FMbroadcasting

FM broadcasting is a method of radio broadcasting that uses frequency modulation to encode an audio signal on a carrier in the very high frequency (VHF) band. Unlike amplitude modulation, FM encodes information in the carrier frequency, yielding higher fidelity and better resistance to amplitude-based noise. The result is clearer sound, particularly for music, with improved stereo and dynamic range.

The development of FM is tied to Edwin H. Armstrong, who demonstrated and promoted the technique in the 1930s and 1940s. After improvements in receivers and standards, FM broadcasting became widely deployed in the postwar era and remains a major form of broadcasting in many countries, valued for reduced static and better audio quality. FM is primarily used for radio broadcasting rather than long-range communication, because it requires a higher, line-of-sight radio path.

Technical aspects: FM in most regions occupies the VHF Band II, roughly 88 to 108 MHz, with stations allocated about 200 kHz of bandwidth. The audio modulates the carrier by changing its frequency within about ±75 kHz. To improve noise performance, high-frequency content is pre-emphasized at the transmitter (typical time constants of 50 μs in Europe and 75 μs in the United States, with de-emphasis at the receiver). Stereo broadcasting uses a 19 kHz pilot tone and a 38 kHz subcarrier to carry the left-right channel difference; data services such as the Radio Data System (RDS) are transmitted at 57 kHz.

Transmission and coverage depend on transmitter power, antenna height, and terrain; FM is generally line-of-sight and does not propagate over the horizon as far as AM. Stations are licensed by national regulators who set technical standards and protect adjacent channels. In many regions, FM uses multiplex for subchannels, allowing multiple audio services on a single 200 kHz channel via stereo subcarriers and data streams.