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COMMUNICATION ENGINEERING

Total questions: 66

Worksheet time: 33mins

Name
Class
Date
1.

The main purpose of a communication system is:

a)

Modulation

b)

To transfer information

c)

To generate carriers

d)

To detect noise

2.

The modulation index in AM is defined as:

a)

Ratio of carrier to message amplitude

b)

Ratio of message to carrier amplitude

c)

Product of carrier and message amplitudes

d)

Ratio of sideband power to carrier power

3.

Over-modulation in AM occurs when modulation index is:

a)

< 1

b)

= 1

c)

> 1

d)

= 0

4.

In AM, the total power is the sum of:

a)

Carrier power only

b)

Sideband power only

c)

Carrier power + Sideband power

d)

Message power only

5.

Bandwidth of AM wave is:

a)

fm

b)

2fm

c)

fc

d)

2fc

6.

FM differs from AM in that:

a)

Amplitude varies in FM

b)

Frequency varies in FM

c)

Phase varies in FM

7.

The modulation index in FM is:

a)

Δf / fm

b)

Δf × fm

c)

fc / Δf

d)

fc / fm

8.

In PM, the modulating signal affects:

a)

Frequency of carrier

b)

Amplitude of carrier

c)

Phase of carrier

d)

Bandwidth

9.

Carson’s rule is used to estimate:

a)

Noise power

b)

FM bandwidth

c)

Sampling rate

d)

Quantization error

10.

Which modulation has the highest noise immunity?

a)

AM

b)

FM

c)

DSB-SC

d)

PM

11.

Gaussian noise is also called:

a)

White noise

b)

Impulse noise

c)

Shot noise

d)

Thermal noise

12.

The power spectral density of white noise is:

a)

Constant

b)

Linear

c)

Parabolic

d)

Exponential

13.

Noise figure of an amplifier is always:

a)

< 1

b)

= 1

c)

> 1

d)

0

14.

Pre-emphasis is applied:

a)

At transmitter

b)

At receiver

c)

Both transmitter & receiver

d)

After demodulation

15.

Nyquist criterion states sampling frequency must be:

a)

fs < 2fm

b)

fs ≥ 2fm

c)

fs ≤ fm

d)

fs = fm

16.

Aliasing occurs when:

a)

fs < 2fm

b)

fs = 2fm

c)

fs > 2fm

d)

fs → ∞

17.

Quantization noise power is proportional to:

a)

Number of levels

b)

Step size squared

c)

1/Number of levels

d)

Carrier frequency

18.

18. PCM stands for:

a)

Phase Coded Modulation

b)

Pulse Code Modulation

c)

Pulse Carrier Modulation

d)

Phase Carrier Multiplexing

19.

In FDM, signals are separated in:

a)

Frequency

b)

Time

c)

Space

d)

Code

20.

Logarithmic companding is mainly used to:

a)

Reduce noise in low amplitude signals

b)

Reduce bandwidth

c)

Increase SNR of high amplitude signals

d)

Avoid aliasing

21.

ASK represents information by varying:

a)

Frequency

b)

Phase

c)

Amplitude

d)

Time

22.

In FSK, binary ‘1’ and ‘0’ are represented by:

a)

Different phases

b)

Different frequencies

c)

Different amplitudes

d)

Different time slots

23.

In BPSK, the phase shift is:

a)

45°

b)

90°

c)

180°

d)

360°

24.

The probability of bit error is least in:

a)

ASK

b)

PSK

c)

FSK

d)

OOK

25.

M-ary signaling increases:

a)

Bandwidth efficiency

b)

Power efficiency

c)

Error probability

d)

Noise level

26.

The optimum receiver for digital signals is:

a)

Energy detector

b)

Matched filter

27.

Synchronization in digital communication is required for:

a)

Correct symbol detection

b)

Power saving

c)

Filtering noise

d)

Bandwidth reduction

28.

In coherent detection, the receiver requires:

a)

A carrier reference

b)

A matched filter

c)

A comparator

d)

Envelope detector

29.

Error probability in digital modulation decreases when:

a)

SNR increases

b)

Bandwidth decreases

c)

Symbol rate increases

d)

Noise power increases

30.

Eye diagram is used to study:

a)

Noise spectrum

b)

ISI (Inter Symbol Interference)

c)

Sampling theorem

d)

Error correction

31.

In BPSK, the number of bits per symbol is:

a)

1

b)

2

c)

3

d)

4

32.

QPSK transmits ___ bits per symbol.

a)

1

b)

2

c)

3

d)

4

33.

Bandwidth of BPSK is:

a)

2Rb

b)

Rb

c)

Rb/2

d)

4Rb

34.

