IT-404 Analog & Digital Communication - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDraw and label the basic components of a communication system. Explain the function of each block in detail.
   How to answer

   • Block diagram of communication system with labels: source, transmitter, channel, receiver, destination
   • Function of information source and input transducer
   • Function of transmitter, channel/noise, receiver and output transducer
   • Signal flow from source to destination
2. 7 Marks
   bWhat do you understand by signal, How do you determine whether a signal is analog or digital? What are the key differences between them?
   How to answer

   • Definition of signal as function carrying information
   • Criteria to decide analog vs digital: continuity, discrete values, time
   • Key differences in table: bandwidth, noise immunity, representation
   • Examples of analog and digital signals
3. 7 Marks
   aFind the Fourier Transform of the following function:

   1. i)Gate
   2. ii)Unit Step
   3. iii)Delta
   How to answer

   • Definition of Fourier Transform formula
   • Fourier Transform of gate function as sinc function
   • Fourier Transform of unit step including impulse plus 1/jw term
   • Fourier Transform of delta function as unity
4. 7 Marks
   bAn audio frequency signal $10 \sin 2*3.14*500t$ is used to amplitude modulate a carrier of $50 \sin 5*3.14*10^5t$. Calculate:

   1. i)Modulation index
   2. ii)Side band frequencies
   3. iii)BW required
   4. iv)Total power delivered to the load of 600
   How to answer

   • Identify message amplitude/frequency and carrier amplitude/frequency
   • Calculate modulation index $m = A_m/A_c$
   • Calculate USB, LSB and bandwidth $BW = 2f_m$
   • Calculate total power delivered to 600 ohm load
5. 7 Marks
   aExplain the concept of double-sideband suppressed carrier (DSB-SC) modulation. What are its advantages and disadvantages compared to conventional AM?
   How to answer

   • Expression and spectrum of DSB-SC signal
   • Generation principle using balanced modulator
   • Advantages: power saving, bandwidth same as AM
   • Disadvantages: complex demodulation, no carrier for sync
6. 7 Marks
   bWith the help of block diagram explain the working of TRF receiver.
   How to answer

   • Block diagram of TRF receiver: RF amplifier, detector, audio amplifier
   • Function of tuned RF stages and selectivity
   • Demodulation and audio amplification stages
   • Limitations leading to superheterodyne
7. 7 Marks
   aIn angle modulation, explain frequency deviation, percent modulation, phase deviation and modulation index with suitable example.
   How to answer

   • Definitions of frequency deviation, phase deviation in angle modulation
   • Concept of percent modulation and modulation index for FM/PM
   • Relation $m_f = \Delta f/f_m$
   • Suitable numerical example
8. 7 Marks
   bDiscuss the operation of a Foster-Seeley discriminator as an FM demodulator with suitable diagram.
   How to answer

   • Circuit diagram of Foster-Seeley discriminator with double-tuned transformer
   • Vector phasor operation above, at and below resonance
   • S-curve output vs frequency characteristic
   • Role as FM demodulator
9. 7 Marks
   aDiscuss the advantages and disadvantages of the direct method compared to the indirect method of FM generation.
   How to answer

   • Principle of direct method using VCO/reactance modulator
   • Principle of indirect Armstrong method using phase modulation
   • Advantages of direct: simplicity; disadvantages: frequency stability
   • Comparison table of stability, complexity, noise
10. 7 Marks
    bState and prove Sampling theorem.
    How to answer

    • Statement of sampling theorem for low-pass band-limited signals
    • Proof using impulse sampling and Fourier Transform
    • Nyquist rate and Nyquist interval $f_s \ge 2f_m$
    • Aliasing and reconstruction condition
11. 7 Marks
    aDraw the block diagram and waveform of Adaptive Delta Modulator and explain in detail. What are the advantages of this modulator over Delta Modulator?
    How to answer

    • Block diagram and waveforms of Adaptive Delta Modulator
    • Working with variable step-size adaptation logic
    • Explanation of slope overload and granular noise reduction
    • Advantages over Delta Modulator
12. 7 Marks
    bFor a PCM system with the following parameters, determine:

    1. i)Minimum sampling rate
    2. ii)Minimum number of bits used in the PCM code
    3. iii)Resolution
    4. iv)Quantization error
    How to answer

    • Minimum sampling rate from Nyquist $f_s = 2f_m$
    • Minimum bits from dynamic range $DR = 1.76+6.02n$
    • Resolution $\Delta = 2V_{max}/2^n$ and quantization error $\Delta/2$
    • Substitution for 4 KHz, ±2.55 V, 46 dB
13. 7 Marks
    aDefine the phase shift keying and explain the working of BPSK transmitter and Receiver with necessary diagram.
    How to answer

    • Definition of PSK and BPSK phase shifts 0 and 180 degrees
    • Block diagram of BPSK transmitter with balanced modulator
    • Block diagram of coherent BPSK receiver
    • Waveforms and working explanation
14. 7 Marks
    bFor a 16QAM modulator with an input data rate equal to 10Mbps and a carrier frequency of 70MHz, find the minimum double sided Nyquist frequency and the baud.
    How to answer

    • Relation between bits, symbols for 16-QAM: 4 bits per symbol
    • Baud rate = bit rate / 4
    • Nyquist bandwidth calculation
    • Minimum double-sided Nyquist frequency
15. 14 Marks
    Write a short note on any two:

    1. a)Time and Frequency Convolution Theorem
    2. b)Selectivity and Fidelity of receivers
    3. c)Time Division Multiplexing
    4. d)QAM
    How to answer

    • Brief definition and principle of chosen topics
    • Relevant formulas/diagrams for each note
    • Advantages/applications
    • Concise conclusion