AM broadcasting

From ArticleWorld

The radio waves used in broadcasting have to be modulated before being transmitted, a process in which audio-frequency waves are super-imposed over carrier waves. If the modulation involves the amplitude of the waves being modified, the process is referred to as amplitude modulation or AM. This is distinct from frequency modulation (FM) and hence AM and FM waves may not be received at the same time. AM was the most dominant method of radio broadcasting initially and continues to be popular today. The first commercial AM services were used in the 1920’s.

Operation of AM broadcasting

AM radio broadcasting, as explained above, involves the modification of the amplitude of audio frequency signal received from the microphone. The audio frequency signal and carrier wave may be amplified independently before being superimposed, i.e. modulated, after which they are sent to the antenna. In another method, the audio signal and carrier wave may be modulated and then amplified before being sent to the antenna. In either case, if amplitude modulation is used, the audio wave’s amplitude is varied accordingly.

Applications of AM radio

Long waves (153-279 KHz) are used for radio broadcasting in non-American regions. The American continents use this band for navigation purposes. Medium waves (530-1710 KHz) are very popular with commercial radio stations. Short waves (3-30 MHz) are used by radio services when transmission distances are very large. Frequencies not falling in the set broadcast bands are used for walkie-talkies, cordless phones and certain remote control operations.