Empirical Earth · Radio & Long-Distance Signals

Radio propagation — why distance needs bending

The claim

“Radio travels in straight lines, so a signal crossing an ocean proves there’s no curve.”

What is measured

AM and shortwave signals reach past the horizon by bouncing off the ionosphere ~100–300 km up. The curve is the reason they need the bounce. See the band-by-band radio distance records and the radio band plan.

What would show this is wrong

over-horizon signals that required no ionospheric refraction around a curved Earth to explain.

Sources

  1. ITU-R Recommendation P.453. The radio refractive index: its formula and refractivity data (water-vapor term, N-units). International Telecommunication Union. ITU-R P.453 link
  2. HF ground-wave & skywave propagation. ARRL Antenna Book & Handbook; ITU-R P.368 (ground wave) and P.533 (HF skywave prediction). skywave propagation link
  3. The ionosphere. D/E/F-layer structure and diurnal HF absorption; NOAA Space Weather Prediction Center; ITU-R P.531. ionosphere link
  4. Tropospheric ducting & Sporadic E. ITU-R P.834 (refraction); ARRL VHF/UHF propagation references — super-refraction ducting and Es VHF reflection. sporadic E link
  5. Marconi's transatlantic transmission (1901) & the Kennelly–Heaviside layer. Marconi, Poldhu → Signal Hill; A. E. Kennelly & O. Heaviside (1902); E. Appleton's confirmation (1920s, Nobel 1947 link
  6. LoRa / LoRaWAN & distance records. Semtech LoRa CSS modulation; The Things Network world records (766 km, 832 km @ 25 mW via high-altitude balloon; ≈1,336 km reported). thethingsnetwork.org link
  7. Fresnel zones in radio path design. Standard RF link engineering — first Fresnel-zone radius and ~60% clearance over earth-curvature (4/3) profiles (ITU-R P.526; microwave path-budget texts) link
  8. Marconi’s 1901 transatlantic “S” — method and the lasting dispute. A high-power spark-gap transmitter at Poldhu fed a kite-lofted wire, received on an untuned coherer and earphone; the Morse link
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