ECE - Communication Systems Quiz (or) MCQ

1 .

A buffer amplifier is_____

A)

A high gain D.C. amplifier

B)

A cathode follower stage

C)

A double-tuned amplifier

D)

None of the above

Correct Answer : A high gain D.C. amplifier

2 .

It is found that a ship to ship communication suffers from fading. This can be avoided by using

A)

Space diversity

B)

Directional antenna

C)

Frequency diversity

D)

Broad band antenna

Correct Answer : Frequency diversity

3 .

A cordless telephone using separate frequencies for transmission in base and portable units is known as

A)

half duplex arrangement

B)

duplex arrangement

C)

Either (A) or (B)

D)

Neither (A) nor (B)

Correct Answer : duplex arrangement

Explanation : Separate frequencies for transmission from base and portable units allows two way transmission and is called duplex arrangement.

4 .

For attenuation of high frequencies we should use

A)

resistance

B)

inductance

C)

shunt capacitance

D)

series capacitance

Correct Answer : series capacitance

Explanation : Since Xc for high frequencies is low, the high frequencies are shunted to ground and are not transmitted.

5 .

A woofer should be fed from the input through a

A)

low pass filter

B)

high pass filter

C)

band stop filter

D)

band pass filter

Correct Answer : low pass filter

Explanation : Woofer is a low frequency loud speaker covering the range 16 Hz to 500 Hz.

6 .

SSB can be generated by

A)

Filter method

B)

Phase cancellation method

C)

Good attenuation characteristics

D)

All of the above

Correct Answer : All of the above

7 .

What is the purpose of peak clipper circuits in radio transmitters?

A)

To reduce bandwidth

B)

To increase bandwidth

C)

To prevent overmodulation

D)

To regulate oscillator I/P voltage

Correct Answer : To prevent overmodulation

8 .

The direction of rotation of a CD is

A)

Clockwise

B)

Anticlockwise

C)

Mostly anticlockwise but some times clockwise

D)

Clockwise or anticlockwise depending on frequency of data stored

Correct Answer : Anticlockwise

9 .

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)

upto 600 bps

Correct Answer : upto 600 bps

Explanation : When data rate in bits per second is upto 600, modem is low speed.

10 .

VSB modulation is preferred in TV because

A)

it reduces the bandwidth requirement to half

B)

it results in better reception

C)

it avoids phase distortion at low frequencies

D)

None of the above

Correct Answer : it reduces the bandwidth requirement to half

Explanation : VSB (vestigial side band) transmission transmits one side band fully and the other side band partially thus, reducing the bandwidth requirement.

11 .

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 changing

B)

frequency interleaving

C)

frequency adjustment

D)

frequency amalgamation

Correct Answer : frequency interleaving

Explanation : In frequency interleaving the space between bundles is used for colour signal.

12 .

Energy content of atmospheric noise

A)

does not depend on frequency

B)

increases as frequency is increased

C)

decreases as frequency is increased

D)

either (a) or (c) depending on the temperature

Correct Answer : decreases as frequency is increased

Explanation : Atmospheric noise decreases as frequency is increased

13 .

In colour TV receiver, varactor diode is used for

A)

tuning

B)

detection

C)

rectification

D)

None of the above

Correct Answer : tuning

Explanation : In varactor diode the applied reverse bias controls the width and therefore capacitance of depletion layer.

This capacitance is used for tuning.

14 .

The number of noise sources in a BJT are

A)

1

B)

2

C)

3

D)

4

Correct Answer : 3

Explanation : Shot noise, partition noise and thermal noise.

15 .

The characteristic impedance of a twin wire feeder used for TV signals is about

A)

1000 ohm

B)

700 ohm

C)

500 ohm

D)

300 ohm

Correct Answer : 300 ohm

16 .

In EM waves, polarization

A)

Is caused by reflection

B)

Is due to transverse nature of waves

C)

Is always vertical in an isotropic medium

D)

Results from longitudinal nature of waves

Correct Answer : Is due to transverse nature of waves

17 .

The frequency range of 300 kHz to 3000 kHz is known as

A)

High frequency

B)

Medium frequency

C)

Low frequency

D)

Very high frequency

Correct Answer : Medium frequency

18 .

A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is

A)

512 W

B)

588 W

C)

650 W

D)

750 W

Correct Answer : 512 W

Explanation :

19 .

A total of 16 equally probable events exist. If it is required to select one out of them, the number of required bits is

A)

2

B)

4

C)

6

D)

8

Correct Answer : 4

Explanation : 2⁴ = 16

20 .

When modulation index of an AM wave is increased from 0.5 to 1, the transmitted power

A)

remains the same

B)

increases by 25%

C)

increases by 33.3%

D)

increases by 50%

Correct Answer : increases by 33.3%

Explanation :

21 .

Quantizing error occurs in

A)

FDM

B)

TDM

C)

PWD

D)

PCM

Correct Answer : PCM

Explanation : An analog number cannot be converted into an exact digital number.

This is called quantizing error.

22 .

The most commonly used transistor amplifier circuit is

A)

CB

B)

CC

C)

CE

D)

CE or CC

Correct Answer : CE

Explanation : Common emitter connection has high power gain, and good current and voltage gains.

23 .

When energy is fed into open wire transmission line the energy may get dissipated due to

A)

radiation

B)

dielectric heating

C)

conductor heating

D)

All of the above

Correct Answer : All of the above

Explanation : All the three cause dissipation of energy as heat.

24 .

If transmitted power is 75 kW, the field strength at 30 km distance will be about

A)

1 V/m

B)

2 mV/m

C)

10 V/m

D)

50 mV/m

Correct Answer : 50 mV/m

Explanation :

25 .

Loudness control gives

A)

high boost to bass and little boost to treble

B)

equal boost to bass and treble

C)

less boost to both bass and treble

D)

less boost to bass and more boost to treble

Correct Answer : high boost to bass and little boost to treble

Explanation : For depth in sound the low frequency notes, (i.e., bass) need more amplification.

26 .

A mobile telephone has a range of about

A)

0.1 km

B)

1 km

C)

10 km

D)

50 km

Correct Answer : 50 km

Explanation : Mobile telephone has about 50 km range.

27 .

A Discone antenna is

A)

a combination of disk and cone far apart

B)

a combination of disk and cone in close approximity

C)

a combination of disk and cone at Î»/2 spacing

D)

a combination of disk and cone at Î»/4 spacing

Correct Answer : a combination of disk and cone in close approximity

Explanation : It is a combination of disc and cone in close approximity.

28 .

In a two tone AM system the two modulating frequencies are 2000 p and 4000 p rad/sec. If carrier frequency is 2p x 10⁶ rad/sec the frequencies of upper sidebands are

A)

1.001 MHz and 1.004 MHz

B)

1.002 MHz and 1.004 MHz

C)

1.001 MHz and 1.002 MHz

D)

1.002 MHz and 1.008 MHz

Correct Answer : 1.001 MHz and 1.002 MHz

Explaination :

29 .

In a system an input resistance of 20 kΩ causes a noise voltage of 15μV. If two such input resistances each of 20 kΩ are used in parallel, the total noise voltage will be about

A)

7.5 μV

B)

10.6 μV

C)

15 μV

D)

30 μV

Correct Answer : 10.6 μV

Explaination :

30 .

Dolby system of noise reduction divides the total audio spectrum into

A)

16 frequency bands

B)

8 frequency bands

C)

4 frequency bands

D)

2 frequency bands

Correct Answer : 4 frequency bands

Explanation : Dolby A system divides the frequency in 4 bands viz.f < 80 Hz, 80 Hz < f < 2999 Hz, f > 3000 Hz, f > 9000 Hz.

31 .

For a system to be designated as hi-fi, the signal to noise ratio should be at least

A)

25 dB

B)

50 dB

C)

75 dB

D)

100 dB

Correct Answer : 50 dB

Explanation : Hi-Fi system has a S/N ratio at least equal to 50 dB.

