Assertion (A): The unit of telephone traffic measurement is erlang.Reason (R): International circuits for communication are fitted with echo suppressors.

Both A and R are correct and R is correct explanation of A

Both A and R are correct but R is not correct explanation of A

Which of the following is a disadvantage of Vestigial Sideband (VSB) system?

It possess the advantages of both DSB and SSB system

Low video frequencies are attenuated

Bandwidth is conserved resulting in a saving of 2 MHz per channel over DSB system

It results in a power boost of two video frequencies

It possess the advantages of both DSB and SSB system

Square law modulators utilise

non-linear region of V-I dynamic characteristics of a triode

linear range of V-I characteristics of a diode

linear range of V-I characteristics of a triode

non-linear region of V-I dynamic characteristics of a diode

non-linear region of V-I dynamic characteristics of a triode

A pre-emphasis circuit provides extra noise immunity by

converting the phase modulation of FM

preamplifying the whole audio band

amplifying the higher audio frequencies

A narrow band FM does not have the following feature

it does not show Amplitude variation

both sideband equal in magnitude

both sideband have same Phase Difference

it does not show Amplitude variation

In amplitude modulation

the amplitude of the carrier remains constant

the amplitude of carrier varies in accordance with the amplitude of the modulating signal.

the modulating frequency lies in the audio range

the amplitude of the carrier remains constant

the amplitude of the carrier varies in accordance with the frequency of the modulating signal.

In AM receiver the oscillator frequency is

always lower than signal frequency

always equal to signal frequency

always higher than signal frequency

always lower than signal frequency

video and audio signals are frequency modulated

video signals are frequency modulated but audio signals are amplitude modulated

both audio and video signals are amplitude modulated

video signals are amplitude modulated and audio signals are frequency modulated

The function of a modulator is to

extract information from the carrier

amplify the audio frequency signal

impress the information on to a RF carrier

In the stabilized reactance modulator AFC system

the discriminator must have a fast time constant to prevent demodulation

phase modulation is converted into amplitude modulation by the equalizer circuit

the discriminator frequency must not be too low or the system will fail

the discriminator must have a fast time constant to prevent demodulation

the higher discriminator frequency, better the oscillator frequency stability

Impedance inversion may be obtained with

complex impedance Z connected in series with line

Armoured submarine cable is used

to prevent insulation breakdown due to high voltage

to protect cable at great depths.

to prevent inadverent damage due to ploughing in

for the shallow shore ends of cable.

9294 + Mcqs in Electronics and Communication Engineering in Engineering Page 181 McqOptions

9001.	Assertion (A): The unit of telephone traffic measurement is erlang. Reason (R): International circuits for communication are fitted with echo suppressors.
A.	Both A and R are correct and R is correct explanation of A
B.	Both A and R are correct but R is not correct explanation of A
C.	A is correct but R is wrong
D.	A is wrong but R is correct
Answer» C. A is correct but R is wrong

Discussion

9002.	In a single sideband suppressed carrier AM system, the modulation index is changed from 0 to 1, the power content of the signal
A.	will be quarter
B.	will be doubled
C.	will increase by 50 percent
D.	will increase by 25 percent
Answer» D. will increase by 25 percent

Discussion

9003.	In TV system in India IF video and IF audio frequencies are
A.	33.4 and 28.4 MHz respectively
B.	38.9 and 33.4 MHz respectively
C.	43.8 and 38.9 MHz respectively
D.	33.4 and 38.9 MHz respectively
Answer» C. 43.8 and 38.9 MHz respectively

Discussion

9004.	The most commonly used system of modulating for telegraphy is
A.	single tone modulation
B.	on-off keying
C.	frequency shift keying
D.	pulse code modulation
Answer» D. pulse code modulation

Discussion

9005.	Which of the following antennas is not wide band?
A.	Marconi
B.	Helical
C.	Folded dipole
D.	Discone
Answer» B. Helical

Discussion

9006.	In figure the output v(t) is
A.	an amplitude modulated signal
B.	a frequency modulated signal
C.	a phase modulated signal
D.	none of the above
Answer» C. a phase modulated signal

Discussion

9007.	A circuit which cannot demodulate SSB is
A.	balanced modulator
B.	product detector
C.	BFO
D.	phase discriminator
Answer» E.

