Tuesday, 8 November 2016

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EE AND ECE IMPORTANT MCQ-COMMUNICATION SYSTEMS PART ONE

ANSWER KEY-Correct answer is indicated by symbol (V) in options.
HINTS-In some questions options E-HINTS is indicating the hints of answer.

1) An AM demodulator can be implemented with a linear multiplier followed by a ________filter.
A [v]) low-pass
B [ ]) high-pass
C [ ]) band-pass
D [ ]) band-stop

2) The intermediate frequency in a standard AM receiver is
A [ ]) 455 Hz
B [v]) 455 kHz
C [ ]) 4.55 MHz.
D [ ]) none of the above

3) In order for a light ray to propagate along a fiber-optic cable, what must the relationship be between the angle of incidence and the critical angle?
A [v]) θi > θc
B [ ]) θi < θc
C [ ]) θi = θc
D [ ]) none of the above

4) Light may be propagated along a fiber-optic cable in which of the following modes?
A [ ]) multimode step index
B [ ]) single-mode step index
C [ ]) multimode graded index
D [v]) all of the above

5) In AM, the carrier is changed by a modulating signal. What parameter of the carrier is changed?
A [v]) amplitude
B [ ]) frequency
C [ ]) pulse width
D [ ]) phase

6) The output spectrum of a ________ modulator includes upper-side and lower-side
frequencies and the carrier frequency.
A [ ]) balanced
B [v]) standard amplitude
C [ ]) all of these
D [ ]) none

7) Amplitude modulation is a ________ process.
A [v]) multiplication
B [ ]) division
C [ ]) sum/difference
D [ ]) none

8) Speed of data transmission in 4-G network of telecom is
A [ ]) 386 kbps - 2 mbps.
B [ ]) 2 mbps
C [ ]) 2 mbps -1 gbps.
D [v]) 100 mbps - 1 gbps.

9) The frequency range for satellite communication is
A [ ]) 1 kHz - 100 kHz
B [ ]) 100 kHz - 1 MHz
C [ ]) 10 MHz - 30 MHz
D [v]) 1 GHz - 30 GHz

10) A cordless telephone using separate frequencies for transmission in base and portable units is known as
A [v]) duplex arrangement
B [ ]) half duplex arrangement
C [ ]) either (a) or (b)
D [ ]) neither (a) nor (b)

11) For attenuation of high frequencies we should use
A [v]) shunt capacitance
B [ ]) series capacitance
C [ ]) inductance
D [ ]) resistance

12) A modem is classified as low speed if data rate handled is
A [ ]) upto 100 bps
B [ ]) upto 250 bps
C [ ]) upto 400 bps
D [v]) upto 600 bps

13) VSB modulation is preferred in TV because
A [v]) it reduces the bandwidth requirement to half
B [ ]) it avoids phase distortion at low frequencies
C [ ]) it results in better reception
D [ ]) none of the above

14) A woofer should be fed from the input through a
A [v]) low pass filter
B [ ]) high pass filter
C [ ]) band pass filter
D [ ]) band stop filter

15) The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of
A [ ]) frequency adjustment
B [v]) frequency interleaving
C [ ]) frequency changing
D [ ]) frequency amalgamation

16) In FM signal with a modulation index mf is passed through a frequency tripler. The
wave in the output of the tripler will have a modulation index of
A [ ]) mf
B [v]) 3mf
C [ ]) mf/3
D [ ]) mf/9

17) In colour TV receiver, varactor diode is used for
A [ ]) detection
B [ ]) rectification
C [v]) tuning
D [ ]) both (a) and (b)

18) Energy content of atmospheric noise
A [ ]) does not depend on frequency
B [v]) decreases as frequency is increased
C [ ]) increases as frequency is increased
D [ ]) either (a) or (c) depending on the temperature

19) A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is
A [ ]) 400 W
B [v]) 512 W
C [ ]) 588 W
D [ ]) 650 W
E [ ]) HINTS- 400(1+0.75²/2)=512W

20) Non-coherently detection is not possible for
A [v]) PSK
B [ ]) ASK
C [ ]) FSK
D [ ]) both (a) and (c)