32 .

In the television system in India, the odd and even fields are scanned

A)

25 times each but alternately

B)

50 times each but alternately

C)

25 times each

D)

50 times each

Correct Answer : 25 times each but alternately

33 .

Vidicon and plumbicon operate on the principle of

A)

photo voltaic

B)

photo emission

C)

Both (A) and (B)

D)

photo conduction

Correct Answer : photo conduction

Explanation : Photo conduction uses the fact that resistivity of some materials depends on intensity of light falling on their surface.

34 .

A TV receiver has a width of 60 cm. The aspect ratio is 4/3. The required EHT supply is about

A)

2.9 kV

B)

4.5 kV

C)

29 kV

D)

45 kV

Correct Answer : 29 kV

Explanation :

35 .

The radio receivers mostly used now a days are

A)

CW receivers

B)

TRF receivers

C)

pulsed receivers

D)

super heterodyne receivers

Correct Answer : super heterodyne receivers

Explanation : Now-a-days only super heterodyne radio receivers are used.

36 .

The modulating frequency in frequency modulation is increased from 10 kHz to 30 kHz. The bandwidth is increased by

A)

6

B)

1/6 times

C)

increase by 20 kHz

D)

increase by 30 kHz

Correct Answer : 6

Explanation : BW = 2f_m(1 + β)
for β >> 1

B.W. a 2f_m.

37 .

The reactance of coupling capacitors, for DC quantities, is

A)

low

B)

infinite

C)

zero

D)

zero or low

Correct Answer : infinite

Explanation : For zero frequency capacitive reactance is infinite.

38 .

Consider the following test signal patterns

1. Ramp
2. Grill
3. Grey shades
4. Sine pulse
5. Picture line up generating equipment

Which of the above are used in TV studios?

A)

1, 2 and 3 only

B)

1, 2 and 5 only

C)

2, 3, 4 and 5 only

D)

All 1, 2, 3, 4 and 5

Correct Answer : All 1, 2, 3, 4 and 5

Explaination : All these are standard test signals used in TV studios.

39 .

Indicate the false statement: If SWR on a transmission line is infinite, the line is terminated in

A)

open circuit

B)

short circuit

C)

complex impedance

D)

pure reactance

Correct Answer : complex impedance

Explanation : If line is OC or SC or terminated in pure reactance, SWR is 1.

40 .

In TV signals colour burst is used

A)

to synchronise colours

B)

to maintain colour sequence

C)

for interlacing of horizontal lines

D)

to ensure I and Q phase correctly

Correct Answer : to ensure I and Q phase correctly

Explanation : Colour burst consists of a short train of about 10 cycles sent to the receiver along with synchronous signals. It ensures I and Q phase correctly.

41 .

The resonant frequency of an RF amplifier is 1 MHz and its bandwidth is 10 kHz. The Q factor will be

A)

10

B)

100

C)

0.01

D)

0.1

Correct Answer : 100

Explanation :

42 .

The total number of pulses in a TV remote control is

A)

14

B)

12

C)

10

D)

8

Correct Answer : 14

Explanation : The 14 pulses are preliminary pulse, start pulse, stop pulse and 11 other pulses.

43 .

Which camera tube has highest sensitivity and very wide spectral response?

A)

Saticon

B)

Vidicon

C)

New vicon

D)

Plumbicon

Correct Answer : New vicon

Explanation : New vicon has very high sensitivity and very wide spectral response which extends well into infrared region.

44 .

A computer monitor uses 180 W in normal operation and 20 W in sleep mode. The computer is on all the 24 hours but is in sleep mode for 18 hours a days. The energy units saved in 30 days are

A)

0.54 units

B)

2.88 units

C)

4.8 units

D)

86.4 units

Correct Answer : 86.4 units

Explaination :

45 .

Consider the following functions

1. It detects the AM video carrier IF so as to produce the video signal
2. It produces and separates out the inter carrier sound IF of 5.5 MHz
3. It amplifies the video signal
4. It amplifies the audio signal

The video detector in a colour TV performs which of the above functions

A)

1 and 2

B)

1, 2 and 3

C)

1, 2 and 4

D)

1, 2, 3 and 4

Correct Answer : 1 and 2

Explaination : Video detector does not amplify any signal.

46 .

In a satellite system circular polarization is to be obtained. The antenna used is

A)

horn

B)

helical

C)

parabolic

D)

log periodic

Correct Answer : helical

Explanation : Helical antenna produces a circularly polarized radiation if its two components are at right angles and are equal. It is very commonly used in radio telemetry.

47 .

A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 Î¼s and retrace time is 12 Î¼s, the transistor is conducting for about

A)

3.1 Î¼s

B)

6.4 Î¼s

C)

31 Î¼s

D)

64 Î¼s

Correct Answer : 31 Î¼s

Explanation :

48 .

A TV remote control works on the principle of

A)

pulse code modulated infrared light

B)

demodulation

C)

pulse code modulated ultra violet light

D)

Either (A) or (B)

Correct Answer : pulse code modulated infrared light

Explanation : Infrared light is used in TV remote control.

49 .

To prevent overloading in the last IF amplifier one should use

A)

squelch

B)

double conversion

C)

variable selectivity

D)

variable sensitivity

Correct Answer : variable sensitivity

Explanation : Variable sensitivity prevents overloading.

50 .

As the magnitude of reverse bias is increased, the capacitance of varactor diode

A)

increases

B)

decreases

C)

first increase, then decreases

D)

first decreases then increases

Correct Answer : decreases

Explanation : When magnitude of reverse bias is increased, thickness of depletion layer increases.

Capacitance is inversely proportional to thickness.

51 .

Push pull amplifier is

A)

class A

B)

class B

C)

class C

D)

Class A or Class C

Correct Answer : class B

52 .

24 telephone channels, each band limited to 3.4 kHz are to be time division multiplexed using PCM. If sampling frequency is 10 kHz and number of quantization levels is 128, the required bandwidth of PCM is

A)

1.68 MHz

B)

3.072 MHz

C)

81.6 kHz

D)

240 kHz

Correct Answer : 1.68 MHz

Explaination :

Bandwidth ≈ 24 (ln₂ 128) 10 kHz = 1.68 MHz.

53 .

Resonant circuits are used in

A)

audio amplifiers

B)

RF amplifiers

C)

Both audio and RF amplifiers

D)

None of the above

Correct Answer : RF amplifiers

Explanation : RF amplifiers use resonant loads (L and C in parallel).

54 .

In the equivalent circuit of a moving coil cone type loudspeaker, the mass of the moving system is represented by

A)

an inductance

B)

a resistance

C)

a capacitance

D)

a conductance

Correct Answer : an inductance

Explanation : Mass has inertia and is analogous to inductance.

55 .

Linear diode detector utilizes

A)

rectification property of diode

B)

linear portion of static characteristics of diode

C)

linear portion of dynamic characteristic of diode

D)

square law portion of dynamic characteristics of diode

Correct Answer : rectification property of diode

Explanation : Detection (also called demodulation) is due to rectification property of diode.

56 .

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)

9 kHz

Correct Answer : 9 kHz

Explanation :

57 .

CATV stands for

A)

Cable Antenna Television

B)

Channel Antenna Television

C)

Community Antenna Television

D)

Common Antenna Television

Correct Answer : Community Antenna Television

Explanation : In USA the first cable service was called community antenna television.

58 .

Household tape recorders use

A)

separate motor for each operation

B)

only one motor for all operations

C)

one motor for capstan and another for take up reel

D)

a total of 3 motors

Correct Answer : only one motor for all operations

Explanation : For reasons of economy only one motor is used.

59 .

