JNTU
JNTU B.Tech III ANALOG COMMUNICATIONS Previous Question Paper (November/December - 2018 - R13)
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.
PART - A
What are the advantages of FM over AM?
Answer
The primary advantages of FM over AM are significantly better noise immunity and higher efficiency. Since information is encoded in frequency variations rather than amplitude, FM is less susceptible to amplitude-based interference and fading.
Write the equations for FM and PM signals and show the difference.
Answer
The FM signal is defined as:
The PM signal is defined as:
The difference is that in FM, the instantaneous frequency deviation is proportional to the message signal m(t), whereas in PM, the instantaneous phase deviation is proportional to the message signal m(t).
Why pre-emphasis and de-emphasis are required in FM system.
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Draw the Vestigial side band system and state the advantages.
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Draw the zero crossing detectors.
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What are the applications of PLL?
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Define sensitivity and selectivity of a receiver.
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Give the expression for noise voltage in a resistor.
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Draw the PAM and it’s corresponding PWM signal.
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Explain the need of AGC.
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PART - B
Derive the expression for AM wave. Define modulation index and express its value in terms of maximum and minimum voltage values of signal.
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An AM modulation has the following: X(t)=10(1+5 Cos2000t)volts. Considering one ohm load and find Side-band power and Modulation Index.
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Explain the coherent detection of DSB-SC wave and the effect of phase and frequency errors on the demodulated output.
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A commercial AM station broadcasts an AM signal at 70.7% modulation. Find the transmission efficiency.
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Briefly explain the comparison of AM techniques and write the applications of different AM systems.
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Explain the significance of vestigial sideband modulation with suitable application. And write the characteristics of the VSB filter.
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Find the percentage of power saving by transmitting SSB wave with respect to DSB-FC wave at 100% tone modulation.
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Explain the phase discrimination method of generating VSB signals with neat diagram.
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Compare the phaser diagrams of narrow band FM signal and AM signal and discuss about the similarities and differences of two signals.
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A carrier wave of frequency 100 MHz is frequency modulated by a sine wave of amplitude 20V and frequency 100 KHz. The frequency sensitivity of the modulator is 25 KHz/V. Determine the approximate BW?
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Explain in detail about capture effect in FM.
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Draw the block diagram and explain the generation of WBFM using indirect method.
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Derive the output SNR of DSB-SC demodulator under noise conditions. Explain the effects.
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An AM receiver, operating with a sinusoidal modulating wave and 80% modulation, has an output SNR of 30dB. What is the corresponding CNR?
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Compare the noise performance of various analog modulation systems. Draw the corresponding graphs. Derive an expression for SNR at the destination for PM and compare this with that of FM.
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Derive the expression for the Noise figure and Noise temperature.
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Explain the operation of Amplitude Limiter with neat diagram.
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What is the difference between Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM). Explain FDM system with neat sketch.
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Find the minimum channel bandwidth required to time division multiplex three signals band limited to 1.8KHz, 3.6KHz and 7.2KHz respectively.
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Explain the terms: i) Automatic Gain Control (AGC), ii) Amplitude limiting, iii) Squelch circuit.
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