Deck 1: Modulation and Demodulation Techniques

Question 1

If the peak message signal amplitude is half the peak amplitude of the carrier signal, the signal is_________modulated.

A)100%
B)2%
C)50%
D)70%

Answer 1

50%

Question 2

A percentage of modulation greater than

A)10%
B)25%
C)50%
D)100%

Answer 2

100%

Question 3

Single sideband AM systems occupy same bandwidth as of conventional AM systems.

Answer 3

False

Question 4

How is the performance of SSB AM systems in fading channels?

A)poor
B)best
C)good
D)average

Question 5

Which of the following is a disadvantage of tone-in-band SSB system?

A)high bandwidth
B)bad adjacent channel protection
C)effects of multipath
D)generation and reception of signal is complicated

Question 6

FFSR in AM systems stands for_________      

A)feedforward signal regeneration
B)feedbackward signal regeneration
C)feedbackward system restoration
D)feedforward system restoration

Question 7

AM demodulation technique can be divided into_________and_________demodulation.

A)direct, indirect
B)slope detector, zero crossing
C)coherent, noncoherent
D)quadrature detection, coherent detection

Question 8

Non coherent detection requires the knowledge of transmitted carrier frequency and phase at the receiver.

Question 9

A product detector in AM systems is also called_________            

A)envelope detector
B)differentiator
C)integrator
D)phase detector

Question 10

AM system use only product detector for demodulation. They never use envelope detectors.

Question 11

LCD uses_________      

A)sematic crystals
B)twisted nematic crystals
C)nematic crystals
D)cholesteric crystals

Question 12

Which of the following stage is present in FM receiver but not in AM receiver?

A)amplitude limiter
B)demodulator
C)am amplifier
D)mixer

Question 13

Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception.

Question 14

Single Sideband Modulation (SSB) is generally reserved for point-to-point communication.

Question 15

For an AM transmitter, class C amplifier can be used after the modulation stage.

Question 16

For which of the modulated system, the linear amplified modulated stage is used?

A)low level amplitude modulated system
B)high level amplitude modulated system
C)high level frequency modulated system
D)low level frequency modulated system

Question 17

When noise is passed through a narrow band filter, the output of filter should be?

A)triangular
B)square
C)parabolic
D)sinusoidal

Question 18

A narrow band noise can exist in

A)am only
B)pcm only
C)fm only
D)am and fm both

Question 19

The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be?

A)35khz and 25khz
B)34khz and 24khz
C)25khz and 35khz
D)0.35khz and 0.25khz

Question 20

Phase array radar can track many targets together.

Question 21

A duplex arrangement use separate frequencies for transmission.

Question 22

VSB modulation is used in televisions because it avoids phase distortion at low frequencies.

Question 23

A cordless telephone that uses separate frequencies for transmission in base and portable units is called_________        

A)half duplex
B)duplex
C)simplex
D)one-way communication

Question 24

Which polarization is used to reduce the depolarization effect on received waves?

A)circular polarization
B)linear polarization
C)atomic polarization
D)dipolar polarization

Question 25

Circular polarization involves critical alignment between transmitting and receiving antenna.

Question 26

It is only the reflected color that decided the color of an object.

Question 27

What do you understand by the term "carrier" in modulation?

A)voltage to be transmitted
B)resultant wave
C)voltage for which amplitude, phase or frequency can be varied
D)voltage for which amplitude, phase or frequency remains constant

Question 28

Carrier wave in modulation is a resultant wave.

Question 29

For a low level AM system, amplifier modulated stage must have_________        

A)harmonic devices
B)linear devices
C)non-linear devices
D)class a amplifiers

Question 30

Which is the greatest disadvantage of Pulse Code Modulation?

A)highly prone to noise
B)cannot travel long distances
C)its inability to handle analog signals
D)large bandwidth is required for it

Question 31

Inductance and capacitance of a line is 0.8

A)158
B)166
C)143
D)127

Question 32

Quantization noise occurs in_________      _________      

A)frequency division multiplexing
B)time division multiplexing
C)delta modulation
D)amplitude modulation

Question 33

What the main advantage of PCM?

A)can travel small distances
B)higher bandwidth
C)lower noise
D)good reception

Question 34

In AM pilot carrier, transmission has

A)carrier and part of one side band
B)two side bands and a carrier
C)two side bands
D)carrier, one side band and part of other side band

Question 35

Quantization noise depends upon both sampling rate and number of quantization levels.

Question 36

Which of the following frequency is not transmitted in AM transmission?

A)upper side band frequency
B)carrier frequency
C)lower side band frequency
D)audio frequency

Question 37

Companding is used in PCM transmitters to allow amplitude limiting in the receivers.

Question 38

What is the use of Companding?

A)in pcm transmitters to allow amplitude limiting in the receivers
B)in pcm receiver to overcome impulse noise
C)to overcome quantizing noise in pcm
D)to protect small signals in pcm from quantizing distortion

Question 39

5 PSD MODULATORS AND DEMODULATORS

Question 40

Which of the following is not an advantage of digital modulation?

