FM takes whatever bandwidth you allow it. The harder you hit it the wider it goes. The limiting factor is when modulation exceeds the bandwidth of the receiver,

FM takes whatever bandwidth you allow it. The harder you hit it the wider it goes. The limiting factor is when modulation exceeds the bandwidth of the receiver, it clips very badly. Narrow band FM is used for aircraft. police, fire, amateur radio communication and since 2021 it's even legal for CB radio in the USA. It's deviation is limited by law to about +/-2.5KHz, from centre frequency. Setting up the modulation depth on an a broadcast FM exciter, I have used a spectrum analyzer and Bessel function information to make sure it was legal.