Quadrant 4 Multiple choice questions (choose the correct ...nptel.vtu.ac.in/VTU-NMEICT/CE/Multiple choice questions .pdf · Quadrant 4 . Multiple choice questions ... of a standard

Quadrant 4

Multiple choice questions (choose the correct answer)

1. A carbon microphone is variable:

(a) Resistance device (b) Inductance device

(c) Capacitance device (d) none of the above

2. The Channel Capacity is exactly equal to:

(a) Bandwidth of demand (b) Amount of information per second

(c) Noise rate in the channel (d) none of these

3. To eliminate ghosts in the picture:

(a)Use a longer transmission line (b) Connect a booster

(c) Change the antenna orientation or location (d) Twist the

transmission line

4. Broadband long distance communication was originally made possible by the

advent of:

(a)Geostationary satellites (b) H.F. radio systems

(c)Repeater amplifier (d) Telegraph cable

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5. In T.V. system, indicate the true statement:

(a) Picture is AM, sound is FM (b) Picture is FM, sound is AM

(c)Picture is AM; sound is AM (d) both are frequency

modulated

6. Channel capacity is basically a measure of:

(a) Entropy (b) Maximum rate of information

(c)Amount of information a channel can take (d) None of these

7. In communication systems, sampling technique leads to:

(a)Cheaper equipment (b) Better efficiency

(c)Higher speed of communication (d) Simpler operation

8. Redundancy in communication system

(a)Reduces efficiency of communication (b) Helps to detect error

(c)Helps to correct error (d) all of these

9. Entropy is basically a measure of

(a)Rate of information (b) Average information

(c)Probability of information (d) Disorder of information

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10. Reliable ship-to-ship communication may be secured with little fading by use

of:

(a)Frequency diversity reception (b) Space diversity reception

(c)More directional antenna (d) Broadband antenna

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Quadrant 4


1. When a receiver has a good blocking performance, it means that:

(a)Its detector is not functioning properly

(b) Its image frequency rejection is poor

(c)It suffers from double spotting

(d) It is unaffected by AGC derived from nearby transmissions

2. Refraction of radio waves in the atmosphere results due to:

(a) Changes in dielectric constant (b) Changes in density of air

(c) Changes in dielectric constant and refractive index

(d) none of these

3. Which of the following is a false statement in connection with

communications receivers?

(a) A product demodulator could be used for the reception of Morse code

(b) Variable sensitivity is used to eliminate selective fading

(c) The noise limiter cuts off the receivers output during a noise pulse

(d) Double conversion is used to improve image rejection

4. The number of repeaters along a coaxial cable link depends on:

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(a) Number of coaxial cables in the tube (b) The bandwidth of the

system

(c)Separation between the equalizer (d) none of these

5. Fading can be avoided or improved by

(a)Providing space diversity reception (b) Providing AVC in a

receiver

(c) Providing frequency diversity reception (d) all are possible

6. Sky wave propagation is used for

(a) Mobile transmission (b) Short Distance Transmission

(c)Medium distance transmission (d) Long Distance Transmission

7. Noise can be measured by:

(a)AC voltmeter (b)DC voltmeter

(c)Either AC or DC voltmeter (d)None of these

8. In a communication system, noise is most likely to affect the signal

(a)In the transmitter (b)In the channel

(c)In the destination (d)At the destination

9. A passive satellite:

(a)Only reflects back signals (b)Only generates signals

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(c)Only absorbs signals (d) Receives, modulates and then

reflects

10. At high frequencies, which noise will become most important:

(a)Short noise (b)Thermal noise

(c)Transit time noise (d)All of the above

11. Which of the following is not a useful quantity for comparing the noise

performance of receivers:

(a)Noise figure (b) Noise temperature

(c)Equivalent noise resistance (d) Input noise voltage

Page 6 of 35

Multiple Choice Questions:

1. The Hilbert transform is a linear operator which transforms

(a) Time domain to Frequency domain

(b) Time domain to Time domain

(c) Frequency domain to Frequency domain

a) Frequency domain to Time domain

2. Hilbert transform phase shifts all the frequency components of the input

signal by

(a) 2 rad when f>0 (b) 2 rad when f>0

(c) 4 rad when f>0 (d) 4 rad when f>0

3. |H(f)|= ____ for all f

(a) 0 (b) 2 (c) (d)1

4. Hilbert Transform of x^(t) is

(a) x(t) (b)x^(t) (c)–x(t) (d)–x^(t)

