‫بسم هللا الرحمن الرحيم‬
King Fahd University of Petroleum and Minerals
Electrical Engineering Department
Second Exam EE 370
Saturday May 7th, 2007
Time:
8:30 PM to 10:00 PM
Student Name
………………………..
Student ID#
………………………..
Problem #1
Problem #2
Problem #3
TOTAL /30
Good Luck
Problem I: (10 points)
Given a signal
m(t)=2sinc(2000t) ,
1. find its Hilbert transform.
2. If m(t) is modulated using and USSB modulator with a carrier frequency of 100 KHz,
write the expression of the modulated wave  USSB (t ) .
3. Draw the spectrum of the modulated wave showing clearly the labels (values on the
frequency axis and amplitude axis).
____________________________________________________
Problem II: (10 points)
1.
2.
3.
4.
5.
A carrier of amplitude A=10 volts and frequency 10 MHz is frequency modulated by an
information signal m(t )  10 cos(1000t ) with k f  100 Hz/V,
Write the expression of the modulated wave
Calculate the frequency deviation;
Calculate the transmission bandwidth.
If the amplitude of m(t) is divided by 5, what would be the new modulation index?
Is the FM wave in question 4 narrow or wide band?
_________________________________________________________
Problem III: (10 points)
The spectrum of a signal g(t) is shown below. This signal is sampled at the Nyquist rate
with a periodic train of rectangular pulses of duration 5 milliseconds and amplitude 1V.
1.
Write the expression of the sampled signal g s (t ) in terms of g(t).
2.
Draw the spectrum of the sampled signal for frequencies from -20 Hz to 100 Hz
showing clearly all the labelled values in the f-axis, and the amplitude axis.
1
G(f)
f
-20 Hz
20 Hz