Reg. No.

MANIPAL INSTITUTE OF TECHNOLOGY(Constituent Institute of Manipal University)

Manipal – 576 104

SIXTH SEMESTER BE (E&C) DEGREE END SEMESTER EXAMINATION

MAY/JUNE - 2008

SUBJECT: COMMUNICATION SYSTEMS(ECE-304) (REVISED CREDIT SYSTEM)

TIME : 3 HOURS MAX. MARKS : 50

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Instructions to candidates

•  Answer ANY FIVE full questions.

•  Missing data may be suitably assumed

1A. A Geostationary communication satellite has an uplink frequency of 6 GHz with an

antenna elevation of 50. Transmitter power is 1 KW. If transmitting antenna gain is

60 dB and receiving antenna gain is 0 dB, calculate the received power at the input

of satellite receiver.

1B. A GaAs laser operating at 850nm has 500µm length and refractive index 3.7. What

are the frequency and wavelength spacing? If at the half power point λ  – λ  p =2nm,

what is the spectral width of gain? (5+5)Marks

2A. Explain the principle and working of LED source which has highly directional

emission pattern.

2B. With a neat block diagram explain the architecture of GSM system. (4+6)Marks

3A. With a neat block diagram explain basic cellular system. Also list the difference

 between macro cell and micro cell.

3B. An optical fiber has the following parameters. Core refractive index=1.55, cladding

refractive index = 1.51 and core diameter = 50µm. If light is launched into this fiber

from a medium of refractive index 1.32, find the numerical aperture and maximum

acceptable angle . If the fiber is to be used at an operating wavelength of 800nm,

determine the V number and the number of modes supported. (5+5)Marks

 

 

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4A. Calculate the maximum transmission distance for a fiber link with an attenuation of

0.5 dB/Km if the power launched is 1mW and the receiver sensitivity is 50µW.

4B. With a block diagram explain the cordless Telephone system

4C. With neat diagrams explain the display systems used in Radar. (2+4+4)Marks

5A. Derive an expression for maximum range of Radar and discuss the different factors

that determine the performance of the Radar.

5B.Derive an expression for the system Noise temperature in terms of relevant

 parameters. Hence find the system noise temperature of the given system below:

TIN = 50K, GRF = 23 dB, TRF =50 dB, GM =0 dB

TM = 500K, GIF = 30 dB, TIF = 1000K,

Operating frequency of the receiver is 8 GHz. (6+4)Marks

6A. A Ga0.47In0.53As pin photodiode with a cross-sectional area of 0.1mm2 produces a

 photocurrent of 0.996µA when illuminated by a beam of 1.3µm wavelength and

1mW/cm2 intensity. Calculate (i) the quantum efficiency and (ii) photocurrent at

1.5 µm and 1.7µm wavelengths.

6B. With an example and graph explain Power budget in an optical fiber

communication link. (5+5)Marks

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