Antennas & Propagation

RF Line of Sight

Model wireless link viability with our RF line of sight tool. Calculate Fresnel zone clearance and Earth bulge effects to ensure reliable point-to-point signals.

Unlock reliable wireless communication by understanding the crucial difference between seeing a target and truly connecting to it. This guide breaks down the science and provides the tools you need to plan a perfect wireless link.

Visual vs. RF Line of Sight

The most common misconception in wireless networking is thinking that if you can see a location, you can get a signal to it. The reality is more complex. Radio waves travel in a wave, not a laser-thin line, requiring a clear volume of space, not just a single path.

Visual Line of Sight (VLoS)

A simple, straight line from Point A to Point B. An obstruction only occurs if something directly blocks this line.

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PATH CLEAR

RF Line of Sight (LoS)

A three-dimensional, ellipsoid-shaped volume between two antennas. Obstructions near the path, even if not directly on it, can severely degrade the signal.

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SIGNAL OBSTRUCTED

The Science Behind the Signal

The Fresnel Zone

The most critical concept in RF LoS is the Fresnel Zone. It's an ellipsoid-shaped area surrounding the direct path of the signal. For a strong connection, this zone must be kept mostly clear of obstructions.

The Rule of Thumb: At least 60% of the first Fresnel Zone must be free from obstructions for a reliable link. More is always better.

Antenna AAntenna B

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Obstruction

Fresnel Zone Boundary

Earth's Curvature

Over long distances, the Earth itself becomes the obstruction! The planet's curve, known as "Earth bulge," can rise up into the signal path, blocking the Fresnel Zone.

This is why long-distance links require antennas to be placed on tall towers—not just to clear trees and buildings, but to overcome the curvature of the Earth.

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Path Blocked by Earth Bulge

Interactive Link Planner

Is your link viable? Adjust the parameters below to model your wireless connection. The chart visualizes the Line of Sight path, the critical Fresnel Zone, and the Earth's curvature, giving you a clear pass/fail result instantly.

Link Distance (km)

Frequency (MHz)

Antenna A Height (m)

Antenna B Height (m)

Solutions & Common Questions

Increase Antenna Height: This is the most effective solution. Using taller towers or mounting points helps clear both ground-level obstructions and the Earth's bulge.
Find a Relay Point: For very long distances or impassable obstacles like mountains, use a third "repeater" site to create two shorter, clear links.
Clear Obstructions: If possible, trimming trees or removing other obstacles within the Fresnel Zone can significantly improve signal quality.
Choose a Better Frequency: While not a fix for LoS, lower frequencies (like 900MHz) can penetrate some obstacles better than higher frequencies (5GHz or 60GHz), which require a near-perfect LoS.

Theoretically, with perfect Line of Sight and enough power, a signal can travel hundreds of kilometers. The practical limit is determined by the "Link Budget," which includes transmit power, antenna gain, and receiver sensitivity. However, for terrestrial links, the primary limitation is almost always achieving Line of Sight due to the Earth's curvature. Use the calculator above to see how quickly the Earth becomes an obstacle!

The K-factor is a correction value used in professional RF planning to account for the fact that radio waves don't travel in a perfectly straight line through the atmosphere. Due to changes in atmospheric pressure and temperature, they tend to bend slightly towards the Earth. A standard K-factor of 4/3 is often used, which effectively makes the Earth seem "flatter" than it is, allowing for slightly longer links. Our calculator uses a K-factor of 4/3 for more realistic results.