Calculator Inputs
Example Data Table
This example shows a realistic microwave-style path using the calculator defaults.
| Link Distance | Frequency | Local Ground | Remote Ground | Remote Height | Obstacle Distance | Obstacle Elevation | Required Local Height | Combined Horizon |
|---|---|---|---|---|---|---|---|---|
| 18.00 km | 5.80 GHz | 120.00 m | 142.00 m | 28.00 m | 9.20 km | 150.00 m | 41.64 m | 48.41 km |
Formula Used
This calculator solves the minimum local antenna height needed to keep the signal path above an obstruction while also covering curvature and Fresnel clearance requirements.
F1 = 17.32 × √((d1 × d2) / (f × D))
Bulge = (d1 × d2) / (12.75 × K)
Target LOS = Obstruction Elevation + Bulge + (F1 × Clearance%) + Safety Margin
LOS(x) = Local Top + ((Remote Top - Local Top) × d1 / D)
Horizon = 3.57 × √(K × h)
Where D is total path length in kilometers, d1 and d2 are split distances to the obstruction, f is frequency in GHz, K is the atmospheric refraction factor, and h is antenna height above local ground in meters.
How to Use This Calculator
- Enter the total link distance and operating frequency.
- Provide ground elevations for both sites using the same reference datum.
- Enter the known remote antenna height above ground.
- Set the obstruction location and its top elevation.
- Choose the Fresnel clearance percentage and safety margin.
- Set the K-factor, usually around 1.333 for standard conditions.
- Optionally enter your current local antenna height to test pass or fail.
- Press Calculate Height to see results, graph, and exports.
Frequently Asked Questions
1) What does this calculator actually estimate?
It estimates the minimum local antenna height needed to clear a defined obstruction after accounting for Earth curvature, a chosen Fresnel clearance percentage, and an added safety margin.
2) Why is Fresnel clearance important?
A path can look visually clear yet still suffer signal loss if the Fresnel zone is blocked. Adequate clearance reduces diffraction, fading, and throughput instability on point-to-point wireless links.
3) What K-factor should I use?
A value near 1.333 is commonly used for standard atmospheric refraction. Lower values represent less bending and usually require more height. Use conservative values for critical designs.
4) Can I use this for Wi-Fi bridges and microwave links?
Yes. It works well for many terrestrial wireless links where you know distance, frequency, elevations, and the controlling obstruction. Always confirm final results with a full path study.
5) Why can the required height become very large?
Large heights usually come from long distances, low frequencies, strong terrain blockage, low K-factor assumptions, or aggressive Fresnel clearance targets. These increase the required line-of-sight elevation.
6) What is the difference between obstruction elevation and effective obstruction?
Obstruction elevation is the physical obstacle height above the chosen datum. Effective obstruction adds Earth bulge at that point, creating the actual clearance target used by the calculation.
7) Does the combined radio horizon guarantee link success?
No. It is a useful visibility estimate, not a full performance guarantee. Real links also depend on antenna gains, cable losses, fade margin, noise, rain effects, and local regulations.
8) When should I add more safety margin?
Add more margin when terrain data is uncertain, vegetation may grow, mounting tolerances are loose, or environmental conditions are harsh. Conservative margins usually produce more reliable deployments.