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## Communications MCQ Set 1

1. TRF receivers are used for ________
a) Detection of modulating signal
b) Removal of unwanted signal
c) Removing noise
d) Both detection of modulating signal and removal of unwanted signal

Answer: d [Reason:] TRF receivers are used for detection of modulating signal and removal of unwanted signal. The receiver receive the modulated signal and detect the information signal from received modulating signal.

2. Calculate the power in a DSB-SC signal, if the modulation is 60% and power of carrier wave is 600W?
a) 120W
b) 108W
c) 111W
d) 102W

Answer: b [Reason:] The total power for DSB is PC (m22) = 600X(0.622) = 108W.

3. One of the advantage of using analog communication over digital communication is that in analog communication less transmission bandwidth is required?
a) True
b) False

Answer: a [Reason:] Due to analog to digital conversion, data rate becomes high in digital communication which increases the bandwidth in digital communication.

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. An ideal square wave contains only components of odd integer harmonics.

5. What is the maximum transmission efficiency of an AM signal?
a) 33.33%
b) 60.25%
c) 38.75%
d) 50.25%

Answer: a [Reason:] The percentage of total power contributed by sidebands of the AM signal is known as transmission efficiency of an amplitude modulated system. The maximum transmission efficiency of an AM signal is 33.33%.

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. Generation of SSB-SC signal is done by ________
a) Phase discrimination method and Frequency discrimination method
b) Phase discrimination method and Product modulator
c) Product modulator and Frequency discrimination method
d) Product modulator and Square law modulator

Answer: a [Reason:] SSB-SC signals are the signals where only one of the side band is transmitted in an AM wave. SSB-SC signal is generated by two methods, frequency discriminator method or filter method and phase discriminator method or phase shift method.

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. In automatic gain control of the AM receiver ________
c) output provided is an AC voltage
d) required power is very low

Answer: a [Reason:] Automatic Gain Control provides controlled signal amplitude at the output even if there are amplitude variations at the input. This controlled output adjusts the input to output gain to a suitable value.

10. Which of the following is an example of continuous wave analog modulation?
a) PCM
b) DPCM
c) AM

Answer: c [Reason:] Analog communication is a type in which the message to be transmitted is analog in nature. Here the message signal modulates a high frequency carrier signal. In AM, amplitude of carrier is varied with respect to the wave which is propagated. It is also an example of continuous wave analog modulation.

## Communications MCQ Set 2

1. What is the purpose of peak clipper circuits in radios?
a) prevent overmodulation
b) reduce bandwidth
c) increase bandwidth
d) regulate oscillator input voltage

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

2. In FM receiver, role of amplitude limiter is to reduce the amplitude of 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.

3. Balanced modulator is used to suppress carrier signal to create a SSB or DSB.
a) True
b) False

Answer: b [Reason:] Balanced modulator is used to produce 100% modulation.

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. What is the main function of a balanced modulator?
a) to limit the noise picked by a receiver
b) to produce balanced modulation of a carrier wave
c) to suppress carrier signal
d) to produce 100% modulation

Answer: d [Reason:] For achieving 100% modulation, balanced modulator is mainly used in circuits.

6. For classifying a modem as low speed its data rate is ________
a) upto 100bps
b) upto 200bps
c) upto 400bps
d) upto 600bps

Answer: d [Reason:] According to standard data for modem, if the data rate is upto 600bps then modem is classified as having a low speed.

7. Varacter diode modulator is an indirect way of generating FM.
a) True
b) False

Answer: b [Reason:] Varacter diode modulator is not an indirect way of generating FM. It is Armstrong modulator which is an indirect way of generating FM.

8. Which of the following is an indirect way of generating FM?
a) By reactance modulator
b) By bipolar transistor
c) By varacter diode
d) By armstrong modulator

Answer: d [Reason:] Armstrong modulator which is the only way for indirect generating of frequency modulation.

9. Convex lens has negative focal power and concave lens have positive focal power.
a) True
b) False

Answer: b [Reason:] Convex lens has positive focal power and concave lens have negative focal power.

10. All lens have positive focal power.
a) True
b) False

Answer: b [Reason:] Convex lens has negative focal power and concave lens have positive focal power.

