On Jul 16, 11:30 pm, isw <i...@witzend.com> wrote:
> In article <1184626829.678755.104...@q75g2000hsh.googlegroups .com>,
> Keith Dysart <Keith.Dys...@gmail.com> wrote:
> > 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.

All true. The simulation offered previously achieves the
required phase relationship (and more, so that the sum and
product versions can be directly compared).

> 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.

I am not convinced. Can you explain? AM modulation with a single
frequency produces a single sum and difference for the sidebands
while FM has an infinite number of frequencies in the sidebands.
This does not seem like a simple phase difference.

....Keith