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Communications MCQ Set 1

1. As the length of a long-wire antenna is increased ________
a) the number of lobes also increase
b) the number of lobes decrease
c) efficiency increase
d) the number of nodes decrease

View Answer

Answer: a [Reason:] An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. If the length of a long wire antenna is increased then the number of lobes also increases.

2. A non-resonant antenna will________
a) not transmit
b) not receive
c) cause SWR on the feed cable
d) transmit and receive the signal at the same time

View Answer

Answer: c [Reason:] A non-resonant antenna have wider bandwidth as compared to resonant antenna. It also has less sensitivity than resonant antenna. A non-resonant antenna will cause SWR on the feed cable.

3. The typical antenna in an AM radio is a ________
a) dipole
b) folded dipole
c) ferrite “loop-stick”
d) loop dipole

View Answer

Answer: c [Reason:] The ferrite rod antenna is a form of RF design that is universally used in portable transistors broadcast receivers. It is also being used increasingly in wireless applications in areas such as RFID. It is a type of typical antenna in an AM radio.

4. A 1-MHz monopole antenna must be ________
a) mounted vertically
b) mounted horizontally
c) atleast one half wavelength long
d) atleast one wavelength long

View Answer

Answer: a [Reason:] A monopole antenna consists of a straight rod shaped conductor. It is often mounted perpendicularly over some type of conductive surface, called a ground plane.

5. “Ground Effects” in antenna effects ________
a) antenna’s radiation
b) antenna’s reception capacity of signals
c) antenna’s SWR
d) antenna’s power

View Answer

Answer: a [Reason:] Ground generally reflects the wave back that comes to it. It also affects antenna by effecting the radiation.

6. An antenna’s beamwidth is measured ________
a) from +90° to -90°
b) between half power points
c) between the minor side lobes
d) from front to back

View Answer

Answer: b [Reason:] The angle between the half power points of the main lobe with respect to the peak effective radiated power is called half power beamwidth. It is generally measured between half power points.

7. What is the front to back ratio of a half wave dipole antenna?
a) 0 dB
b) 10 dB
c) 100 dB
d) infinite

View Answer

Answer: a [Reason:] The front to back ratio mean the ratio of power gain between the front and back of a directional antenna. For a half-wave dipole antenna its value comes out to be 0dB.

8. AM waves is represented by Et cos⁡ ωc t. What does Et denotes?
a) Envelope
b) carrier signal
c) modulating signal
d) amplitude

View Answer

Answer: a [Reason:] AM wave is represented by (A+xt) cos⁡ ωc t or Et cos⁡ ωc t, where xt is modulating signal, A is amplitude and Et is amplitude of AM wave.

9. The radiation of energy from an antenna can be seen in the ________
a) standing wave around antenna
b) radiation resistance of the antenna
c) reflected resistance of the antenna
d) I2R loss of the antenna

View Answer

Answer: b [Reason:] An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. Radiation resistance of the antenna is just a measure of radiation of energy from antenna.

10. The end-to-end length of a half wave dipole antenna is actually ________
a) slightly shorter than a half wavelength
b) slightly longer than a half wavelength
c) one half wavelength
d) one wavelength

View Answer

Answer: a [Reason:] The half way dipole antenna is also known as Hertz antenna. It consists of two straight collinear conductors of equal length separated by a small feeding gap. The length of half wave dipole antenna is slightly shorter than half wavelength.

Communications MCQ Set 2

1. Which statement is true about thermal noise power?
a) it is proportional to B
b) it is proportional to √B
c) it is proportional to B2
d) it is proportional to √B2

View Answer

Answer: a [Reason:] Thermal noise is effectively white noise. It extends over a wide range spectrum. Its noise power is proportional to the bandwidth.

2. What is the probability density function of thermal noise?
a) Poisson
b) Gaussian
c) Binomial
d) Armstrong

View Answer

Answer: b [Reason:] Thermal noise is approximately white, it means that its power spectral density is nearly equal throughout the frequency spectrum. The amplitude of the signal has a Gaussian probability density function.