## Communications MCQ Set 3

1. Which is the standard reference antenna for the directive gain?
a) Isotropic antenna
b) Marconi antenna
c) Helical antenna
d) Log Periodic antenna

Answer: a [Reason:] Isotropic antenna is an ideal antenna that radiates its power uniformly in all directions. In practical, no isotropic antenna exists. It is often used as a reference antenna for the antenna gain.

2. Which one of the following reasons for the use of a ground screen with antennas is false?
a) Impossibility of a good ground connection
b) Provision of an earth for the antenna
c) Protection of personnel working underneath
d) Improvement of radiation pattern of antenna

Answer: c [Reason:] If we consider the use of ground as screen with antenna then there is no chances that it is used for protection of personnel working underneath.

3. Which of the following antennas is best excited from a waveguide?
a) Biconical
b) Horn
c) Helical
d) Discone

Answer: b [Reason:] A horn is an antenna that consists of a flaring metal waveguide which is shaped like a horn. The horn shape helps to direct radio waves in a beam. It is widely used as antennas at UHF.

4. An ungrounded antenna near the ground ________
a) must be horizontally polarized
b) acts as an antenna array
c) is unlikely to need a ground screen
d) acts as a single antenna of twice the height

Answer: b [Reason:] An ungrounded antenna near the ground acts as an antenna array.

5. Field strength at a distance from an antenna is measured with __________
a) a slotted line
b) a dipole
c) an EIRP meter
d) a field strength meter

Answer: d [Reason:] Field strength meter is an instrument which is used to measure the electric field strength emanating from a transmitter.

6. The radiated beam from a parabolic “dish” transmitting antenna is ________
a) dispersed
b) phased
c) collimated
d) scattered

Answer: c [Reason:] The radiated beam from a parabolic “dish” transmitting antenna is collimated. Collimated light is that light whose rays are parallel due to which it disperse minimally as it propagates.

7. Power density spectrum of a resistor R can be expressed as ________
a) 2 kTR
b) 1 kTR
c) 0.75 kTR
d) 3 kTR

Answer: a [Reason:] The Power density spectrum of a resistor R can be expressed as 2 kTR where k is Boltzmann’s constant, T is Temperature and R is given resistance.

8. What is the full form of LPDA?
a) Log Periodic Dipole Array
b) Log Power Dipole Array
c) Low Periodic Dipole Array
d) Low Power Dipole Array

Answer: a [Reason:] LPDA stands for Log Periodic Dipole Array. LPDA consists of a number of half-wave dipole driven elements which gradually increases in length.

9. Arrays in antenna can be __________
a) phased
b) driven
c) parasitic
d) phased, driven or parasitic

Answer: d [Reason:] Arrays in antenna can be phased, driven or parasitic.

10. What is the typical bandwidth of a 2-wire telephone line?
a) 20 Hz to 6 KHz
b) 300 Hz to 3.4 KHz
c) 20 Hz to 20 KHz
d) 200 Hz to 6.5 KHz

Answer: b [Reason:] The bandwidth of a 2-wire telephone line is fixed in a particular range. Its range generally varies between 300 Hz to 3.4 KHz.

## Communications MCQ Set 4

1. A 1000KHz carrier is modulated by 100Hz and 200Hz waves, then which of the following frequencies cannot be present at the output?
a) 1000.1KHz
b) 999.9KHz
c) 1000.2KHz
d) 999.7KHz

Answer: d [Reason:] Frequencies present at output will be 1000 ± 0.1 and 1000 ± 0.2.

2. Aspect ratio is the ratio of ________
a) width to height
b) height to width
c) power to width
d) width to power

Answer: a [Reason:] Aspect ratio is the ratio of width to the height of image (screen).

3. If the levels in PCM are transmitted in 10 unit code having sampling frequency equals to 20KHz. What is its bandwidth?
a) 150KHz
b) 125KHz
c) 100KHz
d) 110KHz

Answer: c [Reason:] Bandwidth = 12 (10 x 20)= 100KHz.

4. Carrier frequency is given by the formula ________

Answer: a [Reason:] Carrier frequency is given by the formula, where L is inductance and C is Capacitance.

