Communication Engineering Set 5

Computer Science Engineering (CSE)

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This set of Communication Engineering Multiple Choice Questions & Answers (MCQs) focuses on Communication Engineering Set 5

Q1 | In which waveform logic 1 is represented by equal amplitude alternating pulses?
  • unipolar rz
  • bipolar rz
  • rz-ami
  • manchester coding
Answer: rz-ami
Explaination:
in rz-ami logic 1 is represented by equal amplitude alternating pulses and logic 0 is represented by the absence of a pulse.
Q2 | The signals which are obtained by encoding each quantized signal into a digital word is called as
  • pam signal
  • pcm signal
  • fm signal
  • sampling and quantization
Answer: pcm signal
Explaination:
pulse code modulation is the name for the class of signals which are obtained by encoding the quantized signals into a digital word.
Q3 | The length of the code-word obtained by encoding quantized sample is equal to
  • l=log(to the base 2)l
  • l=log(to the base 10)l
  • l=2log(to the base 2)l
  • l=log(to the base 2)l/2
Answer: l=log(to the base 2)l
Explaination:
the quantized sample which are digitally encoded into l bit value code- word. the length l can be calculated as l=log(to the base 2)l.
Q4 | In PCM encoding, quantization level varies as a function of                  
  • frequency
  • amplitude
  • square of frequency
  • square of amplitude
Answer: amplitude
Explaination:
in linear pcm the quantization levels are uniform. but in normal pcm encoding the quantization level vary according to the amplitude, based of a-law of myu-law.
Q5 | What is bit depth?
  • number of quantization level
  • interval between two quantization levels
  • number of possible digital values to represent each sample
  • none of the mentioned
Answer: number of possible digital values to represent each sample
Explaination:
one of the properties of pcm signal which determines its stream fidelity is bit depth which is the number of possible digital values that can be used to represent each sample.
Q6 | Choosing a discrete value that is near but not exactly at the analog signal level leads to
  • pcm error
  • quantization error
  • pam error
  • sampling error
Answer: quantization error
Explaination:
one of the limitations of pcm is quantization error which occurs when we choose a discrete value at some near by value and not at the analog signal level.
Q7 | In PCM the samples are dependent on
  • time
  • frequency
  • quanization leavel
  • interval between quantization level
Answer: time
Explaination:
the samples depend on time,an accurate clock is required for accurate reproduction.
Q8 | DPCM encodes the PCM values based on
  • quantization level
  • difference between the current and predicted value
  • interval between levels
  • none of the mentioned
Answer: difference between the current and predicted value
Explaination:
differential pcm encodes the pcm value based on the difference between the previous sample and the present sample value.
Q9 | Delta modulation uses            bits per sample.
  • one
  • two
  • four
  • eight
Answer: one
Explaination:
delta modulation is used for analog to digital conversion and vice versa. it is a simple form of dpcm. its uses 1 bit per sample. it also depends on the difference between the current and previous sample values.
Q10 | Sample resolution for LPCM          bits per sample.
  • 8
  • 16
  • 24
  • all of the mentioned
Answer: all of the mentioned
Explaination:
common sampling resolution for lpcm are 8, 16, 20, 24 bits per sample.
Q11 | Adaptive DPCM is used to
  • increase bandwidth
  • decrease bandwidth
  • increase snr
  • none of the mentioned
Answer: decrease bandwidth
Explaination:
adaptive dpcm is used to decrease required bandwidth for the given snr.
Q12 | Vocoders analyse the speech signals at
  • transmitter
  • receiver
  • channel
  • if filter
Answer: transmitter
Explaination:
vocoders are a class of speech coding systems. they analyse the speech signal at the transmitter. and then transmit the parameters derived from the analysis.
Q13 | Vocoders                      the voice at the receiver.
  • analyse
  • synthesize
  • modulate
  • evaluate
Answer: synthesize
Explaination:
vocoders synthesize the voice at the receiver. all vocoder systems attempt to model the speech generation process as a dynamic system and try to quantify certain physical constraints of the system.
Q14 | 6 CHANNEL VOCODER
  • true
  • false
