On Thu, 23 Oct 2003 19:51:49 -0700, Roy Lewallen
wrote:

Now, imagine that you can draw three sine waves on a long piece of
paper. They would have the frequencies and amplitudes of the three
spectral components above. These are the time domain representations of
the three frequency domain components. (In that sense, you *can* speak
of a carrier or a sideband in the time domain -- so I was perhaps unduly
dogmatic about that point.) But here's the important thing to keep in
mind -- all three of these components have constant amplitudes. They
extend from the beginning of time to the end of time, and don't start,
stop, or change at any time. That's what those spectral lines mean, and
what we get when we transform them back to the time domain.

It is quite easy to visualise this using a spreadsheet program.
However, it would be easier to use a much higher modulation frequency
compared to the carrier frequency. Assuming a carrier frequency of
1000 Hz and a modulating frequency of 100 Hz, so the sidebands would
be at 900 and 1100 Hz.

In column A put the time t and for each line increment the value by
0.0001 s or 0.00005 s.

In column B calculate 0.5*sin(2*pi*900*t).
In column C calculate 1.0*sin(2*pi*1000*t).
In column D calculate 0.5*sin(2*pi*1100*t).
In column E calculate the sum of columns B, C and D.

Duplicate these lines 500 to 1000 times and draw a graph, with column
A or time as the X-axis and display columns B, C, D and E as separate
graphs on the Y-axis.

Paul OH3LWR