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Code No: RA322205

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III B.Tech II Semester Regular Examinations, Apr/May 2009 COMMUNICATION SYSTEMS (Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ?????

(a) Each pulse of duration T0 (b) Pulses are equally likely to be ± 1. (c) All pulses are statistically independent

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1. Consider a random binary waveform that consists of a sequence of pulses with following properties

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(d) The pulses are not synchronized, that is the starting time T of the first pulse is equally likely to be anywhere between 0 and T0 Find the autocorrelation and power spectral density function of X(t).

[16]

2. (a) Define Telemetry and Telecontrol.

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(b) Mention various Types of Telemetry Systems and give some differences of that Telemetry Systems. [4+12]

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3. Show that the system shown in the figure 3 is used to demodulate AM signals. This is a full wave square law rectifier arrangement. Show that the low pass filter in this arrangement must have a cutoff frequency 2ωm . Where ωm is the highest frequency in the message signal f(t).

Figure 3 In general show that the arrangement acts as a envelope detector. Hence it can not demodulate suppressed carrier signals. [16]

4. (a) v(t)=Cos ωc t+ 0.2 Cos ωm t Sin ωc t i. Show that v(t) is a combination AM-FM signal. ii. Sketch the phasor diagram at t=0

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Code No: RA322205

(b) A carrier is frequency modulated by a sinusoidal modulating signal of frequency 2KHz resulting in a frequency deviation of 5KHz.What is the bandwidth occupied by the modulated waveform? The amplitude of the modulating sinusoid is increased by a factor of 3 and its frequency lowered to 1KHz. What is the new bandwidth? [10+6]

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5. (a) What is meant by Intersymbol interference (ISI)? And how it differs from cross talk in the PAM ? (b) Explain the Basic Principles of Sampling and Practical Sampling.

[8+8]

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6. (a) With suitable Block diagram, waveforms explain the principle and operation of Adaptive Delta Modulation.

(b) Explain how Adaptive Delta Modulation overcomes the drawbacks of Delta Modulation with suitable equations and wave forms? [10+6]

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7. (a) Binary data is transmitted over a RF band pass channel with a usable bandwidth of 10MHz at a rate of 4.8x106 bits per second using and ASK signaling method. The carrier amplitude at the receiver antenna is 1mV and the noise power spectral density at the receiver is 10−5 watts/Hz i. Find the error probability of a coherent receiver and ii. Find the error probability of a non coherent receiver

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(b) Derive an expression for the probability of bit error in a PSK system. [10+6] 8. Explain ON OFF signaling and show that it requires twice as much power as polar signaling. [16]

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