rr322205 communication systems

Code No: RR322205 Set No. 1

III B.Tech II Semester Supplementary Examinations, Aug/Sep 2006COMMUNICATION SYSTEMS

(Instrumentation & Control Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

1. (a) State and prove total probability theorem.

(b) Give the classical and axiomatic definitions of probability.

(c) List the axioms of the probability. [8+4+4]

2. (a) Define Telemetry and Telecontrol.

(b) Draw the block diagram of Telemetry and explain about each block clearly.[4+12]

3. The efficiency of a ordinary AM is defined the percentage of the total powercarried by the sidebands, that is =Ps/Pt x100%. Where Ps is the power carriedby the sidebands and Pt is the total power of the AM signal

(a) Find for the =0.5

(b) Show that for a single tone AM max is 33.3% at =1. [8+8]

4. (a) For an FM modulator with an unmodulated carrier vc=20V, a modulationindex m=1,and a load resistance RL=10, determine the power in the modu-lated carrier and each side frequency, and sketch the power spectrum fort hemodulated wave.

(b) Describe the significance of the FM noise triangle. [10+6]

5. (a) What is meant by Natural Sampling and how it differs from Flattop Sampling?explain

(b) For the Modulating signal m(t)=4cos80t+20cos1000t,determine the allow-able Sampling rates and sampling intervals. [8+8]

6. (a) Consider a speech signal with maximum frequency of 3.4KHz and maximumamplitude of 1 volt. This speech signal is applied to a delta modulator whosebit rate is set at 20 kilobits/sec. Discuss the choice of an appropriate step sizefor the modulator.

(b) Write about the Slope Overload Error present in DM. [10+6]

7. (a) Explain QAM error performance?

(b) Which system require the highest Eb /N0 ratio for a probability of error of106, a four level QAM system (or) an 8-PSK system. [10+6]

8. Explain ON OFF signaling and show that it requires twice as much power aspolar signaling. [16]

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1. (a) A random variable X is Gaussian with zero mean and variance x2. A randomvariable Y is given by Y= b+X. show that Y is also a Gaussian variable withdifferent mean and same variance, where b is a constant.

(b) Determine the mean and variance of the following density functions

i. f(x) =1/2 e(x5)2/2 , xf(x)

ii. f(x) =1/a , -a/2xa/2 [8+8]

2. (a) Explain why Hydraulic Systems are used rather than Pneumatic Systems inIndustrial Environment.

(b) Explain the disadvantages in Electrical Telemetry System. [16]

3. (a) Explain the generation of VSB modulated wave. With neat diagram also drawthe response of Side band shaping filter.

(b) Explain the demodulation of DSB-SC wave by using Costas-loopmethod.[8+8]

4. (a) In an FM system, the modulating signal m(t)=2.4Cos(1000t) and the fre-quency deviation is 4.8 KHz. If the amplitude of the modulating signal is nowincreased to 7.2V, what is the new deviation? Find the modulation index ineach case.

(b) For the balanced ring modulator circuit the carrier input frequency is fc=500KHzand modulating input signal frequency ranges from 0 to 5KHz.Determine out-put frequency range and output frequency for a single input frequency of3.4KHz. [8+8]

5. (a) What is meant by Intersymbol interference (ISI)? And how it differs from crosstalk in the PAM ?

(b) Explain the Basic Principles of Sampling and Practical Sampling. [8+8]

6. (a) Pulse Modulation Systems are not digital, whereas pulse code modulationis Justify?

(b) What is quantization error? How does it depend upon the step size, suggestsome steps to overcome it. [8+8]

7. (a) What is the difference between standard FSK and MSK? What is the advan-tage of MSK.

(b) What is the constellation diagram and how it is used with PSK? [8+8]

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8. (a) Calculate the baud rate for the given bit rate and type of modulation.

i. 2000 bps ,FSK

ii. 4000 bps,ASK

iii. 6000 bps,BPSK

iv. 6000 bps,16 QAM.

(b) Calculate the baud rate for the given bit rate and bit combination. [8+8]

i. 2000 bps , dibit

ii. 6000 bps,tribit

iii. 6000 bps,quad bit

iv. 6000 bps ,bit.

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1. (a) Explain the probability density function. List its properties [10]

(b) Fins the value of constant A so thatf(x)= Ax3 (1-x3), 0< x


6. (a) Pulse Modulation Systems are not digital, whereas pulse code modulationis Justify?

(b) What is quantization error? How does it depend upon the step size, suggestsome steps to overcome it. [8+8]

7. Discuss the bit error performance for the various multiphase digital modulationSystems(PSK,QAM,FSK). [16]

8. How many amplitude levels are there for each of the following methods? [16]

(a) Unipolar

(b) NRZ L

(c) NRZ I

(d) RZ

(e) RZ

(f) Manchester

(g) Differential Manchester.

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rr322205 communication systems

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