For me personally, there are many crossovers between radio - flight tracking - electronic devices - computers in general - building of things or opening black boxes labelled "DO NOT OPEN", however, I am not an expert in any of these sections, except maybe in the art of opening labelled boxes.
Frequencies allowed to use by a Radio Amateur station, are given depending on region / country, these sections are also shown on the online receiver linked under the button in the header. HF frequencies listed with modes, priorities and agreements, by SM2DUC (SWE) .
Software Defined Radio SDR
SDR devices is one way to explore the radio spectrum, check the receiver in Twente, click on button in the header. More about SDR devices at home, and how to get started is found on the SDR page.