Very Low Frequency
The Dreamer's Band covers 8.7-9.1kHz in the UK. This is the frequency band allocated for experimental use by Notice of Variation to the Amateur Radio licence. At the time of writing only a handful of UK stations are active on VLF. In Europe, where licence restrictions are less onerous, it seems more stations are becoming active every week. There is also interest in other parts of the world including Alaska, mainland USA, Australia and Japan. A number of stations have set up so-called "grabbers", receivers connected to the internet so that transmitting stations and others interested can see who is being copied and where.
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For your first steps in this area maybe the "Soundcard based USB (Upper SideBand) Receiver" is a helpfull tool.