21) Which of the following is the indirect way of FM generation?
A [ ]) Reactance bipolar transistor modulator
B [v]) Armstrong modulator
C [ ]) Varactor diode modulator
D [ ]) Reactance FM modulator

22) The velocity of sound waves in air
A [ ]) is constant at all temperatures
B [ ]) varies directly as temperature
C [ ]) varies inversely as absolute temperature
D [v]) varies directly as square root of absolute temperature

23) An earth mat for a communication tower consists of
A [ ]) one or two radials extending from base of tower at a depth of about 5 cm below ground
B [ ]) a large number of radials extending from base of tower at a depth of about 3 m
C [v]) a large number of radials extending from base of tower at a depth of about 30 cm
D [ ]) none of the above

24) The rate at which information can be carried through a communication channel
depends on
A [ ]) carrier frequency
B [v]) bandwidth
C [ ]) transmission loss
D [ ]) transmitted power

25) A carrier is simultaneously modulated by two sine waves having modulation indices of 0.4 and 0.3. The total modulation index will be
A [ ]) 0.1
B [ ]) 0.7
C [v]) 0.5
D [ ]) 0.35
E [ ]) HINTS-m₁=0.4,m₂=0.3 mt=√m₁²+m₂²

26) Frequency shift keying is used mostly in
A [v]) telegraphy
B [ ]) telephony
C [ ]) satellite communication
D [ ]) radio transmission

27) It is desired that transmission line and load should match for a range of frequencies.The best method is
A [ ]) to use a balun
B [ ]) to use a single stub of adjustable position
C [v]) to use a double stub
D [ ]) to use a broad band amplifier

28) Signal to noise ratio of microphone is defined as the ratio of output when the sound pressure is __________ to the output in the absence of any sound signal.
A [ ]) 0.5 Pa
B [ ]) 0.2 Pa
C [v]) 0.1 Pa
D [ ]) 0.01 Pa
E [ ]) HINTS=0.1 Pa (= 0.5 x 10⁻⁴W/m²) is taken as standard sound pressure for defining S/N ratio of microphones.

29) Which of the following is taken as reference antenna for directive gain?
A [ ]) Half wave dipole
B [ ]) Elementary doublet
C [v]) Isotropic
D [ ]) Infinitesimal dipole

30) Counterpoise is used in coils having
A [v]) high resistivity
B [ ]) low resistivity
C [ ]) medium resistivity
D [ ]) all of these

31) Which of the following types of noise assumes greater importance at high frequencies?
A [v]) Transit time noise
B [ ]) Shot noise
C [ ]) Impulse noise
D [ ]) Random noise

32) In transistor radio receivers the number of IF amplifier stages are
A [ ]) 1
B [v]) 2
C [ ]) 4
D [ ]) 6

33) If each short element of signal occupies 20 ms, the speed is
A [ ]) 20 bauds
B [v]) 50 bauds
C [ ]) 1/50 bauds
D [ ]) 0.05 bauds
E [ ]) HINTS-Speed=1/20×10⁻³=50

34) Consider the following statements about Yagi Uda antenna
1.It is unidirectional
2.Its gain is about 7 dB
3.It is used at VLF
4.The optimum separation is 0.11
Which of the above are correct?
A [ ]) 1 and 2 only
B [v]) 1, 2, 4 only
C [ ]) 1, 2, 3, 4
D [ ]) 1 and 4 only

35) Fields are said to be circularly polarized if their magnitudes are
A [ ]) equal and they are in phase
B [v]) equal but they differ in phase by ± 90°
C [ ]) unequal and differ in phase by ± 90°
D [ ]) unequal but are in phase

36) To ensure good transient response in audio systems the natural frequencies should be
A [ ]) above 40 Hz and below 15 kHz
B [ ]) above 40 Hz
C [v]) above 15 kHz
D [ ]) below 40 Hz and above 15 kHz

