My most ill prepared attempt ever.
I took my laptop and my BBB4 receiver and some wire as antenna.
Everything installed just minutes before 9:00 UTC at my parents place. I heard the tuning of the transmitter, correction I saw the tuning, heard about nothing. Very weak this time for me. So I let the pictures speak for themselves.
These pictures are taken from the software called spectrum lab. The most left pictures is an overall view from my laptop, showing the filter and settings windows. The middle and right one shows the weak signal of the vlf transmitter.
The left picture is a screenshot made later on the day while analyzing the incoming audio from the “receiver”. I used also Gram 16 for the picture in the middle. You can clearly see the small frequency deviation when keying the transmitter. And how many transmitters can you count on the colorfull screenshot on your right ? This was made with 30m wire as an antenna lying in the ground connected to the receiver.