What Is Radio Line of Sight — And Why It Matters for Your Radio Setup
If you’ve ever wondered why your radio signal drops behind a hill or why a taller antenna makes such a big difference, the answer comes down to one thing: Line of Sight (LoS).
In radio communication, Line of Sight refers to the unobstructed, straight-line path between your transmitting antenna and the receiving antenna. If something blocks that path—like a building, tree, or mountain—your signal may weaken or fail altogether.
How Line of Sight Works
Radio waves in the VHF (Very High Frequency) and UHF (Ultra High Frequency) bands—used by most handhelds like the Baofeng UV-5R, GMRS radios, and HAM setups—travel in straight lines, not around corners. That’s why they rely on clear visibility between antennas to reach their full range.
Even if you can't physically see the other antenna, the radio wave needs an open path in between. This is called radio line of sight.
What Blocks Line of Sight?
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Terrain (hills, mountains, valleys)
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Buildings and urban clutter
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Trees and dense foliage
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Metal structures or vehicles
These obstacles can block, absorb, or reflect your signal—especially above 30 MHz where LoS really matters. This includes FRS, GMRS, MURS, and 2M/70CM HAM bands.
What Is the Radio Horizon?
The radio horizon is the farthest distance your signal can travel in a straight line, given the Earth’s curvature and any obstructions. You can extend your radio horizon by:
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Raising your antenna height
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Moving to higher ground
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Using repeater stations on elevated terrain
As a rule of thumb: the higher your antenna, the farther your signal can go.
What About the Fresnel Zone?
The Fresnel Zone is an invisible, elliptical area surrounding the LoS path. Even if nothing’s directly in your signal path, large objects within this zone can still cause interference by reflecting or refracting your signal.
To optimize your range, try to:
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Keep both the LoS and Fresnel Zone clear
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Mount your antenna higher than surrounding objects
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Use directional antennas for point-to-point setups
Why Preppers and Operators Should Care
For preppers, homesteaders, and tactical radio users, understanding LoS is key to staying connected when the grid is down. Whether you're coordinating with neighbors, scanning weather channels, or running a repeater, knowing how terrain and elevation affect range can make or break your comms plan.
Summary
| Term | Meaning |
|---|---|
| Line of Sight (LoS) | Direct, unobstructed signal path between antennas |
| Radio Horizon | Max possible LoS range before Earth curvature blocks it |
| Fresnel Zone | Surrounding area that can reflect or interfere with signal |
Bottom line: If you want your radio to work at its best—get high, stay clear, and know your terrain. And if you're not sure how to get started, Ready Radio kits, antennas, and comms cards are built to help you transmit with confidence.