In the modern society, radio is the most widely used of broadcasting and electronic communication. It plays a major role in many areas. In radio broadcasts, they use the radio waves, which can be both microwaves, and longer radio waves. These are transmitted in two ways: amplitude modulation (AM) and frequency modulation (FM). These two kinds of waves have many differences.
Amplitude modulation is the oldest method of transmitting voice and music through the airwaves. Amplitude modulation is used by station broadcasting in the AM band and by most international short wave stations. Frequency modulation is a way to convey information, voice, and music on a radio wave is to slightly change the frequency. Frequency modulation is, of course, used on the FM band. And it is used for action band and ham transmission in the frequency range.
Frequency modulation stations generally reach audiences from 15 to 65 miles away.
Because of frequency of the carrier wave is modulated, rather than amplitude, background noise is reduced. In FM transmission, the frequency of the carrier wave varies according to the strength of the audio signal or program. Unlike AM, where the strength of the carrier wave varies, the strength of the carrier in FM remains the same, while its frequency varies above or below a central value broadcast. FM transmission have a broadcast waves that are shorter than AM broadcast waves and do not go as far.
Two types of radio waves are broadcast by AM transmitter: ground waves, which spread out horizontally from the ground and travel along the earth's surface, and air waves, which travel up into the ionosphere, allows AM transmission to travel great distances. AM radio stations with powerful transmitters can reach listeners as far as 1000 miles away. FM radio waves also travel horizontally and skyward.