User:Sgokhale/Temp/TMA -1 (2006).doc

1.State with reasons whether following statements are True or False.

i) Sound wave (longitudinal wave) propagation is most preferred mode in modern communication systems.

ii) Sampling frequency should be lower than the frequency of the signal to be sampled.

iii) Energy signal is periodic type of signal.

iv) Signal to Noise ratio (SNR) can be improved only by hardware techniques.

v) Metallic waveguides are commonly used to carry optical signal.

vi)Efficient transmission occurs when reflection coefficient is equal to 1.

vii)Modulation techniques help in making long distance communication more realistic.

viii)Digital modulation is more effective than analog modulation in the environment with large electromagnetic noise.

ix) Telephone in our house uses half duplex mode of communication.

x)Multiplexing and multiple access is essentially one and the same technique.

2.(a)Explain with suitable diagram, how a parallel signal generated by a picture/scene is transformed into serial form to make it suitable for communication.

(b)Justify the need of non-linear electronic devices in communication circuits.

(c)What are different types of free space transmission?

3.(a)Why repetitive signals are preferred for testing/characterising a communication circuit?

(b)What is the largest decade number than can be represented by 10 binary bits?

(c)Explain with example, how addition of redundant bits helps in error detection in digital communication.

(d)Calculate the Shanon’s limit of channel capacity for bandwidth of 1GHz with SNR of 2047.

4.The field of a laser in dielectric, in MKS unit is. Write down the frequency, wave vector, wavelength, phase velocity (vph) and the equation of wavefront.

5.(a)What is the necessity of matching techniques in case of a transmission lines? Explain how the position of stub is determined in stub matching method.

(b)What is a non-resonant transmission line?

6.(a)An amplitude modulated carrier wave is viewed on an oscilloscope screen. The maximum amplitude is 50V and minimum amplitude is 8V. Calculate the percentage modulation index. What is the amplitude of unmodulated carrier wave?

(b)Describe with suitable diagram any one method of implementing frequency modulation.

7.(a)Design a circuit, with proper devices used as keys, to implement an FSK generator which gives out frequency f0 for binary value 0 and f1 for binary value 1.

(b)Explain with suitable diagram a circuit to convert a pulse width modulated signal in to pulse position modulated signal.

(c)Draw a bipolar non-return to zero and Manchester code for 101100011 data. (Indicate clock pulses also as reference).

8.(a)A telephone service provider has to provide about 1000 connections in an area of 20 km radius around its exchange. What are various possible ways to achieve this task?

(b)Draw a structure of cells in mobile telephony where the frequency allocation is such that there is separation of at least two cells between the cells that reuse the same frequency.

(c)What are the advantages of electronic switching system over electromechanical switching system?(2)

9.(a)If eight channel video signals are to be sent over a TDM system using PAM, what will be the sampling frequency and duty cycle of sampling pulses? What will be the quite time between the samples from two consecutive channels?

(b)If three supermaster groups constitute a hyper group with 880 kHz band gap between two supermaster groups: i) Calculate the number of voice channels contained in a hyper group; ii) Draw the modulation plan for hyper group (using lower side bands) beginning with lowest frequency at 18000 kHz; (iii) What is the bandwidth of a hyper group?

(c)Why the space division multiplexing is usually used in combination with time division multiplexing?

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