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## Communications MCQ Set 1

1. The disadvantage of FM over AM is that high output power is needed.
a) True
b) False

Answer: b [Reason:] The disadvantage of FM over AM is that in frequency modulation large bandwidth is required.

2. Which theorem states that a noiseless Gaussian channel has zero capacity?
a) Beckman-Quarles theorem
b) Bell’s theorem
c) Cameron-Martin theorem
d) Shannon-Hartley theorem

Answer: d [Reason:] According to Shannon Hartley theorem, a noiseless channel has infinite capacity.

3. Linear devices are used in __________
a) high level AM modulator
b) low level AM modulator
c) high level FM modulator
d) low level FM modulator

Answer: b [Reason:] A low level AM is the one where the modulation is applied to low power stage of the transmitter. The drawback of this approach is that linear amplification is required for RF stages.

4. A noiseless Gaussian channel has _____________
a) zero capacity
b) small capacity
c) infinite capacity
d) can’t be determined

Answer: b [Reason:] According to Shannon Hartley theorem, a noiseless channel has infinite capacity.

5. Advantage of high level modulator is that it requires linear amplifiers.
a) True
b) False

Answer: b [Reason:] A high level modulator modulates a high power section of the circuit. It has the advantage that linear amplifiers are not required.

6. Carrier wave in modulation is a wave which is to be transmitted.
a) True
b) False

Answer: b [Reason:] Carrier wave is basically a voltage whose parameters such as amplitude, frequency and phase can be for modulation.

7. It is only the wavelength which decides the color of an object.
a) True
b) False

Answer: b [Reason:] Color of any object is decided by the reflected color for opaque object and wavelength transmitted through it for transparent object.

8. Circular polarization is used in discrimination between reception of adjacent beams.
a) True
b) False

Answer: b [Reason:] In circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate. It is used to reduce depolarization effect on received waves not for discrimination between reception of beams.

9. VSB modulation is used in televisions because it results in better reception.
a) True
b) False

Answer: b [Reason:] VSB modulation is generally preferred for televisions because it reduces the required bandwidth to half.

10. A cordless telephone that uses separate frequencies for transmission is known as half duplex.
a) True
b) False

Answer: b [Reason:] It is Duplex which uses separate frequencies for transmission in base and portable units.

## Communications MCQ Set 2

1. Detection is same as ________
a) Modulation
b) Fidelity
c) Selectivity
d) Demodulation

Answer: d [Reason:] Process of extracting the modulation from signal is called demodulation. Demodulation is also known as detection. For AM, the process of detection can be accomplished by using a diode.

2. Most commonly used modulation system for telegraphy is ________
a) Two tone modulation
b) Single tone modulation
c) PCM
d) FSK

Answer: d [Reason:] FSK (Frequency Shift Keying) is a system of frequency modulation generally used in telegraphy. Simplest form of FSK is binary FSK (BFSK). It uses a pair of discrete frequencies to transmit binary information.

3. What do you understand by the term “carrier”?
a) voltage with constant frequency, phase and amplitude
b) voltage for which frequency, amplitude or phase is varied
c) resultant wave
d) voltage to be transmitted

Answer: b [Reason:] A carrier wave is modulated with an input signal for conveying the information. Carrier wave has generally higher frequency than the input signal.

4. According to Fourier analysis, square wave can be represented as ________
a) fundamental sine wave and even harmonics
b) fundamental sine wave and odd harmonics
c) fundamental sine wave and harmonics
d) fundamental and sub harmonic sine wave

Answer: b [Reason:] A square is a non-sinusoidal periodic waveform in which the amplitude alternates between a fixed maximum and minimum value. According to fourier analysis, square wave is represented as the limit case of an infinite series of sinusoidal waves. A ideal square wave contains only components of odd integer harmonics.

5. PDM is generated by ________
a) combination of two series amplifiers
b) Monostable multivibrator
c) Astable multivibrator
d) Schmitt trigger

Answer: b [Reason:] Monostable multivibrators are used to generate a single output pulse of a particular width. Its output is either high or low when a suitable external pulse is applied. PDM (Pulse Density Modulation) is used to represent an analog signal with the help of a binary signal.

6. Mass of any moving system is represented by ________
a) a resistance
b) a conductance
c) combination of inductor and capacitor
d) an inductance

Answer: d [Reason:] Inductance can also be seen as electromagnetic inertia, a property that opposes changes in electric currents and magnetic fields. Mass has inertia so it is represented by an inductance.

