frequently asked questionsnptel.vtu.ac.in/vtu-nmeict/ce/frequently asked questions.pdf · also its...

Frequently asked questions

1. Define Communication System

2. Describe the block diagram of typical communication systems

3. Mention the different kinds of information sources

4. Explain the role of transmitter in communication system

5. Why modulation is required in communication

6. Different types of modulation and explain

7. What are the reasons for modulation?

8. Explain with neat figure the frequency range for guided wire line channels

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1. List the characteristic of channel in terms of noise

2. Mention the types of noise sources in communication systems

3. With an example explain the Natural/ Atmospheric noise, manmade noise.

4. Write a note on Radio frequency interference

5. How is internal noise sources generated?

6. Mention the types of internal noise

7. Mention the types of communication channel

8. Write a note on Guided Electro-magnetic wave propagation channel.

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Quadrant 4

Frequently asked Questions

1. Which are the two main classifications of signals?

2. Express the deterministic signal in complex exponential with an example.

3. Define impulse function.

4. What are the properties of impulse function?

5. Which is the other basic signal closely related to impulse function signal?

6. Define Fourier series.

7. What are the properties of Fourier series?

8. Define Parseval’s theorem.

9. Is sinusoidal signal having infinite duration is power signal or energy signal?

10. If the signal has finite energy then it typically have finite or zero power?

11. Define power.

12. Define Fourier transform.

13. Define inverse Fourier transform.

14. What are the properties of Fourier transform?

15. Define convolution theorem.

16. Explain Linearity property.

17. Explain Time delay and Scale change property.

18. State uncertainty relation in Communication theory.

19. What is Duality?

20. Explain Frequency Translation theorem.

21. Explain Modulation theorem. Where it is used?

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22. Explain differentiation and integration theorem.

23. What is a System? Give example.

24. Define System Modeling.

25. What is an LTI System?

26. When a System is said to be linear?

27. What is the response of a system to δ(t)

28. Explain how x(t) can be expressed as impulse function?

29. Define Causality.

30. Give a test for Causality.

31. Define Stability.

32. Give a test for Stability.

33. When a System is said to be BIBO stable?

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Quadrant 4


1. What is Hilbert Transform?

2. List some applications of Hilbert Transform.

3. Prove that

j/πt sgn f.

4. List the properties of Hilbert Transform.

5. Prove that x(t) and x^(t) are orthogonal.

6. Prove that m(t)c(t) = m(t)c^(t)

7. Explain the concept of analytic signals.

8. Prove xp(t)= x(t)+jx^(t).

9. Explain complex envelope.

10. Explain the role of Hilbert transform in modulation

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Quadrant 4


1. Explain baseband communication channel.

2. What are the types of effects introduced by channel?

3. What are the types of distortion and differentiate between them?

4. What are the types of linear distortion?

5. Explain the characteristics of ideal channel.

6. Explain the process of equalization.

7. Why the non linear distortion does occur?

8. Explain the characteristics of an ideal amplifier.

9. What is co-channel interference?

10. Why linear distortion is also called as inter-modulation distortion or

harmonic distortion?

11. Delay distortion is tolerable in speech transmission where as data

transmission and video/picture transmission are highly sensitive to delay

distortion.

12. Linear invariant channel depends on application sometimes yes and

sometimes no for wireless if no, justify?

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Quadrant 4


1. What are the advantages of modulation?

2. Noise present in channel is frequency dependent, Justify?

3. What are the different types of modulation?

4. Explain frequency translation.

5. What is the other name given to frequency translation: mixing, heterodyning

6. What are the two characteristics of DSB-SC waveform?

7. BW of the modulated signal is 2B, Justify whether it’s good or bad.

8. Explain DSB-SC modulation.

9. Find the transmitted power in case of DSB-SC.

10. Show that ST=SCSm

11. ct dt =0. Justify

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Quadrant 4


1. Explain the demodulation of Double side band single carrier signals?

2. List out the problems of DSB SC demodulation?

3. Explain the coherence demodulation of DSB SC?

4. Explain the effect of loss of coherence?

5. What is warbling effect?

6. Explain the carrier recovery circuits?

7. What is modulation index?

8. What is the condition for distortion less envelops with respect to modulation?

9. What is power efficiency?

10. Explain the use of diode detector?

11. Explain the demodulation with envelop detector circuit diagram?

12. What should be the charging constant?

13. What is the condition for charging time constant?

14. What should be the discharging time constant?

15. What is the condition for discharging time constant?

16. What is chipping distortions?

17. What is the condition to prevent chipping distortions?

18. Derive the expression for carrier power, side band power, total power,

power efficiency?

19. Write the difference between DSB SC &DSB AM?

20. What is Quadrature carrier multiplexing?

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21. What is suppressed side band modulation? Why we are going for it?

22. What are the advantages of suppressed side band modulation?

23. What are the types of suppressed side band modulation?

24. What is single side band modulation?

25. What is vestigial band modulation?

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1. What are the two methods used to demodulate SSB?

2. In a coherent detection if carrier applied is cos(wct+ᵠ). Prove that there is a

phase error in the output and output consist not only the message signal but

also its Hilbert transform.

