On Sat, 22 Apr 2006 01:44:27 -0500, clifto wrote:

David wrote:
On Fri, 21 Apr 2006 17:46:36 -0500, clifto wrote:
David wrote:
wrote:
Are you sure about the patent cost? I thought sync detection was mostly
implemented through a PLL type circuit.

A PLL and a Product Detector

You can do without the PLL, too. You just create the signal with a
separate stage that overamplifies the signal into clipping, then
you have basically a sorta-square wave to feed into the product
detector.

Does that work when the station carrier fades?

I've wondered the same thing. But there apparently are receivers
using that technique.
http://www.radio-electronics.com/info/receivers/synchdet/sync_det.php
describes the principle; see especially the diagram captioned
"A synchronous detector using a high gain-limiting amplifier
to extract the carrier".
The extracted carrier should be used to lock a locally generated
carrier, with sufficient hysteresis to free run accurately during
selective fades.