Answer: false
Explaination:
vocoders are much more complex than the waveform coders. they can achieve very high economy in transmission bit rate but are less robust.
Q15 | Which of the following is not a vocoding system?
  • linear predictive coder
  • channel vocoder
  • waveform coder
  • formant vocoder
Answer: waveform coder
Explaination:
waveform coder is not a vocoding system. lpc (linear predictive coding) is the most popular vocoding system. other vocoding systems are channel vocoder, formant vocoder, cepstrum vocoder etc.
Q16 | Which of the following pronunciations lead to voiced sound?
  • ‘f’
  • ‘s’
  • ‘sh’
  • ‘m’
Answer: ‘m’
Explaination:
voiced sounds are ‘m’, ‘n’ and ‘v’ pronounciations. they are a result of quasiperiodic vibrations of the vocal chord.
Q17 | Channel vocoders are the time domain vocoders.
  • true
  • false
Answer: false
Explaination:
channel vocoders are frequency domain vocoders. they determine the envelope of the speech signal for a number of frequency bands and then sample, encode and multiplex these samples with the encoded outputs of the other filters.
Q18 |                  is often called the formant of the speech signal.
  • pitch frequency
  • voice pitch
  • pole frequency
  • central frequency
Answer: pole frequency
Explaination:
the pole frequencies correspond to the resonant frequencies of the vocal tract. they are often called the formants of the speech signal. for adult speakers, the formants are centered around 500 hz, 1500 hz, 2500 hz and 3500 hz.
Q19 | Formant vocoders use large number of control signals.
  • true
  • false
Answer: false
Explaination:
formant vocoders use fewer control signals. therefore, formant vocoders can operate at lower bit rates than the channel vocoder. instead of transmitting the power spectrum envelope, formant vocoders attempt to transmit the position of peaks of spectral envelope.
Q20 | Cepstrum vocoder uses                      
  • wavelet transform
  • inverse wavelet transform
  • cosine transform
  • inverse fourier transform
Answer: inverse fourier transform
Explaination:
cepstrum vocoders use inverse fourier transform. it separates the excitation and vocal tract spectrum by fourier transforming spectrum to produce the cepstrum of the signal.
Q21 | The real part of an antenna’s input impedance is due to                  
  • swr
  • radiated signal
  • reflected signal
  • refracted signal
Answer: radiated signal
Explaination:
in antenna impedance, impedance related the voltage and current at the input of the antenna. the real part of antenna impedance represents power that is either radiated away or absorbed within the antenna and the imaginary part of antenna impedance represents power that is stored in the near field of antenna.
Q22 | What is the other name for half-wave dipole antenna?
  • helical antenna
  • isotropic antenna
  • hertz antenna
  • maxwell antenna
Answer: hertz antenna
Explaination:
the hertz antenna is also known as half wave dipole antenna. it consists of two straight collinear conductors of equal length separated by a small feeding gap.
Q23 | Measured on the ground, the field strength of a horizontally polarized half wave dipole antenna is strongest                  
  • in one direction
  • in two directions
  • depends on the number of elements
  • depends on the shape of antenna
Answer: in two directions
Explaination:
as the name suggests, half wave dipole is half wavelength long. this antenna has the shortest resonant length that can be used for a resonant dipole. the field strength of a horizontally polarized half wave dipole antenna is strongest in two directions.
Q24 | When an antenna radiates more energy in one direction than in other directions, it is called                  
  • selectivity
  • directivity
  • active antenna
  • resonance
Answer: directivity
Explaination:
when an antenna radiates more energy in one direction than in other directions is called directivity. an antenna that radiates equally in all directions has effectively zero directionality, and the directivity of this type of antenna should be 1 (or 0db).
Q25 | What is the full form of ERP?
  • effective radiated power
  • effective reflected power
  • equivalent radiated power
  • equivalent reflected power
Answer: effective radiated power
Explaination:
erp stands for effective radiated power. effective radiated power (erp) is always given with respect to a certain direction.
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