Knowledge base

Learn HF propagation

A working sense of HF propagation is the difference between “the bands feel dead today” and “the foF2 dropped, try a lower band.” Each entry is a 5-minute read written for amateur radio operators of any class. The terms below feed directly into what SkyWave shows on the Go screen, so the learning here translates into faster, sharper reads of the app.

Propagation physics

The structure of the ionosphere and the metrics that describe it.

MUF (Maximum Usable Frequency) The highest frequency that reflects on a given path. foF2 The critical frequency of the F2 layer; the anchor for NVIS and MUF. LUF (Lowest Usable Frequency) The lower bound where D-layer absorption swallows signals. Critical frequency The highest frequency a layer reflects at vertical incidence. Skip zone The dead zone between ground wave and the first sky-wave hop. Ionosphere The layered shell of charged particles HF radio depends on. D layer The daytime absorber that closes the lower bands. F2 layer The layer most long-distance HF reflects off.

Propagation phenomena

The named modes and windows operators use.

NVIS propagation Short-skip regional propagation that fills the skip zone. Grey line propagation Sunrise and sunset window of low-loss long-distance paths. Sporadic E Summer surprise openings on 10 meters and 6 meters. Long path Reaching DX the other way around the world. Ground wave vs sky wave The two modes HF signals travel by.

Space weather

The solar and geomagnetic numbers that drive what the ionosphere does.

Kp index The 0 to 9 planetary geomagnetic activity index. F10.7 cm solar flux The daily proxy for solar activity, often called SFI. Sunspot number (SSN) The daily count of active solar regions. Solar cycle The 11-year rhythm that controls long-term HF. Solar flares and X-ray flux Sudden ionospheric disturbances on the sunlit side. Geomagnetic storm When the higher bands close from the top down. Coronal mass ejection (CME) The storm trigger that arrives 1 to 4 days after launch. Aurora propagation When the magnetic field becomes a VHF reflector.

---

Where the data comes from

SkyWave reads the NOAA Space Weather Prediction Center (SWPC) for solar flux, Kp, X-ray flux, and geomagnetic forecasts, and the KC2G MUF map for real-time MUF and foF2 from amateur ionosondes worldwide. A small Cloudflare Worker merges the two feeds into one cached payload that the app reads from your Maidenhead grid square.

← Back to home