulates the signal to be transmitted, by varying one of the properties of a carrier signal with respect to the instantaneous amplitude of the message signal. This process is known as modulation. Receiver demodulates the modulated signal to extract the message signal. Transducer converts the electrical signal to sound wave. Between the transmitter and the radio receiver, is the channel which acts as the medium of transmission.
2. In TV transmission, picture signal is ________ modulated.
a) DSB-SC
b) VSB
c) SSB-SC
d) Pulse
Answer: b
Explanation: All analog television systems use vestigial sideband modulation, which is a form of amplitude modulation, for transmission. In VSB, one sideband is fully transmitted and another sideband is partially removed, which further reduces the bandwidth of transmitted signal. This enables narrower channels to be used.
3. In TV transmission, sound signal is ________ modulated.
a) Phase
b) Pulse
c) Frequency
d) Amplitude
Answer: c
Explanation: Amplitude Modulation is invariably used for picture transmission while frequency modulation is generally used for transmission of sound due to its inherent advantages over amplitude modulation. It is not suitable for transmitting videos due to its large bandwidth.
4. Square Law modulators are ________
a) used for frequency modulation
b) used for pulse width modulation
c) used for amplitude modulation
d) used for phase modulation
Answer: c
Explanation: Square Law modulators are generally used for the generation of amplitude modulated signals. They have nonlinear current-voltage characteristics, such that output current or voltage varies as a square of the input.
5. Ring Modulator is ________
a) used for DSB-SC generation
b) used for SSB-SC generation
c) used for VSB generation
d) used for AM generation
Answer: a
Explanation: Ring Modulator is used for generating DSB-SC modulated waves. It is a product modulator having four diodes connected in the form of a ring. It suppresses the carrier and produces the upper-sideband and lower-sideband at the output.
6. What is the role of the transmitter in the communication system?
a) to decode a signal to be transmitted
b) to convert one form of energy into other
c) to detect and amplify information signal from the carrier
d) to produce radio waves to transmit data
Answer: d
Explanation: Transmitter is used to produce radio waves which are then sent to the antennae to transmitted. It encodes or modulates the message signal before transmission. Transducer converts a signal from one form of energy to other. Receiver detects and amplifies information signal from the carrier.
7. What is the maximum transmission efficiency?
a) 67.88%
b) 33.33%
c) 73%
d) 54.03%
Answer: b
Explanation: The maximum transmission efficiency is 33.33%. It is so because 2/3rd of the total power is contained in the carrier, which conveys no useful information. Thus, only 1/3rd of total power has useful information which is transmitted. This happens in the case of SSB-SC Modulation, where the carrier is suppressed and only either of the sidebands is allowed to pass.
8. AVC stands for ________
a) Abrupt Voltage Control
b) Audio Voltage Control
c) Automatic Volume Control
d) Automatic Voltage Control
Answer: c
Explanation: AVC stands for Automatic Volume Control. It automatically adjusts the volume of an audio signal with respect to the surrounding noise, to make the signal be heard better and also to compensate noise to some extent.
9. What is the role of Amplitude limiter in the FM receiver?
a) Filtration
b) Adjust the gain of receiver
c) Amplify a weaker signal
d) Demodulate a signal
Answer: d
Explanation: Amplitude Limiter in FM receivers are used to eliminate the amplitude changes caused due to noise interference. It does so by clipping the amplitude of output signals to the desired level, irrespective of any variations in the input signal.
10. What is Carrier swing?
a) Frequency deviation
b) Width of sideband
c) Instantaneous frequency
d) Total variation in frequency
Answer: d
Explanation: Carrier swing is defined as the total variation in frequency from the lowest to the highest point. It is equal to twice the frequency deviation of FM signal. The rest of the options are parameters in FM.
Receiver
1. Demodulation is done in ________
a) Channel
b) Receiver
c) Receiving antenna
d) Transducer
Answer: b
Explanation: Demodulation refers to extracting the original message signal from a transmitted modulated wave. The extraction of the message signal is generally carried out in the receiver. Channel is the medium through which the modulated message signal is transferred and Antenna receives the transmitted signal. Transducer converts the electrical signal to sound waves and vice-versa.
