Canadian International College Electrical Communication
Faculty of Engineering Spring 2023/2024
Electronics & Communication De-
partment.
DSB-WC Modulation
7. An audio signal m(t)=15cos(3000πt) amplitude modulates a carrier c(t)=Acos(30000πt).
Find & sketch the modulated signal in both time & frequency domains & determine
the USB & LSB frequency values if we have DSB-TC with m=0.6, Calculate the aver-
age power of s(t) and the power efficiency
8. A modulator is designed such that the signal m(t) and the carrier c(t)= Acos(2πfct) are
added then applied to a square law device y(t)=kx2(t), where k is constant. What type of
AM signals did we obtain? If the vm(t) is band-limited to 10KHz, what is the minimum
value for fc to obtain a distortion-less AM signal?
9. For the modulated signal sAM(t) = 10*[1 + 0.8*cos(2π*4000t)]*cos(2π*60000t),
a) Sketch sAM(t) in time and frequency domains
b) Calculate the power efficiency of the modulated signal
10. For the modulated signal s(t)=10cos(2π*2000t)+3cos(2π*1800t)+ 3cos(2π*2200t),
a) What’s the type of this modulation?
b) Sketch m(t),s(t) in t-domain and f-domain.
c) Find the value of modulation index (modulation factor)
d) Calculate the transmitted power and the power efficiency
11. A single tone audio signal of 4 KHz amplitude modulates a radio carrier of frequency
40KHz .If the percentage modulation is 60% and the carrier amplitude is 15 V.
a) Determine the amplitude of the modulating signal and its average power.
b) Determine the corresponding modulation index.
c) Sketch the modulated carrier signal in f-domain.
d) Determine the average transmitted power and the corresponding power effi-
ciency.
e) If the modulated signal is applied to a BPF that filter outs the USB, Determine the
new modulation efficiency. Compare with d) and comment.
12. A dual tone message expressed as m(t)=4cos(2000πt)+2cos(4000πt) amplitude modu-
lates a carrier of 20KHz and amplitude of 10V.
a) Sketch the modulating signal in f-domain.
b) Determine the B.W. of modulating signal.
c) Determine the average power of modulating signal.
d) Determine the modulation factor
e) Determine the B.W. and the average power of the modulated signal.
f) Determine the modulation power efficiency.
g) Sketch the envelope of the modulated signal in t-domain
Canadian International College Electrical Communication
Faculty of Engineering Spring 2023/2024
Electronics & Communication De-
partment.
13.A radio receiver designer proposed the circuit shown in figure to detect AM broadcast-
ing stations. Evaluate this proposal. If something is wrong, suggest a solution.
