Model question paper

 

III Semester MSc Degree Examination, November 2002

Branch II Physics

PH233E ELECTRONICS –I

Duration: 3 hours

Max. Mark: 75                                     

Part A

(Answer any five questions. Each question carries 3 marks.)

 

I a)  What do you mean by solitons? How can you employ them in a communication system?

 

b)       What do you understand by interfaced scanning? Show how it reduces flickering and conserves band width.

                                                                       

c)       What do you understand by vertical and horizontal resolution? Show that the highest modulating frequency that needs to the handled in the 625 TV system is 5 MHz.

 

d)       Discuss the advantage of coherent optical communications.

 

e)       Outline the importance of optical fibers in the present ‘information age’.

 

f)        Distinguish between positive and negative modulation.  Why is negative modulation preferred for TV transmission?

 

g)       Discuss pulse modulation and explain how pulse amplitude modulation is achieved.

 

h)       Explain the characteristics of frequency modulated wave and compare it with an amplitudemodulated wave.

                                                                                                  

 

Part B

(Answer all questions. Each question carries 15 marks.)

 

 

IIA.         Describe the basic operation of an SSB generation and reception receiver using block diagram.  What is the importance of balanced modulator in communication?

 

Or

 

IIB.          Describe the basic operation of an FM receiver using block diagram.  What is a discriminator?                                                                                                                                                         

 

IIIA.        With the help of a block diagram describe the working of a monochrome television transmitter.  What additional feature incorporated to convert a B/W transmitter into a color TV transmitter?

 

Or

 

IIIB.        Explain in detail the basic principle of RADAR and derive the necessary equation. Discuss in detail about hyperbolic systems of navigation.

 

 

IVA.        Describe the construction and working of a digital optical communication receiver.

Or

IVB.        Outline the important features of the design and operation of a cellular communication system.

               

 

Part C

(Answer any three questions. Each question carries 5 marks.)

 

V.    (a)    The rms antenna current of an AM radio transmitter is 10A when unmodulated and 12A when modulated. Calculate the modulation     index. 

              

(b)     A 30 km optical fibre has an attenuation of 0.8 dB/km at a wavelength of 1300 nm. Find the output optical power through the fibre if the input power is 200 mW.

 

(c)     In an FM wave, the modulating frequency is 2 kHz and the maximum frequency deviation is 10 kHz. If there are 8 significant pair of side bands, find the theoretical and practical bandwidth required.

 

(d)     What is the power developed by an AM wave in a load of 100 ohm, when the peak voltage of the carrier is 100V and the modulation factor is 0.4?

 

(e)     Calculate the width of the depletion region of a photodiode if the transit time of the charge carriers drifting with a speed of 10⁷ cm/s is 100 ps.  Find also the bandwidth of operation of the above diode.

 

(f)      In a PCM system, there are four quantized levels of probabilities 1/2, 1/4, 1/8 and 1/8, respectively. Find its entropy. If the input is 50 Hz continuous signal sampled at Nyquist rate, calculate the sample rate.