Punjab University 2005 B.Tech Electronics and Communications Engineering COMMSIGNALS AND SYSTEMS - Question Paper

EC 202 fourth Sem May 2005
COMM. SIGNALS AND SYSTEMS
Note: part A is compulsory. Attempt any 4 ques. from part B and any 2 ques. from part C.

part A Marks: two every

1.
(a) Determine whether or not, the subsequent signal is periodic
x(t) = two ej(t+?/2) u(t)
(b) elaborate random variables.
(c) describe mean Ergodicity.
(d) When is a random process stated to be stationary?
(e) Write does the mathematical formula for Gaussian pdf?
(f) describe signal to noise ratio.
(g) Write down the units of noise figure.
(h) What is impulse response of a matched filter?
(i) Under what conditions an envelope detector fails to allow the envelope?
(j) describe transfer function of a system.

part B Marks: five every

2. Prove time-shifting property of continuous-time Fourier series.

3. discuss Gaussian probability density function.

4. Let x(t) have the Fourier transform x(j w), and let p(t) be periodic with fundamental frequency wo and Fourier series representation:


Determine an expression for the Fourier transform of :
y(t) = x(t) .p(t)

5. obtain the power spectral density function of:
x(t) = cos 10 ?t + cos 20 ?t
Also sketch the power spectral density function.

6. explain Ergodicity in detail.

part C Marks: 10 every

7. Derive the mean and variance of the exponential distribution directly from the density without using the moment – generating function.

8. (a) explain envelope detector. Where does it obtain its application?
(b) provide the graphical interpretation of convolution theorem.

9 (a) Show that the effective noise temperature of n networks in cascade is provided by:
Te=Te1+T e2/g1 + T e3/(g1 g2) +…….. T en/(g1 g2………gn-1)
(b) What do you mean by noise figure? How do we determine it experimentally?

Earning:   Approval pending.