## 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)