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## Communications MCQ Set 1

1. The IF bandwidth of a radar receiver is inversely proportional to the __________
a) pulse repetition frequency
b) pulse width
c) pulse interval
d) square root of peak transmitted power

Answer: b [Reason:] The IF bandwidth of a radar receiver is inversely proportional to the pulse width.

2. Frequency components of an AM wave are?
a) Carrier frequency (ωc) with amplitude A
b) Lower side band (ωc + ωm) having amplitude mA4
c) Upper side band (ωc – ωm) having amplitude mA4
d) Carrier frequency (ωc) with amplitude A2

Answer: a [Reason:] Actually the frequency components of AM waves are – Carrier frequency (ωc) with amplitude A, Lower side band (ωc – ωm) having amplitude mA2 and Upper side band (ωc + ωm) having amplitude mA2 (where m represents modulation index).

3. Which of the following statement is true, if a return echo arrives after the allocated pulse interval?
a) it will interfere with the operation of transmitter
c) it will not be received
d) target will appear closer than it really is

Answer: d [Reason:] If a return echo arrives after the allocated pulse interval then the target will always appear closer than it really is.

4. Which of the following statement is true about spectrum of frequency modulated wave?
a) carrier frequency starts decreasing at a faster rate when the modulation index is large
b) the amplitude of any sideband is totally depends on modulation index
c) total number of sidebands is completely depend on the modulation index
d) carrier frequency can’t be disappear

Answer: b [Reason:] In frequency modulation, frequency of wave is modulated with respect to the wave being propagated. In frequency modulation, the amplitude of any side band depends on modulation index.

5. If a FM signal has modulation index m, then what will be its modulation index after passing through frequency tripler?
a) m3
b) m
c) 3m
d) 9m

Answer: c [Reason:] Frequency multiplier is an electronic circuit that generates an output signal whose output frequency is a multiple of its input frequency. So after passing through frequency tripler, new modulation index will be 3m.

6. A pre emphasis circuit provides extra noise immunity by __________
a) boosting the base frequencies
b) amplifying the higher audio frequencies
c) preamplifying the whole audio band
d) converting the phase modulation to FM

Answer: b [Reason:] Pre emphasis is used to improve quality of signal at the output of data transmission. A pre emphasis circuit provides extra noise immunity noise amplifying the higher audio frequencies.

7. Which one of the following is not an advantage of FM over AM?
a) Better noise immunity is provided
b) Lower bandwidth is required
c) Transmitting power is useful
d) Less modulating power is required

Answer: b [Reason:] Frequency Modulation has many advantages over amplitude modulation such as it has better noise immune, it requires less modulating power. But it requires lower bandwidth is not an advantage of FM when compared to AM.

8. Which of the following statement about Amplitude Limiter is not true?
a) The circuit is always biased in class C amplifier
b) When the input increases and becomes greater than threshold of limiting, the gain starts decreasing
c) The output must be tuned
d) Leak-type bias must be used

Answer: a [Reason:] Amplitude Limiter removes the amplitude of output signals to a desired margin irrespective of variations in the input signal. It is always biased in class C amplifier by virtue of the leak-type bias.

9. The typical squelch circuit cuts off __________
a) An audio amplifier when the carrier is absent
b) RF interference when the signal is weak
c) An IF amplifier when AGC is maximum
d) An IF amplifier when AGC is minimum

Answer: a [Reason:] The use of squelch circuit is to suppress the audio or video output of a receiver in the absence of a sufficiently strong desired input signal.

10. What do you understand by high level AM?
a) Output power is low
b) Modulation is done at high power of carrier and modulating signal
c) No need to boost the carrier and modulating signal
d) Modulation is done at low power of carrier and modulating signal

Answer: b [Reason:] For a high level AM, modulation is done at high power of carrier and modulating signal so power amplifier is used to boost the carrier and modulating signal.

## Communications MCQ Set 2

1. The velocity required to stay in orbit is ________
a) constant
b) zero
c) lower close to the earth than far from the earth
d) higher close to the earth than far from the earth

Answer: d [Reason:] The velocity in orbit must be higher close to the earth than far from the earth. Then only components can stay in orbit.

2. An antenna is adjusted by adjusting the two “look angles” called _________
a) apogee and perigee
b) declination and elevation
c) azimuth and declination
d) azimuth and elevation

Answer: d [Reason:] Azimuth and Elevation are two look angles of any antenna. So any antenna can be adjusted by adjusting these two angles properly.

3. Power density from an isotropic antenna is equal to ________

Answer: a [Reason:] Power of a transmitter that is radiated from an isotropic antenna will have a uniform power density in all direction. The power density at any distance ‘R’ for an isotropic antenna is equal to Pt/4πR2.

