Many thanks to SWLing Post contributor, Alan, who writes:
Thomas,
You have had quite a few posts on loop antennas. I found a technical article about how to accurately test them.
I have just come across this article which you may find interesting. It comes from the BBC Research and Development:
https://www.bbc.co.uk/rd/publications/measurement-magnetic-loop-antenna-performance
It is written by a real Broadcast Engineer.
Alan
Thanks for the tip, Alan!