wayne wrote:
As i understand it when a AM signal fades you can sometimes still hear the
modulation content but without the AM carrier to support it so it sounds
garbled like listening to a SSB signal on AM, so the SD circuit is adding
the carrier back to the signal sync'd to the original carrier so it does'nt
beat against the existing AM carrier and cause a heterodyne and then the
audio does'nt distort when it looses it supporting carrier because of the
receiver has generated it own carrier.
Correct me if i'm wrong.....

You're essentially correct. When the signal fades it changes the phase
relationship between the carrier and the audio sidebands, which produces
distortion. A sync' detector replaces the defective received carrier
with a locally generated 'clean' one.

http://www.hard-core-dx.com/nordicdx...al/fading.html

http://nitehawk.com/sm5bsz/linuxdsp/selfade/selfade.htm