5. Among all amplifiers, Common Collector has highest power gain.
a) True
b) False

Answer: b [Reason:] It is common emitter who has highest power gain. Common emitter has a very high voltage gain and also has good amount of current, so its power gain is high.

6. Find the carrier frequency if the inductance and capacitance are 30μH and 10nF respectively?
a) 244KHz
b) 523KHz
c) 290KHZ
d) 300KHz

7. Helical antenna is used to obtain ________ polarization.
a) elliptical
b) circular
c) linear
d) perpendicular

Answer: b [Reason:] Helical antenna produce circular polarization. Due to this only it is highly used in radio telemetry.

8. What is number of possible outputs if there is 6 line digital input?
a) 64
b) 32
c) 16
d) 128

Answer: a [Reason:] Total possible outputs will be 26 which is equal to 64.

9. Push pull amplifier is a class B amplifier.
a) True
b) False

Answer: a [Reason:] Push pull amplifier uses a pair of active devices that alternately supply current to a connected load and also absorb current from a connected load. It is a class B amplifier.

10. For removing unwanted signals we should use ________
a) phase shift method
b) filteration ethod
c) distillation method
d) elimination method

Answer: b [Reason:] Filteration method is used to remove unwanted components from signal. It is mainly used to eliminate noise.

## Communications MCQ Set 5

1. If we compared to the core, the index of refraction of cladding must be ________
a) same
b) greater
c) less
d) can be greater or less

Answer: c [Reason:] Core of a optical fiber is a cylinder of glass or plastic that runs along the fiber’s length. The core is surrounded by a medium with a lower index of refraction, called cladding.

2. What is used in making single-mode fiber?
a) plastic
b) glass
c) copper
d) tin

Answer: b [Reason:] Single mode fiber is usually made up of glass. Single-mode fiber is designed to carry light directly down the fiber.

3. A single-mode cable does not suffer from?
a) chromatic dispersion
b) waveguide dispersion
c) modal dispersion
d) complex dispersion

Answer: c [Reason:] Modal dispersion can’t be seen in a single mode cable. It is used for transmission of a single ray.

4. ISI stands for ________
a) Inter Symbol Interference
b) Inter Signal Interference
c) Inter System Interference
d) Inter Service Interference

Answer: a [Reason:] ISI stands for Inter Symbol Interference. It is a form of distortion of a signal in which one symbol gets interfered with different signals.

5. FDDI stands for __________
a) Fiber Digital Data Interface
b) Fiber Digital Delay Interface
c) Fiber Distributed Data Interface
d) Fiber Distributed Delay Interface

Answer: c [Reason:] FDDI stands for Fiber Distributed Data Interface. It is used for data transmission on optical fiber lines in a LAN that can also extend in range upto 200km.

6. What you understand by the term Soliton?
a) it is a defect in the glass
b) it is a type of particle
c) it is a type of pulse
d) it is a type of optical network

Answer: c [Reason:] Soliton is a self-reinforcing solitary wave packet that maintains its shape, when it propagates with a constant velocity. So, it is a type of pulse only.

7. Signal to noise ratio is calculated as signal voltage divided by noise voltage.
a) True
b) False

Answer: b [Reason:] Signal to noise ratio is calculated as signal power divided by noise power.

8. Which statement is true about varacter?
a) it is a diode
b) it is a voltage-controlled capacitor
c) it is used in tuned circuits
d) it is a diode used in tuned circuit and also has a voltage-controlled capacitor

Answer: d [Reason:] Varacter is a diode used in communication for tuning the circuit. It is also known as voltage controlled capacitor (VCO).

9. A frequency synthesizer is _________
a) A VCO phase locked to a reference frequency
b) A VFO phase locked to a reference frequency
c) A fixed frequency RF generator
d) A variable frequency RF generator

Answer: a [Reason:] Frequency synthesizer generates a range of frequencies from a single reference frequency.

10. Why CSMA/CD network has a minimum length for packets?
a) to increase the data rate
b) to decrease the data rate
c) to prevent packets from reaching all other nodes
d) to make sure that all other nodes hear a collision in progress