Seat No.: ________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER–V • EXAMINATION – SUMMER 2013
Subject Code: 151004
Subject Name: Electronic Communication
Time: 10.30 am - 01.00 pm
Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
(a) Derive Friiss formula for noise factor of cascaded amplifier.
(b) Prove that ESD of any signal g(t) is the fourier transform of the 07 autocorrelation function Rg(.)ح
(a) Draw the circuit diagram of capacitive tap and derive the equation for 07 transfer impedance.
(b) Explain Double-conversion superhetrodyne receiver using block diagram. OR
(b) Explain Automatic Gain Control using necessary circuit diagram.
(a) With the help of neat diagram and waveform explain the operation of 07 envelop detector.
(b) Explain the indirect method of FM generation. (Armstrong method). 07
(a) Draw the circuit diagram of ring modulator using diode and explain its 07 operation.
(b) Explain FM detection using PLL.
(a) state and prove the following properties of Fourier transform: (1) Time shifting (2) Frequency shifting
(b) An audio signal 15sin2ᴨ (1500t) amplitude modulates a carrier 60 sin2ᴨ 07 (100,000t).
i) Sketch the audio signal.
ii) Sketch the carrier.
iii) Construct the modulated wave.
iv) Determine the modulation index and percentage modulation. v) What are the frequencies of the audio signal and the carrier? OR
(a) Determine the fourier transform of rectangular pulse shown below.
(b) A 107.6 MHz carrier is frequency modulated by a 7 KHz sine wave. The 07 resultant FM signal has a frequency deviation of 50 KHz.
i) Find the carrier swing of the FM signal.
ii) Determine the highest and lowest frequencies attained by the modulated signal.
iii) What is the...
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