View source for Amplitude modulation

<!-----

== title: Amplitude Modulation (AM) description: published: true date: 2022-07-25T07:54:08.319Z tags: modes, am, amplitude modulation editor: markdown dateCreated: 2022-07-24T12:27:11.526Z ==-->

Amplitude Modulation (AM) is a mode for transmitting voice over the air. It consists of a HF carrier whose amplitude is varied (''i.e.'' modulated) in proportion to the transmitted audio signal (''i.e.'' the [[theory/baseband|baseband]] signal). Spectrally, an AM signal contains this carrier and two [[theory/sidebands|sidebands]] above and below the carrier; the upper sideband is a frequency-shifted copy of the baseband signal, while the lower sideband is a frequency-shifted and frequency-inverted copy of the baseband signal. While it was the first audio mode ever developed, and was the first audio mode used on amateur radio, AM is not very popular in the present day because [[modes/fm|FM]] is more resilient against interference on [[The Practicalities of VHF and UHF|VHF/UHF]] and [[modes/ssb|SSB]] is more spectrally efficient, saving space on the narrow [[bands/hf|HF]] bands on which it is used.