5. If x(t)= cos 2 f0t, then x^(t)= ____

(a) Sin2 f0t (b)-cos2 f0t (c)tan2 f0t (d)cot2 f0t

6. Hilbert Transform of ej2πf0t is

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(a) jsgn(2 f0) ej2πf0t (b)–jsgn(-2 f0) ej2πf0t

(c) jsgn(-2 f0) ej2πf0t (d)–jsgn(2 f0) ej2πf0t

7. x(t) and x^(t) have the same

(a) Power (b)Energy

(c)Energy or power (d)Energy and power

8. Hilbert Transform of m(t)sin ω0t=_____

(a) m(t)cos ω0t (b) -m(t)cos ω0t (c) m(-t)sin ω0t (d) m(t)sin (-ω0t)

9. The Hilbert transform is used for the representation of

(a) Band pass signal (b)Band stop signal

(c) Low pass signal (d) High pass signal

10. dt =

(a) 1 (b)-1 (c)0 (d)∞

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Choose the correct answers

1. An Am signal is demodulated using an envelope detected the carrier

frequency 1MHz and fm =2KHz is suitable for the envelope detector is

(a) 0.2usec (b)1usec (c)20usec (d)500usec

2. The antenna current of Am transmitter of 8 ampere before modulations &

8.5 after modulation .find Ա

(a) 0.5 (b)1 (c)0.2 (d)0.7

3. Consider an AM signal s(t) =4cos 1800πt + 10cos 2000πt +4cos 2200πt .

Calculate bandwidth

(a) 200Hz (b)400Hz (c)600Hz (d)700HZ


Calculate power

(a) 66watts (b)40watts (c)60watt (d)70watts


Calculate efficiency

(a) 0.24 (b)0.4 (c) 0.6 (d) 0.2

6. Amplitude modulation by square waves or rectangular binary pulses is

referred to as

(a) phase-shift keying (b)amplitude-shift keying

(c) frequency-shift keying (d) binary-shift keying

7. With AM which of the following conveys no information?

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(a) lower sideband (b)upper sideband

(c) Both sidebands (d) carrier

8. In amplitude modulation, how much of the transmitted power is in the

carrier?

(a) one-half (b)three-quarters (c)one-third (d)two-thirds

9. Double-sideband suppressed carrier signals are generated by a circuit called

(a) balanced demodulator (b)balanced modulator

(b) beat frequency oscillator (d)notch filter

10. Which of the following is not a major benefit of SSB?

(a) noise in the signal is reduced (b)conserves spectrum space

(c) Less transmitter circuitry is used

(d) More fading of an SSB signal over long distances

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Quadrant 4


1. Which of the following is a form of amplitude modulation?

(a) Single sideband (b) Spread-spectrum

(c) Packet radio (d) Phase shift keying

2. What type of modulation is most commonly used for VHF packet Radio

transmissions?

(a) FM (b) SSB

(c)AM (d) Spread Spectrum

3. Which type of voice modulation is most often used for long-distance or weak

signal contacts on the VHF and UHF bands?

(a)SSB (b) FM

(c ) AM (d) PM

4. Which type of modulation is most commonly used for VHF and UHF voice

repeaters?

(a)FM (b)AM

(c)SSB (d)PSK

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5. Which of the following types of emission has the narrowest bandwidth?

(a) SSB Voice (b) FM voice

(c) CW (d) Slow-scan TV

6. Which sideband is normally used for 10 meter HF, VHF and UHF single-

sideband communications?

(a) Lower sideband (b) Upper sideband

(c) Suppressed sideband (d) Inverted sideband

7. What is the primary advantage of single sideband over FM for voice

transmissions?

(a) SSB signals are less susceptible to interference

(b)SSB signals are easier to tune

(c) SSB signals have narrower bandwidth

(d) All of these choices are correct

8. What is the approximate bandwidth of a single sideband voice signal?

(a) 3 kHz (b) 1 kHz

(c) 6 kHz (d) 15 kHz

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9. What is the approximate bandwidth of a VHF repeater FM phone signal?

(a)Between 5 and 15 kHz (b) Less than 500 Hz

(c)About 150 kHz (d) Between 50 and 125 kHz

10. What is the typical bandwidth of analog fast-scan TV transmissions on the 70

cm band?

(a) About 3 MHz (b) More than 10 MHz

(c) About 6 MHz (d) About 1 MHz

11. What is the approximate maximum bandwidth required to transmit a CW

signal?

