Why FM has less Noise than AM?

[Electronman]

Hi,
I have heard that's because of the higher bandwidth of FM but why the higher bandwidth the lower noise we get?

Thanks

 

[PatM]

Noise is a amplitude signal riding on the carrier.
In FM the amplitude is constant and modulation is due to the rate of change of the fm signal, not dependent on the amplitude variations of the signal as in AM

 

[MikeMl]

FM receivers have "limiters", which remove pulse-type noise and amplitude variations from the signal. Broadcast FM occupies a much wider bandwidth than AM, which accounts for its improved fidelity, and its ability to carry stereo, subcarriers, and digital. The wide-bandwidth is not required for AM noise immunity.

 

[gary350]

AM means Amplitude Modulation.

FM means Frequency Modulation.

Lightning, electric motors, lawn mower ignition, car ignition, etc. all produce static that adds extra peaks of the Amplitude Modulation.

Lightning, electric motors, lawn mower ignition, car ignition, etc. they produce static peaks too but it has no effect on the frequency.

In the final stage of the circuit sound and video are seperated from the carrier wave.

In AM after the carrier wave is removed the static peaks are still there because they have become part of the video and sound.

In FM the static is there but the sound and video come from the difference if frequency change caused by modulation of the carrier wave so the static has no effect of frequency so it has no effect of the output.

 

[crutschow]

Actually a wide deviation FM bandwidth (not directly related to the signal bandwidth) is required for low noise. The reasons for this are somewhat complex and are related to the FM threshold effect of RF signal S/N versus detected audio S/N. A wide bandwidth FM system significantly improves the ratio of the audio S/N versus the RF signal S/N. At narrow FM deviations they become comparable and are similar to AM S/N. For this reason narrow-band FM is not common, and all FM commercial broadcasting is done with wide-band FM.