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Chapter 5 Tutorial
Modulation
4
5
The equation for DSSC is
y(t)=d·m(t)·sin(ω
c
t)
In DSB-SC, the carrier signal is inverted whenever m(t)<0. For QAM,
the second carrier signal would be cos(ω
c
t), making it 90 degrees out of
phase from the first carrier.
Frequency Modulation (FM) Frequency modulation varies a carrier
signal’s frequency according to the modulating signal:
y(t)=A
c
·sin[(ω
c
+d·m(t) )·t]
where m(t) is the modulating signal and d is the frequency deviation. FM
is called narrowband if the deviation is less than 1% of the modulating
signal’s bandwidth, and wideband otherwise. You can approximate the
modulated signal’s bandwidth with the following equations.
BW ≈ 2·(Modulating Signal Bandwidth) for narrowband FM
BW ≈ 2·(Deviation+Modulating Signal Bandwidth) for wideband FM
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