| Ron Baker, Pluralitas! 2007-07-06, 10:33 pm |
|
"isw" <isw@witzend.com> wrote in message
news:isw-9D8AE6. 10201105072007@newsg
roups.comcast.net...
> In article < 468d0174$0$3183$4c36
8faf@roadrunner.com>,
> "Ron Baker, Pluralitas!" <this@aint.me> wrote:
>
>
> 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*.
So does the multiplication in the first example really make
it amplitude modulation?
>
> 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
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