Propagation

The key figures

Solar flux (SFI) is the sun's radio emission at 10.7 cm, measured in Penticton (Canada). It tracks the UV radiation that ionises the F layer: around 70 is the doldrums, above 150 10 and 12 m open reliably by day.

K and A index tell you how disturbed the geomagnetic field is, K per three hours (0 to 9), A as a daily figure. Shown here is the official Kp from GFZ Potsdam. From Kp 5 it's a storm: the F layer thins out, northern paths drop out, aurora reaches further south.

X-ray flux from the GOES satellites, grouped into flare classes A, B, C, M, X. From M upwards the D layer swallows HF on the daylight side for minutes to hours (Dellinger fade-out). The D-RAP layer of the map shows how far that reaches.

Solar wind and Bz: when it's fast (over 500 km/s) with a southward Bz (negative), it couples into the geomagnetic field and a storm often follows.

Ionosondes and MUF

An ionosonde transmits straight up and measures the highest frequency the F2 layer reflects (foF2). From that follows the MUF(3000): the highest frequency a 3000 km hop still supports, roughly three times foF2. The sondes at GIRO report every 5 to 15 minutes; in Europe these include Juliusruh, Průhonice, Dourbes and Chilton.

foEs is the same for sporadic E clouds. From foEs 10 MHz 6 m opens over about 2000 km, from 14 MHz 4 m, from 29 MHz even 2 m.

How we calculate

The map: a model from sun position and solar flux, then for each sonde the ratio of measurement to model, weighted by distance (around 1200 km) and age (around 90 minutes).

The bands: the MUF directly over Germany isn't enough. At night it's often below 9 MHz, and yet 30 and 20 m still reach overseas, because the paths run via midpoints further south or west, where it gets dark later. So we take the midpoints of hops over 3000 and 4000 km in eight directions, calculate the model there for every hour (by day 9 to 15 h, at night 20 to 4 h) and correct it with what the sondes around Germany measured at that local time over the last 24 hours. The best path counts. If a band is below 85 % of that MUF it's good, up to 100 % fair, up to 115 % poor (scatter and short openings only), above that closed. At the bottom absorption sets the limit: below the LUF poor, just above it fair at best. From Kp 5 one step lower, from Kp 7 two.

This is a forecast for typical paths, not a measurement of your antenna. That's why what RBN and PSK Reporter are really hearing sits right next to it.