line of sight propagation calculator

Why a line-of-sight check matters

When engineers build microwave, Wi-Fi backhaul, telemetry, or public safety radio links, they usually start with one practical question: Can these two antennas actually “see” each other? A line-of-sight (LOS) propagation calculator answers that quickly by considering antenna heights, Earth curvature, and frequency-dependent behavior like Fresnel clearance.

Even if two locations look close on a map, the radio path can still fail because of curvature, terrain, buildings, trees, or poor atmospheric conditions. Running LOS math early helps avoid expensive site visits and redesigns later.

What this calculator computes

1) Radio horizon for each antenna

The tool estimates how far each antenna can “reach” over the horizon under an effective Earth radius model. Higher antennas increase horizon distance dramatically because range scales with the square root of height.

2) Maximum combined LOS range

Combined LOS range is simply the sum of the transmitter and receiver horizons. If your planned path distance exceeds this value, curvature alone suggests the path is blocked.

3) Midpoint Fresnel zone radius

LOS is not just a thin straight line. Real links need Fresnel clearance around that line. The calculator provides first Fresnel zone radius at midpoint and 60% recommended clearance. In many designs, keeping at least 60% of F1 clear improves reliability and limits diffraction loss.

4) Free-space path loss (FSPL)

FSPL gives the theoretical attenuation in dB for a clear, unobstructed path. It does not include fading, rain, polarization mismatch, cable losses, or interference, but it is the baseline for link budgeting.

How to use it effectively

• Enter realistic antenna heights: use centerline height above local ground, not tower total height if antenna is lower.
• Use your actual operating frequency: higher frequencies often need tighter alignment and cleaner Fresnel clearance.
• Set k-factor thoughtfully: 1.33 is common, but local climate can shift effective refraction.
• Add planned path distance: this gives a pass/fail style curvature margin against computed LOS range.

Interpreting the output

A positive curvature margin means your planned path is shorter than estimated maximum LOS distance. A negative margin means the path likely fails due to Earth curvature unless antenna heights are increased or relay sites are added.

Use the Fresnel output as a second check. A path can pass basic LOS and still perform poorly if trees or terrain intrude into the first Fresnel zone.

Practical design tips for stronger links

• Target extra margin, not just “barely works.” Weather and foliage change over time.
• Validate with terrain profiles and clutter data after this quick estimate.
• For long paths, include fade margin and multipath planning in your final RF design.
• For urban links, inspect rooftops and potential reflective surfaces.
• Use proper grounding, low-loss feedlines, and accurate antenna alignment.

Limitations to remember

This calculator is intentionally simple and fast. It does not model diffraction over hills, rain attenuation, gaseous absorption, ducting events, building penetration, or regulatory power constraints. Think of it as a planning-stage LOS and baseline loss estimator, not a full propagation engine.

Bottom line

A line-of-sight propagation calculator is one of the highest-value first steps in wireless system planning. In under a minute, you can screen candidate links, estimate required tower heights, and catch impossible paths before field deployment.