4. PCS stands for ________
a) Personal Communication Service
b) Personal Communication Systems
c) Personal Communication Signal
d) Portable Communication Systems

Answer: b [Reason:] PCs stands for Personal Communication Systems. It is a wireless phone service similar to cellular service but emphasizing on personal service and extending mobility.

5. What is the full form of MIN?
a) Manual Identification Number
b) Mobile Identification Number
c) Maximum In-band Noise
d) Minimum In-band Noise

Answer: b [Reason:] MIN stands for Mobile Identification Number. It refers to the 10 digit unique number that a wireless carrier uses to identify a mobile phone.

6. Power density follows inverse square law.
a) True
b) False

Answer: a [Reason:] With increase in distance power density decreases. So, we can also say that power density is inversely related to distance.

7. Which term is used for voice channels, in GSM?
a) traffic channels
b) voice channels
d) transmitter channels

Answer: a [Reason:] Traffic channel is the term used for voice channels, in GSM.

8. Pagers use _________
a) VHF band
b) UHF band
c) both VHF and UHF bands
d) ISM band

Answer: c [Reason:] A pager is a telecommunication device that receives alert signals and short messages. It can use both UHF and VHF band.

9. What is the approximate IEEE specification covering wireless LANs?
a) 802.13
b) 802.12
c) 802.11
d) 802.10

Answer: c [Reason:] 802.11 is the approximate IEEE specification for covering wireless LANs.

10. TDD stands for _________
a) Time Division Duplex
b) Time Delayed Duplex
c) Time Division Difference
d) Time Distance Duplex

Answer: a [Reason:] TDD stands for Time Division Duplex. It refers to duplex communication links where uplink is separated from downlink. They are separated by allocating them different time slots in the sae frequency band.

## Communications MCQ Set 3

1. If peak voltage of a carrier wave is 10V, what is the peak voltage of modulating signal if modulation index is 50%?
a) 10V
b) 20V
c) 8V
d) 5V

Answer: d [Reason:] Using relation, μ = AmAc we have 0.5 = Am10 which gives Am = 5V

2. Maximum Amplitude of an amplitude modulated 10V and minimum amplitude is 5V. Find its modulation index?
a) 0.65
b) 0.9
c) 0.33
d) 1

Answer: c [Reason:] Ac + Am= 10 and Ac – Am = 5 are the two given equations. By adding these two equations we have Ac = 15/2 and Am = 5/2 . We know μ = AmAc so μ = 0.33.

3. 24 channels, each band limited to 3.4 KHz, are to be time division multiplexed. Find the bandwidth required for 128 quantization level? (Given that sampling frequency is 8 KHz)
a) 2436 KHz
b) 1002 KHz
c) 1536 KHz
d) 1337 KHz

Answer: c [Reason:] We know, 2n = 128 which gives number of bits, n = 7. fs = 2fm = 2 x3.4 =6.8 KHz. Bandwidth = [24(7 + 1)] x 8 = 1536 KHz.

4. Sampling frequency of a signal is 6 KHz and is quantized using 7 bit quantizer. Find its bit rate?
a) 48kbPs
b) 64kbPs
c) 16kbPs
d) 8kbPs

Answer: a [Reason:] Bit rate, Rb = 1Tb where so bit rate = n × fs = 7 x 6 = 48kbPs.

5. Calculate power in each sideband, if power of carrier wave is 96W and there is 40% modulation in amplitude modulated signal?
a) 11.84W
b) 6.84W
c) 3.84W
d) 15.84W

Answer: c [Reason:] Modulation index = 0.4 and Pc = 96W. Power in sidebands may be calculated as

6. For 50% modulation, power in each sideband is ________ of that of carrier?
a) 10%
b) 4.32%
c) 5%
d) 6.25%

Answer: d [Reason:] Modulation index = 0.5. Power in sidebands may be calculated as

7. For 100% modulation, total power is ________
a) 1.5Pc
b) 2Pc
c) 3.75Pc
d) 1.25Pc

Answer: a [Reason:] Total power, Pt = Pc (1 +m22) where m is equal to 1 so Pt = Pc(1 +122). On solving it we get Pt = 1.5Pc.

8. If each element of signal occupies 70ms, what will its speed?
a) 11.23 bauds
b) 14.28 bauds
c) 17.39 bauds
d) 13.33 bauds

9. Power of carrier wave is 300W and modulation index is 0.75. Find its total power?
a) 465W
b) 384W
c) 323W
d) 502W

10. If a wave is modulated by two waves. One of them has modulation index equal to 0.75 and other has 0.2, the total modulation index will be ________
a) 0.67
b) 0.58
c) 0.77
d) 0.35

Answer: c [Reason:] Given that m1 = 0.75 and m2 = 0.2. Total modulation index will be equal to By substituting values we have which is equal to 0.77.

