Explain frequency deviation and bandwidth requirements in FM.

Frequency deviation (delta_f) is the maximum shift of carrier frequency from its center, determined by message amplitude. Modulation index beta = delta_f / fm (deviation / message frequency). FM bandwidth approximated by Carson's rule: BW = 2*(delta_f + fm) = 2*fm*(beta + 1). Narrowband FM (beta << 1) has BW similar to AM; wideband FM (beta > 1) has significantly larger bandwidth but better noise performance. Commercial FM broadcasting uses 75kHz deviation with 200kHz channel spacing.