On Jul 15, 3:12 pm, John Fields <jfie...@austininstruments.com> wrote:
> On Sun, 15 Jul 2007 04:14:33 -0700, Keith Dysart
> >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.
>
> ---
> No, it isn't, since in the additive mode any modulation impressed on
> the carrier (1.0e6) will not affect the .9e6 and 1.1e6 in any way
> since they're unrelated.
> ---

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.

Read my comments in that context, or just ignore them if
that context is not of interst.

> >(You can improve the fidelity of the resulting summed version
> >by eliminating the op-amp. Just use three resistors. The op-amp
> >messes up the signal quite a bit.)
>
> ---
> Actually the resistors "mess up the signal" more than the opamp does
> since the signals aren't really adding in the resistors.

I did not write clearly enough. The three resistors I had
in mind were: one to each voltage source and one to ground.

To get there from your latest schematic, discard the op-amp
and tie the right end of R3 to ground.

To get an AM signal that can be decoded with an envelope
detector, V5 needs to have an amplitude of at least 2 volts.

....Keith