Medium wave
The historic AM broadcast band spanning medium frequencies.
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Medium wave (MW) sits within the medium frequency (MF) part of the radio spectrum and is primarily used for AM broadcasting. It offers roughly 120 channels, though audio quality is noticeably lower than what FM stations deliver. During daylight, reception tends to be limited to local broadcasters, depending on signal strength and the quality of the receiver. At night, propagation improves significantly, allowing signals to travel much farther—up to about 2,000 kilometers (1,200 miles).
This long-distance capability can also create interference, since many transmitters around the world share the same frequencies. AM is also more vulnerable to interference from electronic devices like power supplies and computers. High-power transmitters can cover larger areas than FM stations, but they require more energy and longer antennas. Digital systems such as HD Radio are mainly used in the United States, while DRM30 (excluding shortwave) has been tested by India, South Korea, and China.
From the 1920s through the 1950s, MW was the dominant radio band for broadcasting, until FM’s superior sound quality took over. Since the 2010s, many European countries have shut down or reduced their MW transmitters. The term itself is historical, dating from the early 20th century when the radio spectrum was divided by wavelength into long wave, medium wave, and short wave.
Spectrum and channel allocation
In Europe, Africa, and Asia, the MW band has 120 channels with carrier frequencies from 531 to 1602 kHz, spaced every 9 kHz. Adjacent channels are generally not used in the same area to avoid interference. The total allocated spectrum, including modulated audio, runs from 526.5 to 1606.5 kHz.
Australia uses an expanded band that goes up to 1701 kHz. In North and South America, there are 118 channels from 530 to 1700 kHz, spaced every 10 kHz. Frequencies above 1610 kHz are mostly used by low-power stations, often for automated traffic, weather, and tourist information.
Sound quality
Sound quality is limited by the channel spacing. With 9 kHz spacing, the audio bandwidth is normally capped at 4.5 kHz; with 10 kHz spacing, it’s 5 kHz. This is because the audio signal is transmitted twice—once on each sideband—so the total bandwidth is double the audio frequency. This is fine for talk and news but not for high-fidelity music.
Quick Facts
- Channel count (americas)
- 118 channels from 530 to 1700 kHz spaced every 10 kHz
- Maximum transmitter power (europe)
- 2 megawatts daytime
- Nighttime skywave range
- about 2,000 km (1,243 mi) or 1,200 miles
Facts from the source article.
Lore & Background
Medium wave was the main radio band for broadcasting from the beginnings in the 1920s into the 1950s until FM with a better sound quality took over. The term is a historic one, dating from the early XX century, when the radio spectrum was divided on the basis of the wavelength of the waves into long wave (LW), medium wave, and short wave (SW) radio bands. Initially, broadcasting in the United States was restricted to two wavelengths: 'entertainment' at 360 meters (833 kHz) and government reports at 485 meters (619 kHz). In 1923, Commerce Secretary Herbert Hoover announced a new bandplan setting aside 81 frequencies in 10 kHz steps from 550 kHz to 1350 kHz, later extended to 1700 kHz.
Propagation characteristics include groundwave, which allows reception of strong transmitters typically extending 200 to 300 miles, with greater distances over salt water. At night, the lower ionospheric D layer virtually disappears, allowing skywave reflection off the higher F layer for very long-distance broadcasting. This can cause interference, as the same frequencies are re-allocated to different stations several hundred miles apart. In North America, the North American Regional Broadcasting Agreement (NARBA) sets aside certain clear channels for nighttime skywave use by stations broadcasting at higher powers of 10 to 50 kW.
Many countries in Europe have switched off or limited their MW transmitters since the 2010s, including Germany, France, Russia, Poland, Sweden, the Benelux, Austria, Switzerland, Slovenia and most of the Balkans. Large networks remain in the UK, Spain and Romania. In the US and Canada, maximum transmitter power is restricted to 50 kilowatts, while in Europe there are stations with transmitter power up to 2 megawatts daytime. Most US AM radio stations are required by the FCC to shut down, reduce power, or employ a directional antenna array at night.
Reader's Guide
Medium wave broadcasting was the dominant form of radio from the 1920s through the 1950s, before FM with superior sound quality took over. Its significance lies in its ability to cover large areas via groundwave during the day and via skywave at night, enabling long-distance reception up to about 2,000 km. This propagation characteristic, however, also causes interference between distant and local stations on the same frequency. The band's limited audio bandwidth—constrained by 9 or 10 kHz channel spacing—makes it adequate for talk and news but not for high-fidelity music.
Many countries in Europe have decommissioned MW transmitters since the 2010s due to cost-cutting and smaller audiences, while the band remains more active in North America, where clear-channel stations and daytimers operate under specific regulations. Digital modes such as HD Radio (mostly in the US) and DRM30 (test transmissions by India, South Korea, and China) have been introduced, but analog AM remains the primary mode. The legacy of medium wave includes its role as the first mass-market broadcast band and its continued use for regional and long-distance AM radio.
Did You Know?
- In the UK, until 2024 most stations used a bandwidth of 6.3 kHz; Ofcom then expanded the allowed bandwidth to 9 kHz.
More in Radio Spectrum
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Medium wave (CC BY-SA 4.0).
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