A worldwide system of transmitters exists, dedicated to the measurement of the ionosphere. The system is very useful for the prediction or analysis of radio propagation conditions, but is also an indicator for the changing global ecological situation. Many of these stations publish their findings on the internet, freely accessible to all (some military sounders require you to pass through the 'historical information' page, and some do not reveal the most recent information).
These stations - mostly automatically - measure at different intervals, the reflectivity of the different layers of the ionosphere (E, Es, F1 and F2) and do a quite good job at determining from these data the Maximum Usable Frequency (MUF). From their measurements, mostly vertical, they also derive the MUF for different distances.
G3PLX devised a way to use these transmissions, on a passive base - just listening - and extract interesting information from the results. A dozen or so other radioamateurs around the world joined the posse, and, using triangulation techniques, determine the position of undocumented transmitters.
Our sun has a very strong influence on the ionization of the upper layers of our atmosphere. In this section, dedicated to solar activity you will find graphs and images of solar activity from several sources..
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|(c) John Coppens ON6JC/LW3HAZ|