Amateur Radio Classifieds UK

📡 Terrain-Aware Coverage Mapping

This tool generates terrain-aware RF coverage maps using ITU-R P.526 Knife-Edge Diffraction, two-rays ground reflection, terrain-aware clutter, and earth curvature loss. Properly models VHF/UHF propagation including radio horizon limits. To use coverage mapping mode:

• Enter only one location (A or B) - the transmitter site using a locator or postcode
• Set the antenna height, transmitter power, frequency, and polarization/mode
• Polarization:
  • Vertical (FM): Local/repeater coverage, ~100km search radius
  • Horizontal (SSB): Weak-signal DX with extended range, searches up to 350km to find distant hilltop paths across the entire UK!
• Click Analyse to generate a detailed coverage map
• The map shows terrain-aware signal strength using v3.1 Deygout Multiple Knife-Edge Diffraction (120 radials × 75 samples = 9,000 terrain points)
• Models portable operation (3.5m antenna) - operators typically select elevated positions (hills, clearings, car roofs)
• UK-calibrated with reduced clutter loss and extended SSB thresholds (-130dBm) for real-world amateur radio operation
• Color coding (terrain-aware):
  • Blue (Excellent): > -75 dBm with clear line-of-sight or geometric hilltop path
  • Pink (Good): -75 to -100 dBm with partial clearance, clear path, or elevated terrain
  • Orange (Marginal): -100 to -125 dBm with some clearance or elevated terrain
• Distance rings at 5, 10, 20, 40, 80 km help visualize range
• Radial lines every 30° show compass bearings
• Click any coverage area for detailed signal information (distance, signal strength, bearing, clearance)

The coverage calculation uses real terrain data (SRTM 90m) and accounts for: path loss, terrain shadowing, Fresnel zone clearance, Earth curvature (k-factor), and diffraction losses.

Line-of-Sight Analysis (Point-to-Point)

For point-to-point analysis, enter both Location A and Location B. The tool will calculate:

Fresnel Clearance Score

The score is the percentage of sampled points along the path where terrain stays at least 60% below the radius of the first Fresnel zone around the straight line between the two antenna tips.

• Higher is better; 100% means the first Fresnel zone is clear end-to-end.
• Lower scores indicate obstructions and likely diffraction loss.
• Frequency affects the Fresnel radius; higher frequencies have smaller zones.
• Raising antenna heights and choosing clearer paths improve clearance.

Quality of Contact

This is a heuristic quality score of how good a contact is likely to be. It combines:

• Fresnel clearance score as the base reliability.
• Radio horizon from antenna heights with the selected k-factor.
• Share and depth of obstructed segments along the path.
• A small frequency weighting (higher UHF/SHF slightly penalized when clearance is poor).
• Transmit power (W) weighting; higher power increases probability in a log scale.
• A simplified path-loss and SNR model to account for weak-signal contacts.
• 160m groundwave viability considered in band recommendation for short/medium paths.

Hover the chart to see the postcode and town at the terrain point under the cursor.

k‑Factor (Earth Radius Factor)

The k‑factor models atmospheric refraction by scaling Earth's effective radius used in curvature and radio‑horizon calculations. A value of 1.3333 corresponds to the common "4/3 Earth" assumption for VHF/UHF planning.

• Lower k increases effective curvature, reducing horizon distance and clearance.
• Higher k decreases effective curvature, increasing horizon distance and clearance.
• Effective radius: R_eff = 6,371,000 × k; horizon ≈ √(2·R_eff·h_A) + √(2·R_eff·h_B).
• Typical range is 1.2–1.4 depending on weather and ducting; 1.3333 is a good default.

Adjust k to explore how changing conditions affect line‑of‑sight and Fresnel clearance along your path.