Military utility tools / Radio line of sight
Radio line of sight
Two antenna heights in. Radio horizon, optical horizon and the Fresnel clearance you need in the middle.
For the Fresnel and earth bulge figures.
Set the inputs, then work it out.
Radio horizon--km, 4/3 earth
Optical horizon--km, true earth
Horizon from A--km
Horizon from B--km
Fresnel radius--m at midpoint
60% clearance--m, working minimum
Earth bulge--m at midpoint
Wavelength--m
Does this cover HF skywave?
No. This is line of sight, which is the right model for VHF and above. HF propagating via the ionosphere plays by entirely different rules and horizon is not the limiting factor.
Why does frequency appear at all?
Only in the Fresnel calculation. The horizon itself does not depend on frequency, but the required clearance does: lower frequencies need more room.