QUESTION BANK COMMUNICATION THEORY AND SYSTEMS DEGREE: B.E Year/branch : III ECE SEM : V SEMESTER

VINAYAKA MISSIONS UNIVERSITY

V.M.K.V.ENGINEERING COLLEGE, SALEM

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

 QUESTION BANK

COMMUNICATION THEORY AND SYSTEMS

DEGREE: B.E

Year/branch    : III ECE

SEM        : V SEMESTER

UNIT 1

PART A

Define Modulation

 A transmitter supplies 8 KW to the antenna when unmodulated. Determine the total    power radiated when modulated to 40 %

List out the needs for modulation.

Draw the Frequency spectrum of AM wave.

A sinusoidal carrier signal of frequency 1 MHZ and amplitude 100V is modulated by a sinusoidal signal of frequency 5 KHZ producing 40% modulation. Calculate the frequency and amplitude of USB and LSB.

Differentiate between deterministic and random signals

Define Energy & Power signals

State Drichlets conditions

Define Modulation index and mention its range.

As related to AM, what is over modulation, under modulation and 100% modulation?

List the Limitations of AM systems.

Write down the expression for modulation index of multi tone modulation.

The total power content of an AM signal is 1kilowatt.Determine the power being transmitted at the carrier frequency and at each of the sidebands when the percentage of modulation is 100.

Mention the types of linear modulators.

Differentiate linear modulation techniques with nonlinear modulator.

Distinguish between synchronous and asynchronous demodulation techniques

What do you meant by balanced modulator?

What are the requirements in designing BPF in frequency discriminator for generating SSB wave?

List the advantages and disadvantages of SSB.

List the applications of VSB modulation

Draw the magnitude response of VSB filter wave.

Define frequency translation.

Write the applications of Frequency Division Multiplexing.

Define HILBERT transform

What do you mean by VSB modulation?

PART B

1. (i) Derive an expression for a single tone AM signal and draw its frequency spectrum.                                                                                                   (8)       

            (ii) An amplitude modulated signal is represented by

V (t) = 0.1 [1 + 0.1 cos 2512 t + 0.5 cos 6280t] sin (10⁶t + 45⁰) v. What information can you gather from this?                                                                             (4)

      2. (i) Discuss the working principle of square law modulators. Mention its merits &          demerits?                                                                                                   

3. Describe the operation of Coherent detection with necessary diagram and expressions for DSBSC systems .

4. Draw the functional block diagram of Phase shift method, describe its function    to generate SSB modulation with merits and demerits.

5. With block diagram explain VSB wave generation and Mention few  application of  VSB wave.

6. Explain the principle and operation of Balanced Modulator for generation of

     DSB SC Wave with relevant expression.

7.i).With block diagram explain the concept of frequency translation, explain up      conversion and down conversion.

            ii) Compare various Amplitude Modulation systems.                                               

8.With neat block diagram explain Frequency division Multiplexing.          

9. Explain the demodulation process of AM wave with practical envelope detector.

    10. With a neat sketch explain the block diagram of AM transmitter in detail.

UNIT 2

PART A

Mention  the types of Angle modulation techniques

Define Phase modulation.

what is the modulation index for  Frequency modulation.

Illustrate the relationship between Frequency and Phase modulation with block diagram.

Define Frequency deviation.

Define the modulation index of PM.

Distinguish between Narrowband FM and Wideband FM.

State Carson’s rule for transmission bandwidth

 When is FM considered as AM justify your answer?

FM is noise free modulation technique why?

List the nonlinear effects in FM.

What are the components in frequency multiplier?

Distinguish between Narrowband and Wideband FM.

How the effects of residual AM and Harmonic PM can be reduced in a Narrow band FM.

Write the expression for the spectrum of a single tone FM signal

What is the maximum frequency deviation allowed by FM.?

Mention any two advantages of FM over AM.

Define carrier swing.

A 110 MHz carrier is Frequency modulated by a 93 KHz sine wave the resultant FM signal has a frequency deviation of 50 KHz determine the modulation index of the FM wave.

