JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II ANALOG COMMUNICATIONS Previous Question Paper (December - 2017 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
What is modulation?
Answer
Modulation is the process of varying one or more parameters of a high-frequency carrier signal, such as amplitude, frequency, or phase, in accordance with the instantaneous values of a low-frequency message signal (baseband signal).
Describe the power relations in AM waves.
Answer
In an AM wave, the total power is the sum of carrier power and sideband power. The total power is given by:
where Pc is the carrier power and μ is the modulation index. The sideband power is Psb = Pc(μ2/2), meaning at 100% modulation, the sidebands contain only one-third of the total power.
Draw the spectrum of SSB modulated signal.
Answer
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Write the expressions for SSB and VSB waves.
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What is wideband FM and Narrowband FM?
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Draw the phasor diagram of FM signals.
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What is noise? List the various noise sources.
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Write the SNR expression for FM and AM.
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Write the merits and demerits of PAM.
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Give the working principle of super heterodyne receiver.
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Part B
Explain the generation of AM wave using square law modulator with relevant equations and spectrum.
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Explain the operation of the Ring modulator circuit which generates the DSBSC waves.
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Describe the working of a balanced Modulator.
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The efficiency of AM wave is defined by
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Derive an expression for SSB modulated wave for which upper side band is retained.
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What is vestigial side band? Explain the process of generation and detection of VSB modulated wave using a carrier
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With a neat block diagram explain direct method of generating FM wave. Discuss how wide band FM can be generated using this method.
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Explain in detail about FM demodulation using PLL.
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Define white noise and plot the power spectral density (PSD) and auto correlation function (ACF) of white noise.
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Define and explain the following and then obtain the relation between them: i) Noise figure ii) Equivalent noise temperature.
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The carrier amplitude of 1 volt, RMS is available at the input of envelope detector, along with the noise PSD of 10-3 watts/Hz. If the carrier is modulated to a depth of 100% and message B.W, W=3.2KHz, then determine (SNR)0. Derive the relation used.
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Explain the demodulation procedure for PWM signal demodulation.
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Describe how different signals can be multiplexed using TDM system?
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Explain working of TRF receiver.
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What is simple automatic gain control? What are its functions?
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