I have to project an AM demodulator using an Envelope Demodulator. To which kinds of AM (DSB, DSB-SC, VSB, SSD) is it applicable to? Thanks

  • \$\begingroup\$ I know classic tube circuits used diode rectifiers to recovery VSB, which is exemplified in the analog American TV. \$\endgroup\$ – analogsystemsrf Apr 4 '17 at 16:39

Without trying to over complicate things, an envelope detector is generally thought of as only applying to DSB and only when the modulation depth is less than 100%.

Basically if the shape of the modulating signal can be fully seen in the envelope of the modulated carrier, an envelope detector will be the simplest choice.

enter image description here

Hopefully the picture above gives you the idea.

If the carrier is "over" modulated then the envelope of the modulated carrier no longer represents the modulating signal and this certainly applies to DSBSC and any type of single side band modulation.

  • \$\begingroup\$ What about Vestigial Side Band which contains all the components, not only completely. \$\endgroup\$ – scottbear Apr 4 '17 at 16:50
  • \$\begingroup\$ A vsb envelope will be distorted. See this: patentimages.storage.googleapis.com/pages/US3083337-3.png. If you can live with the distortion then an envelope detector is acceptable. \$\endgroup\$ – Andy aka Apr 4 '17 at 16:58
  • \$\begingroup\$ So only pure DSB can be demodulated using Envelope right? And thanks. I read this on wiki about DSB-SC: Demodulation is done by multiplying the DSB-SC signal with the carrier signal just like the modulation process. This resultant signal is then passed through a low pass filter to produce a scaled version of original message signal. DSB-SC can be demodulated by a simple envelope detector. \$\endgroup\$ – scottbear Apr 4 '17 at 17:00
  • \$\begingroup\$ Vsb will be somewhat distorted and you need a decent carrier signal to get distortion reasonably low. \$\endgroup\$ – Andy aka Apr 4 '17 at 17:02
  • \$\begingroup\$ ok, and that of the dsb I wrote? \$\endgroup\$ – scottbear Apr 4 '17 at 17:07

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