Discussion

9008.	Which of the following is a disadvantage of Vestigial Sideband (VSB) system?
A.	Low video frequencies are attenuated
B.	Bandwidth is conserved resulting in a saving of 2 MHz per channel over DSB system
C.	It results in a power boost of two video frequencies
D.	It possess the advantages of both DSB and SSB system
Answer» D. It possess the advantages of both DSB and SSB system

Discussion

9009.	Square law modulators utilise
A.	linear range of V-I characteristics of a diode
B.	linear range of V-I characteristics of a triode
C.	non-linear region of V-I dynamic characteristics of a diode
D.	non-linear region of V-I dynamic characteristics of a triode
Answer» D. non-linear region of V-I dynamic characteristics of a triode

Discussion

9010.	A pre-emphasis circuit provides extra noise immunity by
A.	converting the phase modulation of FM
B.	preamplifying the whole audio band
C.	amplifying the higher audio frequencies
D.	boosting the pass frequencies
Answer» D. boosting the pass frequencies

Discussion

9011.	The maximum permissible distance between two samples of a 2 kHz signal is
A.	1000 sec
B.	500 sec
C.	250 sec
D.	2000 sec
Answer» D. 2000 sec

Discussion

9012.	When the video signal is applied to the picture tube in a TV receiver, the strength of video signal is about
A.	1000 V
B.	200 V
C.	50 V
D.	1 V
Answer» D. 1 V

Discussion

9013.	In the above case if the modulating frequency is increased to 20 kHz the bandwidth will be
A.	0.05 MHz
B.	1 MHz
C.	2 MHz
D.	4 MHz
Answer» D. 4 MHz

Discussion

9014.	A narrow band FM does not have the following feature
A.	it has two sidebands
B.	both sideband equal in magnitude
C.	both sideband have same Phase Difference
D.	it does not show Amplitude variation
Answer» D. it does not show Amplitude variation

Discussion

9015.	Which SNR denotes excellent picture quality in TV?
A.	50 dB
B.	30 dB
C.	15 dB
D.	5 dB
Answer» B. 30 dB

Discussion

9016.	In amplitude modulation
A.	the amplitude of carrier varies in accordance with the amplitude of the modulating signal.
B.	the modulating frequency lies in the audio range
C.	the amplitude of the carrier remains constant
D.	the amplitude of the carrier varies in accordance with the frequency of the modulating signal.
Answer» C. the amplitude of the carrier remains constant

Discussion

9017.	At f = 7 GHz, a 120 cm dish antenna gives a gain of about
A.	50
B.	500
C.	5000
D.	50000
Answer» E.

Discussion

9018.	PIL colour picture tube has the main advantage that
A.	it is cheap
B.	it ensures purity in colour
C.	it is self convergent
D.	both (a) and (b)
Answer» D. both (a) and (b)

Discussion

9019.	What is the frequency of the modulated carrier wave?
A.	1000 Hz
B.	2000 Hz
C.	1000 kHz
D.	2000 kHz
Answer» E.

Discussion

9020.	A sinusoidal carrier voltage, having frequency 1000 Hz is amplitude modulated by a sinusoidal voltage of frequency 15 kHz. The frequency of upper and lower sidebands will be
A.	1015 kHz and 985 kHz
B.	1030 kHz and 970 kHz
C.	13 kHz and 17 kHz
D.	14 kHz and 16 kHz
Answer» E.

Discussion

9021.	In MTI radar, clutter means
A.	echos from moving targets
B.	echos from stationary targets
C.	atmospheric noise
D.	thermal noise
Answer» C. atmospheric noise

Discussion

9022.	Consider the following statements as regards pulse repetition frequency Pulse interval should be as large as possible so that a pulse returns before next pulse is transmitted Greater the number of pulses reflected from a target, greater is the probability of distinguishing it from the noise Which of the above are correct?
A.	1 only
B.	2 only
C.	both 1 and 2
D.	neither 1 nor 2
Answer» D. neither 1 nor 2

Discussion

9023.	Which gives minimum probability of error?
A.	ASK
B.	FSK
C.	PSK
D.	DPSK
Answer» D. DPSK

Discussion

9024.	Household taperecorders generally use
A.	crystal microphone
B.	moving coil microphone
C.	condenser microphone
D.	cardioid microphone
Answer» B. moving coil microphone

Discussion

9025.	In AM receiver the oscillator frequency is
A.	always equal to signal frequency
B.	always equal to 455 kHz
C.	always higher than signal frequency
D.	always lower than signal frequency
Answer» D. always lower than signal frequency

Discussion

9026.	Identical telephone numbers in different parts of a country are distinguished by their
A.	area codes
B.	office codes
C.	access digits
D.	language codes
Answer» B. office codes

Discussion

9027.	The modulation index of an AM wave is measured using a CRO. The waveform is as shown in figure, the modulation index is nearly
A.	43%
B.	30%
C.	23%
D.	17%
Answer» B. 30%

