Definition
Wavelength is the physical distance a radio wave travels during one complete cycle of its oscillation. It is found by dividing the speed of light (~300,000,000 m/s) by the frequency in hertz, so wavelength and frequency are inversely related: the higher the frequency, the shorter the wave. The 915 MHz band common to North American LoRa has a wavelength of about 33 cm; the 868 MHz European band, about 35 cm.
Why it sets antenna size
Antennas are dimensioned in fractions of a wavelength, which is why wavelength is the first number an RF builder calculates. A classic half-wave dipole is one half-wavelength long end to end, and a quarter-wave whip (the stubby antenna on most mesh nodes) is a quarter of it. An antenna cut to the wrong length for its frequency radiates poorly and reflects power back into the radio, so matching antenna length to operating wavelength matters more for real-world range than transmit power does.
Wavelength and propagation
Wavelength also shapes how a signal behaves in the world. Longer waves (lower frequencies) diffract around obstacles and penetrate foliage and buildings better, while shorter waves travel more line-of-sight and are more easily blocked — one reason sub-GHz LoRa reaches farther through terrain than 2.4 GHz Wi-Fi. Wavelength further determines the size of the Fresnel zone that must stay clear along a path.
Wavelength underpins antenna design and path planning alike. See the dipole antenna it sizes and the Fresnel zone it governs.
In Simple Terms
Wavelength is the physical distance a radio wave travels during one complete cycle of its oscillation. It is found by dividing the speed of light…