JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III ANALOG COMMUNICATIONS Previous Question Paper (July/August - 2023 - R13)
Answer any five questions. Part A is compulsory, which carries 25 marks. In Part B, Answer any one question from each unit.
Part A
Define modulation index for AM.
Answer
The modulation index (μ) of an AM wave is defined as the ratio of the peak amplitude of the modulating signal (Am) to the peak amplitude of the unmodulated carrier signal (Ac). It represents the extent of amplitude variation in the carrier.
A 300 W carrier is modulated to a depth of 60%. Determine the total power in the modulated wave.
Answer
Given Pc = 300 W and μ = 0.6. The total power Pt in an AM wave is given by:
Substituting the values:
Distinguish the bandwidth of modulated wave in DSB-SC and SSB.
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Derive the expression for the percentage power saving in AM-SSB-SC with respect to AM-DSB-FC under tone modulation.
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What is a limiter?
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With block diagram, show how FM can be obtained using PM.
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Define noise temperature.
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What is noise? List out various noise sources.
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Explain the concept of intermediate frequency in receivers.
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What is the advantage of PPM over PWM and PAM?
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Part B
Explain the working principle of nonlinear DSB-SC modulator with neat block diagram.
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Develop the equation of a single tone modulation of AM system.
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Describe the coherent detection of DSB-SB modulated waves.
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An audio signal m(t) = 10Sin(1000πt) is used to modulate a carrier of c(t) = 50Sin(2π105t). Calculate bandwidth and power delivered to a load of 600Ω in case of AM and DSB-SC.
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Derive the time domain description of a single sideband suppressed carrier wave.
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Explain VSB. What is the need for VSB transmission? What is the transmission bandwidth of VSB?
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Compare DSB-FC, DSB-SC, SSB-SC and VSB.
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Why VSB modulation is used in TV broad casting? Give the VSB filter characteristics with spectrum.
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Explain the Armstrong method of FM generation.
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An angle modulated signal is given by: S(t) = cos 2π(2×106t + 3 sin150t + 40cos150t). Determine the maximum frequency and phase deviations of S(t).
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Explain the Foster Seeley discriminator method of FM demodulation.
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Consider the frequency modulated signal S(t) = 10 cos [2π×105t + 5sin(2π×1500t) + 7.5sin(2π×1000t)] with carrier frequency of 105 Hz. Determine the modulation index.
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Derive the noise figure for cascade stages.
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Derive expressions for SNR and figure of merit in AM receivers.
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Derive expressions for SNR and figure of merit in FM reception.
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Draw the phasor representation of FM noise.
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List and define the performance parameters of radio receivers in detail.
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Explain the synchronization procedure for PWM and PPM signals.
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Explain generation and detection of PWM and PPM signals.
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