3. Cosmic noise is caused by ________
a) Distant stars
b) Lightning discharge
c) Solar eruptions
d) Disturbances in galaxy

View Answer

Answer: a [Reason:] Cosmic noise a random noise that originates from outside the earth’s atmosphere. It can be detected and heard on radio receivers.

4. Which of the following filter is used only at higher frequencies?
a) Ladder
b) Crystal Gate
c) Half Lattice
d) Full Lattice

View Answer

Answer: a [Reason:] It is the ladder filter which is used only at higher frequencies.

5. Sampling theorem finds application in ________
a) FM
b) PCM
c) AM
d) DM

View Answer

Answer: b [Reason:] Sampling theorem can be seen as a fundamental bridge between continuous time signals and discrete time signals. It finds its application in Pulse Code Modulation (PCM).

6. The channel capacity is exactly equal to which of the following?
a) Bandwidth
b) Noise rate
c) Amount of information per second
d) Loudness

View Answer

Answer: c [Reason:] The channel capacity of a communication system is exactly equal to the amount of information per second.

7. The ionosphere consists of __________ layer?
a) negative charge
b) positive charge
c) more positive charge than negative charge
d) neutral

View Answer

Answer: a [Reason:] The ionosphere is the ionized part of Earth’s upper atmosphere. It consists of negative layer.

8. The noise performance of a square law demodulator of AM signal is ___________
a) Identical with that of a synchronous
b) Better than that of an envelope detector
c) Better than that of a synchronous detector
d) Poorer than that of an envelope detector

View Answer

Answer: c [Reason:] The noise performance of a square law demodulator of AM signal is better than that of a synchronous detector.

9. Which two networks can be used for impedance matching?
a) pi network and T network
b) pi network and bridge network
c) bridge network and T network
d) pi network and omega network

View Answer

Answer: a [Reason:] Generally the two networks which is used for impedance matching are pi and T network.

10. Which system is free from noise?
a) FM
b) AM
c) Both AM and FM
d) PM

View Answer

Answer: a [Reason:] Noise is the unwanted signal or disturbances in a communication system. It is frequency modulated system which remains free from noise.

Communications MCQ Set 3

1. The real part of an antenna’s input impedance is due to ________
a) SWR
b) radiated signal
c) reflected signal
d) shape of antenna

View Answer

Answer: b [Reason:] In antenna impedance, impedance related the voltage and current at the input of the antenna. The real part of antenna impedance represents power that is either radiated away or absorbed within the antenna and the imaginary part of antenna impedance represents power that is stored in the near field of antenna.

2. If power transmitted is 90kW, what is the field at a distance of 45km?
a) 2
b) 1
c) 0.036
d) 0.01

View Answer

Answer: c [Reason:] analog-communications-questions-answers-time-division-multiplexing-q2

3. What is the other name for half-wave dipole antenna?
a) Marconi antenna
b) Isotropic antenna
c) Hertz antenna
d) Maxwell antenna

View Answer

Answer: c [Reason:] The Hertz antenna is also known as half wave dipole antenna. It consists of two straight collinear conductors of equal length separated by a small feeding gap.

4. Measured on the ground, the field strength of a horizontally polarized half wave dipole antenna is strongest ________
a) in one direction
b) in two directions
c) depends on the number of elements
d) depends on the shape of antenna

View Answer

Answer: b [Reason:] As the name suggests, half wave dipole is half wavelength long. This antenna has the shortest resonant length that can be used for a resonant dipole. The field strength of a horizontally polarized half wave dipole antenna is strongest in two directions.

5. A device uses a 8 bit word then the maximum number of words it can transmit is ________
a) 64
b) 256
c) 1024
d) 512

View Answer

Answer: b [Reason:] Number of words it can transmit is 28 = 256.

