Jerry Stuckle wrote in news:lriogq$kba$1@dont-
email.me:

In an FM transmitter, the amount of deviation is proportional to the
amplitude of the modulating signal. That is, the louder the audio, the
greater the deviation.

Transmitter bandwidth cannot be greater than receiver bandwidth without
loss of signal and distortion. Transmitter deviation can be less than
receiver bandwidth; this only results in lower audio. This is why
commercial FM receivers typically have a bandwidth of 170-180 kHz, when
deviation is only 75 kHz. It makes things less critical.


Ok, so a kind of 'headroom' exists then, but is there some agreeable degree
of reduction on transmitter bandwidth to gain a significant reach in RF
propagation and reduction in intrusion across the band, before the whole
exercise fails due to poor SNR on output? My guess is that there may be, but
the decision could be very different depending on whether speech or music
(let alone stereo) is wanted.