A geostationary satellite______

A)

is located at a height of 358, 00 km

B)

is motionless in space but keeps spinning

C)

appears stationary over earth's magnetic pole

D)

orbits the earth within a 24 hour period

Correct Answer : orbits the earth within a 24 hour period

Explanation : It orbits the earth in a 24 hour period. Thus it appears to be stationed over one spot of the globe.

60 .

A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will be

A)

38.5 W

B)

400 W

C)

512.5 W

D)

615.5 W

Correct Answer : 512.5 W

Explanation :

Sideband frequencies will be f_c ± f_m.

61 .

If sound intensity is 8 W/m², the dB level of this sound is about

A)

5 dB

B)

50 dB

C)

129 dB

D)

1290 dB

Correct Answer : 129 dB

62 .

The distance of a direct broadcasting satellite from earth's surface is about

A)

1000 km

B)

10000 km

C)

36000 km

D)

55000 km

Correct Answer : 36000 km

63 .

In asynchronous TDM, for n signal sources, each frame contains m slots, where m is usually

A)

n

B)

2n

C)

Less than n

D)

greater than 2n

Correct Answer : greater than 2n

64 .

UHF range is__________

A)

3 to 30 MHz

B)

30 to 300 MHz

C)

300 to 3000 MHz

D)

3000 to 30000 MHz

Correct Answer : 300 to 3000 MHz

65 .

Which of the following microphones has an inbuilt amplifier?

A)

Carbon

B)

Condenser

C)

Ribbon

D)

Moving coil

Correct Answer : Condenser

66 .

How much is contributed by each bit in the code word of a PCM system under uniform and symmetric quantization to the signal to noise ratio?

A)

3 dB

B)

4 dB

C)

5 dB

D)

6 dB

Correct Answer : 6 dB

67 .

Noise which assumes great importance at high frequencies is

A)

shot noise

B)

flicker noise

C)

Johnson noise

D)

transit-time noise

Correct Answer : transit-time noise

68 .

AM transmitter employing low level modulation

A)

has a poor efficiency

B)

has a higher efficiency

C)

requires higher audio power

D)

uses class C amplifier for amplification

Correct Answer : has a poor efficiency

69 .

Which one is Analog Continuous modulation technique?

A)

DM

B)

PAM

C)

AM

D)

PCM

Correct Answer : AM

70 .

Which of following digital modulation technique?

A)

ASK

B)

FSK

C)

PSK

D)

All of the above

Correct Answer : All of the above

71 .

A discrete zero memory information source has 40 symbols and each symbol is equally likely. The minimum number of bits required to code the source with uniform length code and entropy of the source are

A)

5 and 5.03

B)

5 and 6.64

C)

6 and 5.83

D)

6 and 5.32

Correct Answer : 6 and 5.32

72 .

Armstrong FM transmitter uses

A)

LC oscillator

B)

crystal oscillator

C)

RC oscillator

D)

Either (A) or (B)

Correct Answer : crystal oscillator

73 .

The standard intermediate frequency for FM ratio is

A)

10.7 MHz

B)

4.5 MHz

C)

75 kHz

D)

455.5 kHz

Correct Answer : 10.7 MHz

74 .

The noise figure of individual stages of a two stage amplifier is 2.03 and 1.54 respectively. If gain of first stage is 62, the overall noise figure is

A)

2.03

B)

2.055

C)

3.05

D)

6.05

Correct Answer : 2.055

75 .

A trinitron colour picture tube uses

A)

one electron gun

B)

three electron guns

C)

one electron gun with three separate in line cathodes

D)

None of the above

Correct Answer : one electron gun with three separate in line cathodes

76 .

The output resistance of a microphone is 20 ohms. It is to feed a line of impedance 320 ohms. To ensure maximum power transfer, the turn ratio of transformer is

A)

2

B)

4

C)

16

D)

32

Correct Answer : 4

Explanation : (20)(4)² = 320 ohms.

77 .

Audio cassettes used in household tape recorders have a width of

A)

1"

B)

1/2"

C)

1/4"

D)

1/8"

Correct Answer : 1/4"

Explanation : Home tape recorders use 1/4 in (i.e., 6.3 mm) tape having two tracks of 2.5 mm width each with an in between separation of 1.3 mm.

78 .

The receiver of a pulsed RADAR can detect signal power in the order of

A)

1 W

B)

0.1 W

C)

10â»âµ W

D)

10â»Â¹Â² W

Correct Answer : 10â»Â¹Â² W

Explanation : It can detect very low power signals.

79 .

In a 100% amplitude modulated signal, the power in the upper sideband when carrier power is to be 100 W and modulation system SSBSC, is

A)

25 W

B)

50 W

C)

66 W

D)

100 W

Correct Answer : 25 W

Explanation :

80 .

The dc voltage on plate modulated class C amplifier is 8 kV. If the peak modulating voltage is 4 kV, the peak RF voltage delivered to load is

A)

0.5 kV

B)

12 kV

C)

24 kV

D)

32 kV

Correct Answer : 24 kV

Explanation : Peak RF voltage delivered to load = 2 (8 + 4) = 24 kV.

81 .

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)

1, 2 only

C)

1 and 3

D)

1, 2 and 3

Correct Answer : 1, 2 and 3

Explaination : Hilbert transform is used in all the applications.

82 .

Which camera tube has highest dark current?

A)

Vidicon

B)

Plumbicon

C)

Saticon

D)

GCD imager

Correct Answer : Plumbicon

Explanation : Dark current is the small signal current even when there is no illumination on the face plate of camera tube.

83 .

If a sound wave has a frequency of 50 Hz, the wavelength is

A)

0.66 m

B)

6.6 m

C)

66 m

D)

0.066 m

Correct Answer : 6.6 m

84 .

A telephone channel requires a bandwidth of about

A)

1 kHz

B)

3 kHz

C)

10 kHz

D)

50 kHz

Correct Answer : 3 kHz

85 .

Fourier analysis indicate that a square wave can be represented as

A)

A fundamental sine wave and harmonics

B)

Fundamental and subharmonic sine waves

C)

A fundamental sine wave and even harmonics

D)

A fundamental sine wave and odd harmonics

Correct Answer : A fundamental sine wave and odd harmonics

86 .

If sampling is done at the rate of 10 kHz. The bandwidth required is

A)

35 kHz

B)

70 kHz

C)

1280 kHz

D)

1520 kHz

Correct Answer : 35 kHz

87 .

Which of the following is an indirect way of generating FM?

A)

Reactance FET modulator

B)

Varactor diode modulator

C)

Armstrong modulator

D)

Reactance bipolar transistor

Correct Answer : Armstrong modulator

88 .

In practical commercial FM system, channel bandwidth is

A)

88 MHz

B)

100 kHz

C)

108 MHz

D)

150 kHz

Correct Answer : 150 kHz

Explanation : Frequency Modulation (FM) is a method of transmitting information (such as audio signals) by varying the frequency of the carrier wave in accordance with the modulating signal. In commercial FM radio broadcasting, the audio signal (voice or music) is used to modulate the carrier frequency, and this modulated signal is transmitted over the airwaves to be received by FM radios.

The channel bandwidth refers to the range of frequencies that the FM signal occupies in the radio frequency spectrum. In FM broadcasting, the signal is allocated a specific frequency band, and this band needs to be wide enough to accommodate the modulated signal.

The channel bandwidth is influenced by various factors, including the audio quality, the data rate required for the transmission, and the interference considerations to ensure proper reception. In commercial FM broadcasting, a bandwidth of approximately 150 kHz is chosen as a trade-off between audio quality and spectrum efficiency.

Here's why :

1. Audio Quality: A wider bandwidth allows for higher fidelity audio transmission. The wider the bandwidth, the more accurately the original audio signal can be reconstructed at the receiving end. A 150 kHz bandwidth is considered sufficient to provide good audio quality for commercial FM radio broadcasting.

