| Floyd L. Davidson 2007-06-27, 5:25 pm |
| Paul Cardinale <pcardinale@volcanomail.com> wrote:
>
>I answered it. Reread.
Wrong answer though. You need to research the standard
definitions of terms when there is such a question, not
just continue on assuming that your perception of what
the word means is necessarily correct.
From The Collaborative International Dictionary of
English v.0.48[gcide]:
4. (Electronics) The alteration of hte amplitude,
intensity, frequency, or phase (of the carrier
wave of a radio signal) at intervals, so as to
represent information to be transmitted.
From WordNet (r) 2.0[wn]:
2: (electronics) the transmission of a signal
by using it to vary a carrier wave; changing the
carrier's amplitude or frequency or phase
However, the most authoratative and definitive cite
perhaps comes from the Federal Standard 1037C,
"Telecommunications: Glossary of Telecommunication
Terms" at http://www.its.bldrdoc.gov/fs-1037/
modulation:
The process, or result of the process, of varying
a characteristic of a carrier, in accordance with
an information-bearing signal.
carrier (cxr):
1. A wave suitable for modulation by an
information-bearing signal.
2. An unmodulated emission.
Note:
The carrier is usually a sinusoidal wave
or a uniform or predictable series of
pulses. Synonym carrier wave.
Obviously a DC voltage is not defined as a "carrier" and "modulation"
cannot be applied to it.
>
>Voltage.
That is encoding, not modulation.
>
>If changes in parameter X of thing A cause analogous changes to
>parameter Y of thing B,
>then the X of A is modulating the Y of B. In the case of TTL, binary
>data modulates DC voltage.
The binary data might well change the DC voltage, but it
cannot modulate a voltage, only change it. If the
changes carry information, we say it is encoded, and can
be decoded.
If an AC signal is varied, *that* is modulation.
>
>You seem to think that all modulation must be based upon amplitude
>modulation of a sine wave. It isn't (see above).
True, but he didn't say that is was. He merely said
"e.g.", which is not the same as "i.e." (one is "for
example", meaning there could be many other different
examples, the other is "in essense", meaning all
examples are essentially the same).
>As for an equation
>for TTL, it's trivial: Voltage = (high_level) * (binary data).
That does not define a modulated signal though. *By*
*definition* it defines information encoded using
voltage.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
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