FM Bandwidth and FM Band Explained

FM radio uses the frequency band from 88 MHz to 108 MHz, which is a 20 MHz-wide spectrum. This is the range of carrier frequencies available to stations.

$108\mathrm{MHz}-88\mathrm{MHz}=20\mathrm{MHz}$

However, a single FM station occupies only about 200 kHz. This is the bandwidth of the modulated FM signal.

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1. Why One FM Station Needs ~200 kHz

FM uses frequency modulation. The bandwidth depends on how far the carrier swings.

Carson's Rule gives the approximate FM bandwidth:

$B=2(\mathrm{\Delta f}+f$_m )

Where:

• Δf = maximum frequency deviation (FM standard: 75 kHz)
• f_m = maximum audio frequency (FM audio: 15 kHz)

Substitute the values:

$B=2(75\mathrm{kHz}+15\mathrm{kHz})=180\mathrm{kHz}$

Rounded by broadcasting standards → 200 kHz per FM channel.

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2. Relationship Between Bandwidth and FM Band

The 88–108 MHz band is the “road.” The 200 kHz per station is the “space each car occupies on the road.”

How many channels fit?

$\frac{20\mathrm{MHz}}{200\mathrm{kHz}}=100$

So about 100 FM stations can fit in the FM radio band.

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3.Summary

• The FM band (88–108 MHz) is the range of possible carrier frequencies.
• Each FM station uses only 200 kHz of spectrum.
• This bandwidth comes from FM modulation physics (frequency deviation + audio range).
• Therefore, roughly 100 stations fit in the FM band.

Further Reading