Radio waves are a form of electromagnetic radiation, as are infrared, visible light, ultraviolet light, and gamma rays. The major difference is in the frequency of the waves. The portion of the frequency spectrum that is useful for radio communication at present extends from roughly 100 kHz to about 50 GHz.

Below shows the conventional designations of the various frequency ranges and their associated wavelength ranges.

Frequency Designation
Frequency Range
Wavelength Range
Wavelength Designation
Extremely High Frequency (EHF)
30–300 GHz
1 mm–1 cm
Millimeter Waves
Super High Frequency
3–30 GHz
1–10 cm
starts at 1 GHz)
Ultra High Frequency

300 Mhz–3 GHz
 10 cm–1 m

Very High Frequency

30–300 MHz
1–10 m

High Frequency (HF)
 3–30 MHz
10–100 m
Short Waves
Medium Frequency

300 kHz–3 MHz
100 m–1 km
Medium Waves

Note that microwaves and millimeter waves are wavelength designations and fit only approximately into the frequency designations. Wireless communication as described occupies mainly the VHF, UHF, and SHF portions of the spectrum.

Lower-frequency systems need inconveniently large antennas and involve methods of signal propagation that are undesirable for the systems we look at. Extremely high frequencies are still difficult to generate and amplify at reasonable cost, though that may well change in the future.

Conversion between frequency and wavelength is quite easy. The general equation that relates frequency to wavelength for any wave is

v = ƒλ
v = velocity of propagation of the wave in meters per second
ƒ = frequency of the wave in hertz
λ = wavelength in meters

For radio waves in free space (and air is generally a reasonable approximation to free space) the velocity is the same as that of light: 300 × 106 m/s. The usual symbol for this quantity is c. Equation then becomes: c = ƒλ.

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