"craigm" wrote in message
...
Brenda Ann wrote:


"David" wrote in message
...
The only thing that keeps us from hearing the digital sidebands is
their symmetry (the digital sidebands are out of phase with each other
and cancel out in the receiver).

I'm still trying to figure out how this is supposed to work.. I
understand
the concept, FM stereo does something similar by using phasing to reduce
the bandwidth needed for the L-R signal. The peaks of the L-R fit nicely
into the valleys of the L+R signal and vice versa.

No, this is not how FM works. I suggest you do some google searching. Here
is a start.

You need to check out the math and the practise of FM Stereo MPX. It is as I
have stated previously.

But this doesn't seem like it would work as advertised on a store-stock
AM
radio, because the ordinary envelope detector does not detect both
sidebands, only one of them. So how does it cancel?


An envelope detector does just what its name implies. It works from the
peaks in the time domain signal. The signal applied to the detector is
everything that comes through the filter; the carrier and both sidebands
if
the signal is centered in the filters passband. The only way you can
exclude a sideband is to tune off from the center frequency.

The detector in your basic AM radio is much the same as it has been for
nearly 100 years now. It rectifies one half of the envelope and filters out
the remaining RF to leave an audio waveform. It does not detect both halves
(both sidebands) of the waveform. This is why such things as selectable
sideband make high end radios better able to pick out a signal. The signal
with both sidebands may be applied to the detector, but it's not what comes
out. I stand by my question. If only one sideband is actually detected,
there can be no phase cancellation.