A)greater noise immunity
B)greater security
C)easier multiplexing
D)less bandwidth requirement

Question 41

The performance of modulation scheme is not measured in terms of_________          

A)power efficiency
B)bandwidth efficiency
C)cost and complexity
D)transmitted power

Question 42

In digital communication system, in order to increase noise immunity, it is necessary to increase_________        

A)signal power
B)signal amplitude
C)signal frequency
D)signal magnitude

Question 43

Which of the following is the ratio of signal energy per bit to noise power spectral density?

A)bandwidth efficiency
B)spectral density
C)power efficiency
D)power density

Question 44

Increasing the data rate implies the increase in pulse width of digital symbol.

Question 45

Which of the following is the ratio of the throughput data rate per Hertz?

A)bandwidth efficiency
B)spectral density
C)power efficiency
D)power density

Question 46

Which of the following is defined as the range of frequencies over which the signal has a non zero power spectral density?

A)null to null bandwidth
B)half power bandwidth
C)3 db bandwidth
D)absolute bandwidth

Question 47

               is equal to width of main spectral lobe.

A)null to null bandwidth
B)half power bandwidth
C)3 db bandwidth
D)absolute bandwidth

Question 48

Half power bandwidth is also called

A)absolute bandwidth
B)null to null bandwidth
C)3 db bandwidth
D)zero db bandwidth

Question 49

FM is a part of general class of modulation known as_________  

A)angle modulation
B)phase modulation
C)amplitude modulation
D)frequency modulation

Question 50

Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is differentiated before modulation.

Question 51

Frequency modulation index defines the relationship between the_________  and bandwidth of transmitted signal.

A)frequency of message signal
B)amplitude of message signal
C)amplitude of carrier signal
D)frequency of carrier signal

Question 52

Which of the following are two methods for generating FM signal?

A)coherent method, noncoherent method
B)product detector, envelope detector
C)direct method, indirect method
D)slope detector, zero crossing detector

Question 53

In indirect method, the carrier frequency is directly varied in accordance with the input modulating signal.

Question 54

Which of the following is used to vary the frequency of the carrier frequency in accordance with the baseband signal amplitude variations in direct method of FM generation?

A)integrator
B)envelope detector
C)multivibrator
D)voltage controlled oscillators

Question 55

Frequency demodulator is a frequency to amplitude converter circuit.

Question 56

Which of the following is not a technique for FM demodulation?

A)slope detection
B)zero crossing detection
C)product detector
D)phase locked discriminator

Question 57

Which of the following FM demodulator is sometimes known as pulse averaging discriminator?

A)slope detection
B)zero crossing detection
C)quadrature detection
D)phase locked discriminator

Question 58

PLL in FM detection stands for_________  

A)phase locked loop
B)programmable logic loop
C)phase locked logic
D)programmable locked loop

Question 59

In angle modulation, signal to noise ratio before detection is a function of_________  

A)modulation index
B)input signal to noise ratio
C)maximum frequency of the message
D)if filter bandwidth

Question 60

FM can improve the receiver performance through adjustment of transmitted power.

Question 61

De-emphasis circuit is used_________      

A)before detection
B)after detection
C)before encoding
D)after encoding

Question 62

Why frequency fogging is used in a carrier system?

A)to reduce noise
B)to reduce cross talk
C)to converge frequencies
D)to reduce distortion

Question 63

For a phase modulated signal, the frequency deviation is proportional to

A)frequency only
B)amplitude only
C)only width
D)phase only

Question 64

The frequency deviation is proportional to frequency in phase modulated signal.

Question 65

Which of the following is not necessarily an advantage of FM over AM?

A)less modulating power is required
B)better noise immunity is provided
C)higher bandwidth is required
D)carrier is of any shape

Question 66

What is number of possible outputs if there is 7 line digital input?

A)64
B)32
C)16
D)128

Question 67

What is the frequency of the stereo sub carrier signal in FM broadcasting?

A)19 khz
B)45 khz
C)55 khz
D)38 khz

Question 68

What is the bandwidth required in SSB signal?

A)fm
B)2fm
C)> 2fm
D)< 2fm

Question 69

One of the advantage of using a high frequency carrier wave is that it dissipates very small power.

Question 70

The antenna current is 10A. Find the percentage of modulation when the antenna current increases to 10.4A?

A)50%
B)30%
C)28.5%
D)23%

Question 71

Find the total power, if the carrier of an AM transmitter is 800W and it is modulated to 50%?

A)100w
B)800w
C)500w
D)900w

Question 72

Spread spectrum is used for

A)encrypting signal
B)hiding signal
C)encrypting & hiding signal
D)none of the mentioned

Question 73

Which is a quantization process?

A)rounding
B)truncation
C)rounding & truncation
D)none of the mentioned

Question 74

Quantization is a_________process.

A)few to few mapping
B)few to many mapping
C)many to few mapping
D)many to many mapping

Question 75

Which conveys more information?

A)high probability event
B)low probability event
C)high & low probability event
D)none of the mentioned