Amplitude modulation is a signal manipulation method used in electronics and communications. We multiply a carrier signal (with a certain harmonic) by a modulation signal (or baseband). This allows for easier signal transmission and transmitting multiple signals simultaneously.
Since multiplication the time domain results in a convolution in the frequency domain, modulation shifts the frequency spectrum of the baseband signal.
Circuits
On an oscilloscope, we can enable amplitude modulation by examining the source properties.
In LTspice, we can create modulating signals with bv, a behavioural voltage source.1 We can create two isolated voltage sources, name their output nets, and set the behavioural function as the product of the output nets.