In FM noise is low as compared to AM.
The AM signal covers more distance than FM signal that's why it
gets more distorted.How ever the information in AM signal does not
lose but the noise effects it more than that of FM signal,so we get
signal with more noise than that of FM signal
For FM
Carson's rule
Main article: Carson bandwidth rule
A rule of thumb, Carson's rule states that nearly all (~98%) of
the power of a frequency-modulated signal lies within a bandwidth
of
where , as defined above, is the peak deviation of the
instantaneous frequency from the center carrier frequency .
Noise quieting
The noise power decreases as the signal power increases;
therefore the SNR goes up significantly.
Thanks,
By tauseef ahmed