I got an answer from them today

Dear Mikael,
First of all thanks for reaching out!.
My name is Jessy, I'm 18 years of age and am a telecommunication hobbyist.
This was the first ever experimental transmission here at Radio Bikker on the shortwave and you are the first person that reached out!.
It's so nice to hear that the signal was nicely intelligible on your Kiwi SDR there in the west parts of Sweden.
We are based in the east part of the Netherlands.
We are currently running with a PWM shortwave transmitter that outputs a bit less than 200W (~185W) and the antenna that we are using is a inverted V dipole antenna made for the 6185 KHz at a height of around 15m in the middle.
I'm more than happy with the SINPO and hope to hear from you again in the future.
Once again thanks for reaching out, we hope that you enjoyed the records there on a nice friday evening.