2. Spectrum Efficiency: On the other hand, allocating too much bandwidth for each FM channel would be inefficient in terms of spectrum usage. It would limit the number of radio stations that could coexist within the available radio frequency spectrum, leading to congestion and reduced choices for listeners.

3. Interference: FM channels are typically spaced apart in the radio frequency spectrum to avoid interference between adjacent channels. Allocating a wider bandwidth for each FM channel would require more significant spacing between channels, further reducing the available spectrum for broadcasting.

For these reasons, a practical compromise is made by selecting a channel bandwidth of around 150 kHz in commercial FM systems. This allows for good audio quality while optimizing spectrum utilization and providing enough spacing between channels to minimize interference.

89 .

Non-coherently detection is not possible for

A)

ASK

B)

FSK

C)

PSK

D)

None of the above

Correct Answer : PSK

90 .

Tracking of extra terrestrial objects requires

A)

very sensitive receiver

B)

fully steerable antenna

C)

high transmitting power

D)

All of the above

Correct Answer : All of the above

91 .

In radar systems PRF stands for_________

A)

Pulse Repetition Frequency

B)

Pulse Return Factor

C)

Power Return Factor

D)

Pulse Response Factor

Correct Answer : Pulse Repetition Frequency

Explanation : PRF in radar systems means pulse repetition frequency.

92 .

Which of the following cannot be the Fourier series expansion of a periodic signal?

A)

x(t) = cos t + 0.5

B)

x(t) = 2 cos t + 3 cos 3t

C)

x(t) = 2 cos pt + 7 cos t

D)

x(t) = 2 cos 1.5pt + sin 3.5 pt

Correct Answer : x(t) = cos t + 0.5

Explanation : x(t) = cos t + 0.5

not satisfies the Dirichlet condition.

The integration of constant term is ∞.

93 .

Which of the following is the indirect way of FM generation?

A)

Reactance FM modulator

B)

Armstrong modulator

C)

Varactor diode modulator

D)

Reactance bipolar transistor modulator

Correct Answer : Armstrong modulator

Explanation : It generates FM through phase modulation.

94 .

A telephone exchange has 9000 subscribers. If the number of calls originating at peak time is 10, 000 in one hour, the calling rate is

A)

0.1

B)

0.81

C)

0.9

D)

10/9

Correct Answer : 10/9

Explanation : Calling rate is the number of calls per subscriber.

95 .

In the television system in India, each frame is scanned

A)

10 times

B)

20 times

C)

50 times

D)

100 times

Correct Answer : 50 times

Explanation : Each frame is divided into odd and even fields. Each field is scanned 25 times so that each frame is scanned 50 times.

96 .

Each kilometer of travel in electromagnetic radiation means a time delay of

A)

0.33 Î¼s

B)

3.3 Î¼s

C)

33 Î¼s

D)

330 Î¼s

Correct Answer : 3.3 Î¼s

Explanation : Since velocity of em waves is 300 m/ms, each kilometer means time delay of 3.3 μs.

97 .

In single tone AM modulation, the transmission efficiency for m = 1 is

A)

33.3%

B)

16.65%

C)

50%

D)

100%

Correct Answer : 33.3%

Explanation : Since signal power = 0.5 P_C and total power is 1.5 P_C efficiency is 33.3%.

98 .

A RADAR can be used to

A)

to search submarines

B)

aim a gun at an aircraft

C)

to direct guided missiles

D)

All of the above

Correct Answer : All of the above

Explanation : Radar is used for all the three purposes.

99 .

AM amplifier having noise figure of 20 dB and available power gain of 15 dB is followed by a mixer circuit having noise figure of 9 dB. The overall noise figure as referred to input in dB is

A)

0.63

B)

10.44

C)

11.07

D)

21.52

Correct Answer : 10.44

Explanation :

100 .

Which one of the following is non-resonant antenna?

A)

End fire array

B)

Folded dipole

C)

Rhombic antenna

D)

Broad side array

Correct Answer : Rhombic antenna

Explanation : Rhombic antenna is a non-resonant antenna capable of operating over 3 to 30 MHz range

101 .

If the oscillator output is modulated by audio frequencies upto 10 kHz, the frequency range occupied by the side bands will be

A)

71.2 kHz to 71.20 kHz

B)

692 kHz to 732 kHz

C)

702 kHz to 722 kHz

D)

711.9 kHz to 712.1 kHz

Correct Answer : 702 kHz to 722 kHz

Explanation :

Sideband frequencies will be f_c ± f_m.

102 .

The efficiency of using a binary system for selection of 1 out of 13 equally probable events is

A)

About 71%

B)

About 83%

C)

About 92%

D)

100%

Correct Answer : 100%

103 .

A balun provides an impedance transformation of

A)

2 : 1

B)

4 : 1

C)

8 : 1

D)

16 : 1

Correct Answer : 4 : 1

Explanation : Balun has turn ratio of 2 : 1. Therefore, impedance transformation is 4 : 1.

104 .

If γ = (S₀/N₀)/(S_i/N_m) where S₀ and S₁ are signal power output and signal power input and N₀ and N_m are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are

A)

1 and 1

B)

1 and 2

C)

2 and 1

D)

0.5 and 0.5

Correct Answer : 1 and 1

Explaination : SSB - SC and SSB - DB have γ = 1 and are similar from noise point.

105 .

Which of the following antennas is circularly polarized?

A)

Helical

B)

Yagi-Uda

C)

Parabolic reflector

D)

Small circular loop

Correct Answer : Helical

Explanation : The helical antenna is circularly polarized, i.e., its polarization is evenly divided between vertical and horizontal components.

106 .

A transmitter power of 5 W is increased by 20 dB. The effective radiated power is

A)

5 W

B)

25 W

C)

100 W

D)

500 W

Correct Answer : 500 W

Explanation :

107 .

The percentage saving in power of 100% modulated suppressed carrier AM signal is

A)

50

B)

66.6

C)

75

D)

100

Correct Answer : 66.6

Explanation :

108 .

The maximum distance between television transmission and receiving antennas for reasonably good reception should be

A)

less than 20 km

B)

less than 100 km

C)

less than 500 km

D)

less than 1000 km

Correct Answer : less than 100 km

Explanation : Television transmission is governed by line of sight distance which is about 100 km or less.

109 .

The frequency response of a microphone means

A)

bandwidth of frequencies having output with in Â± 1 dB of the output at 500 Hz

B)

bandwidth of frequencies having output with in Â± 3 dB of the output at 500 Hz

C)

bandwidth of frequencies having output with in Â± 1 dB of the output at 1000 Hz

D)

bandwidth of frequencies having output with in Â± 3 dB of the output at 1000 Hz

Correct Answer : bandwidth of frequencies having output with in Â± 1 dB of the output at 1000 Hz

Explanation : 100 Hz is taken as standard for specifying the output.

110 .

Graphic equaliser system in stereophonic systems generally have

A)

1 band

B)

3 or 4 bands

C)

more than 8 bands

D)

large number of bands

Correct Answer : 3 or 4 bands

Explanation : Stereo systems have 3 or 4 bands at 300 Hz, 1000 Hz, 10000 Hz etc. in graphic equaliser system.

111 .

Some sources of TV programs are

1. TV camera
2. Telecine
3. VTR
4. External signal

Which of the above are actually present in a TV studio?

A)

1 and 3

B)

1, 2, 3

C)

1 2 and 4

D)

1, 2, 3 and 4

Correct Answer : 1, 2, 3 and 4

112 .

Two sinusoidal signals of same amplitude and frequencies 10 kHz and 10.1 kHz are added together. The combined signal is given to an ideal frequency detector. The output of the detector is

A)

a linear function

B)

0.1 kHz sinusoidal

C)

10.1 kHz sinusoidal

D)

None of the above

Correct Answer :

Y(t) = A cos (2p x 10⁴ t) + A cos (2p x 10.1 x 10³ t)

when passed through high pass filter,

Output will be A cos (2p x 10.1 x 10³ t) only.

