Classical modulation procedures - Signals, Processes, and Systems - page 231

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Illustration 158: Simple double sideband AM signal without a carrier

A sine of 16 Hz (first series) serves as a source signal. This source signal has no offset here and lies
symmetrical to the zero axis. The multiplication of this sine by the carrier frequency 256 Hz results in the
double side band AM signal without a carrier in the second series.

Demodulation takes place here (at the receiver) by multiplication of this carrier-less AM signal with a sine
of 256 Hz. As a result of the multiplication we obtain the sum frequencies and the difference frequencies.
The sum frequencies of 256 + 256 -16 Hz and 256 + 256 + 16 (right) are filtered out by the lowpass filter,
the difference frequencies of 256 -(256+16) and 256 -(256-16) form the retrieved source signal.

This signal in the third series is practically the sum from the source signal (to be seen left
at 0 Hz in the frequency domain) and the AM signal, which lies symmetrical to the double
carrier frequency of 512 Hz. If this AM signal is filtered out by means of a lowpass filter,
we obtain the retrieved, time displaced source signal in the lower series.

Single sideband modulation without a carrier
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