Carson's Rule (FM Bandwidth) (B_FM ≈ 2(Δf + f_m))

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B_FM ≈ 2(Δf + f_m)

What each symbol means

SymbolWhat it stands for
f_mHighest modulating frequency (Hz)
ΔfPeak frequency deviation of the carrier (Hz)
B_FMApproximate bandwidth containing ~98% of FM power (Hz)

When to use this

Wideband FM; Carson's rule is an engineering estimate used in JEE for required channel width.