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Demonstration of why AM (carrier + information sidebands) can be demodulated using the simple diode detector while DSBSC (no/suppressed carrier, only information sidebands) cannot. AM produces an entire envelope of the message above and below ground (it does not reverse polarity), which the diode can easily rectify to recover. DSBSC produces two envelopes which are "overlayed" over ground, so each envelope switches polarity every half cycle.
The sources are configured to provide either a deeply modulated AM signal or DSBSC signal by flipping the switch. In either case, the modulated message signal is a 5kHz test tone.
Because the DSBSC signal's envelopes both reverse polarity, if one were to attempt to detect it using this system, they would end up recovering 2*Fmessage, not the actual message signal itself. Which is demonstrated by the circuit.
Even though AM is a spectrally inefficient radio transmission method (as the carrier carries no useful information), it is much easier and cheaper to mass produce receivers for than DSBSC. DSBSC requires more complex methods to demodulate which involves mixers to produce and recover the message from a heterodyne.
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