FM radio

FM radio is a method of radio broadcasting using frequency modulation (FM) technology. Invented by American engineer Edwin H. Armstrong in the 1930s, it provides high-fidelity sound over VHF radio bands, significantly reducing static and interference compared to AM broadcasting. The technology was commercialized after World War II and became the dominant standard for music and high-quality audio transmission, leading to the rise of numerous radio stations and shaping modern popular culture and music industry practices.

History

The development of frequency modulation is credited to Edwin H. Armstrong, who conducted pioneering research at Columbia University and demonstrated a working system in 1935. Despite initial resistance from the Radio Corporation of America and the existing AM broadcasting establishment, Armstrong persisted with his inventions. Following World War II, the Federal Communications Commission (FCC) began authorizing commercial FM stations, with the first such license granted to W47NV in Nashville, Tennessee. The 1960s and 1970s saw explosive growth, fueled by the adoption of stereophonic sound broadcasting and the format's popularity on college radio stations and with the counterculture of the 1960s. Key regulatory decisions by the FCC, such as the Non-Duplication Rule, helped solidify its market position against AM broadcasting.

Technology

FM radio operates by varying the frequency of a carrier wave in proportion to the amplitude of an input audio signal, a method more resistant to amplitude noise than AM broadcasting. Stations transmit in the VHF band, typically between 87.5 and 108.0 megahertz in most of the world, as allocated by the International Telecommunication Union. A stereo FM signal multiplexes left and right audio channels using a pilot tone and subcarrier system, a standard formalized by the Zenith Electronics Corporation. Receivers utilize circuits like the Foster-Seeley discriminator or phase-locked loop for demodulation. Transmission relies on high-power transmitters and antenna arrays often located on radio masts and towers such as the Sutro Tower or Empire State Building.

Advantages and disadvantages

The primary advantage is superior sound quality, with a wider audio bandwidth and better dynamic range than AM broadcasting, making it ideal for music. It is also less susceptible to interference from lightning, electrical equipment, and atmospheric phenomena. However, its VHF signals travel primarily by line-of-sight propagation, limiting broadcast range compared to the groundwave and skywave propagation of AM broadcasting. This necessitates a denser network of transmitters and repeaters for wide coverage. Furthermore, the technology can be susceptible to multipath interference in urban environments, causing distortion, a problem addressed by receivers with Diversity reception systems.

FM broadcasting around the world

Adoption and band plans vary globally under the coordination of the International Telecommunication Union. In the Americas and most of Asia, the 87.5–108.0 MHz band is standard, as used by major broadcasters like the British Broadcasting Corporation (BBC) in the United Kingdom and NHK in Japan. Some countries, like those in Eastern Europe, historically used the 65.8–74 MHz OIRT band. In South Africa, the South African Broadcasting Corporation (SABC) operates extensive networks. Unique implementations include Radio Data System (RDS) for transmitting text information, pioneered in Europe, and FM broadcasting in Japan, which uses a narrower channel spacing.

FM radio in the digital age

While facing competition from satellite radio services like Sirius XM, internet radio platforms such as Pandora Radio and Spotify, and digital audio broadcasting (DAB) standards, it remains widely used. Hybrid technologies like HD Radio, developed by iBiquity, add digital signals to existing broadcasts. Many public broadcasters, including National Public Radio and the Canadian Broadcasting Corporation, continue to rely on it as a primary distribution method. Its resilience is attributed to its simplicity, ubiquitous receivers, and role in local news and emergency alert systems, even as discussions continue regarding a potential spectrum reallocation for broadband services.

Category:Radio communications Category:Broadcasting Category:Audio engineering