"George Dishman" wrote in news:f1mmtj$tr3$1
@news.freedom2surf.net:

Suppose the unmodulated light has a frequency of fc.
If you fire the modulated light at a grating There
are two obvious possibilities, either you get a line
with time varying intensity at an angle corresponding
to fc, or you get a signal which has a carrier fc and
two sidebands at +/- fm

fc
|
fc-fm | fc+fm
______|____|____|______

and each frequency produces a line of constant intensity.
Either way, you don't get any power at the angle
corresponding to fm itself.

IF the amplifiers following the mixer were flat from DC through light, you
WOULD also have output at fm.

Normally, however fm would be lost because it is far from the frequencies
of interest.

My understanding is that the stream contains a mixture
of three frequencies of photons and if you have the
resolving power in the grating, you get three lines

correct.

but a lower resolution will cause the lines to overlap
and the interference then causes the time varying
intensity.

No.

A detector follows the 'envelope' of the modulated signal and
'demodulates' it, producing fm.

[all the above assumes A3A modulation commonly called AM or amplitude
modulation].





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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