The main advantages of FM over AM are:
- Lesser distortion. Frequency modulated wave is less susceptible to intereferences from buildings, traffic etc which provides improved signal to noise ratio (about 25dB) w.r.t. to man made interference.
- Waves at higher frequencies can carry more data than the waves at low frequency.
- Smaller geographical interference between neighboring stations.
- Less radiated power.
- Well defined service areas for given transmitter power.
Disadvantages of FM:
- Since attenuation is directly proportional to frequency, so FM suffers more attenuation tham AM signal.
- FM signals propagate as line-of-sight phenomenon, so if there is a large hill between transmitter and receiver, the receiver will not receive any signal. AM signals, on the other hand, are at low frequencies which are reflected back by ionospehere and thus, using sky-wave-propagation phenomenon, can travel farther distances. FM waves penetrate ionosphere and are not refracted back.
- Much more Bandwidth (as much as 20 times as much).
- More complicated receiver and transmitter.