| jimp@specsol.spam.sux.com 2007-06-27, 3:25 am |
| In sci.physics.electromag Paul Cardinale <pcardinale@volcanomail.com> wrote:
> j...@specsol.spam.sux.com wrote:
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> Yes, it does. In that case, the bits are modulating a DC voltage.
> But ethernet (and many other digital signals) is not voltage encoded.
> In ethernet, a 1 is represented by a transition, and a 0 by the
> absence of a transition. Each cycle carries a minimum of 4 bits.
> Interestingly, not all digital transmission is binary: long distance
> telephone communications uses hexadecimal; encoded using a combination
> of frequency and phase modulation.
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> There are many kinds of modulation. Amplitude modulation of a sin
> wave is just one.
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> It's true that TTL isn't FM, but the frequency is not constant.
> Paul Cardinale
I'm well aware of the myriad of techniques to encode and decode
digital information.
The question remains; does this meet the classical definition of
"modulation"?
If so, what kind of "modulation" is it?
My gut feel is that calling digital information on a DC "carrier"
some kind of "modulation" is just semantic tom foolery.
I would be convinced if someone could come up with a defining
equation, e.g. AM is x(t) = xc * [1 + m * sin (wm t)] * sin (wc t)
Problem is, for DC, wc = 0.
What to do with the annoying carrier term that is required for a
classical definition of "modulation"?
--
Jim Pennino
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