Frequency Deviation

What is this formula?

Frequency deviation is the maximum change of the instantaneous carrier frequency from its unmodulated carrier frequency in frequency modulation systems.

When to use it

Use this formula when analyzing FM transmitters, estimating modulation depth, checking allowable deviation, or preparing bandwidth calculations such as Carson’s Rule.

Example

An FM signal has a modulation index of 5 and a modulating frequency of 3 kHz.

Formula:

df = beta*fm

Substitution:

df = 5*3000

Result:

df = 15000 Hz

The frequency deviation is 15 kHz.

Applications

FM radio systems, telemetry, RF transmitter design, frequency modulation analysis, communication labs, and bandwidth estimation.

Note

This relation is exact for single-tone sinusoidal FM, where beta is defined as frequency deviation divided by modulating frequency. For complex modulating signals, frequency deviation is usually interpreted as the peak deviation caused by the maximum signal amplitude.