113 .

In Vidicon camera tube, the resistance of photoconductive material on the target plate

A)

is more in darkness and less in brightness

B)

is more in brightness but less in darkness and brightness

C)

may be more or less in darkness and brightness

D)

None of the above

Correct Answer : is more in darkness and less in brightness

Explanation : Light dependent resistor (LDR) has high resistance in darkness and low resistance in brightness.

114 .

In VHS format each video head is tilted from azimuth by

A)

1Â°

B)

6Â°

C)

10Â°

D)

20Â°

Correct Answer : 6Â°

Explanation : Tilting of heads is done to reduce cross-talk.

115 .

Convolution of x(t + 5) with impulse function Î´(t - 7) is equal to

A)

x(t - 2)

B)

(t + 2)

C)

x(t - 12)

D)

x(t + 12)

Correct Answer : x(t - 2)

Explanation :

116 .

Which of the following is a better recording medium?

A)

Ferric oxide

B)

Ferrous oxide

C)

Chromium di oxide

D)

Either (A) or (B)

Correct Answer : Chromium di oxide

Explanation : Chromium di oxide has very good retentivity.

117 .

An angle modulated signal is given by s(t) = cos 2p (2 x 10⁶t + 30 sin 150t + 40 cos 150t). The maximum frequency and phase deviations of s(t) are

A)

6 kHz and 80π rad

B)

7.5 kHz, 100π rad

C)

10.5 kHz, 100π rad

D)

10.5 kHz, 140π rad

Correct Answer : 7.5 kHz, 100π rad

Explaination :

118 .

The simplest method of suppression of unwanted side band in AM is

A)

third method

B)

filter method

C)

phase shift method

D)

Both (A) and (B)

Correct Answer : filter method

Explanation : Unwanted frequency is removed by filtering.

119 .

For attenuation of low frequencies we should use

A)

series inductance

B)

shunt inductance

C)

shunt capacitance

D)

series capacitance

Correct Answer : series capacitance

Explanation : Series capacitance has high reactance for low frequencies.

120 .

A line has standing waves with a voltage maximum of 35 mV and minimum of 17.5 mV VSWR is

A)

2

B)

4

C)

4.5

D)

7.3

Correct Answer : 2

121 .

For a bit rate of 8 kbps, the best possible values of the transmitted frequencies in a coherent binary FSK system are

A)

16 kHz and 20 kHz

B)

20 kHz and 32 kHz

C)

20 kHz and 40 kHz

D)

32 kHz and 40 kHz

Correct Answer : 32 kHz and 40 kHz

Explanation :

122 .

If luminance signal Y = 0.3 R + 0.59 G + 0.11 B, the hue of R - Y colour is

A)

- 0.7 R + 0.59 G + 0.11 B

B)

1.3 R - 0.59 G - 0.11 B

C)

0.7 R - 0.59 G - 0.11 B

D)

None of the above

Correct Answer : 0.7 R - 0.59 G - 0.11 B

Explanation : R - Y = R - 0.3R - 0.59C - 0.11B = 0.7R - 0.59G - 0.11B.

123 .

Trap circuits used in video IF amplifier of colour TV are

A)

Low Q, LC resonant circuit

B)

High Q, LC resonant circuit

C)

Low Q, RLC resonant circuit

D)

High Q, RLC resonant circuit

Correct Answer : High Q, LC resonant circuit

Explanation : High Q LC resonant circuit provides high selectivity.

124 .

A 1000 kHz carrier is simultaneously modulated with 300 Hz, 800 Hz and 2 kHz audio sine waves. Which of the following frequency is least likely to be present in the output?

A)

998.0 kHz

B)

999.2 kHz

C)

1000 kHz

D)

1002 kHz

Correct Answer : 1000 kHz

Explanation :

Frequency present in the sidebands is equal to = f_c ± f_m, f_c ± 2f_m, f_c ± 3f_m .

125 .

If the average power of radar transmitters is 2 kW and the peak power of the transmitter is 1000 kW, what will be the duty cycle?

A)

0.002

B)

0.02

C)

0.001

D)

0.01

Correct Answer : 0.002

Explanation : Duty Cycle = 2k/1000k = 0.002

126 .

The HV supply to a TV receiver is 25 kV and the total beam current for the three electron guns is 2000 Î¼A. The power handled by IHVT is

A)

0.5 W

B)

5W

C)

50 W

D)

500 W

Correct Answer : 50 W

Explanation :

25 x 10³ x 2000 x 10^-6 = 50 W.

127 .

Some advantages of optical fibre cables are

1. small diameter
2. Immunity to cross talk and EM interference
3. Laser and LED modulation methods lend themselves ideally to digital operation

Which of the above are correct?

A)

1 only

B)

1 and 2

C)

2 and 3

D)

1, 2, 3

Correct Answer : 1, 2, 3

Explaination : Fibre optic cables have all these advantages.

128 .

The contrast control in colour TV receiver is done by

A)

SAW filter

B)

video detector

C)

chroma amplifier

D)

luminance amplifier

Correct Answer : luminance amplifier

Explanation : Luminance amplifier changes the luminance levels and provides contrast control.

129 .

The received signal frequency at any time of a super-heterodyne receiver having IF = 456 kHz is 1 MHz. The corresponding image signal is

A)

outside the medium band

B)

within the medium band

C)

depend upon modulation index

D)

depends on Modulating frequency

Correct Answer : within the medium band

Explanation : Image signal frequency = Received signal frequency - 2 x Intermediate frequency.

= 1 MHz - 2 x 456kHz

=> 1 MHz - 912 kHz => 88 kHz

which lies in medium bond.

130 .

The requirements of carrier frequency are

A)

precise frequency value

B)

low frequency drift

C)

Both (A) and (B)

D)

Neither (A) nor (B)

Correct Answer : Both (A) and (B)

131 .

The number of spectral component when two cosine waves are multiplied of different frequency

A)

2

B)

4

C)

8

D)

16

Correct Answer : 4

132 .

Radiation resistance of an antenna is a

A)

dc resistance

B)

ac resistance

C)

Either (A) or (B)

D)

None of the above

Correct Answer : ac resistance

133 .

A 1 MHz sinusoidal carrier is amplitude modulated by a symmetrical square wave of period 100 Î¼ sec. Which of the following frequencies will not be in the modulated signal?

A)

990 kHz

B)

1010 kHz

C)

1020 kHz

D)

1030 kHz

Correct Answer : 1020 kHz

134 .

The input to a coherent detector is DSB - SC signal plus noise. The noise at the detector output is

A)

in phase component

B)

the envelope

C)

quadrature component

D)

None of the above

Correct Answer : in phase component

135 .

All of the output pulses are at full transmitter power for a strong signal in all of the following except

A)

PCM

B)

PFM

C)

PWM

D)

PAM

Correct Answer : PAM

136 .

The spectrum of the white noise and an impulse function is similar in following aspects

A)

similar phase spectrum

B)

both have similar magnitude spectrum

C)

no relation

D)

both have similar magnitude and Phase spectrum

Correct Answer : both have similar magnitude spectrum

137 .

In a telephone system, the grade of service means

A)

the type of wires cables used for the system

B)

the quality of sound reception at the receiver telephone

C)

the probability that a called for connection is established

D)

None of the above

Correct Answer : the probability that a called for connection is established

138 .

AGC voltage is applied to the stages which are

A)

before the detector stage

B)

after the detector stage

C)

either before or after the detector stage

D)

None of the above

Correct Answer : before the detector stage

139 .

A longwave AM broadcast transmitter needs

A)

small carrier power

B)

very small carrier power

C)

large carrier power

D)

very large carrier power

Correct Answer : very large carrier power

140 .

LCD uses________

A)

twisted nematic crystal

B)

nematic crystals

C)

sematic crystals

D)

cholesteric crystals

Correct Answer : twisted nematic crystal

141 .