(a) 150 Hz (b) 2.4 kHz

(c) 1000 Hz (d) 15 kHz

12. An SSB signal with a maximum level of 200 V p-p into a 50- load results in a

PEP rating of

(a) 200 W (b) 50 W

(c)100 W (d)800 W

13. State the chief advantage(s) of a standard SSB system

(a) Maximum signal range with minimum transmitted power

(b) Easy carrier reinsertion

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(c) Elimination of carrier interference

(d) Maximum signal range with minimum transmitted power and

elimination of carrier interference

14. The noise advantage of SSB over AM is

(a) 3 – 5 dB (b) 5 – 7 dB

(c) 8 – 10 dB (d) 10 – 12 dB

15. Once an SSB signal has been generated, it must be amplified by

(a) A nonlinear amplifier to conserve bandwidth

(b) A nonlinear amplifier to conserve energy

(c) A linear amplifier to conserve bandwidth

(d) A linear amplifier to avoid distortion

16. The advantages provided by carrier elimination in SSB do not apply to

transmission of

(a) Code (b) Music

(c)Noise (d) All of the above

17. An SSB receiver re-creates the original intelligence signal by

(a) Mixing the USB with LSB signals and filtering out the resulting

different frequencies

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(b) Filtering out the difference between either sideband and the

internally generated carrier signal

(c) Filtering out the harmonics of the received sideband signal

frequencies

(d) Amplifying the dc term produced by mixing action

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Quadrant 4


1. In T.V transmission, the type of modulation used for picture is

(a) SSB amplitude modulation

(b) DSB amplitude modulation

(c) Vestigial side band amplitude modulation

Frequency modulation

Page 16 of 35

Quadrant 4


1. A super heterodyne radio receiver with an intermediate frequency of 455 kHz

is tuned to a station operating at 1200 KHz. The associated image frequency is

________ kHz

(a) 1200 (b) 2110

(c) 1100 (d) 455

2. Sensitivity and selectivity of a heterodyne receiver

(a) Is better than a tuner radio frequency receiver

(b) Sensitivity and selectivity is the same in both

(c) Is poorer than TRF receiver

(d) Sensitivity is better in heterodyne receiver, selectivity is better in

TRF receiver

3. In a super heterodyne receiver, the frequency of local oscillator is

(a) Equal to that of incoming signal

(b) Higher than that of incoming signal

(c) Slightly less than that of incoming signal

(d) Half that of incoming signal

4. In super heterodyne receivers

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(a)IF is always variable

(b) RF is not used

(c) Local oscillator frequency is always less than the signal frequency

(d) Mixer is tuned to signal frequency

5. Which of the following component is not common between a tuned radio

frequency receiver and super heterodyne receiver?

(a) RF amplifier (b) IF amplifier

(c)Detector (d) Auto amplifier

6. An IF amplifier is a super heterodyne receiver meets with which of the

following requirements of the set?

(a) Bandwidth (b) Gain

(c)Sensitivity (d) All of the above

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Quadrant 4


1. The linear mixing process in an FDM system that does not attenuate the signal

uses

(a) a simple resistor network

(b) an RC network

(c) filter circuit

(d) an op amp summer

2. What is the difference between a balanced modulator and a regular modulator?

(a)There is no carrier produced in the output of a balanced modulator

(b)In a balanced modulator, there is 180º phase shift between the

upper and lower sidebands.

(c)In a balanced modulator, only one sideband is produced.

(d)In a balanced modulator, harmonics of the sidebands are

suppressed

3. In a balanced-ring modulator, the carrier suppression is accomplished by

(a)A dual-gate FET having symmetry

(b)The nonlinearity of the diodes that are used

(c)Symmetrical differential amplifier stages

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4. Common types of balanced modulators include

(a) Ring modulator (b) Phase modulator

(c) Lattice modulator (d) All of the above

5. The output of a mixer in a receiver system produces:

a) the difference between the modulated RF and the local oscillator

b) the sum of the modulated RF and local oscillator

c) an audio signal

d) the difference and the sum of both the modulated RF and local oscillator

frequencies

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Quadrant 4


1. Angle modulation includes the following type of modulation:

a) AM b) FM c) PM d) all of these

2. Carson's rule is used to approximate the necessary

a) Frequency Deviation b) Bandwidth c) capture

Ratio d) Modulation index

Page 21 of 35

Quadrant 4

Multiple Choice Questions

1. The amount of Frequency increase and decrease around the center frequency in

an FM Signal is called the ----------

a) Index of modulation b) Frequency deviation

c) Phase Deviation d) Bandwidth of the FM Signal

2. The amount of frequency deviation is dependent on the intelligence frequency in

------------

a) An FM signal b) A PM signal

c) Both FM and PM Signals d) Neither PM and FM Signals

3. An FM Signal has an intelligence frequency of 3 KHz and a maximum deviation

of 20 Khz. If its carrier frequency is set at 172.5MHz, what is its index of

Modulation--------------------?