Discussion

9028.	A three stage telephone switching structure is to have 128 input and 128 output terminals. It has been found that at peak time the utilization probability is 0.1. The number of intermediate links required for non-blocking configuration is 15. If the actual number of intermediate links is 5, the probability of blocking of call is
A.	1%
B.	0.5%
C.	0.2%
D.	0.1%
Answer» D. 0.1%

Discussion

9029.	A photo diode converts light signals to binary.
A.	True
B.	False
Answer» B. False

Discussion

9030.	A pulse width signal can be governed by
A.	free running multi-vibrator
B.	monostable multi-vibrator
C.	Schmitt trigger
D.	JK flip-flop
Answer» C. Schmitt trigger

Discussion

9031.	A CW transmitter radiates
A.	modulated RF carrier
B.	unmodulated RF carrier
C.	both (a) and (b)
D.	none of the above
Answer» B. unmodulated RF carrier

Discussion

9032.	The commonly employed filter in SSB generation is
A.	high pass filter
B.	RC filter
C.	LC filter
D.	mechanical filter
Answer» E.

Discussion

9033.	Which of the following pulse modulation is analog?
A.	PCM
B.	Differential PCM
C.	PWM
D.	Delta
Answer» D. Delta

Discussion

9034.	Pulse stuffing is used in
A.	synchronous TDM
B.	asynchronous TDM
C.	Any TDM
D.	All
Answer» C. Any TDM

Discussion

9035.	In telecast
A.	video and audio signals are frequency modulated
B.	video signals are frequency modulated but audio signals are amplitude modulated
C.	both audio and video signals are amplitude modulated
D.	video signals are amplitude modulated and audio signals are frequency modulated
Answer» E.

Discussion

9036.	The storage capacity of a CD is
A.	360 k bytes per side
B.	360 M bytes per side
C.	540 k bytes per side
D.	540 M bytes per side
Answer» E.

Discussion

9037.	When number of quantization levels are two, then the average transmission power in NRZ polar signalling is __________ that of NIRZ unipolar signalling.
A.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/56-3.94-2.png">
B.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/56-3.94-3.png">
C.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1024-1.png">
D.	None
Answer» D. None

Discussion

9038.	The function of a modulator is to
A.	separate two frequencies
B.	extract information from the carrier
C.	amplify the audio frequency signal
D.	impress the information on to a RF carrier
Answer» E.

Discussion

9039.	Which of the following radio waves are not reflected by ionosphere?
A.	Waves above 1 kHz
B.	Waves above 1 MHz
C.	Waves above 10 MHz
D.	Waves above 30 MHz
Answer» E.

Discussion

9040.	If the radiated power of AM transmitter is 10 kW, the power in the carrier for modulation index of 0.6 is nearly.
A.	8.24 kW
B.	8.47 kW
C.	9.26 kW
D.	9.6 kW
Answer» C. 9.26 kW

Discussion

9041.	Satellite communication uses frequencies in the range of
A.	3 to 6 GHz
B.	3-10 MHZ
C.	10-50 GHz
D.	100-200 GHz
Answer» B. 3-10 MHZ

Discussion

9042.	If in a radio receiver, RF signal has a frequency of 800 kHz and local oscillator that of 1000 kHz, then at the output of the mixer, the frequencies found would be __________ kHz.
A.	800 to 1000
B.	200, 800, 1000, 1800
C.	only 200
D.	only 1800
Answer» D. only 1800

Discussion

9043.	In the stabilized reactance modulator AFC system
A.	phase modulation is converted into amplitude modulation by the equalizer circuit
B.	the discriminator frequency must not be too low or the system will fail
C.	the discriminator must have a fast time constant to prevent demodulation
D.	the higher discriminator frequency, better the oscillator frequency stability
Answer» C. the discriminator must have a fast time constant to prevent demodulation

Discussion

9044.	In AM, the modulation envelope has a peak value double the unmodulated carrier level, when the modulation is
A.	25%
B.	33%
C.	50%
D.	100%
Answer» E.

Discussion

9045.	Super high frequency means more than 3000 MHz.
A.	True
B.	False
Answer» B. False

Discussion

9046.	Impedance inversion may be obtained with
A.	half wave line
B.	a short circuited stub
C.	complex impedance Z connected in series with line
D.	quarter wave line
Answer» E.

