Frequency modulation (FM) varies the carrier frequency within a small range based on the information signal. The peak frequency deviation (Df) is the farthest the FM signal can be from the original carrier frequency (fc). The modulation index (β) represents Df as a multiple of the maximum modulating frequency (fm), with Df = βfm. The FM spectrum has multiple sidebands separated by the modulating frequency on either side of the carrier frequency, with the extent of sidebands approximately (β + 1)fm above and below fc.