"Bob Quintal" wrote in message
news:1124029008.6a4884b0867a39bd55ac7e9b73fef389@t eranews
"Phil Allison" wrote in
:


"Pooh Bear"


The receiver requires to do some weird stuff to
demodulate the stereo component that results in further
signal degradation.


** Weird stuff = switch the audio between L and R
outs at 38 kHz ???

It's a little more complicated than that, Phil. Audio in
a FM signal is sent as a main carrier as L+R, and a
subcarrier of L-R at 38 KHz. You don't switch between the
left and right, you mix the sum with the uninverted
difference to get left, and the sum and an inverted
difference to get the right channel. the performance
issues arise from doubling the 19KHz pilot tone to get
the LO frequency to bring the difference signal back to
baseband.

This paper explores how this is analogous to simply
switching the audio at 38 JHz:

http://members.tripod.com/~transmitters/stereo.htm

"It can however be shown ( not by me though that rapidly
switching between L and R channels at 38 KHz does most of
the hard work and is a near equivalent to the hard way.
Switching channels as above makes a L+R signal and a DSBSC
L-R channel centered around 38 KHz. It also generates a lot
of harmonics but they can be filtered away. All that is left
is to add the Pilot Tone. Maybe the FM MPX standards were
actually decided upon the other way around, the ease of the
switching method lead to it being accepted as the standard ?
Rapidly sampling L and R signals alternatively is called
Time Division Multiplexing (TDM)."

etc.