King Saud University
College of Engineering
Electrical Engineering Department
EE320
HW # 8
Q1) An FM modulator has the output
t
s(t) = 40 cos(2πf c t + 2πk f ∫ m(α )dα )
0
where kf = 10 Hz/V. Assume that m(t) = 5 rect[0.5(t-1)].
a)
b)
c)
d)
e)
f)
Sketch the phase deviation.
Sketch the frequency deviation.
Determine the maximum frequency deviation.
Determine the maximum phase deviation.
Determine the power of the modulator output.
Determine the bandwidth of modulator output.
Q2) An FM modulator has fc = 100MHz and kf = 10. The modulator has input
m(t) = 8 cos(40πt).
a) What is the modulation index?
b) Is this narrowband FM? Why?
c) If the same m(t) is used for a phase modulator, what must kp be to yield the
index given in (a)?
Q3) In Fig.Q3, determine the value of N1, f1, ∆f1, flo, fI, ∆fI, f2, and ∆f2.
NBFM
fc = 200kHz
∆f=160Hz
Multiplier
N1
fI
∆fI
f1
∆f1
flo
Fig.Q3
Multiplier
N2=200
f2
∆f2