[isw]

In article ,
(Floyd L. Davidson) wrote:

isw wrote:
In article ,
(Floyd L. Davidson) wrote:

Most physical channels are inherently analog! Wire
cables and fiber optic cables are two examples. Digital
signals are commonly sent via either of them.

I'll probably regret jumping in here, but:

The *message* may be digital, but the *signals* are most definitely
analog.

That is not correct. Whether a message is or not
digital is entirely unrelated to whether the signal used
to transmit it is analog or digital (and it can indeed
be either, without regard to the message).

You specifically mentioned "wire cables and fiber optic cables", so lets
talk about those and ignore other possible transmission media.

In both of those (as they are actually used in the real world),
communication is accomplished by the propagation along them of
electromagnetic fields; never anything else.

Doesn't matter one whit whether you turn the field on and off, or vary
the amplitude or any other characteristic of it continuously, as a means
of sending a message from one end to the other, those fields can take on
*any value* from the maximum level injected into the cable by the
transmitter down to far below the ambient noise level, depending (for
example) on the length of cable being used. IOW, those signals are,
without exception, *analog*.

Isaac