tools / RF & SDR
Radio Horizon and Line-of-Sight Calculator
Give it the height of each antenna and it returns the line-of-sight distance, using the 4/3-earth model that radio actually follows rather than the plain geometric horizon. Raising the antennas is nearly always the cheapest way to buy range.
Geometric line of sight only. You still need link budget and Fresnel clearance for it to work.
How it works
4/3-earth horizon
Radio bends slightly with the atmosphere, so the useful horizon is 4.12·sqrt(height in metres) km per antenna. The link reaches roughly the sum of both horizons.
FAQ
Does this guarantee a working link?
No. It is the geometric line of sight only. You still need enough link budget and Fresnel-zone clearance for the signal to actually make it.
How much does antenna height help?
A lot, and it follows a square root. Going from 2 m to 10 m roughly doubles the horizon, which is why masts and rooftops matter.
