Line of Sight Calculator

Radio signals and wireless links can only travel as far as the horizon allows — the Line of Sight Calculator tells you the maximum usable range between two antennas before the Earth's curvature blocks the signal. Enter your Transmitter Antenna Height, Receiver Antenna Height, and Height Units, then adjust the K-Factor for atmospheric conditions to get the Line of Sight Distance in both km and miles. Secondary outputs include the Radio Horizon distance and the First Fresnel Zone Radius — the clearance buffer needed to avoid signal diffraction losses.

m

Height of the transmitting antenna above ground

m

Height of the receiving antenna above ground

Atmospheric refraction factor (1.33 is standard)

Results

Line of Sight Distance

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Line of Sight Distance

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Radio Horizon

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Radio Horizon

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First Fresnel Zone Radius

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Frequently Asked Questions

What is line of sight distance in RF communications?

Line of sight distance is the maximum theoretical distance between two antennas where radio waves can travel in a straight line without obstruction from the Earth's curvature or terrain features.

What is the difference between line of sight and radio horizon?

Line of sight is the geometric distance based on antenna heights and Earth's curvature. Radio horizon extends further due to atmospheric refraction, which bends radio waves slightly beyond the geometric horizon.

What is the K-factor and why is it important?

The K-factor accounts for atmospheric refraction effects on radio waves. A standard value of 1.33 represents typical atmospheric conditions where radio waves bend slightly, extending the effective range beyond geometric line of sight.

How does antenna height affect transmission range?

Higher antennas provide greater line of sight distance. The relationship follows a square root function - doubling antenna height increases range by about 41%, not double.

What frequency ranges use line of sight calculations?

Line of sight calculations are primarily used for VHF, UHF, and microwave frequencies (30 MHz and above) where radio waves behave more like light rays and don't bend significantly around obstacles.

What is the First Fresnel Zone and why does it matter?

The First Fresnel Zone is an elliptical area around the line of sight path that must be kept clear of obstacles for optimal signal transmission. Typically 60% clearance is required for good signal quality.

Can terrain affect actual transmission range?

Yes, mountains, hills, buildings, and other obstacles can significantly reduce actual transmission range below the calculated line of sight distance. This calculator provides the theoretical maximum range.

What units can I use for antenna heights?

You can enter antenna heights in either meters or feet. The calculator automatically converts between units and provides results in both kilometers and miles for distance measurements.