Line of Sight Tool

Example data table

Formula used

How to use this calculator

1. Enter both antenna heights and your operating frequency.
2. Choose units, then set a k-factor for your region.
3. Enable link distance if you know the path length.
4. Enable obstacle modeling to test clearance at a ridge or building.
5. Press Calculate to see feasibility, clearance, and a quick profile.
6. Use CSV or PDF export to attach results to link plans.

The following planning notes expand on the computed outputs and how to apply them in wireless backhaul and site surveys. Document assumptions, then confirm with terrain profiles before builds.

Horizon limits define the first feasibility gate

Line-of-sight range grows with the square root of antenna height and the k-factor. For example, 30 m and 25 m endpoints typically yield a combined horizon near 23 km under k≈1.33. If your entered link distance exceeds the computed maximum path, no Fresnel tuning will recover the link without raising sites.

k-factor shifts coverage during refraction changes

The k-factor represents an effective Earth radius under atmospheric refraction. Standard engineering defaults use 4/3, but dry inland conditions may trend lower while strong ducting can trend higher. Raising k from 1.0 to 1.33 increases horizon and reduces curvature losses, improving long spans without changing hardware.

Earth bulge matters most at mid-path

Curvature bulge peaks around the midpoint. On a 12 km span, the bulge is small, but on 35 km it becomes a dominant term at mid-path. This tool reports bulge at the obstacle position so you can model a ridge, tree line, or rooftop that sits where curvature is greatest.

Fresnel clearance scales with frequency and geometry

First Fresnel radius shrinks as frequency increases and grows as the product of segment distances increases. At 5.8 GHz, a 12 km link can have a Fresnel radius of several meters near mid-path; at 11 GHz it is noticeably smaller. Selecting 60% clearance is a common compromise between reliability and tower cost.

Margins convert a “pass” into a stable link

A pass at 0% margin can still fail when foliage moves, snow loads accumulate, or alignment drifts. Adding a fixed clearance margin (for example 0.5 m) helps protect against measurement error and seasonal growth. When clearance fails, the suggested height increase shows the minimum uplift required at the critical point.

Use results to guide field surveys

Treat the output as a planning model, then validate in the field with a visual check, laser rangefinding, or drone survey. If distance is feasible but clearance fails, relocating one endpoint a few hundred meters can outperform adding several meters of mast, especially when the obstacle is close to one site.

FAQs

What does “distance feasibility” mean here?

It compares your entered link distance with the combined radio horizon from both antenna heights. If the link exceeds that limit, increasing height or reducing distance is required.

Why is the k-factor adjustable?

Refraction changes the effective Earth curvature. A higher k increases horizon and reduces bulge; a lower k does the opposite. Adjust k to stress-test links for typical local conditions.

How is the obstacle check evaluated?

The tool computes the line height at the obstacle, subtracts obstacle height plus Earth bulge, then compares the remaining clearance against your Fresnel percentage plus any extra margin.

What Fresnel clearance percentage should I use?

60% is a widely used planning target for point-to-point links. Higher targets improve resilience but may require taller structures. Lower targets can work for short spans with stable environments.

Why does frequency affect clearance?

Higher frequency yields a smaller Fresnel radius, so the same physical obstruction may clear more easily. However, higher bands often have higher path loss and stricter alignment needs.

Is this accurate enough for final installation?

It is suitable for preliminary design and quoting. For final builds, verify terrain, clutter, and regulations using mapped profiles, on-site measurements, and vendor link budgets.