7. Contrast function in TV is done by ________
a) Luminance amplifier
b) Schmitt trigger
c) Band Pass Filter
d) Chroma amplifier

Answer: a [Reason:] Luminance amplifier is mostly used in TV sets. It helps to changes the contrast of television.

8. Bandwidth of RF amplifier for a color TV receiver is ________
a) equal to channel width
b) more than channel width
c) less than channel width
d) twice of channel width

Answer: b [Reason:] RF amplifiers are tuned amplifiers in which the frequency of operation is controlled by a tuned circuit. Bandwidth of RF amplifier is generally kept a little more than channel so that there is no problem in reception.

9. FSK system involves ________
a) frequency modulation
b) pulse modulation
c) amplitude modulation
d) phase modulation

Answer: a [Reason:] FSK i.e. Frequency Shift Keying involves frequency modulation that assigns bit values to discrete frequency while ASK assigns bit values to discrete amplitude.

10. Diameter of antenna is doubled. The maximum range will ________
a) be doubled
b) be halved
c) become four times
d) decrease to one fourth

Answer: a [Reason:] Range of antenna is directly proportional to antenna diameter. So if diameter of antenna is doubled its range also doubled.

## Communications MCQ Set 3

1. If the modulating frequency of a carrier wave varies between 100Hz and 100KHz, find it’s bandwidth?
a) 100 KHz
b) 230.2 KHz
c) 199.8 KHz
d) 123.6 KHz

Answer: c [Reason:] fm= 100KHz – 100Hz = 99.9KHz and Bandwidth = 2fm = 2 x 99.9 = 199.8 KHz.

2. TCP stands for __________
a) Transfer Control Protocol
b) Transmission Control Protocol
c) Transfer Control Process
d) Transmission Control Process

Answer: b [Reason:] TCP stands for Transmission Control Protocol. It is one of the main protocols of Internet. The entire suite is commonly referred as TCP/IP.

3. TCP/IP consists of ________ layers.
a) 5
b) 10
c) 14
d) 18

Answer: a [Reason:] TCP stands for Transmission Control Protocol. It is one of the main protocols of Internet. It is originated in the initial network implementation in which it complemented the Internet Protocol. The entire suite is commonly referred as TCP/IP. It consists 5 layers.

4. What do you understand by IP?
a) virtual circuit
b) non-robust protocol
c) connection oriented protocol
d) connection-less protocol

Answer: d [Reason:] IP stands for Internet Protocol or it can be seen as a connection-less protocol.

5. What is the full form of UDP?
a) User Datagram Protocol
b) User Data Protocol
c) Unique Datagram Protocol
d) Unique Data Protocol

Answer: a [Reason:] UDP stands for User Datagram Protocol. It is alternative for Transmission Control Protocol.

6. What is the lifetime of a packet in an IP network?
a) depends on time elapsed since transmission
b) depends on number of “hops” between nodes
c) approximately 300 milliseconds
d) approximately 500 milliseconds

Answer: b [Reason:] Information is divided into small chunks, called packets. The lifetime of a packet in an IP network depends on number of “hops” between nodes.

7. The standard Internet address or URL is a 16-bit binary number?
a) True
b) False

Answer: b [Reason:] The standard Internet address or URL is a 32-bit binary number. URL is a web resource that specifies its location on a computer network and a mechanism for retrieving it.

8. DNS stands for __________
a) Domain Name Server
b) Domain Name System
c) Domain Name Service
d) Domain Name Security

Answer: a [Reason:] DNS stands for Domain Name Server. Domain Name Server is a host name to IP address translation service. It is a distributed database implemented in a hierarchy of name servers.

9. Which statement is true about a DNS?
a) has become obsolete on the Internet
b) translates words to numbers
c) stores all domain addresses
d) describe the Internet address-naming procedure

Answer: b [Reason:] DNS stands for Domain Name Server. Domain Name Server is a host name to IP address translation service. It is a distributed database implemented in a hierarchy of name servers.DNS can translate words to numbers.

10. An intranet connected to the internet is often protected by __________
a) a DNS
b) a “brick wall”
c) a “fire wall”
d) the use of “spoofing ” protocols

Answer: a [Reason:] Intranet uses internet technologies, but is insulated from the global internet. An intranet connected to the internet is often protected by DNS.

## Communications MCQ Set 4

1. Which of the following devices is used to generate AM waves?
a) Amplifier
b) Square law modulator
c) Transmitter
d) Transducer

Answer: a [Reason:] AM signals is generated by Square-law modulators. The input for generating AM signal should be of type (A + m(t)) instead of m(t). Square-law modulator sums carrier and information signal, then square them using a non linear device.

