Plain-language answer: Line-of-sight propagation is the direct and near-direct path between antennas, with useful range influenced by height, terrain, obstructions, diffraction, and atmospheric refraction.
Why it matters at the radio
At VHF and UHF, raising either antenna can reveal far more path than adding modest transmitter power. HF ground wave and local paths can also include direct components.
What to watch in the field
Plot terrain and antenna heights, then test from controlled locations. Separate a blocked path from an antenna or feed-line fault.
The common misunderstanding
Using the visual horizon as an exact radio cutoff.
Learning boundary
This lesson explains established radio and antenna practice. Current regulations and the exact equipment or antenna guide control legal limits, ratings, compatibility, and safety.