6. When an antenna radiates more energy in one direction than in other directions, it is called ________
a) selectivity
b) directivity
c) active antenna
d) resonance

View Answer

Answer: b [Reason:] When an antenna radiates more energy in one direction than in other directions is called directivity. An antenna that radiates equally in all directions has effectively zero directionality, and the directivity of this type of antenna should be 1 (or 0dB).

7. What is the full form of ERP?
a) Effective Radiated Power
b) Effective Reflected Power
c) Equivalent Radiated Power
d) Equivalent Reflected Power

View Answer

Answer: a [Reason:] ERP stands for Effective Radiated Power. Effective Radiated Power (ERP) is always given with respect to a certain direction.

8. “Ground Effect” in antenna caused by ________
a) faulty connection of the feed cable ground
b) fading
c) buildings and other structures on ground
d) radio signals reflecting off the ground

View Answer

Answer: d [Reason:] Radio signals that are reflecting back from the ground is responsible for ground effects in antenna.

9. The polarization of plane waves received from satellite is changed by ________
a) Faraday rotation
b) Gamma rays
c) Helical rotation
d) Distance travelled

View Answer

Answer: a [Reason:] Generally for satellite communication circular polarization is required. The polarization received by waves from satellite is changed by Faraday rotation.

10. What is the input impedance to a lossless antenna, at resonance?
a) infinite
b) 0
c) resistive
d) capacitive

View Answer

Answer: c [Reason:] In antenna impedance, impedance related the voltage and current at the input of the antenna. The real part of antenna impedance represents power that is either radiated away or absorbed within the antenna and the imaginary part of antenna impedance represents power that is stored in the near field of antenna. The input impedance of a lossless antenna is purely resistive.

Communications MCQ Set 4

1. Distance between direct broadcasting satellite and earth’s surface is ________
a) 4500km
b) 33000km
c) 5200km
d) 36000km

View Answer

Answer: d [Reason:] A communication satellite amplifies radio telecommunications signals with the help of a transponder. The distance between it and earth’s surface is approximately 36000km.

2. UHF stands for ________
a) Ultra High Field
b) Ultraviolet High Frequency
c) Ultra High Frequency
d) Ultraviolet High Field

View Answer

Answer: c [Reason:] Ultra High Frequency is actually the range of radio frequencies between 300MHz and 3GHz. It is also known as the decimetre range.

3. What is the ITU designation range for VHF?
a) 10 to 10000 Megahertz
b) 10 to 1000 Megahertz
c) 30 to 300 Megahertz
d) 30 to 30000 Megahertz

View Answer

Answer: c [Reason:] VHF stands for very high frequency. Its range for radio frequencies lies between 30 to 300 MHz.

4. Effective noise at high frequencies is ________
a) Johnson noise
b) Flicker noise
c) transit-time noise
d) shot noise

View Answer

Answer: c [Reason:] If the time taken by electrons to reach from emitter to collector is comparable to the period of signals being amplified, then it is called transit time.

5. VHF stands for ________
a) very high frequency
b) very high electric field
c) very high magnetic field
d) very high electromagnetic field

View Answer

Answer: a [Reason:] VHF stands for very high frequency. Its range for radio frequencies lies between 30 to 300 MHz.

6. Which among the following is Analog Continuous Modulation technique?
a) PAM
b) PCM
c) AM
d) PM

View Answer

Answer: c [Reason:] AM is a technique used generally for electronic communication, mostly it is used for transmitting information via a radio wave. In today’s world Quadrature Amplitude Modulation is generally used because it makes the efficient use of available bandwidth.

7. ITU stands for ________
a) Indian Telecommunication Union
b) Indian Telephonic Union
c) International Transmittance Union
d) International Telecommunication Union

View Answer

Answer: d [Reason:] ITU is the United nations agency for information and communication technologies. It allocate global radio spectrum and satellite orbits.

