Analog Communication - Dec 2014

Electronics & Communication (Semester 5)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1(a) Show that the area under PDF curve is always equal to unity.(5 marks) 1(b) explain cross correlation functions. Give the properties of cross correlation function.(7 marks) 1(c) A three digit message is transmitted over a noisy channel having a probability of error $$P(E)=\frac{2}{5}$$ per digit. Find out the corresponding CDF.(8 marks) 2(a) Explain the generation of AM wave using square-law modulator along with relevant diagrams and analysis.(7 marks) 2(b) With a neat block digram.explain the balanced modulator method of generating DSB - SC wave.(7 marks) 2(c) Consider a message signal m(t) = 20 cos (2\pi t)volts and a carrier signal is c(t)= 50 cos $$(100\pi t )$$ volts.
i) Sketch to scale resulting AM wave for 75% modulation.
ii) Find the power delivered across a load of 100$$\Omega $$ due to this AM wave.(6 marks) 3(a) Define : i) Hilbert transform; ii) Pre - envelope.(8 marks) 3(b) With a neat digram,explain how SSB wave is generated using phase discriminator method with only USB and rejecting the LSB.(8 marks) 3(c) Find the Hilbert transform of a signal $$x(t)=cos2\pi f_{1}t\ sin \ 2\pi \ f_{2}t\ where f_{2}$$ is message signal and x(t) = cos 2?f₁t sin 2?₂ Where ₂ is message signal and f₁ is carrier signal.(4 marks) 4(a) Explain with relevant equations the working of envelope detection of USB wave plus carrier.(6 marks) 4(b) With a neat block diagram,explain the working of FDM technique.(7 marks) 4(b) With the block digram of super heterodyne receiver and specify the importance of IF value in the receiver.List the advantages of such receivers.(7 marks) 5(a) Derive the equation for FM wave. Define modulation index,maximum deviation and band width of a FM signal.(8 marks) 5(b) Explain FM generation using direct method.(7 marks) 5(c) An FM wave is defined by s(t) 10 cos (2-sin(6?t)),Find the instantaneous frequency of s (t).(5 marks) 6(a) Explain the working of a balanced slope detector used for FM demodulation.(7 marks) 6(b) Explain FM demodulation using zero crossing detectors.(5 marks) 6(c) With a neat block diagram, explain the working of FM stereo multiplexing and demultiplexing.(8 marks) 7(a) What is noise equivalent bandwidth? Derive an expression for the same.(8 marks) 7(b) Derive Friis formula for amplifiers connected in cascade.(8 marks) 7(c) An amplifier with 10db nose figure and 4db power gain is cascaded. With a second amplifier has a 10db power gain and 10db noise figure. What is the overall noise figure and power gain?(4 marks) 8(a) Derive the equation for output signal to noise ration for a DSB - SC system.(7 marks) 8(b) Explain the working of pre-emphasis and de-emphasis in FM.(6 marks) 8(c) Show that the signal to noise ratio of the output for a single tone FM is given by $$SNR_{0}=\frac{3E^{2}_{c}(mf)^{2}}{4\ No\ W}$$ Where the symbols have usual notations.(7 marks)