Mumbai University Previous year question papers
IV Sem IT Examination June 2010
Principles of Communication
N.B.: (1) Question No 1 is compulsory.
(3) Figuresto the right indicatefull marks.
.(4)Assumesuitable data wheneverrequiredbut justify the same.
1. Attempt any four of the followings-
a) Describe three different ways in which the modulation index of an AM signal can be measured.
b) What is the quantisation process in PCM? Defme quantisation error.
c) Explain VSBtechnique of transmission.
d) State and prove sampling theorem.
e) Compare TDM andFDM.
2. (a) Define noise figure. Derive the ftiiss formula for the calculation of the .totalnoise figure for two amplifierconnectedin cascade. (10)
(b) In an AM receiver having no RF stage, the loaded Q of the aerial coupling circuit is 125. If the intermediate ftequency is 465 KHz, Find-
(i) The image ftequency and its rejection at 1MHz and 30 MHz.
(ii) The IF required to make the image rejection ratio as good at 30 MHz as it is at 1MHz. ,.
3. (a) In anFMsystem,the audioftequencyis 1KHz and the audio Voltage is 2 Volts. The deviation is 4 KHz. If the AF voltage is now increased to 8 volts and its .ftequency dropped to 500 Hz, fmd the modulationindexin each case and approximatebandwidthof the signal.
(b) Prove the following properties of the Fourier Transform-
(i) Time shifting;
(ii) Convolution in time domain.
(c) What are the energy signals and power signals? Give the examples }n each case.Howdo you representit in ftequencydoma.in? (06)
4. (a) Sketchthe circuitof a practicaldiodedetectorand explain its working. What is Negative peak clipping? Calculate the :maximum modulation index that the above detector can tolerate without causing negativepeak clipping.
(b) An amplitude modulated waveform has a form-
Xc(t) = [ 10( 1+ 0.6 Cos 20001tt+ 0.4 Cos 40001tt)Cos 20,0001tt}];
(i) Sketchthe amplitudespectrumofXc(t).
(ii) Find the power cop.tentof each spectral component including c~r1’ler.
(iii)Find the total power and sideband power.
(iv) What-is the modulation index?
5. (a) ‘What is multiplexing in communication system? Draw the block(IO) diagram of TDM-PCM system, Explain each block. Also calculate the bit rate at the output of this system.
(b) Draw the circuit diagram of a Foster- Seeley Phase discriminator and explain its Principle of operation with the help of relevant waveform.
6. ‘(a) Draw the block diagram of phase cancellation SSB generator and explain how the Carrier and unwanted sidebands are suppressed. What change is necessary to suppress the other sidebands?
(b)Explain with the help of block diagram of adaptive delta modulation (ADM) for generating digital modulated signal. Why it is preferred over delta modulation? (10)
7. Write short notes on any four of the followings-
(i) Optical Fiber Communication Systems.
(ii) Internationalstandardsfor communicationsystems and assignments.
(iii) Satellite Communication System.
(v) Multiplexing Techniques in Satellite, Optical Communication and Wireless Communication.