AM vs FM

The first difference between AM and FM is what their abbreviations stand for. AM is amplitude modulation where FM is frequency modulation. Modulation is the act of modifying the carrier frequency in accordance to the information being sent. AM modifies the amplitude of the carrier frequency while FM modifies the  frequency of the carrier.

AM is the older, and easier of the two. An AM radio detects the changes in the carrier frequency’s amplitude before sending it through a speaker. The one main downfall with AM broadcasting is that the signals are easily distorted by bad weather conditions. AM travels a much greater distance than FM, but it was only able to output one audio channel. The greater range of AM waves is why talk radios prefer to use AM broadcasting.

FM is much more complex than AM radios. The greatest benefit of an FM radio is that it has the ability to send out two channels of information at the same time. This allows a radio station to broadcast left and right audio channels for greater stereo sound. FM waves can not be easily affected by weather conditions making them more ideal for listeners. FM broadcasts are mainly used for music as opposed to talk radios. The major downfall of FM radios is that FM signals usually drop off at around 50 miles from the broadcast station.

Sources: http://www.differencebetween.net/technology/the-difference-between-am-and-fm/
http://www.pbs.org/wgbh/aso/tryit/radio/images/fmamcompare.gif