2. What is Fidelity?
a) Equally amplifies all the signal frequencies at receiver
b) Ability of receiver to select wanted signal from various incoming signal
c) Minimum magnitude of input signal required to produced a specified output
d) Ability to amplify weak signals
Answer: a
Explanation: Fidelity is the ability of the receiver to reproduce all modulating signals, equally, without any distortion. The ability of receiver to select wanted signal from various incoming signals is called Selectivity while Sensitivity is the minimum magnitude of input signal required to produce a specified output. It is the ability to amplify weak signals.
3. In a receiver, noise is usually developed at ________
a) Audio stage
b) Receiving antenna
c) RF stage
d) IF stage
Answer: c
Explanation: Ability of receiver to selected only wanted signal, and reject other frequencies, out of the various incoming signals, helps the receiver to operate more efficiently. However, at times, the RF amplifier allows a frequency lying close to the desired frequency, to pass to the next stage. This other frequency is undesired and later on is responsible for production of image frequency. Thus, noise is usually developed at RF stage.
4. Which oscillator is used as a local oscillator in radio receiver?
a) Wien-bridge
b) Hartley
c) Crystal
d) Phase Shift
Answer: b
Explanation: Oscillator which is used as a local oscillator in radio receiver is generally a tuned circuit. This tuned circuit consists of inductors and capacitors to determine the resonant frequency, therefore it is an LC tuned circuit. Out of the four options, only Hartley Oscillator has an LC resonant tank circuit.
5. Process of recovering information signal from received carrier is known as ________
a) Sensitivity
b) Selectivity
c) Demodulation
d) Fidelity
Answer: c
Explanation: Demodulation means extracting information or message signal from the transmitted modulated wave, while minimum magnitude of input signal required to produced a specified output is known as Sensitivity. The ability of receiver to select wanted signal from various incoming signals is called Selectivity. Fidelity means reproducing all modulating frequencies equally, without any distortion.
6. What is the use of a varactor diode in radio receiver?
a) Demodulation
b) Mixing
c) Multiplexing
d) Tuning
Answer: d
Explanation: Varactor diode is a diode working in the reverse-bias because of which no current flows through it. It has variable capacitance which varies with applied voltage. Varactor diodes are mainly used in Voltage Controlled Oscillators (VCOs) and RF Filters for tuning the receiver to the incoming signal or different stations.
7. What is the function of radio receiver?
a) to detect and amplify information signal from the carrier
b) to modulate a message signal
c) to produce radio waves
d) to convert one form of energy into other
Answer: a
Explanation: Receiver is to detect and amplify information signal from the carrier. Transmitter is used to modulate message signal and produce radio waves. Transducer is used to convert one signal form of energy into another form.
8. Figure of merit is ________
a) Ratio of output signal to noise ratio to input signal to noise ratio
b) Ratio of input signal to noise ratio to output signal to noise ratio
c) Ratio of output signal to input signal to a system
d) Ratio of input signal to output signal to a system
Answer: a
Explanation: Figure of merit is a numerical quantity based on the characteristic of system that represents a measure of efficiency or effectiveness. It is defined as the ratio of output signal to noise ratio to input signal to noise ratio.
9. Superheterodyne principle provides selectivity at ________
a) RF stage
b) IF stage
c) Demodulating Stage
d) Audio Stage
Answer: b
Explanation: A superheterodyne receiver uses frequency mixing to convert the received high frequency signal to a fixed lower intermediate frequency (IF), which can be processed more conveniently than original received frequency. Thus, the principle of selectivity is applied at the IF stage as it consists of very efficient filters to only select a wanted signal and pass it to the Demodulating Stage.
10. A heterodyne frequency changer is ________
a) Mixer
b) Demodulator
c) Modulator
d) Local Oscillator
Answer: a
Explanation: A mixer is a nonlinear electrical circuit that multiplies two signal frequencies applied to it, and produces a new frequency. Mixers are widely used to shift signals from one frequency range to other, which is known as heterodyning process. Generally, Local Oscillator generates a frequency to be applied at one of the input terminals of the mixer. Demodulator decodes the message signal from modulated signal, while modulator encodes message signal for transmission.