4. The amount an FM carrier frequency deviates for a given modulating input

voltage level is called the -----------------

a) Frequency deviation b) Index of modulation

c) Deviation Constant d) Deviation Ratio

Page 22 of 35

Quadrant 4


1. The linear mixing process in an FDM system that does not attenuate the signal

uses

i) a simple resistor network ii) an RC network

iii)a filter circuit iv) an op amp summer

2. Another name for an FM demodulator is

i) discriminator ii) encoder

iii) multiplexer iv) modulator

3. The basic subsidiary communications authorization signal is a separate

subcarrier of

i) 67 Hz which is amplitude-modulated by audio signals

ii) 67 KHz which is phase-modulated by RF signals

iii) 67 KHz which is frequency-modulated by audio signals

iv) 67 KHz which is amplitude-modulated by audio signals

4. An alternate service provided by some FM stations that allows digital data to be

transmitted to the FM receiver is called

i) Digital Data System ii)Radio Data System

iii)Digital Radio System iv)Satellite Radio

5. If the appropriate system is used, what stage will output the name and artist of

music selections being played by the station?

i) linear combiner ii) frequency doubler

Page 23 of 35

iii) QPSK demodulator iv) FM demodulator

6. In what type of multiplexing does each signal occupy the entire bandwidth of the

channel?

i)frequency-division multiplexing ii) time-division multiplexing

iii)pulse-width multiplexing iv) phase-shift multiplexing

7. Which multiplexer operates as a single-pole multiple-position mechanical or

electronic switch that sequentially samples the multiple analog inputs at a high rate

of speed?

i) frequency-division multiplexer ii)phase-shift multiplexer

iii)pulse-amplitude modulated multiplexer iv) pulse-width multiplexer

8. What type circuits are used to remedy the synchronization problem encountered

in de-multiplexing?

i) Clock recovery circuits ii) clock redundancy circuits

iii) time-multiplex circuits iv) pulse-synch circuits

9. Which of the following is a very popular form of multiplexing where multiple

channels of digital data are transmitted in serial form?

i) frequency-division multiplexing

ii) phase-shift multiplexing

iii) pulse-amplitude modulated multiplexing

Page 24 of 35

iv) pulse-code modulated multiplexing

Page 25 of 35

Quadrant 4


1. PLL consists of

(a) Phase detector (b) VCO

(c) Phase defector (d) all of the above

2. VCO is designed so that at zero voltage it is oscillating at some initial

frequency W0 called

(a) cut-off frequency (b) free-cycle frequency

(c) free-running frequency (d) none of the above

3. The time takes for a PLL to capture the incoming signal is called

(a) pull out time (b) capture time

(c) lock out time (d) none of the above

4. The filter bandwidth of PLL is reduced one of the following effects.

(a) Slow down the capture process (b) increases the pull time

(c) Increases the capture range (d) decreases the interjection-injection

capabilities

5. The basic components of 565 IC is

(a) Phase vector (b) amplifier

(c) VCO (d) all of the above

6. The maximum operated range of PLL 565 is

(a) 0 to 500 kHz (b) 0.001 Hz to 500 kHz

Page 26 of 35

(c) 100 to 400 kHz (d) 10 Hz to 400 kHz

7. Lock in range of PLL 565 is

(a) ΔfL = 7.8f0/V (b) ΔfL = ± 7.8f0/V

(c) ΔfL = − 7.8 f0/V (d) ΔfL = ± 7.8V/f0

8. Frequency multiplier using PLL has VCO output frequency f0 is given by

(a) Nfs (b) fs/N

(c) fs (d) 1/Nfs

9. The frequency shift in frequency translator at the output of the VCO in PLL

(a) f0 = fs − fL (b) f0 + fs = fL

(c) f0 = fs + f1 (d) f0 = fs − f1

10. The main advantage of PLL as a detector with other Am detector is

(a) high degree of selectivity and noise immunity

(b) low noise immunity with high degree of selectivity

(c) high degree of selectivity only

(d) noise immunity only

11. The important characteristics of PLL are

(a) lock in range (b) capture range

(c) pull in time (d) all of the above

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12. _______ filter controls the capture range and lock range of PLL.