11. Find the power saving for DSB-SC wave with 100% modulation?
a) 66%
b) 86%
c) 50%
d) 33%

Answer: a [Reason:] In DSB-SC power is suppressed by two third. So power saving is 23 x 100 = 66%

12. If power transmitted is 45kW, field at a distance of 23km will be ________
a) 0.02
b) 0.75
c) 0.05
d) 0.03

13. Find the number of pulses, if the number of level is 128 in PCM?
a) 3
b) 6
c) 4
d) 7

Answer: d [Reason:] 2n = 128, so n = 7.

## Communications MCQ Set 4

1. TDR stands for ________
a) Total Distance of Reflection
b) Time Domain Response
c) Time Domain Reflectometer
d) Time Delay Ratio

Answer: c [Reason:] TDR stands for Time Domain Reflectometer. It is an electronic instrument that uses time domain reflectometry to locate faults.

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

3. The number of circular polarization modes is _________
a) 1
b) 2
c) many
d) 3

Answer: b [Reason:] In circular polarization either the electric or magnetic vector executes a circle which is further perpendicular to path of propagation. There are two circular polarization modes.

4. Which is the dominant for a circular waveguide?
a) TE 01
b) TM 01
c) TE 11
d) TM 11

Answer: c [Reason:] TE 11 is the most dominant for circular waveguides.

5. The characteristic impedance of a waveguide is fixed.
a) True
b) False

Answer: b [Reason:] The characteristic impedance of a waveguide is not fixed. It depends on the frequency it carries. It also depends on the longer dimension of its cross section.

6. Too much antenna gain causes ________
a) jitter
b) noise
c) a very wide microwave beam
d) a very narrow microwave beam

Answer: d [Reason:] Measurement of gain of any antenna takes place by comparing it with the value of isotropic antenna. Too much gain in antenna can cause a very narrow microwave beam.

7. What do you understand by the term Cross talk?
a) generation of closely lying sidebands
b) a method of increasing bandwidth
c) a method of decreasing bandwidth by converting DSB-SC signal to SSB-SC
d) disturbance caused in nearby circuit due to transmitted signal

Answer: d [Reason:] Disturbances caused in nearby circuit due to some reasons are called cross talk. It is generally caused by undesired coupling.

8. NTSC stands for ________
a) National Television Systems Committee
b) National Television Systems Commission
c) National Television Systems Council
d) National Television Systems Concern

Answer: a [Reason:] NTSC stands for National Television Systems Committee. It is mostly used in North America. It was responsible for developing a set of protocols for television broadcast transmission and reception in the United States. Its specifications was drawn up by EIA.

9. NTSC specifications was drawn up by ________
a) FCC
b) IRE
c) IEEE
d) EIA

Answer: d [Reason:] NTSC stands for National Television Systems Committee. It is mostly used in North America. It was responsible for developing a set of protocols for television broadcast transmission and reception in the United States. Its specifications was drawn up by EIA.

10. What is the aspect ratio of a standard TV receiver?
a) 3:4
b) 525:625
c) 625:525
d) 4:3

Answer: d [Reason:] The ratio of width of an image or screen to the height of it is known as aspect ratio. For a standard TV receiver its aspect ratio is 4:3.

## Communications MCQ Set 5

1. Super heterodyne receivers needs an extra circuitry for frequency conversion.
a) True
b) False

Answer: a [Reason:] Super heterodyne receiver mixes the incoming signal frequency with the locally generated signal frequency. It has better sensitivity and selectivity but it needs an extra circuitry for frequency conversion.

2. Neper is ________ decibel.
a) smaller than
b) larger than
c) equal to
d) exactly twice of

Answer: b [Reason:] Neper is a unit used to express ratios, such as gain, loss and relative values. One neper is equal to 8.685 dB. Hence it is greater than dB.

3. The coupling used in stoneman transmission bridge is________
a) Inductive
b) Resistive
c) Capacitive
d) Combination of inductive and resistive

Answer: c [Reason:] Stoneman transmission bridge is used in telephone communication to separate voice path from signal path and battery. Capacitive coupling is used in it.

4. Which statement is true about Square Law modulators?
a) it is used for frequency modulation
b) it is used for pulse width modulation
c) it is used for amplitude modulation
d) it is used for phase modulation

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. Which statement is true about ring modulator?
a) it is used for DSB-SC generation
b) it is used for SSB-SC generation
c) it is a summation modulator
d) it consists three diodes connected in form of a ring

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. In ergodic process, ensemble and time averages are identical.
a) True
b) False

Answer: b [Reason:] In ergodic process, ensemble and time averages are different.

7. What is the amount of information in continuous signal?
a) zero
b) infinite
c) 2 bits
d) 5 bits

Answer: b [Reason:] In any continuous signal, the amount of information that comes out is always infinite.

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

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. Audio frequency range lies between _________
a) 2 MHz to 20 MHz
b) 20 Hz to 20 KHz
c) 20 KHz to 200 KHz
d) 20 MHz to 200 MHz