Draw the frequency spectrum of FM wave.

Find the Bandwidth required for a FM wave in which the modulating frequency signal is 5 KHz and the Maximum frequency deviation is 17 KHz?

Give the Frequency spectrum of Narrowband FM

Mention the major drawbacks of FM.

A 108.5 MHz carrier signal is frequency modulated by an 8 KHz sine wave. The resultant FM signal has frequency deviation of 50 KHz. Calculate the highest and lowest frequencies attained by the modulated signal.

What is the Modulation index of an FM signal having a carrier swing of 100 KHZ when the modulating signal has a frequency of 7 KHZ?

PART B

With neat block diagram explain the generation of Narrowband FM and give the phase comparison between FM, AM for sinusoidal modulation.

Derive an expression of single tone FM modulation systems and draw its frequency spectrum.

Describe the generation of WBFM from the basic principle using Armstrong method with neat phasor and block diagram.

How FM signal can be detected with the use of slope detector, explain with relevant frequency response and derive necessary parameters.

a) Explain in detail the Transmission Bandwidth of FM signal, with suitable diagram.                                                                                                        (8)

b) Discuss the similarity between FM and PM                                               (4)

       6.  Explain the working principle of a varactor diode method for generation of FM wave.

       7. Discuss the working of Ratio detector with neat circuit diagram.

      8. Explain the working of balanced slope detector with relevant diagram.

      9. With a neat sketch explain the Block diagram of FM Transmitter in detail.   

  10. (i)Explain the principle of operation of FM super heterodyne Receiver            (6)

            (ii) Derive the expression for PM wave.                                                         (6)

UNIT-3

       PART-A:

Define noise and mention the classifications of noise.

What is meant by thermal noise?

What is meant by shot noise?

What are the different types of man made noises which arise in the communication system.

Define noise figure.

Define noise temperature.

Define probability density function.

Give the Gaussian Probability density function.

Define fading.

What is the need of frequency domain representation of noise?

What is the signal to noise ratio at the output of DSB system coherent modulation?

 Find the thermal noise voltage developed across a resistor of 800W the bandwidth of the measurement instruments is 9Mhz and the ambient temperature is 31°C

What is Frii’s formula?

What is white noise?

Draw the In phase and Quadrature component of narrowband noise

Draw the block diagram AM receiver model

Mention the advantage of the noise in terms of Quadrature components.

List the properties of narrow band noise.

Define partition noise.

Classify the types of noise sources.

Define flicker noise.

Define equivalent noise resistance.

PART-B:

1. What are the different types of noise? Explain each of them.

2. What is narrowband noise? What are the two specific representation of a NB noise?

3. (i)Explain what is meant by effective noise temperature of cascaded amplifier.

(ii) Derive the relationship between noise figure and effective input temperature when two amplifiers are connected in cascade.

4. Explain in detail about shot noise and thermal noise.

     5. Obtain an expression for noise figure of CE amplifier.

Obtain an expression for noise figure of CB amplifier.

Derive the Quadrature and Inphase components of a narrowband noise

      8.  Obtain the Friis formula for effective noise figure of cascaded stages & express it in terms of noise temperature.

     

9.  Explain in detail about noise temperature & derive its expression.

     10.An amplifier has an input resistance of 1M Ohm.If the effective bandwidth of amplifier is 12 KHZ. Calculate the value of thermal noise voltage at the input terminal.     The temperature can be assumed to be 20 degree celcius.

 UNIT-4

       PART A:

How to achieve threshold reduction in FM receivers

What is FM threshold effect?

What is the (S/N) o / (S/N) I for AM envelope detector?

Draw the phasor representation of FM noise

What is the SNR for AM with small noise case?

Draw the block diagram of FM superhetrodyne receiver

Draw the block diagram of FMFB demodulator

Mention the figure of merit for FM receiver

Define signal to noise ratio.

Define figure of merit.

Define threshold effect.

What is capture effect in FM.?

What is the necessity of pre-emphasis and de-emphasis in FM receiver?

What are the advantages of super heterodyne receiver?

