FM (Frequency Modulation)

A modulation method that transmits by varying the frequency of a carrier wave according to an information signal, and the radio broadcasting standard that uses it

FM (Frequency Modulation)

Overview

FM (Frequency Modulation) is an analog modulation method that transmits signals by varying the frequency of a carrier wave according to the amplitude of the information signal. It was put into practical use by Edwin H. Armstrong in 1933, and thanks to its advantages of resistance to noise and excellent sound quality, it established itself as a core technology of modern radio broadcasting and communication. Today, "FM" is widely used not only to refer to the modulation method itself but also generically to FM radio broadcasting, which uses the 87.5–108 MHz band.

Main Content

Modulation Principle

Unlike AM (amplitude modulation), which changes the strength of the carrier wave according to the signal, FM carries information by finely shifting the carrier frequency around the center frequency. The magnitude of the signal is expressed by the size of the frequency deviation, and the waveform of the signal by the rate of change of the deviation. Because the amplitude of the carrier wave is constant, the influence of amplitude noise (atmospheric noise, electrical sparks, etc.) can be fundamentally reduced.

Advantages and Disadvantages of FM

Advantages: Strong against amplitude noise, clean sound quality, high signal-to-noise ratio (SNR), and relatively excellent resistance to adjacent-channel interference. Advantageous for stereo broadcasting and supplementary data transmission (RDS).
Disadvantages: Requires a wider bandwidth (about 200 kHz) than AM, the transceiver structure is complex, and due to the capture effect, if two signals are on the same channel, the weaker signal is completely ignored. Also, because it has strong directivity, shadow areas easily occur.

FM Broadcasting Band and Operation

Bands differ by region according to International Telecommunication Union (ITU) recommendations. Korea, the United States, and most of Europe use 87.5–108 MHz, while Japan uses 76–90 MHz (with discussions since 2024 of expansion to 99 MHz). In Korea, 88–108 MHz is allocated for broadcasting, and the channel spacing is 200 kHz. Coverage is determined by output and antenna height, and mountainous and shadow areas are supplemented by relay stations or low-power FM broadcasting.

Stereo and Supplementary Services

Stereo FM multiplexes the left and right channel signals using the sum-difference (L+R, L−R) method and demodulates them using a 38 kHz subcarrier. Here, RDS (Radio Data System) is carried on a 57 kHz subcarrier to provide the station name, program information, traffic information, and automatic frequency switching (AF). Recently, extended data services such as RT+ and TPEG are also operated.

History and Turning Points

In 1933, Armstrong filed a patent for wideband FM, and the first FM station opened in 1939.
In 1961, the United States introduced the stereo FM standard, and it rose as the main medium for music broadcasting.
In Korea, Seoul FM (now affiliated with KBS 1FM) began in 1961, and music and traffic broadcasting expanded in the 1970s–80s.
Since the 1990s, the emergence of satellite, cable, and Internet radio has diversified listening methods.

Latest Trends (2024–2025)

Crisis and Survival of Analog FM

Due to the spread of streaming and podcasts, real-time FM radio listenership is steadily declining, but the prevailing view is that abolition is difficult in the short term because of reliability in car infotainment and disaster and emergency broadcasting. In particular, FM emergency broadcasts linked with disaster text messages are being reevaluated as backup infrastructure that works even when communication networks are paralyzed.

Digital Transition

DAB/DAB+ is becoming common centered on Europe, and some countries are considering phased FM shutdown. The United States operates the HD Radio method, which overlays digital signals on the existing FM band, in parallel. Korea is developing centered on DMB and Internet radio, with weight placed on maintaining FM analog broadcasting.

EVs and Changes in the Reception Environment

Electromagnetic noise from EV motors and inverters makes AM reception difficult, leading some automakers to remove AM radio, while FM is maintained because of its relatively greater noise resistance. At the same time, automotive DAB+, streaming-linked hybrid radio is spreading as standard options.

Low-Power and Ultra-Small Applications

FM modulation technology is still widely used in wireless microphones, hearing-aid loops, Arduino/Raspberry Pi-based ultra-small FM transmitters, wireless sensor networks, and other applications in addition to radio broadcasting, and application research combined with low-power wide-area communication (LPWAN) continues.