In FM, as the modulating frequency decreases and the modulating voltage amplitude

A)

decrease, the modulation index increases

B)

remains constant, the modulation index increases

C)

increases, the modulation index increases

D)

remains constant, the modulation index decreases

Correct Answer : remains constant, the modulation index increases

142 .

The function of duplexer in a RADAR is

A)

to amplify the received signal

B)

to provide gain to the transmitted power

C)

to permit the use of same antenna for transmission and reception

D)

Both (A) and (B)

Correct Answer : to permit the use of same antenna for transmission and reception

143 .

An audio frequency of 5 kHz is translated to a radio frequency carrier of frequency 1 MHz and transmitted it to space through an antenna. The required height of antenna is

A)

75 m

B)

150 m

C)

300 m

D)

600 m

Correct Answer : 150 m

144 .

Pre-emphasis circuit is used

A)

after detection

B)

after modulation

C)

before detection

D)

before modulation

Correct Answer : before modulation

145 .

In commercial FM Broadcasting, A radio station transmitting the signal at 98.3 MHz, it is

A)

carrier frequency

B)

message frequency

C)

channel frequency

D)

modulation frequency

Correct Answer : carrier frequency

146 .

In which frequency range is the noise figure in a transistor minimum

A)

low frequencies

B)

high frequencies

C)

very high frequencies

D)

intermediate frequencies

Correct Answer : intermediate frequencies

147 .

The message carrying efficiency is best in

A)

AM

B)

FM

C)

AM-SC

D)

Phase modulation

Correct Answer : AM-SC

148 .

An SSB-AM signal cannot be demodulated by

A)

Product detector

B)

Balanced modulator

C)

Diode balanced modulator

D)

Complete phase shift generator

Correct Answer : Balanced modulator

149 .

The modulation index of wideband FM signal is

A)

unity

B)

nearly 0.67

C)

less than unity

D)

greater than unity

Correct Answer : greater than unity

150 .

The pre-emphasis circuit is used

A)

prior to modulation

B)

after demodulation

C)

for low frequency components of the signal

D)

None of the above

Correct Answer : prior to modulation

151 .

MTI stands for

A)

Multiplexed Telemetry Index

B)

Moving Target Indicator

C)

Maximum Transmission Index

D)

Microprocessor Tracking Index

Correct Answer : Moving Target Indicator

152 .

Which of the following is an oscillator with best frequency stability?

A)

Crystal oscillator

B)

Multivibrator

C)

Clapp oscillator

D)

Phase shift circuit

Correct Answer : Crystal oscillator

153 .

The IF frequencies in a TV receiver

A)

38.9 MHz for both video and audio

B)

33.4 MHz for both video and audio

C)

38.9 MHz for video and 33.4 MHz for audio

D)

33.4 MHz for video and 38.9 MHz for audio

Correct Answer : 38.9 MHz for video and 33.4 MHz for audio

154 .

The most noise resistant modulation system is

A)

FM

B)

PCM

C)

SSB suppressed carrier

D)

pulse position modulation

Correct Answer : PCM

155 .

Which of the following is the digital system?

A)

PAM

B)

PPM

C)

PCM

D)

PWM

Correct Answer : PCM

156 .

Which of the following types of noise assumes greater importance at high frequencies?

A)

Shot noise

B)

Impulse noise

C)

Random noise

D)

Transit time noise

Correct Answer : Transit time noise

Explanation : At high frequencies time period of wave and transit time become comparable.

157 .

In transistor radio receivers the number of IF amplifier stages are

A)

1

B)

2

C)

4

D)

6

Correct Answer : 2

Explanation : Two IF amplifier stages are very commonly used.

158 .

To relay outdoor remotely located live programs, TV transmitter use

A)

microwave links

B)

open wire link

C)

coaxial cable link

D)

Either (A) or (B)

Correct Answer : microwave links

159 .

It is found that in a telephone system 60 subscribers initiate calls during a 30 minute interval and the total duration of all the calls is 100 minutes. The load is

A)

2

B)

3 erlang

C)

3.333 erlang

D)

0.333 erlang

Correct Answer : 3.333 erlang

Explanation :

160 .

Directivity means

A)

zero directive gain

B)

minimum directive gain

C)

Both (A) and (B)

D)

maximum directive gain

Correct Answer : maximum directive gain

Explanation : Directivity means maximum directive gain.

161 .

The power to the portable unit of a cordless telephone is provided by

A)

dry cells

B)

AC mains

C)

pencil cells

D)

rechargeable cells

Correct Answer : rechargeable cells

162 .

In a AM wave the carrier and one of the side bands is suppressed. If m = 0.5, the percentage saving in power is

A)

100%

B)

94.4%

C)

83.3%

D)

50%

Correct Answer : 94.4%

163 .

Computer communication networks have

A)

tree configuration

B)

star configuration

C)

loop/mesh configuration

D)

All of the above

Correct Answer : All of the above

164 .

Which of the following is present in both TRF receiver and superheterodyne receiver?

A)

Mixer

B)

IF amplifier

C)

Detector

D)

Local oscillator

Correct Answer : Detector

Explanation : Detection (also called demodulation) is an essential function.

165 .

In a CD the sampling frequency is nearly

A)

double the highest frequency in audio signal

B)

half the highest frequency in audio signal

C)

equal to highest frequency in audio signal

D)

four times the highest frequency in audio signal

Correct Answer : double the highest frequency in audio signal

Explanation : For proper sampling and faithful reproduction sampling frequency must be at least twice the highest frequency in the signal.

166 .

One of the advantages of base modulation over collector modulation of a transistor class C amplifier is

A)

Better linearity

B)

Improved efficiency

C)

High power output per transistor

D)

The lower modulating power requirement

Correct Answer : The lower modulating power requirement

167 .

Leak type bias is used in plate modulated class C amplifier to

A)

Increase the bandwidth

B)

Prevent excessive grid current

C)

Prevent over modulation

D)

Prevent tuned circuit damping

Correct Answer : Prevent excessive grid current

168 .

FM transmitting and receiving equipment as compared to AM equipment is

A)

Costly

B)

Cheaper

C)

Almost equally costly

D)

None of the above

Correct Answer : Costly

169 .

For AM receivers the standard IF frequency is

A)

1.07 MHz

B)

10.7 MHz

C)

106 kHz

D)

455 kHz

Correct Answer : 455 kHz

170 .

In Pulse Code Modulation system

A)

Large bandwidth is required

B)

Quantising noise can be overcome by companding

C)

Suffers from the disadvantage of its incompatibly with TDM

D)

Quantising noise can be reduced by decreasing the number of standard levels

Correct Answer : Large bandwidth is required

171 .

An audio signal (say from 50 Hz to 10000 Hz) is frequency translated by a carrier having a frequency of 106 Hz. The values of initial (without frequency translation) and final (after frequency translation) fractional change in frequency from one band edge to the other are

A)

200 and 200

B)

200 and 100.1

C)

200 and 1.01

D)

200 and 10.01

Correct Answer : 200 and 1.01

172 .

DVD uses_____

A)

Video head for recording and laser beam for playback

B)

Laser beam for recording and video head for playback

C)

Laser beam for both recording and playback

D)

None of the above

Correct Answer : Laser beam for both recording and playback

173 .

As per Shannon-Hartley theorem, a noise less Gaussian channel has

A)

Zero capacity

B)

Infinite capacity

C)

Small capacity

D)

None of the above

Correct Answer : Infinite capacity

174 .

In a TV receiver antenna the length of reflector rod

A)

Is less than that of dipole

B)

Is more than that of dipole

C)

Is the same as that of dipole

D)

May be equal, more or less than that of dipole

Correct Answer : Is more than that of dipole

175 .

