On May 10, 11:25 am, Chuck wrote:
Thank you for nicely elucidating the
distinctions in emphasis between
"science" and engineering, Keith.

I believe a perfect (just to keep this
at an abstract level) SA reveals the
underlying reality of the modulated AM
carrier.

Let me offer two examples.

I turn on my RF signal generator. I turn up the RF Level,
then I turn it down, then up, then down, ....
I can see this varying RF level on my oscilloscope (slow
sweep), and even on my RF voltmeter.
I know I am varying the level of the RF.
But I also know that I could produce exactly the same
output by adding 3 signals of slightly different frequency
together. I am not at all comfortable with saying the latter
is 'real' while the former isn't. I know I was varying the RF
Level.

Or,
I turn on my RF signal generator with some level for 1
minute. I turn it off for a week. I turn it on for one minute.
I turn it off. I compute the Fourier transform. I can create
exactly the same signal by adding all the Fourier terms,
extending forward and backwards in time, forever.
But is this more real than: I turn it on, then off, then
on, then off?

Using these examples, I can find no reason why the
multiple signal explanation is more real than the
varying amplitude explanation. And I suggest, that for
these two cases, the varying amplitude explanation
is probably more useful.

....Keith