In article <1184626829.678755.104800@q75g2000hsh.googlegroups .com>,
Keith Dysart <Keith.Dysart@gmail.com> wrote:

> On Jul 16, 11:31 am, John Fields <jfie...@austininstruments.com>
> wrote:
> > On Sun, 15 Jul 2007 14:57:17 -0700, Keith Dysart
> > <Keith.Dys...@gmail.com> wrote:
> > >I thought the experiment being discussed was one where the
> > >modulation was 1e5, the carrier 1e6 and the resulting
> > >spectrum .9e6, 1e6 and 1.1e6.
> >
> > ---
> > That was my understanding, and is why I was surprised when you made
> > the claim, above:
> >
> > "It does not matter how the .9e6, 1.0e6 and 1.1e6 are put into
> > the resulting signal. One can multiply 1e6 by 1e5 with a DC
> > offset, or one can add .9e6, 1.0e6 and 1.1e6. The resulting
> > signal is identical."
> >
> > which I interpret to mean that three unrelated signals occupying
> > those spectral positions were identical to three signals occupying
> > the same spectral locations, but which were created by heterodyning.
> >
> > Are you now saying that wasn't your claim?
> > ---
>
> No, that was indeed the claim. As a demonstration, I've
> attached a variant of your original LTspice simulation.
> Plot Vprod and Vsum. They are on top of each other.
> Plot the FFT for each. They are indistinguishable.

-- lots o' snipping goin' on --

OK. I haven't been (had the patience to keep on) following this
discussion, so I apologize if this is totally inappropriate, but

If the statements above refer to creating that set of signals by using a
bunch of signal generators, or alternately by using some sort of actual
"modulation", the answer is, there is a very significant difference.

In the case where the set is created by modulating the "carrier" with
the low frequency, there is a very specific phase relationship between
the signals which would be essentially impossible to achieve if the
signals were to be generated independently. In fact, the only difference
between AM and FM/PM is that the phase relationship between the carrier
and the sideband set differs by 90 degrees between the two.

Isaac