Line of Sight

Line of sight (LOS) is the direct, unobstructed path between a transmitting and receiving antenna. At the VHF, UHF, and sub-GHz frequencies used by mesh radios, signals travel in essentially straight lines and are heavily attenuated by hills, buildings, and dense foliage. Achieving good LOS — often by raising antennas above the clutter — is usually the single biggest factor in how far a LoRa link actually reaches, more so than transmit power or antenna gain.

The Fresnel zone caveat

True radio LOS is more demanding than visual LOS. Energy travels not just along the straight ray but through an elliptical region around it called the Fresnel zone. Obstacles intruding into this zone cause diffraction and destructive interference even when the two antennas can technically "see" each other. A common engineering rule of thumb is to keep at least 60% of the first Fresnel zone clear, with under 20% obstruction strongly preferred. The zone is widest at the path midpoint and grows with distance and lower frequency.

Working with the terrain

Because the Earth curves and obstacles loom, antenna height is leverage: lifting a node a few metres onto a roof or mast can convert a dead link into a solid one by clearing the Fresnel zone over nearby rooftops and trees. In rolling terrain, a single elevated relay node can bridge two pockets that have no direct LOS to each other, which is exactly how a mesh extends coverage.

Pair good line of sight with appropriate antenna gain (dBi) and let mesh routing hop around the obstacles you cannot clear.