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AM radio
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AM radio

AM radio is radio broadcasting using amplitude modulation. This was the dominant system of radio in the first two thirds of the 20th century, and it remains important today.

Because of the inferior sound quality of AM broadcasting, the medium lends itself particularly to talk radio, while music radio has in recent decades tended to be broadcast using FM.

AM radio technology is simpler than other types of radio, such as FM radio and DAB. An AM receiver detects the power of the radio wave and amplifies changes in the power measurement to drive a speaker or earphones. The earliest crystal radio receivers used this principle.

AM radio was used for small-scale voice and music broadcasts before World War I. The great increase in the use of AM radio came the following decade. The first commercial radio services began on AM in the 1920s. Radio programming boomed during the "Golden Age of Radio" (1920s to 1950s). Dramas, comedy and all other forms of entertainment were produced, as well as broadcasts of news and music.

AM radio is broadcast in on several frequency bands:

(In the US, the allocation of these bands is managed by the FCC.)

Medium wave is by far the most used for commercial radio broadcasting; this is the "AM radio" that most people are familiar with.

Long wave is used in Europe, Africa, Asia, and Australasia (ITU regions 1 and 3). In the Americas, however, this band is reserved for aeronautical navigation.

For the long- and medium-wave bands, the wavelength is long enough that the wave diffracts around the curve of the Earth by ground wave propagation, giving AM radio, in particular long wave and medium wave at night, a long range.

Short wave is used by radio services intended to be heard at great distances away from the transmitting station; the far range of short wave broadcasts comes at the expense of lower audio fidelity. The mode of propagation for short wave is different, see High frequency. AM is used mostly for broadcast uses – other shortwave users may use a modified version of AM such as SSB or an AM-compatible version of SSB such as SSB with carrier reinserted.

Frequencies between the broadcast bands are used for other forms of radio communication, such as baby monitors, walkie talkies, cordless telephones, radio control, amateur radio, etc.

See also