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Tune a car radio to 101.1 MHz, and you catch music; switch on GPS at 1.575 GHz, and your phone pinpoints your exact location on Earth.
Both signals are electromagnetic waves traveling at the speed of light, but their behaviors differ drastically based on where they sit across the radio frequency spectrum.
How do we link the speed, frequency, and physical size of these waves into a structured system?

The Wave Equation and the Decade Rule

In 1865, James Clerk Maxwell formulated electromagnetic theory, proving that all radio waves travel through a vacuum at the speed of light, cβ‰ˆ3Γ—108Β m/sc \approx 3 \times 10^8\text{ m/s}.
The wave equation c=fΞ»c = f \lambda connects the speed of light cc, frequency ff (cycles per second in hertz, Hz\text{Hz}), and wavelength Ξ»\lambda (the spatial peak-to-peak distance in meters, m\text{m}).
The International Telecommunication Union (ITU) standardizes the radio spectrum into decades where each band spans from 3Γ—10nΒ Hz3 \times 10^n\text{ Hz} to 3Γ—10n+1Β Hz3 \times 10^{n+1}\text{ Hz}.
Because cβ‰ˆ3Γ—108Β m/sc \approx 3 \times 10^8\text{ m/s}, this factor-of-three rule ensures that the corresponding wavelengths always start and end on neat metric powers of ten (like 100 m, 10 m, or 1 m).
What does this mean for the lower end of the spectrum, where single waves can be kilometers long?

The Lower Bands: LF, MF, and HF

Low Frequency (LF) spans 30Β kHz30\text{ kHz} to 300Β kHz300\text{ kHz} with kilometric wavelengths between 10Β km10\text{ km} and 1Β km1\text{ km}, widely used for long-range navigation beacons and military submarine communications.
Medium Frequency (MF) spans 300Β kHz300\text{ kHz} to 3Β MHz3\text{ MHz} (1Β km1\text{ km} to 100Β m100\text{ m}, hectometric waves), best known for commercial AM broadcasting and avalanche transceivers.