The main advantage of QPSK over BPSK is:

a)

Lower error probability

b)

Higher bandwidth efficiency

c)

Simpler receiver

d)

Constant envelope

35.

In BFSK, two signals differ in:

a)

Amplitude

b)

Frequency

c)

Phase

d)

Time

36.

MSK is a special case of:

a)

QAM

b)

FSK

c)

PSK

d)

OOK

37.

The constellation diagram of QPSK has:

a)

2 points

b)

4 points

c)

8 points

d)

16 points

38.

M-ary QAM combines:

a)

ASK and FSK

b)

ASK and PSK

c)

FSK and PSK

d)

PAM and TDM

39.

Power spectrum of MSK has:

a)

Wide side lobes

b)

Narrow side lobes

c)

No side lobes

d)

Gaussian shape

40.

Symbol rate in QPSK is:

a)

Equal to bit rate

b)

Half of bit rate

c)

Double bit rate

d)

One-fourth bit rate

41.

In Binary ASK, bit '1' is represented by

a)

High frequency

b)

High amplitude

c)

Phase change

d)

No signal

42.

The main criterion for the optimum receiver is

a)

Maximum signal amplitude

b)

Minimum delay

c)

Minimum probability of error

d)

Maximum bandwidth

43.

In a Binary PSK (BPSK) system, the minimum Euclidean distance between constellation points is

a)

1

b)

2

c)

√2

d)

0

44.

The coherent detection of PSK requires

a)

Envelope detector

b)

PLL for synchronization

c)

Integrator

d)

Bandpass filter

45.

The QPSK signal carries how many bits per symbol

a)

1

b)

2

c)

4

d)

8

46.

In BFSK, information is carried by

a)

Frequency

b)

Amplitude

c)

Phase

d)

Time duration

47.

Minimum Shift Keying (MSK) is a

a)

Non-coherent technique

b)

Type of PSK

c)

Continuous-phase FSK

d)

Variant of ASK

48.

The bandwidth of MSK is

a)

Less than QPSK

b)

Equal to QPSK

c)

More than QPSK

d)

Infinite

49.

M-ary PSK improves

a)

Power efficiency

b)

Bandwidth efficiency

c)

Timing accuracy

d)

Modulation depth

50.

In synchronization, timing recovery is essential to

a)

Decode phase

b)

Detect carrier

c)

Recover bit boundaries

d)

Calculate BER

51.

The number of bits transmitted per symbol in a 16-QAM system is

a)

2

b)

4

c)

8

d)

16

52.

For binary ASK with amplitude levels A and 0, average transmitted power is

a)

A²

b)

A²/2

c)

A

d)

A/2

53.

Power spectrum of BPSK has

a)

Peaks at harmonics

b)

Null at carrier frequency

c)

Main lobe and side lobes

d)

No spectral components

54.

In M-ary QAM, both __________ are varied.

a)

Amplitude and time

b)

Frequency and amplitude

c)

Amplitude and phase

d)

Frequency and phase

55.

In coherent detection of QPSK

a)

Phase reference is not needed

b)

Two carrier phases are used

c)

Reference carrier must be available

d)

Carrier is not necessary

56.

MSK has better spectral efficiency because

(a)  

57.

PN sequence stands for:

a)

Periodic Noise sequence

b)

Pseudo Noise sequence

c)

Phase Noise sequence

d)

Pulse Noise sequence

58.

An m-sequence is generated using:

a)

Shift registers

b)

Oscillators

c)

Phase modulators

d)

ADC

59.

In DSSS, bandwidth is:

a)

Compressed

b)

Expanded

c)

Constant

d)

Reduced

60.

Processing gain in DSSS is defined as:

a)

Ratio of chip rate to bit rate

b)

Ratio of noise to signal

c)

Ratio of bandwidths of carrier and message

d)

Ratio of power levels

61.

FHSS avoids jamming by:

a)

Coding

b)

Changing frequency rapidly

c)

Reducing bandwidth

d)

Increasing SNR

62.

In CDMA, multiple users are separated by:

a)

Frequency

b)

Time

c)

Code

d)

Amplitude

63.

TDMA separates users in:

a)

Frequency slots

b)

Time slots

c)

Code slots

d)

Phase slots

64.

FDMA is inefficient due to:

a)

Guard bands

b)

Noise

c)

Power consumption

d)

High SNR

65.

Synchronization in spread spectrum is essential for:

a)

Multiplexing

b)

Despreading

c)

Power saving

d)

Modulation index

66.

CDMA is widely used in:

a)

AM radio

b)

GSM

c)

3G cellular networks

d)

Television broadcast

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