2. Consider a wave, v = 15 sin (3πt + 5sin1300t), what is the carrier and signal frequency?
a) 2.5Hz and 200Hz
b) 1.5Hz and 100Hz
c) 1.5Hz and 207Hz
d) 5.5Hz and 500Hz

Answer: c [Reason:] Carrier and signal frequency are respectively 3. SWR is 1 for ________
a) Open circuit and Short circuit
b) Open circuit only
c) Short circuit only
d) Complex circuit

Answer: a [Reason:] If the line is open or short circuited, SWR is always 1.

4. The resonance frequency of an amplifier is 7MHz and it is having a bandwidth of 10KHz. What is its Q factor?
a) 102Hz
b) 105Hz
c) 103Hz
d) 10Hz

Answer: c [Reason:] 5. Which chart is used for calculations of transmission lines?
a) Andre chart
b) Smith chart
c) Wilson chart
d) Federer chart

Answer: b [Reason:] Smith chart is highly used in radio frequency engineering. Because it is highly useful in solving problems related with transmission lines and matching circuits. It is highly useful for displaying multiple parameters like impedance, admittance etc simultaneously.

6. What is the effective power if the transmitted power of 5W is increased to 50dB?
a) 1000KW
b) 3000KW
c) 5000KW
d) 7000KW

Answer: c [Reason:] According to given problem 10log10P5 = 50. So, P = 500KW

7. Field intensity follows ________
a) Bragg’s law
b) Inverse square law
c) Coulomb’s law
d) Gauss’s law

Answer: b [Reason:] Strength of an electric field due to a charge Q is inversely proportional to the square of the distance from the source.

8. If the power density at a given distance ‘R’ is one microwatt per square meter and the effective area of antenna is one square meter then the power captured by antenna is one microwatt.
a) True
b) False

Answer: a [Reason:] The above statement is true because power density is equal to 9. The gain of antenna (G) is the ratio of power radiated in a particular direction to the power radiated from an isotropic antenna.
a) True
b) False

Answer: a [Reason:] Gain of antenna, 10. EM waves are attenuated as they travel.
a) True
b) False

Answer: a [Reason:] EM waves are attenuated as they travel because both field and power gets decreases as distance increases.

## Communications MCQ Set 5

1. What is the main disadvantage of FM over AM?
a) high modulating power is needed
b) noise is very high for high frequencies
c) high output power is required
d) large bandwidth is required

Answer: d [Reason:] The main disadvantage of FM over AM is that in frequency modulation large bandwidth is required.

2. To prevent over modulation in radio transmitters we use ___________
a) peak clipper
b) oscillator
c) double oscillator
d) either peak clipper or oscillator

Answer: a [Reason:] Clipper is used to prevent the exceeding of output from a predetermined fixed value. It does not distorted the remaining part of the applied waveform.

3. IN EM waves, polarization ___________
a) is always vertical
b) is caused by reflection
c) is due to transverse nature of waves
d) is due to longitudinal nature of waves

Answer: c [Reason:] In electromagnetic waves polarization is mainly due to the transverse nature of waves only.

4. In FM receiver, role of amplitude limiter is to amplify low frequency signals.
a) True
b) False

Answer: b [Reason:] Role of amplitude limiter in frequency modulation is to eliminate any change in amplitude of received FM signals.

5. Advantage of high level modulator is that it requires linear amplifiers.
a) True
b) False

Answer: b [Reason:] A high level modulator modulates a high power section of the circuit. It has the advantage that linear amplifiers are not required.

6. In a FM receiver, amplitude limiter ________
a) eliminates any change in amplitude of received FM signals
b) eliminates any change in frequency of received FM signals
c) reduce the amplitude of received signals
d) amplifies low frequency signals

Answer: a [Reason:] In frequency modulation, amplitude limiter eliminates any change in amplitude of received FM signals.

7. Base modulation is preferred over collector modulation of a class C transistor because of its better efficiency.
a) True
b) False

Answer: b [Reason:] Base modulation is preferred over collector modulation of a class C transistor because low modulating power is required.

8. Base modulation is preferred over collector modulation of a class C transistor because it has high power output per transistor.
a) True
b) False

Answer: b [Reason:] Base modulation is preferred over collector modulation of a class C transistor because low modulating power is required.

9. What is the standard IF frequency for AM receivers?
a) 100 KHz
b) 456 KHz
c) 1.07 MHz
d) 10.7 MHz