Fresnel Zone Calculator

How to Use

First choose the mode.

Calculate by Link Distance if you already know the path length
Calculate by Site Coordinates if you want the tool to work out the distance from the two site locations

Enter the frequency, both site elevations (ASL), and both antenna heights (AGL).

If trees or buildings sit on the path, turn on Building / Vegetation.

If there is one known object between the sites, such as a ridge, tank or tower, turn on Specific Obstruction.

Click Calculate. The tool will show the first Fresnel zone radius and tell you whether the path is CLEAR or BLOCKED against 60% clearance.

The path profile appears below the results. It shows the ground, LOS, Fresnel zones, towers and any object you added.

You can copy elevations from Google Earth. If both sites are at the same ground level, leave the ASL fields empty.

Link Parameters

Calculate by Link Distance Calculate by Site Coordinates

Path Distance (km)

Frequency (MHz)

Site A Elevation (ASL) (m)

Leave blank to assume both sites are on the same ground level. Values can be copied from Google Earth.

Antenna Height Site A (AGL) (m)

Site B Elevation (ASL) (m)

Antenna Height Site B (AGL) (m)

K-factor

Fixed at 1.33 for standard atmospheric refraction.

Target Clearance (%)

Fixed at 60% of the first Fresnel zone.

If Building / Vegetation Exist Between Point A & Point B

Specific Obstruction

Results

1st Fresnel Zone Radius (mid-path 100%)

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60% Clearance Required

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Antenna AMSL Site A

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Antenna AMSL Site B

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Assumed Mid-path Ground ASL

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Path Distance

—

Status

Enter parameters and click Calculate

PATH PROFILE

Elevation ASL (m)

The brown line is ground. Towers, vegetation, and obstruction start on that line and go up. Fresnel ellipses are clipped so they never render below ground.

Brown = ground surface · Hatch = underground / ASL only · Blue = LOS · Solid ellipse = 100% F1 clipped at ground · Dashed ellipse = 60% F1 clipped at ground · Pink ticks = vegetation on ground · Gray box = obstruction on ground

How it Works

This tool checks if a point-to-point wireless link has a usable line of sight. It looks at whether the first Fresnel zone stays clear of the ground, trees, and any object you add.

Ground model

If you enter both site elevations (ASL), the ground is taken as a straight slope from Site A to Site B. If you leave ASL empty, both sites are treated as the same level. Antenna height is always AGL, measured from the ground up, not from sea level.

Fresnel zone

The first Fresnel radius at any point on the path is:

r₁ = √(λ × d₁ × d₂ / D)

λ is c / f.

At the middle of the path, the 100% radius is √(λ × D / 4).

The clearance check uses 60% of that radius.

Clearance check

LOS is a straight line between the two antenna tips.

The lower edge of the 60% zone is LOS minus 0.6 × r₁.

If vegetation or a specific obstruction crosses that edge, the link is BLOCKED. Otherwise it is CLEAR.

Path profile

The vertical scale is stretched so the Fresnel zone is easy to see. On a long path that zone is only a few metres high, so a true-scale drawing would look almost flat.

The 100% zone is the solid blue ellipse. The 60% zone is the dashed ellipse inside it. Nothing is drawn below the brown ground line.

K-factor

K is fixed at 1.33, which is the usual value for atmospheric refraction. This version does not load terrain from Google Earth or SRTM.

Link Parameters

Results

Ground model

Fresnel zone

Clearance check

Path profile

K-factor

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