How to achieve threshold reduction in FM receiver?

Draw the phasor representation of FM noise.

What is the signal to noise ratio at the output of the DSB system in coherent detection?

Draw the noise spectrum of SSB-SC AM.

Differentiate between coherent & non-coherent detection.

Compare figure  of merits  for different types AM detectors.

        PART-B:

Obtain an expression for SNR of coherent reception of DSB-SC modulated wave.

Obtain an expression for SNR of AM system using envelope detector in the receiver.

Derive an expression for SNR in FM system.

Draw the block diagram of a super heterodyne receiver and explain the function of each block.

With the help of block diagram explain Pre-emphasis and de-emphasis.

Compare the noise performance of various continuous wave modulation system.

Derive the noise power spectral density of the FM demodulator and Explain its performance with diagram.

Explain the noise performance of SSB-SC AM system .

Explain the FM receivers model with the help of block diagram and determine the figure of merit.

     10. Define threshold effect and explain in brief.

     

 

 

 

 

 

 

 

 

UNIT 5

PART A

Define Information.

What do you mean by Entropy?

List the properties of Entropy.

State Shannon’s theorem.

Define coding efficiency.

Differentiate between Prefix code & Extended codes.

Mention the significance of Huffman coding.

What do you meant by discrete memory less channel?

Define Mutual information.

List the properties of Mutual Information

Define channel capacity.

Differentiate between source coding & channel coding.

State channel coding theorem.

Define code rate.

Define Information capacity.

Differentiate between Huffman coding & Shanon fano coding.

Determine the entropy for an equiprobable events

What is channel redundancy?

Name any two source coding techniques.

What is the capacity of the channel having infinite Bandwidths?

A source is emitting symbols x1, x2, & x3 with probabilities 0.5, 0.3, & 0.2 .what is the entropy of the source.

A source emits four symbols with probabilities P0=1/3, P1=3/8, P2=3/8 and P3=1/8. Find out the average information.

Write down the formula for the mutual information

An event has six possible outcomes with probabilities 1/2,1/4,1/8,1/16,1/32,1/32. Find the entropy of the system.

25. Explain the significance of the entropy H(X/Y) of a communication system               where X is the transmitter and Y is the receiver.

PART B        

Construct binary optical code for the following probability symbols using Huffman procedure and calculate code efficiency

 [0.2, 0.18, 0.12, 0.1, 0.1, 0.08, 0.06, 0.06, 0.06, 0.04]

Explain in detail Huffman coding algorithm and compare this coding technique with other coding techniques

Apply the Shannon fano coding procedure for the following message ensemble

                      [x]= { x1 x2 x3 x4 x5 x6 x7 }

                      [p]= {0.4, 0.2, 0.12, 0.1, 0.08, 0.06, and 0.04}

Derive the channel capacity for a continuous band limited white Gaussian noise channel.

Write short notes on a) Channel coding theorem b) Source coding theorem

A discrete memory less source has an output of seven symbols with probabilities for its output as given below:

Symbol	x1	x2	x3	x4	x5	x6	x7
Probability	0.4	0.2	0.12	0.08	0.08	0.08	0.04

Compute the Huffman code. Let the encoding alphabet be -101, M = 3. Find its efficiency.

  7.    Encode the following source using Huffman procedure and find the coding        efficiency.

Symbol	S0	S1	S2	S 3	S 4	S 5	S 6
Probability	0.25	0.25	0.125	0.125	0.125	0.0625	0.0625

                                              

8. Apply Shannon fano coding for the following message ensemble

X=	x 1	x 2	x 3	x 4	x 5	x 6	x 7
P=	0.4	0.2	0.12	0.08	0.08	0.08	0.04

Calculate its efficiency.

9. Write short notes on:i).Discrete memory less channel.                                       ( marks)

ii).Noise free channel.                                                               (5 marks)

10. Prove that

       i).H(X, Y) =H(X/Y) +H(Y)                                                       (6 marks)

       ii).H(X, Y) = H(Y/X) +H(X)                                                    (6 marks)