comment on the advantages and disadvantages of DSB-SC modulation compared with AM
AM modulation is characterized by its amplitude modulation index m which can be calculated as:
m = Vm / Vc
where
Vm is the peak voltage of the modulating signal.
Vc is the peak voltage of the carrier.
or
m = (Vmax - Vmin) / (Vmax + Vmin)
where
Vmax is the maximum voltage of the AM signal.
Vmin is the minimum voltage of the AM signal.
Note:
Vmin is positive for m < 1 and zero for m = 1
Vmin is negative for m > 1
Vmin = -Vmax for m = infinity
So let us explore 4 cases based on m:
Case 1: 0 < m < 25% (known as AM or DSB)
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Modulation is relatively easy.
Demodulation is very easy using diode detector.
But...
Power efficiency is relatively low.
Case 2: 25% < m < 100% (also known as AM or DSB)
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Modulation is not difficult.
Demodulation is easy by using an active detector.
But...
Power efficiency is not high.
Case 3: 100% < m < infinity (known DSB-RC, RC= Reduced Carrier)
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Modulation is also not difficult.
Power efficiency tends to be high (it increases with m).
But...
Demodulation needs to be of the synchronous type (PLL is used to generate the local carrier).
Case 4: m = infinity (known DSB-SC)
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Modulation is also not difficult (same as case 2 and 3).
Power efficiency is highest.
But...
Demodulation needs a digital costly system to restore the carrier (both frequency and phase).
As expected from above, DSC-SC system is usually not recommended for the general use since its demodulation is not as practical as in DSB and DSB-RC systems.
But... :wink:
A simple DSB-SC demodulator does exist (much like of case 3) and it has to wait for the scientific community, usually in charge of the science progress (academic and applied), to hear of it first!
Kerim
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