Amplitude modulation meaning

In communications and spectrum regulation, amplitude modulation (AM) is a method of radio transmission in which the carrier wave’s amplitude is varied to carry speech or data. It is a technical expression rather than a defined legal term, but it appears in Ofcom and ComReg licences, interface requirements and radio equipment conformity documents, often by reference to the ITU Radio Regulations and ETSI standards. AM is used for: - Medium wave broadcasting in the UK and Ireland (approximately 531–1602 kHz). - Shortwave (HF) broadcasting (roughly 3–30 MHz). - Aeronautical VHF voice communications (about 118–137 MHz), where AM is specified for safety and interoperability. - Certain private radio services, including citizens’ band (CB): in the UK and Ireland CB is predominantly FM, with AM and single sideband permitted on designated CEPT channels subject to licence exemption and equipment standards. In legal practice, identifying AM is relevant to spectrum licensing conditions, permitted emissions and bandwidth, interference management, and radio equipment compliance (for example under the Wireless Telegraphy Act 2006 and the Radio Equipment Regulations 2017 in the UK, and the Wireless Telegraphy Acts and the Radio Equipment Directive in Ireland). Usage and regulatory treatment are broadly consistent across England & Wales, Scotland, Northern Ireland and Ireland.