3. Explain VSB in frequency domain.

4. With block diagram explain the generation of VSB modulated wave.

5. Explain with block diagram and relevant waveforms the demodulation of

VSB.

6. SSB is suitable for messages with little low frequency content which implies

separation of two sidebands feasible.

7. Transmission BW of VSB =B +β

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1. Explain the time domain description of VSB with frequency response

diagrams and derive the expression for VSB modulated wave.

2. Explain the frequency translation process with proper mathematical

equations.

3. Picture transmission in TV uses VSB modulation. Why?

4. To achieve VSB filters required to have vestigial symmetry.

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1. Explain super heterodyne receiver.

2. What are the properties that any good receiver should possess?

3. Explain the block diagram of radio receiver.

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1. What are the methods of mixing?

2. Explain the operation of ring modulator or balanced diode modulator with

block diagram and waveforms.

3. Explain with proper equation the working of envelope detector for the

following two cases

Case i) when interference is too large

Case ii) when interference is small

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1. Describe the angle modulation, frequency modulation and phase modulation.

2. Derive the equation for phase modulated wave.

3. Derive the equation for frequency modulated wave.

4. Explain the spectrum of an angle modulated signal when modulating signal

is pure sinusoidal signal.

5. Explain the spectral analysis of sinusoidal FM.

6. Define terms frequency deviation and modulation index related to frequency

modulation.

7. What is Carson’s rule?

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1. Explain the generation of FM waves using direct and indirect method.

2. Explain Armstrong method.

Quadrant 4


1. List out the advantages and disadvantages of direct and indirect method.

2. Derive the B.W for angle modulated signal.

3. Compare AM and NBFM.


1. Explain the demodulation of FM wave.

2. Explain the demodulation of phase modulator.

3. Why we require limiter? What is the function of limiter?

4. Explain the operation of limiter with block diagram and waveform.

5. Explain two methods of realization of differentiator.

6. Explain the realization of differentiator using two band pass filter.

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Quadrant 4


1. Explain the block diagram of two band pass filter.

2. What are the techniques used for combining envelope detector outputs.

3. Discuss different frequency demodulator circuits.

4. Explain slope detection with relevant waveform and mathematical equations.


1. Write the block diagram and explain

2. Explain the realization of phase detector

3. Explain the modeling of VOC.

4. Explain the non linear model of PLL.

5. Explain the linear model of PLL.

6. How the PLL work in locked conditions.

7. Explain the phase plane plot.

8. How PLL works at steady state.

9. What is value of steady state error form phase plane plot.

10. What is the steady state error?

11. For what condition there is no stable point at all.

12. What are the conditions for lock to occur in PLL?

13. What is the locking range of PLL?

14. When we can go for the linear approximation of PLL

15. Explain demodulation of PM signals using PLL

16. What are the conditions for best operation of PLL?

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17. What we made to remove the disadvantage of first order loop.

18. Why PLL without loop filters is called the first order loop.

19. What are the disadvantages of PLL without loop filters?

20. What is leaking through integration?

Quadrant 4


1. Which system is called the frequency compressive feedback?

2. Explain the block diagram of frequency compressive feedback.

3. What is the difference between PLL and frequency compressive feedback.

4. Explain the FM demodulation using frequency compressive feedback.

5. What is equation at the discriminator input?

6. Explain the important of signal at input of the discriminator.

7. What are the advantages of frequency compressive feedback?

8. What are the two methods for FM demodulation using feedback circuits?

9. Explain the effect of interference in PM or FM demodulator.

10. Explain the output of discriminator with interference in PM demodulator.

11. What is de-emphasizing filter?

12. Why we are using de-emphasizing filter

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1. What is effect of total interference on FM receivers?

2. How can we reduce the total interference on FM receivers?’

3. What is pre emphasizes filters.

4. What are the conditions that pre-emphasizes fitters satisfies

5. What are the conditions that de-emphasizes fitters satisfies

6. Explain the operation of transmitter and receiver with pre-emphasizes fitters &

de-emphasizes fitters

7. What is the frequency range used in FM receivers.

8. What is the peak frequency deviation in multiple FM receivers?

9. What is the range of intermediate frequency used in FM receivers?

10. What is stereophonic effect?

11. Explain the stereophonic effect in FM receivers

12. What is a monophonic receiver?

13. Explain the transmitter part of the stereophonic FM

14. Explain the receiver part of the stereophonic FM

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Quadrant 4


1. Explain TV transmission system.

2. Explain the scanning mechanism of TV transmission system.

3. Explain how the TV camera works.

4. Mention the two scanning patterns of TV transmission system.

5. Explain the horizontal scanning patterns.

6. Explain the vertical scanning patterns

7. Explain how videos are transmitted in TV system.

8. Draw the block diagram of transmitter of TV system

9. Draw the block diagram of receiver of TV system

10. Define bandwidth.

11. Define sampling rate

12. Mention the two problems in colour TV system

13. How the two problems in colour TV system are solved.

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1. Define random experiments.

