Further to my comment on VLF WSPR, I am still thinking about doing some earth-mode (through the ground) transmission tests at a couple of frequencies between the 8kHz dreamer's band and 136kHz. I'd like to test in the old 73kHz band (legal with earth mode and minimal radiation) and possibly around 37kHz too. A radiated test in the old 73kHz band would not be legal despite low uWs ERP unless I applied for the modern equivalent of a testing and development licence and paid £50 a year, stupid for a couple of tests taking a few hours. Getting MoD approval for that would likely take months and months too.
As my FT817 does not cover this frequency range, and the frequencies will be too high for direct sound card reception, I shall have to build an up-converter for the FT817 with a couple of front-end filters to pre-select the desired LF frequencies or a down converter to feed a sound card directly. A loop, E-field probe or earth electrodes would be used on RX ahead of the converter with the eventual output feeding a PC running appropriate weak signal software (Spectrum Lab, Spectran, WSPR etc).
I made a request to OFCOM very many months ago to permit me to do some low ERP radiated tests in the band between 9 and 136kHz on the basis that the potential for interference with very low ERP (uWs) and transmissions lasting no more that a few hours at a time would be extremely low. Such a request required lateral thinking and empowered decisions. Many, but not all, people at OFCOM seem incapable of making common sense decisions any more. They are also hindered by stupid bureaucracy. Ho hum.