Channel
1. Notch is a ________
a) High pass filter
b) Low pass filter
c) Band stop filter
d) Band pass filter
Answer: c
Explanation: Notch filter is a band stop filter that allows most frequencies to pass through it, except frequencies in a specific range. It is just opposite of a band-pass filter. High pass filter allows higher frequencies to pass while Low pass filter allows lower frequencies to pass through it.
2. Sin wave is ________
a) Aperiodic Signal
b) Periodic Signal
c) Random Signal
d) Deterministic Signal
Answer: b
Explanation: Periodic signal is that which repeats itself after a regular interval. Sin wave is a periodic function since it’s value can be determined at any point of time, as it repeats itself at a regular interval. Aperiodic Signal does not repeat itself at regular interval of time. Random signals are the signals which have uncertain values at any time. While Deterministic signals are the signals which are constant over a period of time.
3. What is the role of channel in communication system?
a) acts as a medium to send message signals from transmitter to receiver
b) converts one form of signal to other
c) allows mixing of signals
d) helps to extract original signal from incoming signal
Answer: a
Explanation: Channel acts as a medium to transmit message signal from source transmitter to the destination receiver. Transducer converts a signal from one form of energy to other. Mixer allows mixing of signals while Demodulator helps to extract original message signal from incoming signal.
4. Sum of a periodic and aperiodic signal always be an aperiodic signal.
a) True
b) False
Answer: b
Explanation: Periodic signal is a signal which repeats itself after a regular interval. While Aperiodic Signal does not repeat itself at regular interval of time.
For example: Let f(x) = sin(x), be a periodic function with period 2π and g(x) = −sin(x) + sin(√2x), be an aperiodic function. Now the sum of both i.e. f(x) + g(x) = sin(√2x), which is a periodic function.
Therefore, the sum of a periodic and aperiodic signal can be periodic.
5. Noise is added to a signal ________
a) In the channel
b) At receiving antenna
c) At transmitting antenna
d) During regeneration of information
Answer: a
Explanation: Noise is an unwanted signal that gets mixed with the transmitted signal while passing through the channel. The noise interferes with the signal and provides distortion in received signal. The transmitting antenna transmits modulated message signal while the receiving antenna receives the transmitted signal. Regeneration of information refers to demodulating the received signal to produce the original message signal.
6. Agreement between communication devices are called ________
a) Transmission medium
b) Channel
c) Protocol
d) Modem
Answer: c
Explanation: Protocol is a set of rules that looks after data communication, by acting as an agreement between communication devices. Channel is the transmission medium or the path through which information travels. Modem is a device that modulates and demodulates data.
7. What is the advantage of superheterodyning?
a) High selectivity and sensitivity
b) Low Bandwidth
c) Low adjacent channel rejection
d) Low fidelity
Answer: a
Explanation: The main advantage of superheterodyning is that it provides high selectivity and sensitivity. It’s bandwidth remains same. It has high adjacent channel rejection and high fidelity.
8. Low frequency noise is ________
a) Flicker noise
b) Shot noise
c) Thermal noise
d) Partition Noise
Answer: a
Explanation: Flicker noise is a type of electronic noise which is generated due to fluctuations in the density of carrier. It’s also known as 1/f as it’s power spectral density increases with a decrease in frequency or increase in offset from a signal.
9. Relationship between amplitude and frequency is represented by ________
a) Time-domain plot
b) Phase-domain plot
c) Frequency-domain plot
d) Amplitude-domain plot
Answer: c
Explanation: Relationship between amplitude and frequency is represented by a frequency-domain plot. Also, it represents the relation between phase and frequency. While a time-domain plot shows how a signal varies over time.
10. A function f(x) is even, when?
a) f(x) = -f(x)
b) f(x) = f(-x)
c) f(x) = -f(x)f(-x)
d) f(x) = f(x)f(-x)
Answer: b
Explanation: Geometrically a function f(x) is even, if plot of the function is symmetric over y-axis. Algebraically, for any function f(x) to be even, f(x) = f(-x).
While for a function f(x) to be odd, f(x) = -f(-x).