2. What is sample point?

3. What is a sample space?

4. Define the event.

5. Mention different types of events.

6. Mention the Axioms of probability

7. What is a probability assignment?

8. Explain the independent events

9. Explain the concept of conditional probability.

10. What are random variables?

11. Explain the probability distribution functions

12. List the properties of probability distribution functions

13. Explain the some typical PDF.

14. What is the Gaussian probability density function?

15. What is the relays probability density function?

16. What is the exponential probability density function?

17. What is the uniform probability density function?

18. Define the expected value of random variables.

19. Define the moments of random variables.

20. Explain the types of moments

21. Explain the central moments.

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22. Define variance, mean.

23. Explain Gaussian random variables.

24. Explain joint probability density function.

25. Explain the multiple random variables

Quadrant 4


1. What is statically independent random variable?

2. Explain statistical independent random variable

3. Write the equation for expected value of two random variables

4. Define correlation of random variables.

5. What is need of studying random processor?

6. What is the frame work of random processor?

7. Define random variable.

8. Explain the characterization of random processor

9. Explain the Classification of random processor

10 Explain auto correlation function

11. Why auto correlation called as second order function.

12. What is equation for auto correlation for stationary processes?

13. What is equation for auto correlation for non stationary processes?

14. Mention the properties of auto correlation functions.

15. Define the wide-sense stationarity

16. Define the mean value function.

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17. Define the six sense stationarity .

18. Explain the power density function.

20. What is ergodicity?

21. Define the white noise process.

22. Explain cross co-relation function

23. Explain Gaussian processes.

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1. What is the condition for a set of random variables is jointly Gaussian

2. What is the condition for x (t) is Gaussian.

3. State & explain the central limit theorem

4. Explain why the Gaussian processes used as models

5. Explain the properties of Gaussian processes.

6. Suppose we pass a Gaussian processes to a linear filter what kind of processes at

the output

7. How do we characterize the density of Gaussian processes?

8. How we representation of narrowband random processes.

9. How do we representation narrowband signal

10. How can we characterize the Gaussian Processes?

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Quadrant 4


1. How we can model the noise

2. Define the figure of merit for communication systems.

3. Taking the example voice signals explain signal to noise ratio

4. Taking the example Television signals explain signal to noise ratio.

5. Define baseband systems.

6. Explain SNR for baseband system.

7. Explain the SNR for AM system.

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Quadrant 4


1. Explain the SNR for SSB-SC system.

2. Explain the SNR for VSB-SC system.

3. Explain the SNR for DSB-SC system.

4. Explain the SNR for AM with envelop detector system.

5. Explain the SNR for AM with synchronous carriers system

6. Explain the SNR for demodulation of AM signal using envelop detector

provided that noise is comparatively smaller than the carrier

7. Explain the SNR for demodulation of AM signal using envelop detector

provided that noise is comparatively larger than the carrier

8. Explain the calculation of threshold SNR.

9. Explain noise in angle modulated system.

10. Write the phase diagram of the signal & noise.

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Quadrant 4


1. Explain noise in frequency modulated system.

2. Write the general compares between the FM & AM.SNR.

3. Derive the expression for output SNR for FM.

4. Explain the SNR threshold in angle modulation.

5. What is threshold effect

6. Explain the pre-emphasise in angle modulation system.

7. Explain the de-emphasise in angle modulation system.

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1. Name the type of carriers that can be used in transmission of signals

2. What is the need for pulse modulation

3. Which are the occasions that show the importance of pulse modulation over

frequency modulation?

4. What is the importance of sampling theorem in Pulse modulation Schemes?

5. Mention the parameters of a pulse

6. Explain the concept of Pulse Amplitude Modulation

7. How can we obtain PAM signals from impulse sampling signals?

8. Explain the method of demodulation of PAM signal

9. How do we generate PWM signals?

10. What is the need of a comparator in generating a PWM signals?

11. When can a PWM be used?

12. Define PPM

13. Mention some of the applications of PPM

14. Why is sinusoidal & pulse modulation of message signals said to be analog

in nature?

15. List the Advantages of Digital Communication over Analog Communication

16. What is the function of a regenerative repeater?

17. Differentiate between Repeater and an Amplifier

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Quadrant 4


1. What is Delta Modulation?

2. Explain the modulation and demodulation process of Delta modulation with

a block diagram

3. Mention the difficulties associated with Delta modulation?

4. What is a granular noise situation?

5. What is Adaptive Delta Modulation? Explain with a block diagram

6. What is CVSD- Delta Modulator?

7. Why is the feedback connection is taken from the DM output and not

immediately after the limiter in the Adaptive Delta Modulation?

8. What is Sigma delta modulation?

9. In DM, transmission disturbance/ noise leads to cumulative errors in

demodulation signals- True/False

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Quadrant 4


1. What is pulse code modulation?

2. Why is quantization step necessary in PCM?

3. What is the difference between quantization noise and other noises?

4. What is the SNR one can expect in PCM which uses certain level of

quantization levels?

5. Explain the types of quantization in detail

6. What is companding?

7. Explain the PCM receiver.

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