The Alexanderson transmitter at Grimeton is a massive VLF one. It is a huge 500hp motor and gearbox that drives a alternator to produce a 17.2kHz signal. It transmits at various times of the year but only routinely on Christmas Eve and end of June / beginning of July. Its a fun thing to listen out for and is a good test of your VLF receiver.
The video below is of my reception in July 2020
To receive the transmissions a fairly simple setup is required. My preference is for the Airspy HF discovery + and a YouLoop from the same company. you don’t need much else. The receiver is tiny, about the same size as box of matches but half the thickness and is a perfect companion to the SDR# software you can get from (yes you guessed it) Airpsy
At the time of this recording I played about with a few antennas. the W3EDP I have here, the YouLoop and a mini whip and the YouLoop was by far the best.
If you manage to receiver the transmissions, and you can see from the map that they pretty much worldwide, then fill in the listener report and you’ll get added to the interactive map and a nice QSL card.