jimg wrote:
in basic comm text books this is called is called 'coherent'
detection. under certain conditions it can be demonstrated that the
coherent demodulated snr is a 3-4 dB better than the "diode"
(non-linear self-mixing) demod and a 3-5 dB worse than synchronous
demodulation. under severe fading the coherent demod can actually
underperform the diode demod depending upon the mixer/post-filter/etc.
whereas the synchronous pll output can maintain the mixer input even
if the signal disappears briefly (wrt the loop time constant and phase
detector type)

because of the fading performance, the ease creating high quality
quadrature pll outputs, and the inherent input phase noise attenuation
in the pll, it's (coherent demodulation) almost never used anymore in
mixed signal designs...

Hi guys!

I saw this term mentioned in the specs of a radio. What does it mean
exactly? That if you hope and listen long enough you can convince yourself
it's synchronous?

Lucky


jimg
Oregon
USA