Tecsun PL-368 Manual page 28

Example 4: The carrier phase shift is caused by the asymmetry of the
skywave transmission or radio intermediate frequency phase.
Spectrum
Carrier
LSB USB
LSB USB
Carrier
Carrier
USB
LSB
Carrier
LSB USB
The chart shows the demodulation output waveforms of the envelope
detector and synchronous detector. In each situation, the synchronous
detector gives an undistorted output (the frequency response may be
uneven, but there is no distortion). This is not the case with the envelope
detector. The envelope detector can only work correctly when the carrier
is large enough and the upper and lower sidebands are complete mirror
images of each other in amplitude and phase.
Synchronous detectors do not have the limitations of envelope detectors
and can demodulate a wide range of AM signals, for example
double-sideband, double-sideband with a suppressed carrier (DSB-SC),
single sideband without a carrier or with a suppressed carrier, vestigial
sideband (VSB), quadrature AM (QAM) and other signals.
Phasor Diagram
USB
Carrier
LSB
USB
Carrier
LSB
USB
Carrier
LSB
USB
Carrier
LSB
Envelope
Signal
Detector Output
24
Synchronous
Detector Output