|
| In article < 468d0174$0$3183$4c36
8faf@roadrunner.com>,
"Ron Baker, Pluralitas!" <this@aint.me> wrote:
> "John Fields" < jfields@austininstru
ments.com> wrote in message
> news:8ktp839la05dj6t
049kidjbpkj7rkf98ii@
4ax.com...
>
> <snip>
>
>
> Is there multiplication in DSB? (double sideband)
Yes, and in fact, that multiplication referred to above creates a
DSB-suppressed-carrier signal. To get "real" AM, you need to add back
the carrier *at the proper phase*.
FWIW, if you do the multiplication and then add back a carrier which is
in quadrature (90 degrees) to the one you started with, what you get is
phase modulation, a "close relative" of FM, and indistinguishable from
it for the most part.
A true DSB-suppressed carrier signal is rather difficult to receive
precisely because of the absolute phase requirement; tuning a receiver
to the right frequency isn't sufficient -- the phase has to match, too,
and that's really difficult without some sort of reference.
A SSB-suppressed carrier signal is a lot simpler to detect because an
error in the frequency of the regenerated carrier merely produces a
similar error in the frequency of the detected audio (the well-known
"Donald Duck" effect).
Isaac
|
|