Calculator
Responsive 3 / 2 / 1 gridEnter project values, then press Calculate. You can export the most recent result as a PDF or CSV.
Example data table
These sample rows illustrate typical planning inputs and resulting heights. Adjust to match terrain, frequency band, and service target.
| Distance (km) | Receiver height (m) | k-factor | Frequency | Obstacle at (km) | Obstacle height (m) | Clearance (%) | Final height (m) |
|---|---|---|---|---|---|---|---|
| 8 | 1.5 | 1.333 | 900 MHz | — | — | — | 24 |
| 15 | 10 | 1.333 | 2.4 GHz | 6 | 18 | 60 | 42 |
| 25 | 1.5 | 1.20 | 700 MHz | 10 | 12 | 60 | 60 |
Example outputs are rounded to common section heights and depend on obstacle details.
Formula used
Radio horizon (planning)
This tool uses an effective Earth-radius factor k and the common line-of-sight approximation:
d ≈ 3.57 · √(k) · ( √ht + √hr )
- d in kilometers
- ht, hr in meters above local ground
- k typically 1.333 under average refraction
Fresnel clearance at an obstacle
For an obstacle located between antennas, the first Fresnel radius is estimated by:
r1 ≈ 17.32 · √( d1·d2 / ( fGHz·(d1+d2) ) )
- d1, d2 in kilometers
- fGHz in GHz
- Required clearance = r1 · clearance%
The final tower height is the maximum of horizon and obstacle requirements, plus your safety and mounting allowances, optionally rounded up to whole tower sections.
How to use this calculator
- Pick Find tower height from distance for new planning.
- Enter the target link distance and the receiver height.
- Set k to 1.333 unless you have a site model.
- Enable the obstacle check if a ridge, trees, or buildings exist.
- Enter obstacle distance, height, and any known ground elevations.
- Choose your safety margin and mounting offset allowances.
- Press Calculate and review the “Final build height”.
- Use Download PDF or Download CSV to save results.
Coverage distance and horizon planning
A practical first pass for tower height uses the radio-horizon relationship. With k=1.333 and a 1.5 m handset, a 10 km target link often needs about 12 m before margins. If the receiver is a 10 m rooftop, the required tower height drops because √hr increases. This calculator shows the horizon-only height and the maximum distance when tower height is known. For budgeting, pair the computed height with wind loading class and foundation feasibility checks.
k-factor selection for site conditions
The k-factor models refraction by scaling effective Earth radius. Typical planning uses 1.333, while dry, unstable air can behave closer to 1.0, reducing reach. Higher k can extend distance, but it should be justified by local studies. Coastal inversions may temporarily raise k. Use the k input to test sensitivity and record the assumption in exported reports.
Frequency effects and Fresnel clearance
Obstacle clearance is not only a straight line; losses rise when Fresnel zones are blocked. The first Fresnel radius grows with path geometry and shrinks with higher frequency. At 2.4 GHz with an obstacle 6 km into a 15 km link, r1 is roughly 7–8 m, so 60% clearance targets about 4–5 m above the obstacle top. Lower bands produce larger Fresnel zones.
Build height, margins, and section rounding
Construction decisions need allowances beyond theoretical minimums. Add a safety margin for survey error, seasonal foliage, and future loading, then add mount offset for brackets, rods, and separation. Many towers use 3 m or 6 m modules; rounding up to full sections converts 41 m into a buildable 42 m, simplifying procurement and scheduling.
Field checks and compliance workflow
Use results as a baseline, then validate with terrain profiles, clutter, and permitting limits. Confirm obstacle locations and elevations with a survey, and verify antenna centerlines against drawings. Export PDF for design reviews and export CSV for logs. If results are tight, run scenarios with different k and clearance.
FAQs
1) How accurate is the horizon-based height result?
It is a planning estimate using effective Earth curvature. It does not include terrain shielding, clutter losses, or regulatory limits. Validate with a path profile and site survey before final design.
2) What k-factor should I use for typical projects?
Use 1.333 for standard planning unless you have local propagation studies. For conservative checks, also test around 1.0 to see how much height or distance changes under weaker refraction.
3) Why does frequency matter in obstacle checks?
Frequency drives Fresnel zone size. Lower frequencies create larger Fresnel zones, so the required clearance above an obstacle increases. Higher frequencies shrink the zone but can suffer more attenuation in rain or foliage.
4) Do I need exact ground elevations to use the tool?
Exact elevations improve the obstacle calculation. If you only know relative heights, set elevations to zero and enter obstacle height above local ground. For critical links, use surveyed elevations and coordinates.
5) What does section rounding do to my result?
It rounds the recommended height up to the next multiple of your chosen module length. This matches common tower fabrication and helps procurement. If you disable rounding, you get the theoretical recommended height.
6) When should I involve a structural or RF engineer?
When heights are near zoning limits, wind loading is high, or backhaul requires strict availability. Engineers can confirm structural class, foundation sizing, interference, and detailed propagation modelling for your specific topology.