Analog Communication - Dec 2015

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) Describe mean, correlation and covariance functions with respect to stationary random process.(6 marks) 1 (b) State and discuss central limit theorem.(8 marks) 1 (c) Let X be a continuous random variable having a uniform probability distribution defined in the range 2≤x≤4. Let y=3X+2. Find the means m_x and m_y.(6 marks) 2 (a) Explain the need for modulation.(6 marks) 2 (b) Describe the generation of AM wave using square law modulator with mathematical analysis.(8 marks) 2 (c) The antenna current of an AM transmitter is 8 amps, when only the carrier is sent. But it increase to 8.93 amps, when the carrier is modulated by a single sine wave. Find the percentage modulation. Determine the antenna, when the percentage modulation changes to 0.8.(6 marks) 3 (a) What is Hilbert transformation? Derive the expression for impulse response of the Hilbert transformer.(7 marks) 3 (b) Write the canonical representation of band pass signal and derive the expression for time function of SSBSC waveform.(8 marks) 3 (c) Calculate the percentage power saving when the carrier and one of the sidebands are suppressed in an AM wave modulated to a depth of (i) 100% and (ii) 50%.(5 marks) 4 (a) With neat block diagram, explain the generation of VSB wave by phase discrimination method.(7 marks) 4 (b) Discuss envelope detection of VSB plus carrier.(6 marks) 4 (c) Explain the transmission of a number of independent signals over a single communication channel by modulating different carrier signals.(7 marks) 5 (a) Explain the generation of wide band frequency modulated wave by Armstrong method.(7 marks) 5 (b) A 100 MHz carrier wave has a peak voltage of 5 volts. The carrier is frequency modulated by a sinusoidal modulating waveform of frequency 2 KHz such that the frequency deviation is 75 KHz. The modulated wave form passes through zero and is increasing at time t-0. Write the expression for frequency modulated signal.(5 marks) 5 (c) Show that the spectrum of FM contains infinite number of side bands.(8 marks) 6 (a) With neat schematic and frequency response, explain the operation of balanced discriminator for demodulation of FM wave.(7 marks) 6 (b) With relevant mathematical analysis, explain reconstruction of message signal form FM wave by PLL.(8 marks) 6 (c) Discuss non linear effects in FM systems.(5 marks) 7 (a) What are the types of noise, which affect communication system? Explain thermal noise in detail.(7 marks) 7 (b) An amplifier operating over the frequency range of 450 KHz to 460 KHz is having a input resistance of 75 KΩ. If the temperature is 15°C, find :
i) The RMS noise voltage at the input to the amplifier.
ii) The amplifier noise power.
iii) Power spectral density.(6 marks) 7 (c) Discuss the noise factor of amplifier in cascade and obtain the Friss formula.(7 marks) 8 (a) Show that the figure of Merit of SSBSC system is unity.(8 marks) 8 (b) Discuss threshold effect in FM receiving system.(4 marks) 8 (c) Explain in detail the pre-emphasis and de-emphasis in frequency modulation.(8 marks)