FM Frequency Deviation

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Describes the maximum difference between an FM modulated frequency and the nominal carrier frequency. FM applications use peak deviations of 75 kHz (200 kHz spacing), 5 kHz (25 kHz spacing), 2.5 kHz (12.5 kHz spacing), and 2 kHz (8.33 kHz spacing).

In ham radio it is common to have an FM transmitter that, as an example, with a 2.5KHz audio tone (modulation frequency) will have an FM frequency deviation of about 5 KHz.

Modulation Index = Peak Deviation / Modulation Frequency