On Dec 21, 9:13*am, "Szczepan Bialek" wrote:
"Well, it's like this. The story starts in 1915, when mankind discovered
sidebands. Now possessing this superior understanding of the AM signal,
radio scientists began to understand the implications of their discovery.
Soon afterwards, our old friends at Bell Labs, who have discovered
practically everything, developed a method for removing one of the sidebands
of an AM signal but retaining all the essential modulation components. As an
expert of that day supposedly said, "both sidebands are saying the same
thing" (Goodman, 1948). " From:http://www.hamradiomarket.com/articles/SSBHistory.htm

I was born after 1915. I am supposing that in that time was possibility to
tune to the three different frequences.
Am I right?
S*

Only three? If the modulation is a complex signal (not just a single
sinusoid), you'll get (ideally) a carrier on a single frequency, and
upper and lower sidebands spanning a range of frequencies. Any decent
spectrum analyzer will easily resolve these components.
Communications receivers with narrow bandwidth, sharp cutoff filters
can also resolve them, of course.

And only "in that time"? You still can: there are plenty of AM
stations broadcasting in the 0.5MHz to 30MHz range (and some outside
that). But in 1915, it may well have been easier to analyze the
signal mathematically than with hardware. The hardware may not have
been very common, but certainly the math identities required were
readily available, as was Fourier analysis.

What if both sidebands are NOT "saying the same thing"? Then, for
instance, you can broadcast stereo in a way that receivers mixing the
two sidebands will still receive an acceptable mono signal.

Cheers,
Tom