To eliminate ghosts in the picture

A)

Connect a booster

B)

Twist the transmission line

C)

Use a longer transmission line

D)

Change the antenna orientation of location

Correct Answer : Change the antenna orientation of location

176 .

Circular polarization__________

A)

Is useful in reducing depolarization effect on received wave

B)

Is useful in discrimination between reception of adjacent beams

C)

Involves critical alignment of transmitting and receiving antenna

D)

None of the above

Correct Answer : Is useful in reducing depolarization effect on received wave

177 .

As the frequency increases, the absorption of ground wave by earth's surface

A)

increases

B)

decreases

C)

remains the same

D)

Either (A) or (B)

Correct Answer : increases

Explanation : Because of this reason ground waves can be used for frequencies upto about 1600 kHz only.

178 .

The velocity of sound waves in air

A)

varies directly as temperature

B)

is constant at all temperatures

C)

varies inversely as absolute temperature

D)

varies directly as square root of absolute temperature

Correct Answer : varies directly as square root of absolute temperature

179 .

The range of a cordless telephone is about

A)

10 m

B)

100 m

C)

500 m

D)

1000 m

Correct Answer : 100 m

Explanation : The range depends on quality of instrument and is about 100 m.

180 .

Degaussing in a picture tube means

A)

Adding magnetism in mask and mounting frame

B)

Increasing resistance of coils to decrease time constant

C)

Removing residual magnetism in mask, shield etc...

D)

Decreasing resistance of coils to increase time constant.

Correct Answer : Removing residual magnetism in mask, shield etc...

Explanation : Since gauss is a unit of magnetic flux, degaussing means removal of magnetism.

181 .

The rate at which information can be carried through a communication channel depends on

A)

bandwidth

B)

carrier frequency

C)

transmission loss

D)

transmitted power

Correct Answer : bandwidth

Explanation : Rate of information depends on bandwidth.

182 .

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)

0.5

C)

0.7

D)

0.9

Correct Answer : 0.5

Explanation :

183 .

Some types of traps used in video IF amplifier of colour TV are

A)

series traps

B)

shunt traps

C)

absorption traps

D)

All of the above

Correct Answer : All of the above

184 .

In standing wave pattern on a transmission line

A)

voltage and current nodes coincide

B)

voltage and current antinodes coincide

C)

voltage nodes and current antinodes as well as current nodes and voltage antinodes coincide

D)

Both (A) and (B)

Correct Answer : voltage nodes and current antinodes as well as current nodes and voltage antinodes coincide

Explanation : When standing wave is set up voltage maxima and current minima and voltage minima and current maxima coincide.

185 .

Frequency shift keying is used mostly in

A)

telegraphy

B)

telephony

C)

radio transmission

D)

satellite communication

Correct Answer : telegraphy

Explanation : Frequency shift keying (FSK) is a system of frequency modulation used in telegraphy.

186 .

The time required for horizontal blanking is 16% of that for each horizontal line. If horizontal time is 63.5 Î¼s, the horizontal blanking time for each line is about

A)

1 Î¼s

B)

10 Î¼s

C)

100 Î¼s

D)

1000 Î¼s

Correct Answer : 10 Î¼s

187 .

In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves by the factor.

A)

8

B)

12

C)

16

D)

8/6

Correct Answer : 16

Explanation :

Given n₁ = 6, n₂ = 8,

then (SNR)_Q = 22^{(n₂ - n₁)} =>16.

188 .

For 10 bit PCM system, the signal to quantization noise ratio is 62 dB. If the number of bits is increased by 2, then the signal to quantization noise ratio will

A)

increased by 6 dB

B)

increased by 12 dB

C)

decreased by 6 dB

D)

decreased by 12 dB

Correct Answer : increased by 12 dB

189 .

The video heads, in VCR, feed the other circuit

A)

directly windings

B)

through a transformer having two rotating windings

C)

through a transformer having two stationary windings

D)

through a transformer having one stationary and one rotatory winding

Correct Answer : through a transformer having one stationary and one rotatory winding

Explanation : Rotatory transformer, in VCR, has one stationary and one rotating winding.

190 .

When the carrier is unmodulated, a certain transmitter radiates 9 kW when the carrier is sinusoidally modulated the transmitter radiates 10.125 kW. The modulation index will be

A)

0.5

B)

0.4

C)

0.1

D)

0.01

Correct Answer : 0.5

191 .

In a TV, the output from RF tuner is about

A)

0.5 Î¼V

B)

1 Î¼V

C)

100 Î¼V

D)

1000 Î¼V

Correct Answer : 1000 Î¼V

Explanation : It is about 1 mV.

192 .

24 telephone channels, each band limited to 3.4 kHz, are to be time division multiplexed by using PCM, calculate the bandwidth of PCM system for 128 quantization levels and an 8 KHz sampling frequency

A)

1.299 MHz

B)

1.54 MHz

C)

2 MHz

D)

192 kHz

Correct Answer : 1.54 MHz

Explanation :

Given, n = 24, f_m = 3.4 kHz

M = 128,

2^N = 128 => n = 7

But f_s = 2f_m, here we will consider f_s (sampling) frequency

instead at 2f_m => 2 x 3.4 kHz => 6.8 KHz.

B.W. = [24(7 + 1)] 8 kHz = 1.54 MHz.

193 .

Generally a VCR has_______

A)

two stationary video heads

B)

four stationary video heads

C)

two rotating video heads

D)

four rotating video heads

Correct Answer : two rotating video heads

Explanation : VCR has two rotating leads about 180° apart.

194 .

A remote control of TV uses a 10 bit word. The maximum number of total commands it can transmit is

A)

64

B)

256

C)

512

D)

1024

Correct Answer : 1024

Explanation : 2¹⁰ = 1024.

195 .

Kell factor is about

A)

0.7

B)

3

C)

5

D)

7

Correct Answer : 0.7

Explanation : Kell factor indicates reduction in vertical resolution and varies from 0.65 to 0.85.

196 .

TV signal strength when expressed in dB m has the reference of

A)

1 Î¼V/m

B)

2 Î¼V/m

C)

5 Î¼V/m

D)

10 Î¼V/m

Correct Answer : 1 Î¼V/m

197 .

A sinusoidal voltage amplitude modulates a carrier of peak value 5 kV. Each side band has an amplitude of 500 V. The modulation index is

A)

0.1

B)

0.2

C)

0.4

D)

0.7

Correct Answer : 0.2

Explanation :

198 .

It is required to increase the maximum range of a radar by a factor of two. The peak power transmitted in the radar system has to be increased by a factor of

A)

2

B)

4

C)

6

D)

8

Correct Answer : 2

Explanation :

Range μ (Power)^0.25

199 .

The filter circuit for feeding tweeter has

A)

a capacitance in series and a resistance in parallel

B)

a resistance in series and a capacitance in parallel

C)

a capacitance in series and an inductance in parallel

D)

an inductance in series and a capacitance in parallel

Correct Answer : a capacitance in series and an inductance in parallel

Explanation : Series capacitance and shunt inductance is high pass circuit.

200 .

A source generates three symbols with probabilities 0.25, 0.25, 0.50 at a rate of 3000 symbols per second. Assuming independent generation of symbols, the most efficient source encoder would have average bit rate is as

A)

1500 bits/sec

B)

3000 bits/sec

C)

4500 bits/sec

D)

6000 bits/sec

Correct Answer : 4500 bits/sec

Explaination :

201 .

Video signals are transmitted through

A)

frequency modulation

B)

amplitude modulation

C)

either amplitude or frequency modulation

D)

neither amplitude nor frequency modulation

Correct Answer : amplitude modulation

202 .

A TV receiver has 20 kV EHT supply and total beam current (for 3 electron guns) of 1500 Î¼A. The power handled by IHVT is

A)

3 W

B)

30 W

C)

300 W

D)

500 W

Correct Answer : 30 W

Explanation :

P = 20 x 10³ x 1500 x 10^-6 = 30 W.

