Amplitude modulation in the frequency domain. Heron2 [CC BY-SA 3.0], via Wikimedia Commons. Looking at the two graphs depicting the AM signal, we can start to appreciate some of the system’s flaws.

But for a weekend project, [Vinod.S] took the ultrasonic transmitter and receiver from a distance-meter module and used amplitude modulation ... a clear signal by watching the modulated wave ...

For example, in AM radio, the voltage (amplitude) of a carrier with a fixed center frequency (the station's channel) is varied (modulated) by the analog audio signal.

The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM ...