FM radio Fmod max = 20KHz, Fdev = 75KHz mod index = 3.75. Narrowband FM (amateurs/police/fire. . ) Fmod max = 3KHz, Fdev = 5KHz mod index = 1.6. Analogue satellite Tv transmission Fmod max = 5MHz, Fdev 27 MHz mod index = 5.4 . The thing to think about is triangulation noise. The demodulated noise varies as bandwidth^2. So it important to utilise the whole bandwidth. To help with the demodulated noise FM radio audio is "pre-emphasizied" i.e. given a treble boost with a time constant of 75 microseconds. This is removed in the receiver with a "de-emphasis" circuit with the same time constant which also removes some of the noise.
Frank