Discussion

9047.	The atmospheric absorption of radio waves depends on
A.	frequency of wave
B.	the distance from transmitter
C.	wave polarisation
D.	atmospheric polarisation
Answer» B. the distance from transmitter

Discussion

9048.	In a channel voice coder, the outputs of sixteen 20 Hz low pass filters are sampled, multiplexed and A/D converted. If sampling is at 40 samples/second and 3 bits/sample represents each voltage sample, the bit rate is about
A.	1.9 k bits/sec
B.	0.95 k bits/sec
C.	3.8 k bits/sec
D.	7.6 k bits/sec
Answer» B. 0.95 k bits/sec

Discussion

9049.	Efficiency of general AM signal with e_m = E₁ cos ₁t + E₂ cos ₂ t_j e_c = E_c cos _ct; E₁ cos ₁t with modulation index m₂ is __________ .
A.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1020-1.png">
B.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1020-2.png">
C.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1020-3.png">
D.	<img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1020-4.png">
Answer» B. <img src="/_files/images/electronics-and-communication-engineering/communication-systems/539-1020-2.png">

Discussion

9050.	Armoured submarine cable is used
A.	to prevent insulation breakdown due to high voltage
B.	to protect cable at great depths.
C.	to prevent inadverent damage due to ploughing in
D.	for the shallow shore ends of cable.
Answer» E.

Discussion

Explore topic-wise MCQs in Engineering.

Assertion (A): The unit of telephone traffic measurement is erlang.Reason (R): International circuits for communication are fitted with echo suppressors.

In a single sideband suppressed carrier AM system, the modulation index is changed from 0 to 1, the power content of the signal

In TV system in India IF video and IF audio frequencies are

The most commonly used system of modulating for telegraphy is

Which of the following antennas is not wide band?

In figure the output v(t) is

A circuit which cannot demodulate SSB is

Which of the following is a disadvantage of Vestigial Sideband (VSB) system?

Square law modulators utilise

A pre-emphasis circuit provides extra noise immunity by

The maximum permissible distance between two samples of a 2 kHz signal is

When the video signal is applied to the picture tube in a TV receiver, the strength of video signal is about

In the above case if the modulating frequency is increased to 20 kHz the bandwidth will be

A narrow band FM does not have the following feature

Which SNR denotes excellent picture quality in TV?

In amplitude modulation

At f = 7 GHz, a 120 cm dish antenna gives a gain of about

PIL colour picture tube has the main advantage that

What is the frequency of the modulated carrier wave?

A sinusoidal carrier voltage, having frequency 1000 Hz is amplitude modulated by a sinusoidal voltage of frequency 15 kHz. The frequency of upper and lower sidebands will be

In MTI radar, clutter means

Which gives minimum probability of error?

Household taperecorders generally use

In AM receiver the oscillator frequency is

Identical telephone numbers in different parts of a country are distinguished by their

The modulation index of an AM wave is measured using a CRO. The waveform is as shown in figure, the modulation index is nearly

A photo diode converts light signals to binary.

A pulse width signal can be governed by

A CW transmitter radiates

The commonly employed filter in SSB generation is

Which of the following pulse modulation is analog?

Pulse stuffing is used in

In telecast

The storage capacity of a CD is

When number of quantization levels are two, then the average transmission power in NRZ polar signalling is __________ that of NIRZ unipolar signalling.

The function of a modulator is to

Which of the following radio waves are not reflected by ionosphere?

If the radiated power of AM transmitter is 10 kW, the power in the carrier for modulation index of 0.6 is nearly.

Satellite communication uses frequencies in the range of

If in a radio receiver, RF signal has a frequency of 800 kHz and local oscillator that of 1000 kHz, then at the output of the mixer, the frequencies found would be __________ kHz.

In the stabilized reactance modulator AFC system

In AM, the modulation envelope has a peak value double the unmodulated carrier level, when the modulation is

Super high frequency means more than 3000 MHz.

Impedance inversion may be obtained with

The atmospheric absorption of radio waves depends on

In a channel voice coder, the outputs of sixteen 20 Hz low pass filters are sampled, multiplexed and A/D converted. If sampling is at 40 samples/second and 3 bits/sample represents each voltage sample, the bit rate is about

Efficiency of general AM signal with em = E1 cos 1t + E2 cos 2 tj ec = Ec cos ct; E1 cos 1t with modulation index m2 is __________ .

Armoured submarine cable is used

Assertion (A): The unit of telephone traffic measurement is erlang.
Reason (R): International circuits for communication are fitted with echo suppressors.

Efficiency of general AM signal with e_m = E₁ cos ₁t + E₂ cos ₂ t_j e_c = E_c cos _ct; E₁ cos ₁t with modulation index m₂ is __________ .