Understanding key radio propagation concepts

Radio propagation is the behavior of radio waves as they travel from one point to another. As a form of electromagnetic radiation, radio waves are affected by reflection, refraction, diffraction, absorption, polarization, and scattering.

Quick resume of the following complete table:

• Low HF (160m–80m): Controlled mainly by D-layer absorption and nighttime F-layer reflection.
• Mid HF (40m–20m): Dominated by F2 propagation and grey line effects.
• High HF (15m–10m): Strongly solar-cycle dependent; Sporadic E plays a major role.
• VHF/UHF (6m–70cm): Mostly line-of-sight, but enhanced by Es, ducting, aurora, meteor scatter, and TEP.

Why This Matters

• When you hear a signal from 2000 km away on 6 meters in June, it’s probably Sporadic E.
• When 20 meters stays open all night during solar peak, that’s strong F2 propagation.
• When 2 meters suddenly carries signals 1500 km across the sea, that’s likely tropospheric ducting.
• Recognizing these patterns urns random luck into informed operating strategy — and that’s where radio becomes truly fascinating.

Radio propagation explained

Concept	What It Is	Typical Distance	Most Common Bands	When It Happens	What It Feels Like
D-Layer Absorption	The lowest ionospheric layer (50–90 km) that absorbs HF signals, especially lower frequencies.	Limits range rather than extending it	160m, 80m	Daytime	Low bands seem “dead” during the day
E-Layer Propagation	Reflection/refraction from the E layer (~90–120 km).	800–1500 km	40m, 20m, sometimes VHF	Daytime	Strong regional skip
Sporadic E (Es)	Intense, temporary ionized patches in the E layer that reflect higher frequencies than usual.	600–2500 km	10m, 6m, 2m (rare)	Late spring & summer; sometimes mid-winter	Bands suddenly explode with strong short skip signals
F2 Propagation	Reflection from the highest ionospheric layer (~250–400 km), enabling long-distance HF communication.	3000–15000+ km	20m, 17m, 15m, 10m	Daytime; strongest at solar maximum	Reliable global DX
Grey Line Propagation	Signal enhancement along the sunrise/sunset line where D-layer absorption drops but F-layer remains active.	Intercontinental	30m, 40m, 20m	Around local sunrise and sunset	Signals peak dramatically for a short time
Auroral Propagation	Reflection/scatter from ionized particles during geomagnetic storms near the poles.	1000–2500 km	6m, 2m, 70cm	During geomagnetic storms	Signals sound distorted and raspy
Transequatorial Propagation (TEP)	Signals travel across the geomagnetic equator via ionospheric irregularities.	4000–8000 km	6m, 10m	Near equinoxes	Strong north-south openings
Meteor Scatter	Signals reflect off ionized trails left by meteors entering the atmosphere.	500–2000 km	6m, 2m	During meteor showers; also random daily	Short bursts of strong signals
Tropospheric Ducting	Signals trapped in atmospheric temperature inversion layers near the surface.	300–2500 km	2m, 70cm	High-pressure weather systems	Stable, long VHF/UHF contacts
Troposcatter	Weak scatter from irregularities in the lower atmosphere.	300–600 km	2m, 70cm	Anytime	Weak but steady long-range VHF signals
Ground Wave	Signals follow the curvature of the Earth without ionospheric reflection.	Up to ~200 km	160m, 80m	Daytime	Reliable local/regional coverage