203 .

Beam width of an antenna is expressed in

A)

degrees

B)

metres

C)

ratio of two angles

D)

ratio of two powers

Correct Answer : degrees

Explanation : Beam width is the angular separation between the two half power points on the power density radiation pattern. It is expressed in degrees.

204 .

If frames are repeated at 60 Hz and each frame has 525 lines, the time for scanning one horizontal line (for progressive scanning and no interlacing) is about

A)

0.32 Î¼s

B)

3.2 Î¼s

C)

32 Î¼s

D)

320 Î¼s

Correct Answer : 32 Î¼s

205 .

In a picture tube, the video signal is applied to

A)

grid

B)

any anode

C)

Both (A) and (B)

D)

cathode

Correct Answer : cathode

Explanation : Video signal is applied to cathode.

206 .

Compact discs use_____

A)

magnetic recording and retrieval

B)

optical recording and retrieval

C)

optical recording but magnetic retrieval

D)

magnetic recording but optical retrieval

Correct Answer : optical recording and retrieval

Explanation : CD uses optical recording and retrieval.

207 .

A carrier is phase modulated (PM) with frequency deviation of 10 kHz by a single tone frequency of 1 kHz. If the single tone frequency is increased to 2 kHz, assuming that phase deviation remains unchanged, the bandwidth of the PM signal is

A)

21 kHz

B)

22 kHz

C)

42 kHz

D)

44 kHz

Correct Answer : 44 kHz

Explaination :

208 .

In a communication receiver, a squelch circuit is normally inserted

A)

after detector

B)

before mixer

C)

before detector

D)

after power amplifier

Correct Answer : after detector

Explanation : Squelch, i.e., muting is added after detector to suppress noise when no carrier is present at input.

209 .

A 1000 kHz carrier is simultaneously modulated by 300 Hz and 2 kHz audio sine wave. Which of the following frequencies will not be present in the output?

A)

1000.3 kHz

B)

999.7 kHz

C)

998 kHz

D)

700 kHz

Correct Answer : 700 kHz

Explanation : 1000 ± 0.3 and 1000 ± 2 kHz will be present.

210 .

The direction of pick up in a CD is

A)

linear from edge to centre

B)

nonlinear from centre to edge

C)

linear from centre towards edge

D)

nonlinear from edge to center

Correct Answer : linear from centre towards edge

Explanation : It is linear from centre to edge.

211 .

The discone antenna is

A)

used in UHF range

B)

used in radar

C)

circularly polarized

D)

used as a direction finding antenna

Correct Answer : used in UHF range

Explanation : Discone antenna is a combination of disc and cone. It is omnidirectional and is used in VHF and UHF range especially at airports.

212 .

In PCM the amplitude levels are transmitted in a 7 unit code. Sampling frequency is 10 kHz. The bandwidth should be

A)

5 kHz

B)

35 kHz

C)

70 kHz

D)

5 MHz

Correct Answer : 35 kHz

213 .

A TV receiver is 40 cm wide and 30 cm high. The EHT supply required is about

A)

53 kV

B)

40 kV

C)

20 kV

D)

10 W

Correct Answer : 20 kV

Explanation :

214 .

A 1000 kHz carrier wave modulated 40% at 40000 Hz is applied to a resonant circuit tuned to a carrier frequency and having Q = 140. What is the degree of modulator after transmission through the circuit?

A)

40%

B)

20%

C)

0.54

D)

0.27

Correct Answer : 0.27

Explaination :

215 .

The EHT voltage in a picture tube of TV is

A)

about 1 kV

B)

about 15 kV

C)

about 100 kV

D)

about 1000 kV

Correct Answer : about 15 kV

Explanation : EHT voltage is 1 kV for each diagonal inch of CRT screen.

216 .

In cellular telephone each cell is designed to handle

A)

45 two way communications

B)

45 one way communications

C)

90 two way communications

D)

180 two way communications

Correct Answer : 45 two way communications

Explanation : Each cell is designed for 45 two way conversations.

217 .

24 telephone channels are frequency division multiplexed using an SSB modulation. Assuming 3 kHz per channel, the required band width is

A)

8 kHz

B)

21 kHz

C)

27 kHz

D)

72 kHz

Correct Answer : 72 kHz

Explanation : Since SSB modulation is used, bandwidth = 24 x 3 = 72 kHz.

218 .

A transmitter power of 10 W is increased by 30 dB. The effective radiated power is

A)

100 W

B)

1000 W

C)

10000 W

D)

100000 W

Correct Answer : 10000 W

Explanation :

219 .

It is desired to couple a coaxial line to a two parallel wire line. It is best to use

A)

balun

B)

slotted line

C)

directional coupler

D)

quarter wave transformer

Correct Answer : balun

Explanation : Balun gives 4 : 1 impedance transformation and is suited for coupling a coaxial line to two wire line.

220 .

For an ideal 3000 Hz channel, Nyquist rate is

A)

3000 bps

B)

6000 bps

C)

9000 bps

D)

12000 bps

Correct Answer : 6000 bps

Explanation : For 3000 Hz.

Nyquist rate is twice, i.e., 6000 bps.

221 .

In a high speed modem the data rate handled is about

A)

1000 bps

B)

5000 bps

C)

20000 bps

D)

50000 bps

Correct Answer : 5000 bps

Explanation : When data rate is in the range of 2400 to about 10800 bits per second, modem is designated as high speed.

222 .

The first pulse in a TV remote control is

A)

preliminary pulse

B)

start pulse

C)

erase pulse

D)

either start pulse or preliminary pulse

Correct Answer : preliminary pulse

Explanation : The first pulse is preliminary pulse followed by start pulse.

223 .

If the ratio of ac to dc load impedance of a diode detector is low, the result will be

A)

poor AF response

B)

diagonal clipping

C)

poor AGC operation

D)

negative peak clipping

Correct Answer : negative peak clipping

224 .

A tweeter should be fed from the input through a

A)

low pass filter

B)

high pass filter

C)

band pass filter

D)

band stop filter

Correct Answer : high pass filter

Explanation : Tweeter is high frequency loudspeaker covering the range above 5000 Hz.

225 .

A noiseless 3 kHz channel can't transmit binary bit at the rate

A)

3000 bps

B)

6000 bps

C)

12000 bps

D)

None of the above

Correct Answer : 12000 bps

Explanation :

Noiseless channel: Nyquist's Theorem - If the signal has V discrete levels over a transmission medium of bandwidth H, the maximum data rate = 2H log₂ V bits/sec.

A noiseless 3-kHz channel cannot transmit binary signals at a rate exceeding 6000 bps (= 2 x 3000 log₂ 2).

226 .

In an AM wave the carrier and one of the side bands is suppressed. If m = 1, the percentage saving in power is

A)

25%

B)

50%

C)

66.6%

D)

83.3%

Correct Answer : 83.3%

227 .

In a tape recorder the output from RF oscillator is given to

A)

only erase head coil

B)

only record head coil

C)

coils of both erase head and record head

D)

None of the above

Correct Answer : only erase head coil

228 .

A + 1.9 lens has a focal length of 25 mm. The diameter of lens is about

A)

1.3 mm

B)

130 mm

C)

13 mm

D)

None of the above

Correct Answer : 13 mm

229 .

Which of the following terms are applicable to troposcatter propagation?

A)

SIOs

B)

Fading

C)

Faradays rotation

D)

Atmospheric storms

Correct Answer : Fading

Explanation : Tropospheric scatter propagation is subject to two types of fading called Rayleigh fading (due to multipath propagation) and fading due to variations in atmospheric conditions along the propagation path.

230 .

In TV scanning sequence of lines is

A)

right to left

B)

left to right

C)

left to right for odd fields and right to left for even field

D)

left to right for even fields and right to left for odd field

Correct Answer : left to right