(a) LPF (b) HPF

(c) BPF (d) None of the above

13. The other name for phase detector is

(a) Comparator (b) multiplier

(c) Adder (d) none of the above

14. The application of PLL are

(a) Frequency multiplier (b) AM, FM demodulator

(c) Frequency demodulator (d) all of the above

15. The operating voltage of range of IC 565 is

(a) ±6 V to ±12 V (b) ± 10 to ± 12 V

(c) ± 8 to ± 12 V (d) ±12 V

16. An external capacitor connected across 565 will act as

(a) Passive device (b) low pass filter

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(c) Charging device (d) discharging device

17. Let to free running frequency, VC voltage shift from VCO, the new

frequency shift from VCO in a PLL is

(a) f0 + KVVC (b) f0 − KVVC

(c) KVC (d) f0

18. The voltage VC required to derive VCO is

(a) Ve · T(f) · A (b) Ve/T(f) · A

(c) AVe/T(f) (d) T(f)/Ve·A

19. The capture range is _______ located with respect to vco free runing

frequency f0 in pll

(a) asymmetrical (b) symmetrical

(c) opposite (d) none of the above

20. The output waveform of pll 566 is

(a) square and triangular (b) square and sine wave

Page 29 of 35

(c) triangular and sine wave (d) none of the above

21. The number of pins in IC-566

(a) 10 (b) 16

(c) 12 (d) 8

22. The output frequency of VCO can be changed by

(a) RT (b) CT

(c) VC (d) all of the above

Page 30 of 35

Quadrant 4


1. De- emphasis circuit is used :

(a) After modulation (b) Before Modulation

(c)Before detection (d) after detection

2. Pre- emphasis circuit is used:

(a) After modulation (b) Before modulation

(c)Before detection (d) After detection

3. For a Gaussian process, autocorrelation also implies:

(a) Statistical dependence (b) statistical independence

(b) Ergodic process (d) stationary dependence

4. A pre- emphasis circuit provides extra noise immunity by

(a) Boosting the bass frequency

(b) Amplifying the higher audio frequencies

(c) Pre amplifying the whole audio bound

(d) Converting the phase modulation to FM

Page 31 of 35

Quadrant 4


1. Two events A and B are said to be mutually exclusive if:

(a) If occurrence of A is dependent on B

(b) If occurrence of B is independent of A

(c) Occurrence A and B are independent of each other

(d) None of these

Page 32 of 35

Quadrant 4


1. Probability density function of thermal noise is

(a) Binomial (b) Gaussian

(c)Poisson (d) None of these

Page 33 of 35

Quadrant 4


1. Why Morse code isn’t well suited to today's telegraphic equipment?

(a) It uses an automatic request for repetition.

(b) It has excessive redundancy built into the code.

(c) The parity bit is difficult to detect

(d) Differing between various widths of the pulses is an extremely complicated

process.

2. Which is not a type of pulse modulation?

(a) Pulse-amplitude modulation (PAM) ( b) Pulse-width modulation (PWM)

(c) Pulse-frequency modulation (PFM) (d) Pulse-position modulation (PPM)

3. If the number of bits per sample in a Pulse Coded Modulation (PCM) system is

increased from 5 bits to 6 bits, the improvement in signal to quantization noise

ratio will be

(a) 3 dB (b) 6 dB

(c) 2pi dB (d) 0 dB

4. PPM and PWM are superior to PAM systems in

(a) Noise characteristics (b) Bandwidth characteristics

(c)Simplicity in design (d) Frequency response of the intelligence signal

Page 34 of 35

http://en.wikipedia.org/wiki/Pulse-code_modulation

5. Half-duplex operation involves communication

(a) In one direction only (b) In both directions, but only one can talk at a time

(c)Where both parties can talk at the same time (d)All the above

6. The AT&T T1 lines

(a) Use 16-bit PCM code and include 24 voice channels

(b)Use delta modulation and include 48 voice channels

(c)Use 8-bit PCM code and include 24 voice channels

(d)Use delta modulation and include 24 voice channels

Page 35 of 35

Quadrant 4 Multiple choice questions (choose the correct ...nptel.vtu.ac.in/VTU-NMEICT/CE/Multiple choice questions .pdf · Quadrant 4 . Multiple choice questions ... of a standard

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