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splat

Terrain-aware path analysis for VHF and above, from real elevation data

What it does

Analyses a point-to-point radio path across real terrain: it reads elevation data, draws the terrain profile between two sites with the Fresnel zone over it, and reports path loss using the Longley-Rice irregular terrain model. It will also produce coverage maps showing the area a transmitter reaches from a given height and power.

Why you would want it

Above about 30 MHz the question is line of sight and what is in the way, and that is a terrain problem rather than a propagation one. Before putting a repeater on a hill, planning a microwave link, or arguing about whether a mast needs another six metres, this answers it from data rather than from optimism.

Before it will work

Elevation data in SPLAT's own SDF format. splat-sdf makes it from the elevation of your map regions (D-061, amended 2026-10-02), with the srtm2sdf tools this package ships; hammunition maps splat then points SPLAT! at it through ~/.splat_path. Without map regions, convert SRTM tiles yourself with the same tools. gnuplot, which the package depends on, draws the profiles.

How it installs

  • apt: splat

Known problems

Without SDF terrain files it will run and assume a flat earth, which produces plausible output that is worthless -- the failure mode is a confident answer, not an error. Longley-Rice is a statistical model calibrated for particular frequency and distance ranges; using it far outside them gives numbers that look precise and are not. Buildings and trees are not in SRTM data, so an urban path will read better than reality.

Keeping it current

  • probe: apt policy
  • strategy: apt_upgrade

Where to get help with the software itself

John Magliacane, KD2BD. The project page carries the manual, which is unusually good and explains the model rather than just the flags.

Source: catalog/packages/splat.yaml