8. If AM transmitter has low level modulation then it has ________
a) high efficiency
b) poor efficiency
c) high modulating power
d) high resistancy towards noise

View Answer

Answer: b [Reason:] In AM transmitter, electricity flowing into the transmitter antenna makes electrons vibrate up and down to produce radio waves. If the transmitter has low level modulation then it not generate radio waves easily and thus has poor efficiency.

9. Radiation resistance of an antenna is ________
a) a dc resistance
b) an ac resistance
c) either a dc or ac resistance
d) neither ac nor dc resistance

View Answer

Answer: b [Reason:] Radiation resistance is that part of an antenna which is caused by radiation of electromagnetic waves from the antenna. Radiation resistance of an antenna is usually an ac resistance.

10. What do you understand by isotropic antenna?
a) it radiates its power uniformly in all directions
b) it radiates its power non-uniformly in all directions
c) it radiates its power specifically in one direction only
d) it not radiates any power

View Answer

Answer: a [Reason:] Isotropic antenna is considered as an ideal antenna because it radiated its power uniformly in all directions. Generally this type of antenna not exists.

Communications MCQ Set 5

1. Modulation is done in ________
a) Receiver
b) Transducer
c) Between transmitter and radio receiver
d) Transmitter

View Answer

Answer: d [Reason:] Transmitter combines the signal which is to be carried with the radio frequency signal, or carrier signal. This process is called modulation.

2. In TV transmission, picture signal is ________ modulated.
a) Phase
b) Amplitude
c) Frequency
d) Pulse

View Answer

Answer: b [Reason:] All analog television systems use vestigial sideband modulation, which is a form of amplitude modulation. In VSB one sideband is partially removed which further reduces the bandwidth of transmitted signal.

3. In TV transmission, sound signal is ________ modulated.
a) Phase
b) Pulse
c) Frequency
d) Amplitude

View Answer

Answer: c [Reason:] 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 it’s 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

View Answer

Answer: c [Reason:] Square Law modulators are generally used for generation of amplitude modulation. They have nonlinear current-voltage characteristics. They are highly nonlinear in low voltage region.

5. Ring Modulator is ________
a) used for DSB-SC generation
b) used for SSB-SC generation
c) is a summation modulator
d) consists three diodes connected in form of a ring

View Answer

Answer: a [Reason:] Ring Modulator is used for generating DSB-SC waves. It is a product modulator having four diodes connected in the form of a ring.

6. What is the role of transmitter in communication system?
a) to transmit message
b) to convert one form of energy into other
c) to detect and amplify information signal from the carrier
d) to process the electrical signal from different aspects

View Answer

Answer: d [Reason:] Transmitter is used process the electrical signal from different aspects. Transducer is used to convert one form of energy into another form and the role of receiver is to detect and amplify information signal from the carrier and Channel is a medium through which a message is transmitted.

7. What is the maximum transmission efficiency?
a) 67.88%
b) 33.33%
c) 73%
d) 54.03%

View Answer

Answer: b [Reason:] The maximum transmission efficiency is 33.33%. Since 2/3 of power is in carrier which conveys no useful information. So we left with only 1/3 of power.

8. AVC stands for ________
a) Abrupt Voltage Control
b) Audio Voltage Control
c) Automatic Volume Control
d) Automatic Voltage Control

View Answer

Answer: c [Reason:] AVC stands for Automatic Volume Control. It automatically adjusts the volume of an audio signal to make it better and also to compensate noise to some extent.

9. What is the role of Amplitude limiter in FM receiver?
a) Filteration
b) Amplification
c) Demodulation
d) Remove amplitude variation due to noise

View Answer

Answer: d [Reason:] If there are any variations in the amplitude of received wave, it is due to noise. The limiter eliminates this by clipping the received modulated wave.

10. What is Carrier swing?
a) Frequency deviation
b) Width of sideband
c) Frequency deviation less than carrier frequency
d) Total variation in frequency

View Answer

Answer: d [Reason:] Carrier swing is defined as the total variation in frequency from the lowest to highest point. It is equal to two times frequency deviation of FM signal.