Ham Radio Propagation Guide
Propagation — the way radio waves travel from one point to another — is one of the most fascinating and unpredictable aspects of amateur radio. Understanding propagation means knowing why 20 metres is wide open to Europe at noon but completely dead by evening, why a contact with New Zealand is possible on 10 metres for just 20 minutes around dawn, and why 6 metres suddenly opens to stations 2,000 kilometres away on a summer afternoon with no warning. This section covers HF propagation fundamentals, solar effects, specialised modes, and the tools and resources for monitoring current conditions.
Why does HF propagation change throughout the day?
The ionosphere — the upper atmosphere that reflects HF radio waves — is created and sustained by solar radiation. During daylight hours, solar energy ionises the upper atmosphere, creating layers that reflect different frequency ranges. The D-layer, which absorbs lower frequencies like 40m and 80m, exists only during daylight and disappears at night. The F-layer, which supports long-distance HF contacts, persists through the night but changes its reflecting properties. This is why 40m works better at night for DX, while 20m is a daytime band.
What is the solar cycle and why does it matter for ham radio?
The sun's activity follows an approximately 11-year cycle between solar minimum (few sunspots, low activity) and solar maximum (many sunspots, high activity). At solar maximum, increased solar radiation produces a more highly ionised ionosphere that supports propagation on higher frequency bands like 10m, 12m, and 15m. At solar minimum, these bands may be completely closed for months. The 40m and 80m bands are less affected by the solar cycle but still show diurnal variation.
What bands should I try first for HF propagation?
20 metres (14 MHz) is the most reliable DX band and works for worldwide contacts during daylight hours throughout the solar cycle. 40 metres (7 MHz) is the most versatile band — it works for regional contacts during the day and extends to DX at night. These two bands are the best starting points for understanding HF propagation. As you gain experience, explore 80m, 17m, 15m, 10m, and the WARC bands.