Variables
Description
What is this formula?
Carson’s Rule estimates the transmission bandwidth required for a frequency-modulated (FM) signal. It accounts for both the peak frequency deviation and the highest modulating frequency.
When to use it
Use this formula when designing FM communication systems, allocating radio spectrum, evaluating channel occupancy, or estimating required transmission bandwidth.
Example
An FM transmitter has a peak frequency deviation of 75 kHz and a maximum modulating frequency of 15 kHz.
Formula:
BW = 2(df + fm)
Substitution:
BW = 2(75000 + 15000)
Result:
BW = 180000 Hz
BW = 180 kHz
Applications
FM radio broadcasting, wireless communications, spectrum management, RF system design, telemetry systems, and communication engineering education.
Note
Carson’s Rule is an engineering approximation rather than an exact physical law. It typically captures approximately 98% of the transmitted FM signal power and is widely used for practical bandwidth estimation. Actual occupied bandwidth may differ depending on modulation characteristics, filtering, and regulatory measurement methods.