37) An AM signal and a narrow band FM signal with identical carriers, modulating signals
and modulation index of 0.1 are added together. The resultant signal can be closely
approximated by
A [ ]) Broadband FM
B [v]) SSB with carrier
C [ ]) DSB-SC
D [ ]) SSB without carrier

38) The equation v(t) = A cos [ωct + φ(t)] where A and ωc are constant and φ(t) is a
function of base signal represents
1.Phase modulation
2.Amplitude modulation
3.Angle modulation
4.Frequency modulation
Which of the above are true?
A [ ]) 3 only
B [v]) 1, 3 and 4
C [ ]) 1, 2, 3, 4
D [ ]) 3 and 4 only

39) An FM signal with deviation δ is passed through mixer. Its frequency is reduced five
fold. The deviation in output of mixer is
A [ ]) 0.28
B [v]) δ
C [ ]) 5 δ
D [ ]) very very high
E [ ]) HINTS-Deviation is not affected by mixer.

40) The total number of channels allotted for cellular telephone is
A [v]) 666
B [ ]) 333
C [ ]) 221
D [ ]) 111
E [ ]) HINTS-Cellular telephones have been assigned 666 channels (826 to 845 MHz and 870 to 890 MHz). Each channel has width of 30 kHz.

41) The bandwidth of DSB suppressed carrier modulation system when the modulating
frequency varies between 500 Hz and 5 kHz is
A [ ]) 555 kHz
B [ ]) 505 kHz
C [ ]) 500 kHz
D [v]) 9 kHz
E [ ]) HINTS-fm = 5 kHz - 500 Hz= 4.5 kHz
Bandwidth = 2 fm =2 x 4.5 kHz = 9 kHz.

42) The filter circuit for feeding a wooffer has
A [v]) an inductance in series and capacitance in parallel
B [ ]) a capacitance in series and an inductance in parallel
C [ ]) a resistance in series and an inductance in parallel
D [ ]) an inductance in series and a resistance in parallel

43) In ionosphere incidence angle is 60°. The maximum usable frequency fm is equal to
A [v]) 2fc
B [ ]) fc
C [ ]) 0.5 fc
D [ ]) 3 fc

44) The number of channels available in MF band (300 kHz - 3 MHz) for AM modulating
signal of 20 kHz is
 A [ ]) 70
B [v]) 67
C [ ]) 150
D [ ]) 200
E [ ]) HINTS-In MF band, frequency space available= 3000 - 300= 2700 kHz
when AM is used Bandwidth of each channel.= 2 x 20 kHz = 40 kHz
No of channel=2700/40=67.5=67 exact

45) The receiver of a pulsed RADAR can detect signal power in the order of
A [ ]) 1 W
B [ ]) 0.1 W
C [ ]) 10⁻⁵W
D [v]) 10⁻¹² W

46) Consider the following
1.Generation of SSB signals
2.Design of minimum phase type filters
3.Representation of band pass signals
Which of the above applications is Hilbert transform used?
A [ ]) 1 only
B [v]) 1, 2 and 3
C [ ]) 1, 2 only
D [ ]) 1 and 3

47) Consider the following statements about loop antenna
1.It is suitable for direction finding application
2.It is a single turn or multi turn coil carrying RF current
3.The loop is surrounded by a magnetic field everywhere perpendicular to the loop
Which of the above statements are correct?
A [ ]) 1 and 2 only
B [ ]) 1 only
C [v]) 1, 2, 3
D [ ]) 2 and 3 only

48) Which of the following is present in both TRF(tuned radio frequency)receiver and
superheterodyne receiver?
A [v]) Detector
 B [ ]) Mixer
C [ ]) IF amplifier
D [ ]) Local oscillator

49) The number of channels in a stereophonic system is
A [ ]) 8
B [ ]) 4
C [v]) 2
D [ ]) 1

50) Consider the following reasons for using antenna coupler
1.To prevent illegal radiation of spurious frequencies
2.To tune out reactive components of antenna impedance
3.To have correct value of load impedance for transmitter.
Which of the above are correct?
A [v]) 1, 2, 3
B [ ]) 1, 2
C [ ]) 1 only
D [ ]) 2, 3
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