AM (Amplitude Modulation – double sideband, full carrier) is the oldest form of voice modulation. A CW carrier signal is controlled (modulated) by an audio voltage, so that the amplitude of the radio carrier ranges from zero (at negative audio peaks) to 200% (at positive audio peaks). Generation and reception of traditional AM can be done with relatively simple circuits, and it is still in use by a small, but hardy group of amateurs. Nevertheless, most ham voice activity on HF has moved to SSB